Research ArticlePerformance of Different Herbicides inDry-Seeded Rice in Bangladesh

Sharif Ahmed12 and Bhagirath Singh Chauhan2

1 Bangladesh Agricultural University 2202 Mymensingh Bangladesh2 International Rice Research Institute Los Banos DAPO Box 7777 4031 Metro Manila Philippines

Correspondence should be addressed to Bhagirath Singh Chauhan bchauhanirriorg

Received 16 September 2013 Accepted 22 December 2013 Published 6 February 2014

Academic Editors W Ma R M Mian Y Miao and T Takamizo

Copyright copy 2014 S Ahmed and B S ChauhanThis is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in anymedium provided the originalwork is properly cited

A field study was conducted in the boro season of 2011-12 and aman season of 2012 at Jessore Bangladesh to evaluate theperformance of sequential applications of preemergence herbicides (oxadiargyl 80 g ai haminus1 pendimethalin 850 g ai haminus1 acetachlor+ bensulfuranmethyl 240 g ai haminus1 and pyrazosulfuron 15 g ai haminus1) followed by a postemergence herbicide (ethoxysulfuron18 g ai haminus1) in dry-seeded rice All evaluated herbicides reduced weed density and biomass by a significant amount Amongherbicides pendimethalin oxadiargyl and acetachlor + bensulfuranmethyl performed very well against grasses pyrazosulfuronon the other hand was not effectiveThe best herbicide for broadleaf weed control was oxadiargyl (65ndash85 control) pendimethalinand acetachlor + bensulfuraonmethyl were not effective for this purpose The best combination for weed control was oxadiargylfollowed by ethoxysulfuron in the boro season and oxadiargyl followed by a one-time hand weeding in the aman season Comparedwith the partial weedy plots (hand weeded once) oxadiargyl followed by ethoxysulfuron (413 t haminus1) provided a 62 higher yieldin the boro season while oxadiargyl followed by a one-time hand weeding (408 t haminus1) provided a 37 higher yield in the amanseason

1 Introduction

In many Asian countries growers recently started to shifttheir rice cultivation practices from the traditional puddled-transplanted rice (PTR) to dry-seeded rice (DSR) Puddlingor repeated tillage under wet conditions is a labor- water-and energy-intensive method [1 2] The cost of farm labor isincreasing because workers engaged in agriculture are nowmoving to the cities for employment in nonfarm jobs such asin the textile and garment industries As a result it is difficultto find labor at the peak period of transplanting which delaystransplanting and often leads to the use of aged seedlingsAt the peak of the transplanting period the labor demandpushes wage above normal rates

Conventional rice production systems such as PTRrequire large quantities of water It has been estimatedthat seasonal water input for typical PTR ranges from 660to 5280mm depending on the growing season climaticconditions soil type and hydrological condition [3] Of thetotal amount of water required for rice culture in a season

about 30 is used for land preparation in puddled systems[4] Water for agriculture is becoming increasingly scarceworldwide including Bangladesh

The key concerns therefore are how the water require-ment of rice culture can be reduced and how farmers canavoid puddling and transplanting operations without yieldloss The development of alternative methods that are morewater-efficient and less labor-intensive is thus important toenable farmers to produce more with less cost These factorsdemand a major shift from PTR production to dry seeding ofrice in irrigated areas DSR has the potential to reduce waterand labor use compared with the conventional transplantedrice by eliminating the puddling phase and not requiringcontinuous standing water

DSR systems have several advantages over PTR systemsHowever weeds are a serious problem in DSR and reduce theproductivity of the system [5ndash7]Weeds aremore problematicin DSR than in PTR because without standing water tosuppress weed emergence and growth crop and weed emergesimultaneously [5 6 8] Yield losses in DSR systems can

Hindawi Publishing Corporatione Scientific World JournalVolume 2014 Article ID 729418 14 pageshttpdxdoiorg1011552014729418

2 The Scientific World Journal

go as high as 90 if control measures are not taken [9]Timely weed control is therefore crucial in improving theproductivity and profitability of DSR [9]

Various weed management strategies such as thor-ough land preparation high seeding rate appropriate fertil-izer application optimum water management and manualmechanical and chemical weed control are used in DSRcultivation [10 11] Manual weeding is common in Asiancountries but its use is decreasing because of labor scarcityat the critical time of weeding and increasing labor costs[12] In addition some weeds (eg Echinochloa colona (L)Link and E crus-galli (L) Beauv) at their early growthstages look similar to rice seedlings making hand weeding(HW)difficult inDSRChemicalmethods ofweed control aretherefore the most practical and cost-efficient [8 13]Severalpreemergence (eg pendimethalin oxadiazon oxdiargyland pyrazosulfuron) and postemergence herbicides (egbispyribac-sodium azimsulfuron penoxsulam fenoxapropethoxysulfuron and 24-D) are nowavailable in variousAsiancountries and have been reported to provide effective weedcontrol [11]

In a previous study the sequential preemergence appli-cation of pendimethalin (1000 g ai haminus1) followed by poste-mergence application of bispyribac-sodium (30 g ai haminus1) at15 days after sowing (DAS) was found best for the control ofweeds in DSR [14] In another study the best result was foundwith the application of oxadiazon (750 g ai haminus1) applied at 2DAS followed by fenoxaprop + ethoxysulfuron (45 g ai haminus1)applied at 28 DAS [12] Results from different studies revealthat no single herbicide can control all weeds effectivelyin DSR systems Moreover the continuous use of a singleherbicide over a long period of time may develop herbicideresistance in weeds and shifts in weed flora [2 15] The rightselection of herbicides is thus very important in DSR

In Bangladesh chemical weed control is becoming pop-ular because of labor scarcity and also because it costs lessthan HW [16 17] However information on the performanceof herbicides is only available for transplanted rice and not forDSR systems This study was therefore conducted to evaluatethe performance of sequential applications of various pre-emergence herbicides followed by postemergence herbicidesin DSRmdashthe first was study conducted in Bangladesh for thispurpose

2 Materials and Methods

Field experiments were conducted at the research farm ofthe Regional Agricultural Research Station of the BangladeshAgricultural Research Institute (23∘111015840 N 89∘141015840 E and 671mabove mean sea level) in Jessore Bangladesh in the boro(dry) season of 2011-12 and in the aman (wet) season of2012 The area belongs to agroecological zone number 11known as the High Ganges River Floodplain The climatein the area is subtropical with an average annual rainfallof 1590mm (90 of which falls from May to September)minimum temperatures of 6ndash9∘C in January and maximumtemperatures of 36ndash44∘C in April-May Amount of rainfalland the minimum and maximum temperatures recorded at

the experimental site during the experimental periods arepresented in Figure 1 The weather data were collected fromthe Regional Agricultural Research Station located 300mfrom the experimental fieldThe soil in the experimental fieldat 0ndash15 cm depth was clay loam in texture (378 clay 315sand and 307 silt) with a bulk density of 158 g cmminus3 pH of78 and organic carbon content of 1

Prior to the start of the experiment the field was leveledusing a laser leveler Different rice varieties are recommendedfor use in different seasons and from which BRRI dhan28(140 d duration) and BRRI dhan49 (135 d duration) wereselected for the boro and aman seasons respectively In bothseasons certified seeds were used (source Bangladesh Agri-culture Development Corporation Jessore Bangladesh)Theexperiments in each season were arranged in a randomizedcomplete block design with three replications Unit plot sizewas 18 (6 times 3) m2

Ten weed control treatments were used in each season(i) weed-free (ii) partial weedy (iii) oxadiargyl (80 g ai haminus1applied at 2 DAS) followed by ethoxysulfuron (18 g ai haminus1applied at 21 DAS) (iv) pendimethalin (850 g ai haminus1 appliedat 2 DAS) followed by ethoxysulfuron (18 g ai haminus1 applied at21 DAS) (v) acetachlor + bensulfuranmethyl (240 g ai haminus1applied at 2 DAS) followed by ethoxysulfuron (18 g ai haminus1applied at 21 DAS) (vi) pyrazosulfuron (15 g ai haminus1 appliedat 2 DAS) followed by ethoxysulfuron (18 g ai haminus1 appliedat 21 DAS) (vii) oxadiargyl (80 g ai haminus1 applied at 2 DAS)followed by a one-time hand weeding (HW) at 35 DAS (viii)pendimethalin (850 g ai haminus1 applied at 2 DAS) followed by aone-timeHWat 35DAS (ix) acetachlor + bensulfuranmethyl(240 g ai haminus1 applied at 2 DAS) followed by a one-time HWat 35 DAS and (119909) pyrazosulfuron (15 g ai haminus1 applied at 2DAS) followed by a one-time HW at 35 DAS

Herbicides were applied using a knapsack-sprayer fittedwith three flat fan nozzles on a boom delivering 350 Lof solution haminus1 In weed-free plots weeds were removedmanually (5 times in the aman season and 7 times in theboro season) In the partial weedy plots HW was done onceat 35 DAS weeds were allowed to grow before and after itWeeds allowed to grow throughout the season may result inan almost 100 yield loss in DSR systems [9] In additionfarmers in irrigated areas rarely leave their rice fields infestedwith weeds throughout the season

Dry rice seeds were sown at a rate of 40 kg haminus1 and withrow spacing of 20 cm using a power tiller operated seed drillfitted with a fluted-type seed-metering device The crop wasplanted on November 22 2011 and June 17 2012 in the boroand aman seasons respectively Fertilizers were applied atthe rate of 160-20-60-12-22 kg haminus1 of N P K S and Znrespectively in the boro season and 120-15-48-12-22 kg haminus1of N P

K S and Zn respectively in the aman season AllP K S and Zn were applied immediately before sowingFertilizer N was applied in four equal splits (25 each) at14 DAS at the start of tillering at maximum tillering and atbooting stage

Light irrigation was supplied just after sowing and thefield was kept saturated up to 40 DAS in the boro season

The Scientific World Journal 3

Boro 2011-12

Nov Dec Jan Feb Mar Apr May 05

1015202530354045

0

10

20

30

40

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Months (2011-12)

Rain

fall

(mm

)

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(a)

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fall

(mm

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1015202530354045

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(b)

Figure 1 Maximum and minimum temperatures and total rainfall (mm) recorded at the experimental site in the boro and aman seasons of2011-12

and up to 20 DAS in the aman season after which irrigationwas supplied based on tensiometer readings using a thresholdvalue of 15 kPa at 15 cm soil depth Water was maintained at5 cm depth with each irrigation In the boro season the riceplants were severely infested with blast and leaf spots Fungi-cide tebuconazole + trifloxystrobin 75WP (300 g ai haminus1) wasthus applied at 35 and 70DAS Fipronil 3 G (10 kg ai haminus1) wasapplied at 70 DAS in the boro season and 40DAS in the amanseason to control stem borers

Rice plant density was counted at 14 DAS from fourrandomly selected 1m row lengths in each plot To evaluatethe efficacy of preemergence herbicide weed density wascounted groupwise (ie grasses broadleaves and sedges)at 20 DAS (ie before the application of postemergenceherbicide)These data were collected only in the aman seasonand weed biomass data was not measured because of the verysmall size of weed seedlings

To evaluate the efficacy of postemergence herbicide weeddensity and weed biomass were measured at 35 DAS andat anthesis At each sampling time two 40 cm times 40 cmquadrats were placed randomly in each plot Weeds werethen collected from each quadrat segregated by species andcounted Biomass was measured species-wise after sampleswere oven-dried at 70∘C for 72 h Rice tillers were collectedfrom the same quadrats used for weed sampling and thencounted and rice biomass was measured At harvest thenumber of rice panicles was counted from four randomlyselected 1m row lengths in each plot The number of grainsper panicle (filled and unfilled spikelets) was counted by arandom sampling of 20 panicles per plot Rice grain yield wasdetermined from the harvested area of 88 (40 times 22m) m2Grain yield was converted to t haminus1 at 14 moisture contentand 1000-grain weight was measured

Data were analyzed using analysis of variance (ANOVA)to evaluate differences among treatments Means were sep-arated using least significant differences (LSD) at 5 level

of significance using CropStat 72 (IRRI Philippines) Weeddensity and biomass data were subjected to square-roottransformation (radic119909 + 05)

3 Results and Discussion

31 Effect of Herbicides on Rice Plant Density Weed controltreatments affected rice plant density in the aman seasonbut not in the boro season Plant density range was 162ndash201 plants mminus2 in the boro season and 128ndash169 plants mminus2in the aman season (Figure 2) In both seasons the lowestplant density was found in plots treated with pendimethalinPendimethalin-treated plots had 14 and 22 lower plantdensities in the boro and aman seasons respectively com-pared with the plots that were not treated with any herbicideOther herbicide-treated plots had similar plant densities inboth seasons In the aman season heavy rains occurred afterherbicide application (Figure 1) which could be the maincause of low plant density in the pendimethalin-treated plotsNo heavy rains occurred after herbicide application in theboro seasonThe results suggest that pendimethalin can causephytotoxicity if heavy rainfall occurs after application ofherbicide Similar results were reported for oxadiazon herbi-cide in which rice plant density was lower compared withnontreated plots when heavy rains occurred immediatelyafter herbicide application [18] These studies suggest thatsoil water content is an important factor that can influenceherbicide phytotoxicity in rice Such toxicity can result inpoor crop establishment especially where low seeding ratesare used

32 Effect of Weed Control Treatments on Weed Density andBiomass Weed species varied with the growing seasonsSome species were not common in both seasons For exam-ple Amaranthus spinosus L Anagalis arvensis L Cleomerutidosperma DC and Cynodon dactylon (L) Pers were

4 The Scientific World Journal

0

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Boro 2011-12

LSD

Weed control treatments

Wee

d-fre

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Part

ial w

eedy

Oxa

diar

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etho

xysu

lfuro

n

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hoxy

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ron

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or+

bens

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at 3

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at 3

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mminus2)

(a)

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ial w

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etho

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n

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1H

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at 3

5 D

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halin

fb1

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at 3

5 D

AS

Acet

achl

or+

bens

ulfu

ranm

ethy

lfb

1 H

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35

DA

S

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zosu

lfuro

nfb

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Pyra

zosu

lfuro

nfb

etho

xysu

lfuro

n

Plan

t den

sity

(no

mminus2)

(b)

Figure 2 Effect of weed control treatment on rice plant density (number mminus2) at 14 days after sowing

Table 1 Effect of weed control treatments on weed density (number mminus2) at 20DAS (before application of post-emergence herbicide) Weeddensity data were subjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Grasses Broadleaf Sedges TotalPartial weedy 1368 (1875) 1541 (2385) 1010 (1021) 2298 (5281)Oxadiargyl 680 (458) 898 (802) 562 (313) 1256 (1573)Pendimethalin 504 (250) 1231 (1510) 915 (839) 1613 (2599)Acetachlor + bensulfuranmethyl 675 (453) 941 (885) 690 (474) 1348 (1812)Pyrazosulfuron 1300 (1688) 846 (714) 597 (354) 1662 (2756)LSD005 129 164 155 139119875 value lt0001 lt0001 0001 lt0001DAS days after sowing LSD least significant difference at 5 level of significance 119875 probability

present only in the boro season and Ageratum conyzoidesL was present only in the aman season Such variationsmight be the result of the seasonal adaptation of weeds Inaddition nonrice crops were grown before the start of theexperiment This may be another reason for the variation Inthe boro season temperatures were low up to 60 DAS but itlater increased (Figure 1) Because of low initial temperaturescrop and weed growth was slow However the growth ofsome species (eg Cyperus rotundus L Cynodon dactylonand Cleome rutidosperma) was unaffected by the low tem-peratures and severely suppressed crop growth at its earlystages in the boro season Another interesting observationwas that someweed species (egA arvensisGalinsoga ciliateBlake and Phyllanthus niruri L) emerged later than usualwhich could be their strategy to ldquoescaperdquo the application ofpreemergence herbicides

The dominant weed species in the experiments wereCelosia argentea L Cyperus rotundusDactyloctenium aegyp-tium (L) Willd Digitaria ciliaris (Retz) Koel E colonaEleusine indica (L) GaertnG ciliate and P niruriThe appli-cation of preemergence herbicides significantly reducedweeddensity compared with the control plots (partial weedy)At 20 DAS (before application of postemergence herbicide)plots treated with preemergence herbicides had 45ndash70lower weed density than the partial weedy plots (Table 1)

Among the herbicide treatments oxadiargyl-treated plotshad the lowest total weed density (157 plants mminus2) followedby those treated with acetachlor + bensulfuranmethyl (181plants mminus2) The highest weed density was recorded in theplots treated with pyrazosulfuron In terms of weed groupsthe lowest grass density was recorded in the plots treated withpendimethalin (88 less than in the partial weedy check) and

The Scientific World Journal 5

Table 2 Effect of weed control treatments on weed density (number mminus2) at 35DAS in the boro season Weed density data were subjectedto square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Amaranthusspinosus

Celosiaargentea

Cleomerutidosperma

Cyperusrotundus

Cynodondactylon

Echinochloacolona

Total weeddensity

Partial weedy 544 (292) 906 (854) 622 (385) 886 (790) 383 (146) 877 (792) 1800 (3258)Oxadiargyl fbethoxysulfuron 071 (00) 071 (00) 071 (00) 532 (281) 255 (63) 256 (83) 650 (427)

Pendimethalin fbethoxysulfuron 071 (00) 426 (177) 071 (00) 607 (365) 215 (52) 197 (42) 797 (635)

Acetachlor +bensulfuranmethyl fbethoxysulfuron

071 (00) 563 (313) 456 (208) 690 (479) 174 (31) 197 (42) 1036 (1073)

Pyrazosulfuron fbethoxysulfuron 071 (00) 509 (260) 071 (00) 609 (375) 193 (63) 562 (313) 1007 (1010)

Oxadiargyl fb 1HW at35DAS 071 (00) 071 (00) 071 (00) 790 (635) 193 (63) 071 (00) 830 (698)

Pendimethalin fb 1HW at35DAS 071 (00) 524 (271) 071 (00) 940 (892) 152 (31) 071 (00) 1093 (1194)

Acetachlor +bensulfuraonmethyl fb1HW at 35DAS

372 (135) 582 (333) 353 (125) 707 (500) 151 (21) 371 (135) 1120 (1250)

Pyrazosulfuron fb 1HW at35DAS 367 (135) 614 (375) 071 (00) 754 (573) 396 (156) 747 (583) 1342 (1823)

LSD005 070 165 090 203 NS 214 208119875 value lt0001 lt0001 lt0001 0009 020 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

the highest was recorded in the plots treated with pyrazosul-furon (only 10 less than in the partial weedy check) Againstbroadleaved and sedges acetachlor + bensulfuraonmethyloxadiargyl and pyrazosulfuron performed well (63ndash70fewer broadleavedweeds and 54ndash70 fewer sedges comparedto the partial weedy check) while pendimethalin performedpoorly (suppressed only 37 and 18 of broadleaved andsedges resp) The observed effectiveness of pendimethalinin the control of grasses and its poor control of sedgesand broadleaved weeds are consistent with the findings ofprevious published studies [8 16 17 19]

At 35 DAS (after application of postemergence herbicidesand before HW) total weed density and weed biomass weregreatly affected by herbicide treatments Plots treated withpreemergence herbicides had 39ndash76 and 23ndash45 lowerweed densities (326 and 293 plants mminus2 in the boro andaman seasons resp) compared with the partial weedy check(Tables 2 and 3) However the values were 66ndash88 and 46ndash65 respectively when plots were treated with both pre- andpostemergence herbicides

Among the herbicide treatments oxadiargyl-treatedplots performed best followed by those treated withpendimethalin and acetachlor + bensulfuranmethyl Poorperformance was observed in the pyrazosulfuron-treatedplots A similar trend was found for total weed biomass(Tables 4 and 5) Plots that were treated with only preemer-gence herbicides had 50ndash66 and 29ndash57 less weed biomassthan the partial weedy plots in the boro and aman seasonsrespectively Plots that received both pre- and postemergence

herbicides had 70ndash80 and 44ndash67 less weed biomass in theboro and aman seasons respectively The effect of herbicideson individual weed density and biomass was significant inboth seasons except on C dactylon suggesting that applyingherbicidewas not effective against this weed species Oxadiar-gyl was superior to other herbicides in reducing weed densityand biomass of several individual weed species including Ecolona Ageratum conyzoides Amaranthus spinosus Cleomerutidosperma and Celosia argentea The next best treatmentwas pendimethalin which suppressed all weeds that weresuppressed by oxadiargyl except C argentea and P niruriHowever both herbicides were ineffective againstC rotundusin both seasons

Plots treated with both pre- and postemergence herbi-cides always had less total weed density and biomass thanthose that were treated with only preemergence herbicidesFor example the plots that received only preemergenceherbicides had a weed density range of 70ndash182 and 157ndash233plants mminus2 in the boro and aman seasons respectively In theplots that received both pre- and postemergence herbicidesweed density range was 43ndash107 and 84ndash152 plants mminus2respectively The same trend was observed in weed biomasswhich indicates that the postemergence herbicide ethoxy-sulfuron significantly lowered weed density and biomassEthoxysulfuron suppressed a range of broadleaved weedspecies (eg Ageratum conyzoides Amaranthus spinosusCleome rutidosperma Celosia argentea and P niruri) andsedges (eg C rotundus) but not grasses (eg E colona DciliarisandC dactylon) Ethoxysulfuron has been reported to

6 The Scientific World Journal

Table 3 Effect of weed control treatments on weed density (number mminus2) at 35DAS in the aman season Weed density data were subjectedto square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Ageratumconyzoides

Cyperusrotundus

Celosiaargentea

Digitariaciliaris

Echinochloacolona

Phyllanthusniruri

Total weeddensity

Partial weedy 585 (344) 736 (542) 419 (177) 1002 (102) 803 (642) 456 (208) 1712 (2933)Oxadiargyl fb ethoxysulfuron 071 (00) 37 (136) 111 (11) 663 (438) 469 (218) 071 (00) 920 (843)Pendimethalin fb ethoxysulfuron 071 (00) 360 (167) 412 (167) 599 (385) 486 (231) 388 (146) 1074 (1148)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 301 (115) 387 (146) 860 (74) 671 (458) 071 (00) 1209 (1458)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 215 (83) 111 (11) 900 (854) 760 (573) 071 (00) 1231 (1521)Oxadiargyl fb 1HW at 35DAS 235 (104) 738 (542) 174 (31) 727 (563) 581 (333) 071 (00) 1253 (1573)Pendimethalin fb 1HW at 35DAS 497 (25) 814 (667) 472 (219) 533 (282) 492 (240) 356 (125) 1334 (1781)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 181 (52) 572 (323) 544 (292) 834 (693) 826 (677) 071 (00) 1410 (1984)

Pyrazosulfuron fb 1HW at 35DAS 291 (104) 640 (417) 521 (271) 949 (904) 769 (615) 134 (21) 1513 (2331)LSD005 265 281 126 310 165 085 209119875 value 0005 0002 lt0001 005 0001 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 4 Effect of weed control treatments on weed biomass (gmminus2) at 35 days after sowing in the boro season Weed biomass data weresubjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Amaranthusspinosus

Celosiaargentea

Cleomerutidosperma

Cyperusrotundus

Cynodondactylon

Echinochloacolona

Total weedbiomass

Partial weedy 182 (28) 219 (46) 135 (14) 324 (101) 100 (05) 225 (47) 492 (241)Oxadiargyl fb ethoxysulfuron 071 (00) 071 (00) 071 (00) 219 (43) 086 (02) 089 (03) 231 (49)Pendimethalin fb ethoxysulfuron 071 (00) 119 (09) 071 (00) 236 (51) 092 (04) 079 (01) 265 (66)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 124 (10) 139 (15) 207 (38) 101 (06) 080 (01) 274 (70)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 123 (10) 071 (00) 185 (30) 109 (10) 115 (09) 251 (59)Oxadiargyl fb 1HW at 35DAS 071 (00) 071 (00) 071 (00) 301 (86) 103 (08) 071 (00) 313 (94)Pendimethalin fb 1HW at 35DAS 071 (00) 107 (06) 071 (00) 350 (119) 073 (00) 071 (00) 360 (126)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 122 (10) 140 (15) 084 (02) 242 (55) 076 (01) 096 (04) 302 (87)

Pyrazosulfuron fb 1HW at 35DAS 127 (11) 140 (15) 071 (00) 209 (39) 098 (05) 161 (23) 310 (93)LSD005 016 044 020 052 NS 040 063119875 value lt0001 lt0001 lt0001 lt0001 084 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

be effective in controlling a wide range of broadleaved weedsas well as sedges [20 21] Our results are also supported bya previous study on the furrow-irrigated raised-bed DSR inwhich ethoxysulfuron (18 g ai haminus1) applied at 21 DAS waseffective in controlling broadleaved weeds [8]

Weed density and biomass as affected by different weedcontrol treatments at anthesis are given in Tables 6ndash9 Fromthe data it is clear that all herbicide treatments resulted inlower weed density and biomass compared to the partialweedy plots (ie HW at 35 DAS) Similar with observationsmade at 35 DAS total weed density and biomass werealso greatly affected by weed control treatments at anthesisConsidering the total weed density plots treated with pre-followed by postemergence herbicides always had lower weeddensity than those treated with preemergence herbicides

followed by a one-time HW at 35 DAS (Tables 6 and 7)Weed biomass maintained a similar trend as weed densityin the boro season In the aman season however plots thatreceived preemergence herbicides followed by a one-timeHW had lower weed biomass than those that received pre-and postemergence herbicides (Tables 8 and 9)

In the aman season crop vegetative growth went very fastat the early growth stages Rice in the plots that received a one-time HW at 35 DAS suppressed weed growth at later stagesIn the boro season however rice growth was very poor up to65 DAS because of low temperatures Sequential applicationof pre- and postemergence herbicides reduced weed biomassby 31ndash55 and 20ndash52 in the boro and aman seasons respec-tively and preemergence herbicide application followed by aone-timeHWreduced biomass by 15ndash40and 40ndash62 in the

The Scientific World Journal 7

Table 5 Effect of weed control treatments on weed biomass (gmminus2) at 35 days after sowing in the aman season Weed biomass data weresubjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Ageratumconyzoides

Cyperusrotundus

Celosiaargentea

Digitariaciliaris

Echinochloacolona

Phyllanthusniruri

Total weedbiomass

Partial weedy 260 (63) 377 (138) 312 (93) 629 (391) 623 (384) 242 (56) 1063 (1124)Oxadiargyl fb ethoxysulfuron 100 (07) 203 (41) 142 (25) 353 (121 ) 369 (132) 071 (00) 574 (325)Pendimethalin fb ethoxysulfuron 114 (12) 212 (51) 304 (88) 374 (140) 342 (113) 201 (37) 667 (441)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 178 (33) 279 (73) 550 (306) 465 (213) 071 (00) 790 (625)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 145 (27) 127 (14) 577 (343) 503 (249) 071 (00) 797 (633)Oxadiargyl fb 1HW at 35DAS 129 (19) 403 (16) 127 (13) 387 (147) 392 (149) 071 (00) 701 (487)Pendimethalin fb 1HW at 35DAS 257 (64) 461 (209) 356 (122) 362 (130) 354 (125) 140 (15) 817 (663)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 071 (07) 324 (101) 449 (197) 536 (287) 545 (296) 071 (00) 941 (834)

Pyrazosulfuron fb 1HW at 35DAS 142 (18) 370 (133) 386 (145) 600 (357) 517 (279) 083 (02) 966 (801)LSD005 100 145 091 144 129 083 098119875 value 0003 0002 lt0001 0001 0003 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

respective seasons all compared with the partial weedy check(ie one-time HW)

Among the herbicide treatments plots treated with oxa-diargyl followed by ethoxysulfuron reduced total weed den-sity by 65ndash70 compared with the partial weedy plots (378ndash477 plants mminus2) (Tables 6 and 7) The next best treatmentswere pendimethalin followed by ethoxysulfuron (60ndash62reduction in weed density) and acetachlor + bensulfuran-methyl followed by ethoxysulfuron (52ndash55 reduction inweed density) Compared with the partial weedy plots thosetreated with pyrazosulfuron followed by ethoxysulfuron sup-pressed weed density by only 39ndash48

33 Effect of Weed Control Treatments on Yield and Yield-Contributing Parameters Yield and yield-contributingparameters except 1000-grain weight were highly influencedby weed control treatments and the results were consistent inboth seasons (Tables 10 and 11) The highest panicle numbers(253ndash347mminus2) were recorded in the weed-free plots Paniclenumber was always lower in the herbicide-treated plotsthan in the weed-free plots and always higher than in thepartial weedy plots In the boro season the highest paniclenumbers (281ndash316mminus2) were recorded in the plots thatreceived pre- followed by postemergence herbicides In theaman season these values (204ndash236 panicles mminus2) werehighest when the plots received preemergence herbicidesfollowed by a one-time HW Among herbicide treatmentsthe highest panicle numbers (230ndash315mminus2) were recordedin the oxadiargyl-treated plots The next best herbicidetreatment was pendimethalin with panicle numbers (230ndash301mminus2) comparable to that of the oxadiargyl-treatedplots The lowest panicle numbers were recorded in thepyrazosulfuron-treated plots in both seasons

The number of spikelets panicleminus1 was consistent acrossthe herbicide-treated plots in the boro season but it sig-nificantly differed in the aman season (Tables 10 and 11)

Herbicide-treated plots always had a higher number ofspikelets panicleminus1 (5ndash26 higher) than the partial weedyplots and always had a lower number than the weed-free plots(3ndash21 lower)

Grain yieldwas strongly influenced byweed control treat-ments (Tables 10 and 11) The highest yield (476ndash498 t haminus1)was obtained in the weed-free plots Herbicide-treated plotsalways yielded more than the partial weedy plots Amongthe herbicide treatments the highest yield was recorded inthe plots treated with oxadiargyl followed by ethoxysulfuron(413 t haminus1) in the boro season and oxadiargyl followed aone-timeHW(41 t haminus1) in the aman season Pendimethalin-treated plots produced a similar grain yield (41 t haminus1) Theplots treated with pyrazosulfuron produced the lowest yieldin both seasons Compared with the control treatmentherbicide-treated plots produced a 20ndash62higher yieldwhentreated with both pre- and postemergence herbicides thesevalues were 30ndash41 when plots received only preemergenceherbicide and a one-timeHWAlthough herbicide treatmentsresulted in a yield advantage over the control treatment noneof the herbicide treatments reached the yield levels fromthe weed-free plots Grain yield from the best-performingherbicide treatment was 13ndash18 lower than that from theweed-free plots suggesting that there is a considerable scopeto increase yield with improved weed control practices inDSR In the boro season yield was higher in the plots treatedwith preemergence followed by postemergence herbicidesbut the results were not consistent in both seasons In theaman season vegetative growth started early In the plots thatreceived preemergence herbicide followed by a one-timeHWcanopy closure occurred fast which suppressed weed growthat the later stages These results suggest that in the amanseason application of preemergence herbicide followed byHW was better than applying both preemergence and poste-mergence herbicides However these results also depend onothers factors such as efficacy of the postemergence herbicide

8 The Scientific World Journal

Table6Eff

ecto

fweedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

theb

oroseason

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

1267(161)

866

(748)

503

(25)

576

(327)

436

(188)

739(563)

304

(115

)868

(781)

438

(188)

2180(4773)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

856

(729)

773(604)

426

(188)

071

(00)

235

(104)

071

(00)

240

(55)

071

(00)

1298(1679)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

937(896

)70

3(49)

466

(215

)071

(00)

393

(156)

071

(00)

222

(47)

278

(94)

1378(1897)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

1014

(105)

779(604)

486

(240)

071

(00)

509

(260)

071

(00)

071

(00)

071

(00)

1458(2156)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

846

(729)

707(542)

642

(417

)233

(63)

652

(438)

448

(208)

071

(00)

291

(8)

1575(2476)

Oxadiargylfb

1HW

at35

DAS

595

(354)

834

(704)

709(50)

463

(302)

071

(00)

249

(58)

071

(00)

599

(375

)071

(00)

1514

(2293)

Pend

imethalin

fb1H

Wat35

DAS

424

(181)

1154(133)

571

(323)

424

(177

)071

(00)

179(33)

071

(00)

591

(354)

288

(83)

1546(2384)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

563

(313

)1035

(109)

619

(385)

460

(292

)071

(00)

399

(167)

071

(00)

492

(240)

071

(00)

1577(2489)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

636

(435)

643

(458)

650

(427)

374

(135)

747(678

)312

(94)

510

(257)

312

(94)

1593(2578)

LSD

005

107

249

NS

NS

091

367

136

171

124

284

119875value

lt0001

003

042

063

lt0001

0007

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 9

Table7Eff

ectofw

eedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

thea

man

season

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eind

icaGalinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

467

(217

)468

(240)

772(596

)255

(63)

1013

(102)

289

(81)

1062(117)

625

(398

)1945(3783)

Oxadiargylfb

etho

xysulfu

ron

211(40)

071

(00)

514

(260)

071

(00)

761(575)

071

(00)

343

(117

)396

(156)

1074

(1148)

Pend

imethalin

fbetho

xysulfu

ron

138(23)

071

(00)

601

(358)

071

(00)

654

(425)

294

(82)

575

(327)

514

(260)

1216

(1476

)Ac

etachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

597

(354)

295

(104)

905(817

)071

(00)

448

(210

)562

(313

)1342(1798)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

769(646)

252

(61)

1017

(104)

300

(87)

435

(203)

515

(273

)1519

(2307)

Oxadiargylfb

1HW

at35

DAS

281

(75)

279

(75)

468

(219

)071

(00)

460

(208)

071

(00)

1005(101)

438

(188)

1332

(1771)

Pend

imethalin

fb1H

Wat35

DAS

249

(73)

341

(115

)552

(300)

071

(00)

636

(400)

071

(00)

940(881)

475

(248)

1422(2017)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

260

(63)

363

(134)

465

(219

)200

(43)

945(906)

158(24)

991(983)

590

(354)

1650(2726)

Pyrazosulfu

ronfb

1HW

at35

DAS

255

(63)

397

(154)

325

(104)

192(42)

988(990

)232

(52)

910(833)

643

(415

)1630(2653)

LSD

005

134

147

216

147

170

077

242

NS

107

119875value

lt0001

lt0001

0029

001

lt0001

0001

lt0001

012

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

10 The Scientific World Journal

Table8Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )at

anthesisin

thebo

roseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Phyllanthu

sniruri

Galinsoga

ciliata

Totalw

eed

biom

ass

Partialw

eedy

710(52)

467

(217

)365

(129)

364

(13)

412

(19)

526

(27)

316

(13)

403

(16)

744(560)

1519

(2302)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

589

(353)

659

(429)

335

(111)

071

(00)

192(61)

071

(00)

071

(00)

285

(79)

1019

(1033)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

664

(443)

554

(303)

382

(145)

071

(00)

275

(78)

071

(00)

260

(81)

290

(81)

1066(1131)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

656

(437)

616

(375

)450

(203)

071

(00)

461

(21)

071

(00)

071

(00)

071

(00)

1106(1228)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

538

(277

)615

(417

)475

(221)

210

(49)

609

(39)

409

(17)

264

(65)

071

(00)

1262(1589)

Oxadiargylfb

1HW

at35

DAS

323

(101)

607

(364)

544

(291

)251

(74)

071

(00)

259

(62)

071

(00)

071

(00)

670

(444)

1158(1337)

Pend

imethalin

fb1H

Wat35

DAS

330

(11)

675

(453)

455

(206)

341

(113

)071

(00)

226

(48)

071

(00)

234

(56)

664

(441)

1196(14

27)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

392

(149)

618

(384)

486

(244)

373

(183)

071

(00)

299

(89)

071

(00)

071

(00)

530

(283)

1156(1332)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

503

(248)

531

(285)

561

(318

)370

(132)

598

(385)

362

(131)

257

(62)

628

(39)

1397(19

51)

LSD

005

111

190

NS

NS

123

245

134

130

155

124

119875value

lt0001

000

6015

011

lt0001

0001

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 11

Table9Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )atanthesisin

theam

anseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

biom

ass

Partialw

eedy

299

(86)

267

(73)

711(506)

178(28)

909(826)

201

(36)

712(511)

559

(313

)1543(2378)

Oxadiargylfb

etho

xysulfu

ron

224

(47)

071

(00)

537

(285)

071

(00)

800

(635)

071

(00)

259

(64)

328

(103)

1067(1135)

Pend

imethalin

fbetho

xysulfu

ron

185(36)

071

(00)

534

(2810)

071

(00)

676

(456)

206

(38)

429

(182)

494

(240)

1109(1231)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

454

(210

)228

(55)

946(896

)071

(00)

348

(129)

401

(162)

1204(14

52)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

688

(479

)19

8(35)

1008(1015)

212

(40)

418

(193

)388

(147)

1383(1908)

Oxadiargylfb

1HW

at35

DAS

221

(44)

165(23)

415

(171)

071

(00)

392

(153)

071

(00)

639

(405)

323

(102)

945(897

)Pend

imethalin

fb1H

Wat35

DAS

170(29)

197(36)

483

(232)

071

(00)

540

(287)

071

(00)

584

(337)

401

(171)

1046(1092)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

177(28)

194(340)

350

(118

)14

9(20)

719(515

)13

9(17)

569

(326)

489

(242)

1142(1301)

Pyrazosulfu

ronfb

1HW

at35

DAS

198(35)

195(33)

348

(116

)15

2(21)

825

(685)

162(24)

516

(264)

511(256)

1199(14

35)

LSD

005

089

076

133

087

139

055

188

146

130

119875value

0001

lt0001

lt0001

000

4lt0001

lt0001

0002

003

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

12 The Scientific World Journal

Table 10 Effect of weed control treatments on yield and yield components of rice in the boro season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 34700 8235 9352 1902 476Partial weedy 15967 5933 9279 1803 158Oxadiargyl fb ethoxysulfuron 31567 7838 9367 1870 413Pendimethalin fb ethoxysulfuron 30100 8025 9249 1854 408Acetachlor + bensulfuranmethyl fb ethoxysulfuron 30300 7793 9277 1861 401Pyrazosulfuron fb ethoxysulfuron 28167 7605 9174 1805 346Oxadiargyl fb 1HW at 35DAS 27833 7642 9167 1836 348Pendimethalin fb 1HW at 35DAS 26400 7612 9190 1823 338Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 27033 7662 9199 1890 342Pyrazosulfuron fb 1HW at 35DAS 24833 7547 9000 1862 322LSD005 2341 565 163 NS 028119875 value 119875 lt 0001 119875 lt 0001 0008 0074 119875 lt 0001

DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 11 Effect of weed control treatments on yield and yield components of rice in the aman season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 25333 12020 8871 1779 498Partial weedy 17233 9028 8893 1797 259Oxadiargyl fb ethoxysulfuron 23000 10230 9127 1755 353Pendimethalin fb ethoxysulfuron 21967 10252 8843 1774 343Acetachlor + bensulfuranmethyl fb ethoxysulfuron 18667 10057 8544 1719 307Pyrazosulfuron fb ethoxysulfuron 18033 9577 8953 1672 300Oxadiargyl fb 1HW at 35DAS 23633 11268 8663 1817 408Pendimethalin fb 1HW at 35DAS 23067 11363 8757 1828 405Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 21733 11070 8999 1707 395Pyrazosulfuron fb 1HW at 35DAS 20400 10797 8629 1700 385LSD005 1930 1071 255 NS 019119875 value lt0001 0001 0002 032 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

used weed flora in the field rice variety used and soil andclimatic conditions Information to support these results isnot available in the literature

Our study shows that even after the use of preemergencefollowed by postemergence herbicides at 21 DAS or preemer-gence followed by a one-time HW complete weed controlcannot be achieved In additionmanual weeding is becomingless popular due to high labor wages it will be difficult to findlabor for weeding in the futureTherefore additional researchneeds to be conducted on the performance of combinationsof different pre- and postemergence herbicides applicationtimings and herbicide doses across various seasons andenvironmental conditions

We found that some weed species emerged later in theseason (eg A arvensis P niruri and G ciliata) and thusescaped the postemergence herbicide application or the HWat 35 DAS Previous studies report that weeds emerging laterin the season may not reduce rice yield significantly but

add seeds to the soil seed bank and result in heavy weedinfestation in subsequent seasons [22 23] In both seasons wefound a significant and negative linear correlation betweengrain yield and weed biomass at anthesis (Figure 3) Therelationship was slightly stronger in the boro season (1198772 =075) than in the aman season (1198772 = 065) These resultsare supported by previous studies in India [10] and thePhilippines [18] both of which found that grain yield wasnegatively correlated with weed biomass

In conclusion it is clear that weeds are a serious problemin DSR production systems and herbicides are the essentialtool to control them However continuous use of a singleherbicide over a long period may cause the development ofherbicide-resistant weed biotypes Therefore it is crucial toevaluate herbicides and determine which are less harmfulto the crop and have the ability to control a wide rangeof weeds In addition when many effective herbicides areavailable farmers will have the option to rotate the use

The Scientific World Journal 13

Boro 2011-12

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

Gra

in y

ield

(t h

aminus1)

Gy = 579 minus 0016x

R2= 075

(a)

Aman 2012

Gy = 479 minus 0009x

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

R2= 065G

rain

yie

ld (t

haminus

1)

(b)

Figure 3 The relationship between grain yield and weed biomass

of different herbicides and will help reduce the risk ofresistance developing inweeds and shifts inweed flora towardproblematic weeds

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] GMahajan B S Chauhan J Timsina P P Singh and K SinghldquoCrop performance and water- and nitrogen-use efficiencies indry-seeded rice in response to irrigation and fertilizer amountsin northwest Indiardquo Field Crops Research vol 134 pp 59ndash702012

[2] B S Chauhan G Mahajan V Sardana J Timsina and M LJat ldquoProductivity and sustainability of the rice-wheat croppingsystem in the Indo-Gangetic Plains of the Indian subcontinentproblems opportunities and strategiesrdquoAdvances inAgronomyvol 117 pp 315ndash369 2012

[3] B A M Bouman and T P Tuong ldquoField water managementto save water and increase its productivity in irrigated lowlandricerdquo Agricultural and Water Management vol 49 no 1 pp 11ndash30 2001

[4] R Gopal R K Jat R K Malik et al ldquoDirect dry seeded riceproduction technology and weed management in rice basedsystemsrdquo Technical Bulletin International Maize and WheatImprovement Center New Delhi India 2010

[5] B S Chauhan and D E Johnson ldquoThe role of seed ecologyin improving weed management strategies in the tropicsrdquoAdvances in Agronomy vol 105 pp 221ndash262 2010

[6] G Mahajan and B S Chauhan ldquoEffects of planting pattern andcultivar on weed and crop growth in aerobic rice systemrdquoWeedTechnology vol 25 no 4 pp 521ndash525 2011

[7] S Singh J K Ladha R K Gupta et al ldquoEvaluation ofmulching intercropping with Sesbania and herbicide use forweed management in dry-seeded rice (Oryza sativa L)rdquo CropProtection vol 26 no 4 pp 518ndash524 2007

[8] S Singh L Bhushan J K Ladha R K Gupta A N Rao andB Sivaprasad ldquoWeed management in dry-seeded rice (Oryzasativa) cultivated in the furrow-irrigated raised-bed plantingsystemrdquo Crop Protection vol 25 no 5 pp 487ndash495 2006

[9] B S Chauhan and D E Johnson ldquoRow spacing and weedcontrol timing affect yield of aerobic ricerdquo Field Crops Researchvol 121 no 2 pp 226ndash231 2011

[10] B S Chauhan V P Singh A Kumar and D E JohnsonldquoRelations of rice seeding rates to crop and weed growth inaerobic ricerdquo Field Crops Research vol 121 no 1 pp 105ndash1152011

[11] B S Chauhan ldquoWeed ecology andweedmanagement strategiesfor dry-seeded rice in AsiardquoWeed Technology vol 26 no 1 pp1ndash13 2012

[12] B S Chauhan and JOpena ldquoWeedmanagement and grain yieldof rice sown at low seeding rates in mechanized dry-seededsystemsrdquo Field Crops Research vol 141 pp 9ndash15 2013

[13] L Bastiaans R Paolini and D T Baumann ldquoFocus on eco-logical weed management what is hindering adoptionrdquo WeedResearch vol 48 no 6 pp 481ndash491 2008

[14] G Mahajan B S Chauhan and D E Johnson ldquoWeed man-agement in aerobic rice in northwestern indo-gangetic plainsrdquoJournal of Crop Improvement vol 23 no 4 pp 366ndash382 2009

[15] D D Buhler M Liebman and J J Obrycki ldquoTheoretical andpractical challenges to an IPM approach to weed managementrdquoWeed Science vol 48 no 3 pp 274ndash280 2000

[16] S Ahmed M R Islam M M Alam M M Haque and A JM S Karim ldquoRice production and profitability as influencedby integrated crop and resources managementrdquo Eco-FriendlyAgriculture vol 11 pp 720ndash725 2011

[17] MHasanuzzamanO Islam and S Bapari ldquoEfficacy of differentherbicides over manual weeding in controlling weeds in trans-planted ricerdquoAustralian Journal of Crop Science vol 2 no 1 pp18ndash24 2008

[18] B S Chauhan and J Opena ldquoImplications of plant geometryand weed control options in designing a low-seeding seed-drillfor dry-seeded rice systemsrdquo Field Crops Research vol 144 pp225ndash231 2013

[19] D L Jordan P K Bollich A B Burns and D MWalker ldquoRice(Oryza sativa) response to clomazonerdquo Weed Science vol 46no 3 pp 374ndash380 1998

[20] J D Beaty B Guy and J Edmund ldquoBroadleaf weed control andcotton response with bensulfuron in ricerdquo in Proceedings of theSouthern Weed Science Society vol 46 pp 91ndash96 1993

[21] M Hess and R Rose ldquoHOE 095404 a new herbicide forbroadleaf weed and sedge control in ricerdquo in Proceedings of theBrighton Crop Protection ConferenceWeeds vol 2 pp 763ndash768Brighton UK 1995

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

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2 The Scientific World Journal

go as high as 90 if control measures are not taken [9]Timely weed control is therefore crucial in improving theproductivity and profitability of DSR [9]

Various weed management strategies such as thor-ough land preparation high seeding rate appropriate fertil-izer application optimum water management and manualmechanical and chemical weed control are used in DSRcultivation [10 11] Manual weeding is common in Asiancountries but its use is decreasing because of labor scarcityat the critical time of weeding and increasing labor costs[12] In addition some weeds (eg Echinochloa colona (L)Link and E crus-galli (L) Beauv) at their early growthstages look similar to rice seedlings making hand weeding(HW)difficult inDSRChemicalmethods ofweed control aretherefore the most practical and cost-efficient [8 13]Severalpreemergence (eg pendimethalin oxadiazon oxdiargyland pyrazosulfuron) and postemergence herbicides (egbispyribac-sodium azimsulfuron penoxsulam fenoxapropethoxysulfuron and 24-D) are nowavailable in variousAsiancountries and have been reported to provide effective weedcontrol [11]

In a previous study the sequential preemergence appli-cation of pendimethalin (1000 g ai haminus1) followed by poste-mergence application of bispyribac-sodium (30 g ai haminus1) at15 days after sowing (DAS) was found best for the control ofweeds in DSR [14] In another study the best result was foundwith the application of oxadiazon (750 g ai haminus1) applied at 2DAS followed by fenoxaprop + ethoxysulfuron (45 g ai haminus1)applied at 28 DAS [12] Results from different studies revealthat no single herbicide can control all weeds effectivelyin DSR systems Moreover the continuous use of a singleherbicide over a long period of time may develop herbicideresistance in weeds and shifts in weed flora [2 15] The rightselection of herbicides is thus very important in DSR

In Bangladesh chemical weed control is becoming pop-ular because of labor scarcity and also because it costs lessthan HW [16 17] However information on the performanceof herbicides is only available for transplanted rice and not forDSR systems This study was therefore conducted to evaluatethe performance of sequential applications of various pre-emergence herbicides followed by postemergence herbicidesin DSRmdashthe first was study conducted in Bangladesh for thispurpose

2 Materials and Methods

Field experiments were conducted at the research farm ofthe Regional Agricultural Research Station of the BangladeshAgricultural Research Institute (23∘111015840 N 89∘141015840 E and 671mabove mean sea level) in Jessore Bangladesh in the boro(dry) season of 2011-12 and in the aman (wet) season of2012 The area belongs to agroecological zone number 11known as the High Ganges River Floodplain The climatein the area is subtropical with an average annual rainfallof 1590mm (90 of which falls from May to September)minimum temperatures of 6ndash9∘C in January and maximumtemperatures of 36ndash44∘C in April-May Amount of rainfalland the minimum and maximum temperatures recorded at

the experimental site during the experimental periods arepresented in Figure 1 The weather data were collected fromthe Regional Agricultural Research Station located 300mfrom the experimental fieldThe soil in the experimental fieldat 0ndash15 cm depth was clay loam in texture (378 clay 315sand and 307 silt) with a bulk density of 158 g cmminus3 pH of78 and organic carbon content of 1

Prior to the start of the experiment the field was leveledusing a laser leveler Different rice varieties are recommendedfor use in different seasons and from which BRRI dhan28(140 d duration) and BRRI dhan49 (135 d duration) wereselected for the boro and aman seasons respectively In bothseasons certified seeds were used (source Bangladesh Agri-culture Development Corporation Jessore Bangladesh)Theexperiments in each season were arranged in a randomizedcomplete block design with three replications Unit plot sizewas 18 (6 times 3) m2

Ten weed control treatments were used in each season(i) weed-free (ii) partial weedy (iii) oxadiargyl (80 g ai haminus1applied at 2 DAS) followed by ethoxysulfuron (18 g ai haminus1applied at 21 DAS) (iv) pendimethalin (850 g ai haminus1 appliedat 2 DAS) followed by ethoxysulfuron (18 g ai haminus1 applied at21 DAS) (v) acetachlor + bensulfuranmethyl (240 g ai haminus1applied at 2 DAS) followed by ethoxysulfuron (18 g ai haminus1applied at 21 DAS) (vi) pyrazosulfuron (15 g ai haminus1 appliedat 2 DAS) followed by ethoxysulfuron (18 g ai haminus1 appliedat 21 DAS) (vii) oxadiargyl (80 g ai haminus1 applied at 2 DAS)followed by a one-time hand weeding (HW) at 35 DAS (viii)pendimethalin (850 g ai haminus1 applied at 2 DAS) followed by aone-timeHWat 35DAS (ix) acetachlor + bensulfuranmethyl(240 g ai haminus1 applied at 2 DAS) followed by a one-time HWat 35 DAS and (119909) pyrazosulfuron (15 g ai haminus1 applied at 2DAS) followed by a one-time HW at 35 DAS

Herbicides were applied using a knapsack-sprayer fittedwith three flat fan nozzles on a boom delivering 350 Lof solution haminus1 In weed-free plots weeds were removedmanually (5 times in the aman season and 7 times in theboro season) In the partial weedy plots HW was done onceat 35 DAS weeds were allowed to grow before and after itWeeds allowed to grow throughout the season may result inan almost 100 yield loss in DSR systems [9] In additionfarmers in irrigated areas rarely leave their rice fields infestedwith weeds throughout the season

Dry rice seeds were sown at a rate of 40 kg haminus1 and withrow spacing of 20 cm using a power tiller operated seed drillfitted with a fluted-type seed-metering device The crop wasplanted on November 22 2011 and June 17 2012 in the boroand aman seasons respectively Fertilizers were applied atthe rate of 160-20-60-12-22 kg haminus1 of N P K S and Znrespectively in the boro season and 120-15-48-12-22 kg haminus1of N P

K S and Zn respectively in the aman season AllP K S and Zn were applied immediately before sowingFertilizer N was applied in four equal splits (25 each) at14 DAS at the start of tillering at maximum tillering and atbooting stage

Light irrigation was supplied just after sowing and thefield was kept saturated up to 40 DAS in the boro season

The Scientific World Journal 3

Boro 2011-12

Nov Dec Jan Feb Mar Apr May 05

1015202530354045

0

10

20

30

40

50

Months (2011-12)

Rain

fall

(mm

)

Tem

pera

ture

(∘C)

MaxTMinTRainfall

(a)

Jun Jul Aug Sep Oct Nov

Aman 2012

0

10

20

30

40

50

Rain

fall

(mm

)

05

1015202530354045

Tem

pera

ture

(∘C)

Months (2012)

MaxTMinTRainfall

(b)

Figure 1 Maximum and minimum temperatures and total rainfall (mm) recorded at the experimental site in the boro and aman seasons of2011-12

and up to 20 DAS in the aman season after which irrigationwas supplied based on tensiometer readings using a thresholdvalue of 15 kPa at 15 cm soil depth Water was maintained at5 cm depth with each irrigation In the boro season the riceplants were severely infested with blast and leaf spots Fungi-cide tebuconazole + trifloxystrobin 75WP (300 g ai haminus1) wasthus applied at 35 and 70DAS Fipronil 3 G (10 kg ai haminus1) wasapplied at 70 DAS in the boro season and 40DAS in the amanseason to control stem borers

Rice plant density was counted at 14 DAS from fourrandomly selected 1m row lengths in each plot To evaluatethe efficacy of preemergence herbicide weed density wascounted groupwise (ie grasses broadleaves and sedges)at 20 DAS (ie before the application of postemergenceherbicide)These data were collected only in the aman seasonand weed biomass data was not measured because of the verysmall size of weed seedlings

To evaluate the efficacy of postemergence herbicide weeddensity and weed biomass were measured at 35 DAS andat anthesis At each sampling time two 40 cm times 40 cmquadrats were placed randomly in each plot Weeds werethen collected from each quadrat segregated by species andcounted Biomass was measured species-wise after sampleswere oven-dried at 70∘C for 72 h Rice tillers were collectedfrom the same quadrats used for weed sampling and thencounted and rice biomass was measured At harvest thenumber of rice panicles was counted from four randomlyselected 1m row lengths in each plot The number of grainsper panicle (filled and unfilled spikelets) was counted by arandom sampling of 20 panicles per plot Rice grain yield wasdetermined from the harvested area of 88 (40 times 22m) m2Grain yield was converted to t haminus1 at 14 moisture contentand 1000-grain weight was measured

Data were analyzed using analysis of variance (ANOVA)to evaluate differences among treatments Means were sep-arated using least significant differences (LSD) at 5 level

of significance using CropStat 72 (IRRI Philippines) Weeddensity and biomass data were subjected to square-roottransformation (radic119909 + 05)

3 Results and Discussion

31 Effect of Herbicides on Rice Plant Density Weed controltreatments affected rice plant density in the aman seasonbut not in the boro season Plant density range was 162ndash201 plants mminus2 in the boro season and 128ndash169 plants mminus2in the aman season (Figure 2) In both seasons the lowestplant density was found in plots treated with pendimethalinPendimethalin-treated plots had 14 and 22 lower plantdensities in the boro and aman seasons respectively com-pared with the plots that were not treated with any herbicideOther herbicide-treated plots had similar plant densities inboth seasons In the aman season heavy rains occurred afterherbicide application (Figure 1) which could be the maincause of low plant density in the pendimethalin-treated plotsNo heavy rains occurred after herbicide application in theboro seasonThe results suggest that pendimethalin can causephytotoxicity if heavy rainfall occurs after application ofherbicide Similar results were reported for oxadiazon herbi-cide in which rice plant density was lower compared withnontreated plots when heavy rains occurred immediatelyafter herbicide application [18] These studies suggest thatsoil water content is an important factor that can influenceherbicide phytotoxicity in rice Such toxicity can result inpoor crop establishment especially where low seeding ratesare used

32 Effect of Weed Control Treatments on Weed Density andBiomass Weed species varied with the growing seasonsSome species were not common in both seasons For exam-ple Amaranthus spinosus L Anagalis arvensis L Cleomerutidosperma DC and Cynodon dactylon (L) Pers were

4 The Scientific World Journal

0

50

100

150

200

250

Boro 2011-12

LSD

Weed control treatments

Wee

d-fre

e

Part

ial w

eedy

Oxa

diar

gylfb

etho

xysu

lfuro

n

Pend

imet

halin

fbet

hoxy

sulfu

ron

Acet

achl

or+

bens

ulfu

ranm

ethy

l fb

etho

xysu

lfuro

n

Pyra

zosu

lfuro

nfb

etho

xysu

lfuro

n

Oxa

diar

gylfb

1H

W

at 3

5 D

AS

Pend

imet

halin

fb1

HW

at 3

5 D

AS

Acet

achl

or+

bens

ulfu

ranm

ethy

lfb

1 H

W at

35

DA

S

Pyra

zosu

lfuro

nfb

1H

W at

35

DA

S

Plan

t den

sity

(no

mminus2)

(a)

Aman 2012

LSD

Weed control treatments

Wee

d-fre

e

Part

ial w

eedy

Oxa

diar

gylfb

etho

xysu

lfuro

n

Pend

imet

halin

fbet

hoxy

sulfu

ron

Acet

achl

or+

bens

ulfu

ranm

ethy

l fb

etho

xysu

lfuro

n

Oxa

diar

gylfb

1H

W

at 3

5 D

AS

Pend

imet

halin

fb1

HW

at 3

5 D

AS

Acet

achl

or+

bens

ulfu

ranm

ethy

lfb

1 H

W at

35

DA

S

Pyra

zosu

lfuro

nfb

1H

W at

35

DA

S

0

50

100

150

200

250

Pyra

zosu

lfuro

nfb

etho

xysu

lfuro

n

Plan

t den

sity

(no

mminus2)

(b)

Figure 2 Effect of weed control treatment on rice plant density (number mminus2) at 14 days after sowing

Table 1 Effect of weed control treatments on weed density (number mminus2) at 20DAS (before application of post-emergence herbicide) Weeddensity data were subjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Grasses Broadleaf Sedges TotalPartial weedy 1368 (1875) 1541 (2385) 1010 (1021) 2298 (5281)Oxadiargyl 680 (458) 898 (802) 562 (313) 1256 (1573)Pendimethalin 504 (250) 1231 (1510) 915 (839) 1613 (2599)Acetachlor + bensulfuranmethyl 675 (453) 941 (885) 690 (474) 1348 (1812)Pyrazosulfuron 1300 (1688) 846 (714) 597 (354) 1662 (2756)LSD005 129 164 155 139119875 value lt0001 lt0001 0001 lt0001DAS days after sowing LSD least significant difference at 5 level of significance 119875 probability

present only in the boro season and Ageratum conyzoidesL was present only in the aman season Such variationsmight be the result of the seasonal adaptation of weeds Inaddition nonrice crops were grown before the start of theexperiment This may be another reason for the variation Inthe boro season temperatures were low up to 60 DAS but itlater increased (Figure 1) Because of low initial temperaturescrop and weed growth was slow However the growth ofsome species (eg Cyperus rotundus L Cynodon dactylonand Cleome rutidosperma) was unaffected by the low tem-peratures and severely suppressed crop growth at its earlystages in the boro season Another interesting observationwas that someweed species (egA arvensisGalinsoga ciliateBlake and Phyllanthus niruri L) emerged later than usualwhich could be their strategy to ldquoescaperdquo the application ofpreemergence herbicides

The dominant weed species in the experiments wereCelosia argentea L Cyperus rotundusDactyloctenium aegyp-tium (L) Willd Digitaria ciliaris (Retz) Koel E colonaEleusine indica (L) GaertnG ciliate and P niruriThe appli-cation of preemergence herbicides significantly reducedweeddensity compared with the control plots (partial weedy)At 20 DAS (before application of postemergence herbicide)plots treated with preemergence herbicides had 45ndash70lower weed density than the partial weedy plots (Table 1)

Among the herbicide treatments oxadiargyl-treated plotshad the lowest total weed density (157 plants mminus2) followedby those treated with acetachlor + bensulfuranmethyl (181plants mminus2) The highest weed density was recorded in theplots treated with pyrazosulfuron In terms of weed groupsthe lowest grass density was recorded in the plots treated withpendimethalin (88 less than in the partial weedy check) and

The Scientific World Journal 5

Table 2 Effect of weed control treatments on weed density (number mminus2) at 35DAS in the boro season Weed density data were subjectedto square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Amaranthusspinosus

Celosiaargentea

Cleomerutidosperma

Cyperusrotundus

Cynodondactylon

Echinochloacolona

Total weeddensity

Partial weedy 544 (292) 906 (854) 622 (385) 886 (790) 383 (146) 877 (792) 1800 (3258)Oxadiargyl fbethoxysulfuron 071 (00) 071 (00) 071 (00) 532 (281) 255 (63) 256 (83) 650 (427)

Pendimethalin fbethoxysulfuron 071 (00) 426 (177) 071 (00) 607 (365) 215 (52) 197 (42) 797 (635)

Acetachlor +bensulfuranmethyl fbethoxysulfuron

071 (00) 563 (313) 456 (208) 690 (479) 174 (31) 197 (42) 1036 (1073)

Pyrazosulfuron fbethoxysulfuron 071 (00) 509 (260) 071 (00) 609 (375) 193 (63) 562 (313) 1007 (1010)

Oxadiargyl fb 1HW at35DAS 071 (00) 071 (00) 071 (00) 790 (635) 193 (63) 071 (00) 830 (698)

Pendimethalin fb 1HW at35DAS 071 (00) 524 (271) 071 (00) 940 (892) 152 (31) 071 (00) 1093 (1194)

Acetachlor +bensulfuraonmethyl fb1HW at 35DAS

372 (135) 582 (333) 353 (125) 707 (500) 151 (21) 371 (135) 1120 (1250)

Pyrazosulfuron fb 1HW at35DAS 367 (135) 614 (375) 071 (00) 754 (573) 396 (156) 747 (583) 1342 (1823)

LSD005 070 165 090 203 NS 214 208119875 value lt0001 lt0001 lt0001 0009 020 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

the highest was recorded in the plots treated with pyrazosul-furon (only 10 less than in the partial weedy check) Againstbroadleaved and sedges acetachlor + bensulfuraonmethyloxadiargyl and pyrazosulfuron performed well (63ndash70fewer broadleavedweeds and 54ndash70 fewer sedges comparedto the partial weedy check) while pendimethalin performedpoorly (suppressed only 37 and 18 of broadleaved andsedges resp) The observed effectiveness of pendimethalinin the control of grasses and its poor control of sedgesand broadleaved weeds are consistent with the findings ofprevious published studies [8 16 17 19]

At 35 DAS (after application of postemergence herbicidesand before HW) total weed density and weed biomass weregreatly affected by herbicide treatments Plots treated withpreemergence herbicides had 39ndash76 and 23ndash45 lowerweed densities (326 and 293 plants mminus2 in the boro andaman seasons resp) compared with the partial weedy check(Tables 2 and 3) However the values were 66ndash88 and 46ndash65 respectively when plots were treated with both pre- andpostemergence herbicides

Among the herbicide treatments oxadiargyl-treatedplots performed best followed by those treated withpendimethalin and acetachlor + bensulfuranmethyl Poorperformance was observed in the pyrazosulfuron-treatedplots A similar trend was found for total weed biomass(Tables 4 and 5) Plots that were treated with only preemer-gence herbicides had 50ndash66 and 29ndash57 less weed biomassthan the partial weedy plots in the boro and aman seasonsrespectively Plots that received both pre- and postemergence

herbicides had 70ndash80 and 44ndash67 less weed biomass in theboro and aman seasons respectively The effect of herbicideson individual weed density and biomass was significant inboth seasons except on C dactylon suggesting that applyingherbicidewas not effective against this weed species Oxadiar-gyl was superior to other herbicides in reducing weed densityand biomass of several individual weed species including Ecolona Ageratum conyzoides Amaranthus spinosus Cleomerutidosperma and Celosia argentea The next best treatmentwas pendimethalin which suppressed all weeds that weresuppressed by oxadiargyl except C argentea and P niruriHowever both herbicides were ineffective againstC rotundusin both seasons

Plots treated with both pre- and postemergence herbi-cides always had less total weed density and biomass thanthose that were treated with only preemergence herbicidesFor example the plots that received only preemergenceherbicides had a weed density range of 70ndash182 and 157ndash233plants mminus2 in the boro and aman seasons respectively In theplots that received both pre- and postemergence herbicidesweed density range was 43ndash107 and 84ndash152 plants mminus2respectively The same trend was observed in weed biomasswhich indicates that the postemergence herbicide ethoxy-sulfuron significantly lowered weed density and biomassEthoxysulfuron suppressed a range of broadleaved weedspecies (eg Ageratum conyzoides Amaranthus spinosusCleome rutidosperma Celosia argentea and P niruri) andsedges (eg C rotundus) but not grasses (eg E colona DciliarisandC dactylon) Ethoxysulfuron has been reported to

6 The Scientific World Journal

Table 3 Effect of weed control treatments on weed density (number mminus2) at 35DAS in the aman season Weed density data were subjectedto square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Ageratumconyzoides

Cyperusrotundus

Celosiaargentea

Digitariaciliaris

Echinochloacolona

Phyllanthusniruri

Total weeddensity

Partial weedy 585 (344) 736 (542) 419 (177) 1002 (102) 803 (642) 456 (208) 1712 (2933)Oxadiargyl fb ethoxysulfuron 071 (00) 37 (136) 111 (11) 663 (438) 469 (218) 071 (00) 920 (843)Pendimethalin fb ethoxysulfuron 071 (00) 360 (167) 412 (167) 599 (385) 486 (231) 388 (146) 1074 (1148)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 301 (115) 387 (146) 860 (74) 671 (458) 071 (00) 1209 (1458)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 215 (83) 111 (11) 900 (854) 760 (573) 071 (00) 1231 (1521)Oxadiargyl fb 1HW at 35DAS 235 (104) 738 (542) 174 (31) 727 (563) 581 (333) 071 (00) 1253 (1573)Pendimethalin fb 1HW at 35DAS 497 (25) 814 (667) 472 (219) 533 (282) 492 (240) 356 (125) 1334 (1781)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 181 (52) 572 (323) 544 (292) 834 (693) 826 (677) 071 (00) 1410 (1984)

Pyrazosulfuron fb 1HW at 35DAS 291 (104) 640 (417) 521 (271) 949 (904) 769 (615) 134 (21) 1513 (2331)LSD005 265 281 126 310 165 085 209119875 value 0005 0002 lt0001 005 0001 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 4 Effect of weed control treatments on weed biomass (gmminus2) at 35 days after sowing in the boro season Weed biomass data weresubjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Amaranthusspinosus

Celosiaargentea

Cleomerutidosperma

Cyperusrotundus

Cynodondactylon

Echinochloacolona

Total weedbiomass

Partial weedy 182 (28) 219 (46) 135 (14) 324 (101) 100 (05) 225 (47) 492 (241)Oxadiargyl fb ethoxysulfuron 071 (00) 071 (00) 071 (00) 219 (43) 086 (02) 089 (03) 231 (49)Pendimethalin fb ethoxysulfuron 071 (00) 119 (09) 071 (00) 236 (51) 092 (04) 079 (01) 265 (66)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 124 (10) 139 (15) 207 (38) 101 (06) 080 (01) 274 (70)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 123 (10) 071 (00) 185 (30) 109 (10) 115 (09) 251 (59)Oxadiargyl fb 1HW at 35DAS 071 (00) 071 (00) 071 (00) 301 (86) 103 (08) 071 (00) 313 (94)Pendimethalin fb 1HW at 35DAS 071 (00) 107 (06) 071 (00) 350 (119) 073 (00) 071 (00) 360 (126)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 122 (10) 140 (15) 084 (02) 242 (55) 076 (01) 096 (04) 302 (87)

Pyrazosulfuron fb 1HW at 35DAS 127 (11) 140 (15) 071 (00) 209 (39) 098 (05) 161 (23) 310 (93)LSD005 016 044 020 052 NS 040 063119875 value lt0001 lt0001 lt0001 lt0001 084 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

be effective in controlling a wide range of broadleaved weedsas well as sedges [20 21] Our results are also supported bya previous study on the furrow-irrigated raised-bed DSR inwhich ethoxysulfuron (18 g ai haminus1) applied at 21 DAS waseffective in controlling broadleaved weeds [8]

Weed density and biomass as affected by different weedcontrol treatments at anthesis are given in Tables 6ndash9 Fromthe data it is clear that all herbicide treatments resulted inlower weed density and biomass compared to the partialweedy plots (ie HW at 35 DAS) Similar with observationsmade at 35 DAS total weed density and biomass werealso greatly affected by weed control treatments at anthesisConsidering the total weed density plots treated with pre-followed by postemergence herbicides always had lower weeddensity than those treated with preemergence herbicides

followed by a one-time HW at 35 DAS (Tables 6 and 7)Weed biomass maintained a similar trend as weed densityin the boro season In the aman season however plots thatreceived preemergence herbicides followed by a one-timeHW had lower weed biomass than those that received pre-and postemergence herbicides (Tables 8 and 9)

In the aman season crop vegetative growth went very fastat the early growth stages Rice in the plots that received a one-time HW at 35 DAS suppressed weed growth at later stagesIn the boro season however rice growth was very poor up to65 DAS because of low temperatures Sequential applicationof pre- and postemergence herbicides reduced weed biomassby 31ndash55 and 20ndash52 in the boro and aman seasons respec-tively and preemergence herbicide application followed by aone-timeHWreduced biomass by 15ndash40and 40ndash62 in the

The Scientific World Journal 7

Table 5 Effect of weed control treatments on weed biomass (gmminus2) at 35 days after sowing in the aman season Weed biomass data weresubjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Ageratumconyzoides

Cyperusrotundus

Celosiaargentea

Digitariaciliaris

Echinochloacolona

Phyllanthusniruri

Total weedbiomass

Partial weedy 260 (63) 377 (138) 312 (93) 629 (391) 623 (384) 242 (56) 1063 (1124)Oxadiargyl fb ethoxysulfuron 100 (07) 203 (41) 142 (25) 353 (121 ) 369 (132) 071 (00) 574 (325)Pendimethalin fb ethoxysulfuron 114 (12) 212 (51) 304 (88) 374 (140) 342 (113) 201 (37) 667 (441)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 178 (33) 279 (73) 550 (306) 465 (213) 071 (00) 790 (625)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 145 (27) 127 (14) 577 (343) 503 (249) 071 (00) 797 (633)Oxadiargyl fb 1HW at 35DAS 129 (19) 403 (16) 127 (13) 387 (147) 392 (149) 071 (00) 701 (487)Pendimethalin fb 1HW at 35DAS 257 (64) 461 (209) 356 (122) 362 (130) 354 (125) 140 (15) 817 (663)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 071 (07) 324 (101) 449 (197) 536 (287) 545 (296) 071 (00) 941 (834)

Pyrazosulfuron fb 1HW at 35DAS 142 (18) 370 (133) 386 (145) 600 (357) 517 (279) 083 (02) 966 (801)LSD005 100 145 091 144 129 083 098119875 value 0003 0002 lt0001 0001 0003 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

respective seasons all compared with the partial weedy check(ie one-time HW)

Among the herbicide treatments plots treated with oxa-diargyl followed by ethoxysulfuron reduced total weed den-sity by 65ndash70 compared with the partial weedy plots (378ndash477 plants mminus2) (Tables 6 and 7) The next best treatmentswere pendimethalin followed by ethoxysulfuron (60ndash62reduction in weed density) and acetachlor + bensulfuran-methyl followed by ethoxysulfuron (52ndash55 reduction inweed density) Compared with the partial weedy plots thosetreated with pyrazosulfuron followed by ethoxysulfuron sup-pressed weed density by only 39ndash48

33 Effect of Weed Control Treatments on Yield and Yield-Contributing Parameters Yield and yield-contributingparameters except 1000-grain weight were highly influencedby weed control treatments and the results were consistent inboth seasons (Tables 10 and 11) The highest panicle numbers(253ndash347mminus2) were recorded in the weed-free plots Paniclenumber was always lower in the herbicide-treated plotsthan in the weed-free plots and always higher than in thepartial weedy plots In the boro season the highest paniclenumbers (281ndash316mminus2) were recorded in the plots thatreceived pre- followed by postemergence herbicides In theaman season these values (204ndash236 panicles mminus2) werehighest when the plots received preemergence herbicidesfollowed by a one-time HW Among herbicide treatmentsthe highest panicle numbers (230ndash315mminus2) were recordedin the oxadiargyl-treated plots The next best herbicidetreatment was pendimethalin with panicle numbers (230ndash301mminus2) comparable to that of the oxadiargyl-treatedplots The lowest panicle numbers were recorded in thepyrazosulfuron-treated plots in both seasons

The number of spikelets panicleminus1 was consistent acrossthe herbicide-treated plots in the boro season but it sig-nificantly differed in the aman season (Tables 10 and 11)

Herbicide-treated plots always had a higher number ofspikelets panicleminus1 (5ndash26 higher) than the partial weedyplots and always had a lower number than the weed-free plots(3ndash21 lower)

Grain yieldwas strongly influenced byweed control treat-ments (Tables 10 and 11) The highest yield (476ndash498 t haminus1)was obtained in the weed-free plots Herbicide-treated plotsalways yielded more than the partial weedy plots Amongthe herbicide treatments the highest yield was recorded inthe plots treated with oxadiargyl followed by ethoxysulfuron(413 t haminus1) in the boro season and oxadiargyl followed aone-timeHW(41 t haminus1) in the aman season Pendimethalin-treated plots produced a similar grain yield (41 t haminus1) Theplots treated with pyrazosulfuron produced the lowest yieldin both seasons Compared with the control treatmentherbicide-treated plots produced a 20ndash62higher yieldwhentreated with both pre- and postemergence herbicides thesevalues were 30ndash41 when plots received only preemergenceherbicide and a one-timeHWAlthough herbicide treatmentsresulted in a yield advantage over the control treatment noneof the herbicide treatments reached the yield levels fromthe weed-free plots Grain yield from the best-performingherbicide treatment was 13ndash18 lower than that from theweed-free plots suggesting that there is a considerable scopeto increase yield with improved weed control practices inDSR In the boro season yield was higher in the plots treatedwith preemergence followed by postemergence herbicidesbut the results were not consistent in both seasons In theaman season vegetative growth started early In the plots thatreceived preemergence herbicide followed by a one-timeHWcanopy closure occurred fast which suppressed weed growthat the later stages These results suggest that in the amanseason application of preemergence herbicide followed byHW was better than applying both preemergence and poste-mergence herbicides However these results also depend onothers factors such as efficacy of the postemergence herbicide

8 The Scientific World Journal

Table6Eff

ecto

fweedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

theb

oroseason

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

1267(161)

866

(748)

503

(25)

576

(327)

436

(188)

739(563)

304

(115

)868

(781)

438

(188)

2180(4773)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

856

(729)

773(604)

426

(188)

071

(00)

235

(104)

071

(00)

240

(55)

071

(00)

1298(1679)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

937(896

)70

3(49)

466

(215

)071

(00)

393

(156)

071

(00)

222

(47)

278

(94)

1378(1897)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

1014

(105)

779(604)

486

(240)

071

(00)

509

(260)

071

(00)

071

(00)

071

(00)

1458(2156)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

846

(729)

707(542)

642

(417

)233

(63)

652

(438)

448

(208)

071

(00)

291

(8)

1575(2476)

Oxadiargylfb

1HW

at35

DAS

595

(354)

834

(704)

709(50)

463

(302)

071

(00)

249

(58)

071

(00)

599

(375

)071

(00)

1514

(2293)

Pend

imethalin

fb1H

Wat35

DAS

424

(181)

1154(133)

571

(323)

424

(177

)071

(00)

179(33)

071

(00)

591

(354)

288

(83)

1546(2384)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

563

(313

)1035

(109)

619

(385)

460

(292

)071

(00)

399

(167)

071

(00)

492

(240)

071

(00)

1577(2489)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

636

(435)

643

(458)

650

(427)

374

(135)

747(678

)312

(94)

510

(257)

312

(94)

1593(2578)

LSD

005

107

249

NS

NS

091

367

136

171

124

284

119875value

lt0001

003

042

063

lt0001

0007

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 9

Table7Eff

ectofw

eedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

thea

man

season

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eind

icaGalinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

467

(217

)468

(240)

772(596

)255

(63)

1013

(102)

289

(81)

1062(117)

625

(398

)1945(3783)

Oxadiargylfb

etho

xysulfu

ron

211(40)

071

(00)

514

(260)

071

(00)

761(575)

071

(00)

343

(117

)396

(156)

1074

(1148)

Pend

imethalin

fbetho

xysulfu

ron

138(23)

071

(00)

601

(358)

071

(00)

654

(425)

294

(82)

575

(327)

514

(260)

1216

(1476

)Ac

etachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

597

(354)

295

(104)

905(817

)071

(00)

448

(210

)562

(313

)1342(1798)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

769(646)

252

(61)

1017

(104)

300

(87)

435

(203)

515

(273

)1519

(2307)

Oxadiargylfb

1HW

at35

DAS

281

(75)

279

(75)

468

(219

)071

(00)

460

(208)

071

(00)

1005(101)

438

(188)

1332

(1771)

Pend

imethalin

fb1H

Wat35

DAS

249

(73)

341

(115

)552

(300)

071

(00)

636

(400)

071

(00)

940(881)

475

(248)

1422(2017)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

260

(63)

363

(134)

465

(219

)200

(43)

945(906)

158(24)

991(983)

590

(354)

1650(2726)

Pyrazosulfu

ronfb

1HW

at35

DAS

255

(63)

397

(154)

325

(104)

192(42)

988(990

)232

(52)

910(833)

643

(415

)1630(2653)

LSD

005

134

147

216

147

170

077

242

NS

107

119875value

lt0001

lt0001

0029

001

lt0001

0001

lt0001

012

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

10 The Scientific World Journal

Table8Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )at

anthesisin

thebo

roseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Phyllanthu

sniruri

Galinsoga

ciliata

Totalw

eed

biom

ass

Partialw

eedy

710(52)

467

(217

)365

(129)

364

(13)

412

(19)

526

(27)

316

(13)

403

(16)

744(560)

1519

(2302)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

589

(353)

659

(429)

335

(111)

071

(00)

192(61)

071

(00)

071

(00)

285

(79)

1019

(1033)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

664

(443)

554

(303)

382

(145)

071

(00)

275

(78)

071

(00)

260

(81)

290

(81)

1066(1131)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

656

(437)

616

(375

)450

(203)

071

(00)

461

(21)

071

(00)

071

(00)

071

(00)

1106(1228)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

538

(277

)615

(417

)475

(221)

210

(49)

609

(39)

409

(17)

264

(65)

071

(00)

1262(1589)

Oxadiargylfb

1HW

at35

DAS

323

(101)

607

(364)

544

(291

)251

(74)

071

(00)

259

(62)

071

(00)

071

(00)

670

(444)

1158(1337)

Pend

imethalin

fb1H

Wat35

DAS

330

(11)

675

(453)

455

(206)

341

(113

)071

(00)

226

(48)

071

(00)

234

(56)

664

(441)

1196(14

27)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

392

(149)

618

(384)

486

(244)

373

(183)

071

(00)

299

(89)

071

(00)

071

(00)

530

(283)

1156(1332)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

503

(248)

531

(285)

561

(318

)370

(132)

598

(385)

362

(131)

257

(62)

628

(39)

1397(19

51)

LSD

005

111

190

NS

NS

123

245

134

130

155

124

119875value

lt0001

000

6015

011

lt0001

0001

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 11

Table9Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )atanthesisin

theam

anseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

biom

ass

Partialw

eedy

299

(86)

267

(73)

711(506)

178(28)

909(826)

201

(36)

712(511)

559

(313

)1543(2378)

Oxadiargylfb

etho

xysulfu

ron

224

(47)

071

(00)

537

(285)

071

(00)

800

(635)

071

(00)

259

(64)

328

(103)

1067(1135)

Pend

imethalin

fbetho

xysulfu

ron

185(36)

071

(00)

534

(2810)

071

(00)

676

(456)

206

(38)

429

(182)

494

(240)

1109(1231)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

454

(210

)228

(55)

946(896

)071

(00)

348

(129)

401

(162)

1204(14

52)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

688

(479

)19

8(35)

1008(1015)

212

(40)

418

(193

)388

(147)

1383(1908)

Oxadiargylfb

1HW

at35

DAS

221

(44)

165(23)

415

(171)

071

(00)

392

(153)

071

(00)

639

(405)

323

(102)

945(897

)Pend

imethalin

fb1H

Wat35

DAS

170(29)

197(36)

483

(232)

071

(00)

540

(287)

071

(00)

584

(337)

401

(171)

1046(1092)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

177(28)

194(340)

350

(118

)14

9(20)

719(515

)13

9(17)

569

(326)

489

(242)

1142(1301)

Pyrazosulfu

ronfb

1HW

at35

DAS

198(35)

195(33)

348

(116

)15

2(21)

825

(685)

162(24)

516

(264)

511(256)

1199(14

35)

LSD

005

089

076

133

087

139

055

188

146

130

119875value

0001

lt0001

lt0001

000

4lt0001

lt0001

0002

003

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

12 The Scientific World Journal

Table 10 Effect of weed control treatments on yield and yield components of rice in the boro season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 34700 8235 9352 1902 476Partial weedy 15967 5933 9279 1803 158Oxadiargyl fb ethoxysulfuron 31567 7838 9367 1870 413Pendimethalin fb ethoxysulfuron 30100 8025 9249 1854 408Acetachlor + bensulfuranmethyl fb ethoxysulfuron 30300 7793 9277 1861 401Pyrazosulfuron fb ethoxysulfuron 28167 7605 9174 1805 346Oxadiargyl fb 1HW at 35DAS 27833 7642 9167 1836 348Pendimethalin fb 1HW at 35DAS 26400 7612 9190 1823 338Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 27033 7662 9199 1890 342Pyrazosulfuron fb 1HW at 35DAS 24833 7547 9000 1862 322LSD005 2341 565 163 NS 028119875 value 119875 lt 0001 119875 lt 0001 0008 0074 119875 lt 0001

DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 11 Effect of weed control treatments on yield and yield components of rice in the aman season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 25333 12020 8871 1779 498Partial weedy 17233 9028 8893 1797 259Oxadiargyl fb ethoxysulfuron 23000 10230 9127 1755 353Pendimethalin fb ethoxysulfuron 21967 10252 8843 1774 343Acetachlor + bensulfuranmethyl fb ethoxysulfuron 18667 10057 8544 1719 307Pyrazosulfuron fb ethoxysulfuron 18033 9577 8953 1672 300Oxadiargyl fb 1HW at 35DAS 23633 11268 8663 1817 408Pendimethalin fb 1HW at 35DAS 23067 11363 8757 1828 405Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 21733 11070 8999 1707 395Pyrazosulfuron fb 1HW at 35DAS 20400 10797 8629 1700 385LSD005 1930 1071 255 NS 019119875 value lt0001 0001 0002 032 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

used weed flora in the field rice variety used and soil andclimatic conditions Information to support these results isnot available in the literature

Our study shows that even after the use of preemergencefollowed by postemergence herbicides at 21 DAS or preemer-gence followed by a one-time HW complete weed controlcannot be achieved In additionmanual weeding is becomingless popular due to high labor wages it will be difficult to findlabor for weeding in the futureTherefore additional researchneeds to be conducted on the performance of combinationsof different pre- and postemergence herbicides applicationtimings and herbicide doses across various seasons andenvironmental conditions

We found that some weed species emerged later in theseason (eg A arvensis P niruri and G ciliata) and thusescaped the postemergence herbicide application or the HWat 35 DAS Previous studies report that weeds emerging laterin the season may not reduce rice yield significantly but

add seeds to the soil seed bank and result in heavy weedinfestation in subsequent seasons [22 23] In both seasons wefound a significant and negative linear correlation betweengrain yield and weed biomass at anthesis (Figure 3) Therelationship was slightly stronger in the boro season (1198772 =075) than in the aman season (1198772 = 065) These resultsare supported by previous studies in India [10] and thePhilippines [18] both of which found that grain yield wasnegatively correlated with weed biomass

In conclusion it is clear that weeds are a serious problemin DSR production systems and herbicides are the essentialtool to control them However continuous use of a singleherbicide over a long period may cause the development ofherbicide-resistant weed biotypes Therefore it is crucial toevaluate herbicides and determine which are less harmfulto the crop and have the ability to control a wide rangeof weeds In addition when many effective herbicides areavailable farmers will have the option to rotate the use

The Scientific World Journal 13

Boro 2011-12

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

Gra

in y

ield

(t h

aminus1)

Gy = 579 minus 0016x

R2= 075

(a)

Aman 2012

Gy = 479 minus 0009x

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

R2= 065G

rain

yie

ld (t

haminus

1)

(b)

Figure 3 The relationship between grain yield and weed biomass

of different herbicides and will help reduce the risk ofresistance developing inweeds and shifts inweed flora towardproblematic weeds

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] GMahajan B S Chauhan J Timsina P P Singh and K SinghldquoCrop performance and water- and nitrogen-use efficiencies indry-seeded rice in response to irrigation and fertilizer amountsin northwest Indiardquo Field Crops Research vol 134 pp 59ndash702012

[2] B S Chauhan G Mahajan V Sardana J Timsina and M LJat ldquoProductivity and sustainability of the rice-wheat croppingsystem in the Indo-Gangetic Plains of the Indian subcontinentproblems opportunities and strategiesrdquoAdvances inAgronomyvol 117 pp 315ndash369 2012

[3] B A M Bouman and T P Tuong ldquoField water managementto save water and increase its productivity in irrigated lowlandricerdquo Agricultural and Water Management vol 49 no 1 pp 11ndash30 2001

[4] R Gopal R K Jat R K Malik et al ldquoDirect dry seeded riceproduction technology and weed management in rice basedsystemsrdquo Technical Bulletin International Maize and WheatImprovement Center New Delhi India 2010

[5] B S Chauhan and D E Johnson ldquoThe role of seed ecologyin improving weed management strategies in the tropicsrdquoAdvances in Agronomy vol 105 pp 221ndash262 2010

[6] G Mahajan and B S Chauhan ldquoEffects of planting pattern andcultivar on weed and crop growth in aerobic rice systemrdquoWeedTechnology vol 25 no 4 pp 521ndash525 2011

[7] S Singh J K Ladha R K Gupta et al ldquoEvaluation ofmulching intercropping with Sesbania and herbicide use forweed management in dry-seeded rice (Oryza sativa L)rdquo CropProtection vol 26 no 4 pp 518ndash524 2007

[8] S Singh L Bhushan J K Ladha R K Gupta A N Rao andB Sivaprasad ldquoWeed management in dry-seeded rice (Oryzasativa) cultivated in the furrow-irrigated raised-bed plantingsystemrdquo Crop Protection vol 25 no 5 pp 487ndash495 2006

[9] B S Chauhan and D E Johnson ldquoRow spacing and weedcontrol timing affect yield of aerobic ricerdquo Field Crops Researchvol 121 no 2 pp 226ndash231 2011

[10] B S Chauhan V P Singh A Kumar and D E JohnsonldquoRelations of rice seeding rates to crop and weed growth inaerobic ricerdquo Field Crops Research vol 121 no 1 pp 105ndash1152011

[11] B S Chauhan ldquoWeed ecology andweedmanagement strategiesfor dry-seeded rice in AsiardquoWeed Technology vol 26 no 1 pp1ndash13 2012

[12] B S Chauhan and JOpena ldquoWeedmanagement and grain yieldof rice sown at low seeding rates in mechanized dry-seededsystemsrdquo Field Crops Research vol 141 pp 9ndash15 2013

[13] L Bastiaans R Paolini and D T Baumann ldquoFocus on eco-logical weed management what is hindering adoptionrdquo WeedResearch vol 48 no 6 pp 481ndash491 2008

[14] G Mahajan B S Chauhan and D E Johnson ldquoWeed man-agement in aerobic rice in northwestern indo-gangetic plainsrdquoJournal of Crop Improvement vol 23 no 4 pp 366ndash382 2009

[15] D D Buhler M Liebman and J J Obrycki ldquoTheoretical andpractical challenges to an IPM approach to weed managementrdquoWeed Science vol 48 no 3 pp 274ndash280 2000

[16] S Ahmed M R Islam M M Alam M M Haque and A JM S Karim ldquoRice production and profitability as influencedby integrated crop and resources managementrdquo Eco-FriendlyAgriculture vol 11 pp 720ndash725 2011

[17] MHasanuzzamanO Islam and S Bapari ldquoEfficacy of differentherbicides over manual weeding in controlling weeds in trans-planted ricerdquoAustralian Journal of Crop Science vol 2 no 1 pp18ndash24 2008

[18] B S Chauhan and J Opena ldquoImplications of plant geometryand weed control options in designing a low-seeding seed-drillfor dry-seeded rice systemsrdquo Field Crops Research vol 144 pp225ndash231 2013

[19] D L Jordan P K Bollich A B Burns and D MWalker ldquoRice(Oryza sativa) response to clomazonerdquo Weed Science vol 46no 3 pp 374ndash380 1998

[20] J D Beaty B Guy and J Edmund ldquoBroadleaf weed control andcotton response with bensulfuron in ricerdquo in Proceedings of theSouthern Weed Science Society vol 46 pp 91ndash96 1993

[21] M Hess and R Rose ldquoHOE 095404 a new herbicide forbroadleaf weed and sedge control in ricerdquo in Proceedings of theBrighton Crop Protection ConferenceWeeds vol 2 pp 763ndash768Brighton UK 1995

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

Nutrition and Metabolism

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Food ScienceInternational Journal of

Agronomy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

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AgricultureAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BiodiversityInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Plant GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biotechnology Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Forestry ResearchInternational Journal of

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Journal of BotanyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International

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Cell BiologyInternational Journal of

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Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World Journal 3

Boro 2011-12

Nov Dec Jan Feb Mar Apr May 05

1015202530354045

0

10

20

30

40

50

Months (2011-12)

Rain

fall

(mm

)

Tem

pera

ture

(∘C)

MaxTMinTRainfall

(a)

Jun Jul Aug Sep Oct Nov

Aman 2012

0

10

20

30

40

50

Rain

fall

(mm

)

05

1015202530354045

Tem

pera

ture

(∘C)

Months (2012)

MaxTMinTRainfall

(b)

Figure 1 Maximum and minimum temperatures and total rainfall (mm) recorded at the experimental site in the boro and aman seasons of2011-12

and up to 20 DAS in the aman season after which irrigationwas supplied based on tensiometer readings using a thresholdvalue of 15 kPa at 15 cm soil depth Water was maintained at5 cm depth with each irrigation In the boro season the riceplants were severely infested with blast and leaf spots Fungi-cide tebuconazole + trifloxystrobin 75WP (300 g ai haminus1) wasthus applied at 35 and 70DAS Fipronil 3 G (10 kg ai haminus1) wasapplied at 70 DAS in the boro season and 40DAS in the amanseason to control stem borers

Rice plant density was counted at 14 DAS from fourrandomly selected 1m row lengths in each plot To evaluatethe efficacy of preemergence herbicide weed density wascounted groupwise (ie grasses broadleaves and sedges)at 20 DAS (ie before the application of postemergenceherbicide)These data were collected only in the aman seasonand weed biomass data was not measured because of the verysmall size of weed seedlings

To evaluate the efficacy of postemergence herbicide weeddensity and weed biomass were measured at 35 DAS andat anthesis At each sampling time two 40 cm times 40 cmquadrats were placed randomly in each plot Weeds werethen collected from each quadrat segregated by species andcounted Biomass was measured species-wise after sampleswere oven-dried at 70∘C for 72 h Rice tillers were collectedfrom the same quadrats used for weed sampling and thencounted and rice biomass was measured At harvest thenumber of rice panicles was counted from four randomlyselected 1m row lengths in each plot The number of grainsper panicle (filled and unfilled spikelets) was counted by arandom sampling of 20 panicles per plot Rice grain yield wasdetermined from the harvested area of 88 (40 times 22m) m2Grain yield was converted to t haminus1 at 14 moisture contentand 1000-grain weight was measured

Data were analyzed using analysis of variance (ANOVA)to evaluate differences among treatments Means were sep-arated using least significant differences (LSD) at 5 level

of significance using CropStat 72 (IRRI Philippines) Weeddensity and biomass data were subjected to square-roottransformation (radic119909 + 05)

3 Results and Discussion

31 Effect of Herbicides on Rice Plant Density Weed controltreatments affected rice plant density in the aman seasonbut not in the boro season Plant density range was 162ndash201 plants mminus2 in the boro season and 128ndash169 plants mminus2in the aman season (Figure 2) In both seasons the lowestplant density was found in plots treated with pendimethalinPendimethalin-treated plots had 14 and 22 lower plantdensities in the boro and aman seasons respectively com-pared with the plots that were not treated with any herbicideOther herbicide-treated plots had similar plant densities inboth seasons In the aman season heavy rains occurred afterherbicide application (Figure 1) which could be the maincause of low plant density in the pendimethalin-treated plotsNo heavy rains occurred after herbicide application in theboro seasonThe results suggest that pendimethalin can causephytotoxicity if heavy rainfall occurs after application ofherbicide Similar results were reported for oxadiazon herbi-cide in which rice plant density was lower compared withnontreated plots when heavy rains occurred immediatelyafter herbicide application [18] These studies suggest thatsoil water content is an important factor that can influenceherbicide phytotoxicity in rice Such toxicity can result inpoor crop establishment especially where low seeding ratesare used

32 Effect of Weed Control Treatments on Weed Density andBiomass Weed species varied with the growing seasonsSome species were not common in both seasons For exam-ple Amaranthus spinosus L Anagalis arvensis L Cleomerutidosperma DC and Cynodon dactylon (L) Pers were

4 The Scientific World Journal

0

50

100

150

200

250

Boro 2011-12

LSD

Weed control treatments

Wee

d-fre

e

Part

ial w

eedy

Oxa

diar

gylfb

etho

xysu

lfuro

n

Pend

imet

halin

fbet

hoxy

sulfu

ron

Acet

achl

or+

bens

ulfu

ranm

ethy

l fb

etho

xysu

lfuro

n

Pyra

zosu

lfuro

nfb

etho

xysu

lfuro

n

Oxa

diar

gylfb

1H

W

at 3

5 D

AS

Pend

imet

halin

fb1

HW

at 3

5 D

AS

Acet

achl

or+

bens

ulfu

ranm

ethy

lfb

1 H

W at

35

DA

S

Pyra

zosu

lfuro

nfb

1H

W at

35

DA

S

Plan

t den

sity

(no

mminus2)

(a)

Aman 2012

LSD

Weed control treatments

Wee

d-fre

e

Part

ial w

eedy

Oxa

diar

gylfb

etho

xysu

lfuro

n

Pend

imet

halin

fbet

hoxy

sulfu

ron

Acet

achl

or+

bens

ulfu

ranm

ethy

l fb

etho

xysu

lfuro

n

Oxa

diar

gylfb

1H

W

at 3

5 D

AS

Pend

imet

halin

fb1

HW

at 3

5 D

AS

Acet

achl

or+

bens

ulfu

ranm

ethy

lfb

1 H

W at

35

DA

S

Pyra

zosu

lfuro

nfb

1H

W at

35

DA

S

0

50

100

150

200

250

Pyra

zosu

lfuro

nfb

etho

xysu

lfuro

n

Plan

t den

sity

(no

mminus2)

(b)

Figure 2 Effect of weed control treatment on rice plant density (number mminus2) at 14 days after sowing

Table 1 Effect of weed control treatments on weed density (number mminus2) at 20DAS (before application of post-emergence herbicide) Weeddensity data were subjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Grasses Broadleaf Sedges TotalPartial weedy 1368 (1875) 1541 (2385) 1010 (1021) 2298 (5281)Oxadiargyl 680 (458) 898 (802) 562 (313) 1256 (1573)Pendimethalin 504 (250) 1231 (1510) 915 (839) 1613 (2599)Acetachlor + bensulfuranmethyl 675 (453) 941 (885) 690 (474) 1348 (1812)Pyrazosulfuron 1300 (1688) 846 (714) 597 (354) 1662 (2756)LSD005 129 164 155 139119875 value lt0001 lt0001 0001 lt0001DAS days after sowing LSD least significant difference at 5 level of significance 119875 probability

present only in the boro season and Ageratum conyzoidesL was present only in the aman season Such variationsmight be the result of the seasonal adaptation of weeds Inaddition nonrice crops were grown before the start of theexperiment This may be another reason for the variation Inthe boro season temperatures were low up to 60 DAS but itlater increased (Figure 1) Because of low initial temperaturescrop and weed growth was slow However the growth ofsome species (eg Cyperus rotundus L Cynodon dactylonand Cleome rutidosperma) was unaffected by the low tem-peratures and severely suppressed crop growth at its earlystages in the boro season Another interesting observationwas that someweed species (egA arvensisGalinsoga ciliateBlake and Phyllanthus niruri L) emerged later than usualwhich could be their strategy to ldquoescaperdquo the application ofpreemergence herbicides

The dominant weed species in the experiments wereCelosia argentea L Cyperus rotundusDactyloctenium aegyp-tium (L) Willd Digitaria ciliaris (Retz) Koel E colonaEleusine indica (L) GaertnG ciliate and P niruriThe appli-cation of preemergence herbicides significantly reducedweeddensity compared with the control plots (partial weedy)At 20 DAS (before application of postemergence herbicide)plots treated with preemergence herbicides had 45ndash70lower weed density than the partial weedy plots (Table 1)

Among the herbicide treatments oxadiargyl-treated plotshad the lowest total weed density (157 plants mminus2) followedby those treated with acetachlor + bensulfuranmethyl (181plants mminus2) The highest weed density was recorded in theplots treated with pyrazosulfuron In terms of weed groupsthe lowest grass density was recorded in the plots treated withpendimethalin (88 less than in the partial weedy check) and

The Scientific World Journal 5

Table 2 Effect of weed control treatments on weed density (number mminus2) at 35DAS in the boro season Weed density data were subjectedto square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Amaranthusspinosus

Celosiaargentea

Cleomerutidosperma

Cyperusrotundus

Cynodondactylon

Echinochloacolona

Total weeddensity

Partial weedy 544 (292) 906 (854) 622 (385) 886 (790) 383 (146) 877 (792) 1800 (3258)Oxadiargyl fbethoxysulfuron 071 (00) 071 (00) 071 (00) 532 (281) 255 (63) 256 (83) 650 (427)

Pendimethalin fbethoxysulfuron 071 (00) 426 (177) 071 (00) 607 (365) 215 (52) 197 (42) 797 (635)

Acetachlor +bensulfuranmethyl fbethoxysulfuron

071 (00) 563 (313) 456 (208) 690 (479) 174 (31) 197 (42) 1036 (1073)

Pyrazosulfuron fbethoxysulfuron 071 (00) 509 (260) 071 (00) 609 (375) 193 (63) 562 (313) 1007 (1010)

Oxadiargyl fb 1HW at35DAS 071 (00) 071 (00) 071 (00) 790 (635) 193 (63) 071 (00) 830 (698)

Pendimethalin fb 1HW at35DAS 071 (00) 524 (271) 071 (00) 940 (892) 152 (31) 071 (00) 1093 (1194)

Acetachlor +bensulfuraonmethyl fb1HW at 35DAS

372 (135) 582 (333) 353 (125) 707 (500) 151 (21) 371 (135) 1120 (1250)

Pyrazosulfuron fb 1HW at35DAS 367 (135) 614 (375) 071 (00) 754 (573) 396 (156) 747 (583) 1342 (1823)

LSD005 070 165 090 203 NS 214 208119875 value lt0001 lt0001 lt0001 0009 020 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

the highest was recorded in the plots treated with pyrazosul-furon (only 10 less than in the partial weedy check) Againstbroadleaved and sedges acetachlor + bensulfuraonmethyloxadiargyl and pyrazosulfuron performed well (63ndash70fewer broadleavedweeds and 54ndash70 fewer sedges comparedto the partial weedy check) while pendimethalin performedpoorly (suppressed only 37 and 18 of broadleaved andsedges resp) The observed effectiveness of pendimethalinin the control of grasses and its poor control of sedgesand broadleaved weeds are consistent with the findings ofprevious published studies [8 16 17 19]

At 35 DAS (after application of postemergence herbicidesand before HW) total weed density and weed biomass weregreatly affected by herbicide treatments Plots treated withpreemergence herbicides had 39ndash76 and 23ndash45 lowerweed densities (326 and 293 plants mminus2 in the boro andaman seasons resp) compared with the partial weedy check(Tables 2 and 3) However the values were 66ndash88 and 46ndash65 respectively when plots were treated with both pre- andpostemergence herbicides

Among the herbicide treatments oxadiargyl-treatedplots performed best followed by those treated withpendimethalin and acetachlor + bensulfuranmethyl Poorperformance was observed in the pyrazosulfuron-treatedplots A similar trend was found for total weed biomass(Tables 4 and 5) Plots that were treated with only preemer-gence herbicides had 50ndash66 and 29ndash57 less weed biomassthan the partial weedy plots in the boro and aman seasonsrespectively Plots that received both pre- and postemergence

herbicides had 70ndash80 and 44ndash67 less weed biomass in theboro and aman seasons respectively The effect of herbicideson individual weed density and biomass was significant inboth seasons except on C dactylon suggesting that applyingherbicidewas not effective against this weed species Oxadiar-gyl was superior to other herbicides in reducing weed densityand biomass of several individual weed species including Ecolona Ageratum conyzoides Amaranthus spinosus Cleomerutidosperma and Celosia argentea The next best treatmentwas pendimethalin which suppressed all weeds that weresuppressed by oxadiargyl except C argentea and P niruriHowever both herbicides were ineffective againstC rotundusin both seasons

Plots treated with both pre- and postemergence herbi-cides always had less total weed density and biomass thanthose that were treated with only preemergence herbicidesFor example the plots that received only preemergenceherbicides had a weed density range of 70ndash182 and 157ndash233plants mminus2 in the boro and aman seasons respectively In theplots that received both pre- and postemergence herbicidesweed density range was 43ndash107 and 84ndash152 plants mminus2respectively The same trend was observed in weed biomasswhich indicates that the postemergence herbicide ethoxy-sulfuron significantly lowered weed density and biomassEthoxysulfuron suppressed a range of broadleaved weedspecies (eg Ageratum conyzoides Amaranthus spinosusCleome rutidosperma Celosia argentea and P niruri) andsedges (eg C rotundus) but not grasses (eg E colona DciliarisandC dactylon) Ethoxysulfuron has been reported to

6 The Scientific World Journal

Table 3 Effect of weed control treatments on weed density (number mminus2) at 35DAS in the aman season Weed density data were subjectedto square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Ageratumconyzoides

Cyperusrotundus

Celosiaargentea

Digitariaciliaris

Echinochloacolona

Phyllanthusniruri

Total weeddensity

Partial weedy 585 (344) 736 (542) 419 (177) 1002 (102) 803 (642) 456 (208) 1712 (2933)Oxadiargyl fb ethoxysulfuron 071 (00) 37 (136) 111 (11) 663 (438) 469 (218) 071 (00) 920 (843)Pendimethalin fb ethoxysulfuron 071 (00) 360 (167) 412 (167) 599 (385) 486 (231) 388 (146) 1074 (1148)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 301 (115) 387 (146) 860 (74) 671 (458) 071 (00) 1209 (1458)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 215 (83) 111 (11) 900 (854) 760 (573) 071 (00) 1231 (1521)Oxadiargyl fb 1HW at 35DAS 235 (104) 738 (542) 174 (31) 727 (563) 581 (333) 071 (00) 1253 (1573)Pendimethalin fb 1HW at 35DAS 497 (25) 814 (667) 472 (219) 533 (282) 492 (240) 356 (125) 1334 (1781)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 181 (52) 572 (323) 544 (292) 834 (693) 826 (677) 071 (00) 1410 (1984)

Pyrazosulfuron fb 1HW at 35DAS 291 (104) 640 (417) 521 (271) 949 (904) 769 (615) 134 (21) 1513 (2331)LSD005 265 281 126 310 165 085 209119875 value 0005 0002 lt0001 005 0001 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 4 Effect of weed control treatments on weed biomass (gmminus2) at 35 days after sowing in the boro season Weed biomass data weresubjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Amaranthusspinosus

Celosiaargentea

Cleomerutidosperma

Cyperusrotundus

Cynodondactylon

Echinochloacolona

Total weedbiomass

Partial weedy 182 (28) 219 (46) 135 (14) 324 (101) 100 (05) 225 (47) 492 (241)Oxadiargyl fb ethoxysulfuron 071 (00) 071 (00) 071 (00) 219 (43) 086 (02) 089 (03) 231 (49)Pendimethalin fb ethoxysulfuron 071 (00) 119 (09) 071 (00) 236 (51) 092 (04) 079 (01) 265 (66)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 124 (10) 139 (15) 207 (38) 101 (06) 080 (01) 274 (70)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 123 (10) 071 (00) 185 (30) 109 (10) 115 (09) 251 (59)Oxadiargyl fb 1HW at 35DAS 071 (00) 071 (00) 071 (00) 301 (86) 103 (08) 071 (00) 313 (94)Pendimethalin fb 1HW at 35DAS 071 (00) 107 (06) 071 (00) 350 (119) 073 (00) 071 (00) 360 (126)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 122 (10) 140 (15) 084 (02) 242 (55) 076 (01) 096 (04) 302 (87)

Pyrazosulfuron fb 1HW at 35DAS 127 (11) 140 (15) 071 (00) 209 (39) 098 (05) 161 (23) 310 (93)LSD005 016 044 020 052 NS 040 063119875 value lt0001 lt0001 lt0001 lt0001 084 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

be effective in controlling a wide range of broadleaved weedsas well as sedges [20 21] Our results are also supported bya previous study on the furrow-irrigated raised-bed DSR inwhich ethoxysulfuron (18 g ai haminus1) applied at 21 DAS waseffective in controlling broadleaved weeds [8]

Weed density and biomass as affected by different weedcontrol treatments at anthesis are given in Tables 6ndash9 Fromthe data it is clear that all herbicide treatments resulted inlower weed density and biomass compared to the partialweedy plots (ie HW at 35 DAS) Similar with observationsmade at 35 DAS total weed density and biomass werealso greatly affected by weed control treatments at anthesisConsidering the total weed density plots treated with pre-followed by postemergence herbicides always had lower weeddensity than those treated with preemergence herbicides

followed by a one-time HW at 35 DAS (Tables 6 and 7)Weed biomass maintained a similar trend as weed densityin the boro season In the aman season however plots thatreceived preemergence herbicides followed by a one-timeHW had lower weed biomass than those that received pre-and postemergence herbicides (Tables 8 and 9)

In the aman season crop vegetative growth went very fastat the early growth stages Rice in the plots that received a one-time HW at 35 DAS suppressed weed growth at later stagesIn the boro season however rice growth was very poor up to65 DAS because of low temperatures Sequential applicationof pre- and postemergence herbicides reduced weed biomassby 31ndash55 and 20ndash52 in the boro and aman seasons respec-tively and preemergence herbicide application followed by aone-timeHWreduced biomass by 15ndash40and 40ndash62 in the

The Scientific World Journal 7

Table 5 Effect of weed control treatments on weed biomass (gmminus2) at 35 days after sowing in the aman season Weed biomass data weresubjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Ageratumconyzoides

Cyperusrotundus

Celosiaargentea

Digitariaciliaris

Echinochloacolona

Phyllanthusniruri

Total weedbiomass

Partial weedy 260 (63) 377 (138) 312 (93) 629 (391) 623 (384) 242 (56) 1063 (1124)Oxadiargyl fb ethoxysulfuron 100 (07) 203 (41) 142 (25) 353 (121 ) 369 (132) 071 (00) 574 (325)Pendimethalin fb ethoxysulfuron 114 (12) 212 (51) 304 (88) 374 (140) 342 (113) 201 (37) 667 (441)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 178 (33) 279 (73) 550 (306) 465 (213) 071 (00) 790 (625)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 145 (27) 127 (14) 577 (343) 503 (249) 071 (00) 797 (633)Oxadiargyl fb 1HW at 35DAS 129 (19) 403 (16) 127 (13) 387 (147) 392 (149) 071 (00) 701 (487)Pendimethalin fb 1HW at 35DAS 257 (64) 461 (209) 356 (122) 362 (130) 354 (125) 140 (15) 817 (663)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 071 (07) 324 (101) 449 (197) 536 (287) 545 (296) 071 (00) 941 (834)

Pyrazosulfuron fb 1HW at 35DAS 142 (18) 370 (133) 386 (145) 600 (357) 517 (279) 083 (02) 966 (801)LSD005 100 145 091 144 129 083 098119875 value 0003 0002 lt0001 0001 0003 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

respective seasons all compared with the partial weedy check(ie one-time HW)

Among the herbicide treatments plots treated with oxa-diargyl followed by ethoxysulfuron reduced total weed den-sity by 65ndash70 compared with the partial weedy plots (378ndash477 plants mminus2) (Tables 6 and 7) The next best treatmentswere pendimethalin followed by ethoxysulfuron (60ndash62reduction in weed density) and acetachlor + bensulfuran-methyl followed by ethoxysulfuron (52ndash55 reduction inweed density) Compared with the partial weedy plots thosetreated with pyrazosulfuron followed by ethoxysulfuron sup-pressed weed density by only 39ndash48

33 Effect of Weed Control Treatments on Yield and Yield-Contributing Parameters Yield and yield-contributingparameters except 1000-grain weight were highly influencedby weed control treatments and the results were consistent inboth seasons (Tables 10 and 11) The highest panicle numbers(253ndash347mminus2) were recorded in the weed-free plots Paniclenumber was always lower in the herbicide-treated plotsthan in the weed-free plots and always higher than in thepartial weedy plots In the boro season the highest paniclenumbers (281ndash316mminus2) were recorded in the plots thatreceived pre- followed by postemergence herbicides In theaman season these values (204ndash236 panicles mminus2) werehighest when the plots received preemergence herbicidesfollowed by a one-time HW Among herbicide treatmentsthe highest panicle numbers (230ndash315mminus2) were recordedin the oxadiargyl-treated plots The next best herbicidetreatment was pendimethalin with panicle numbers (230ndash301mminus2) comparable to that of the oxadiargyl-treatedplots The lowest panicle numbers were recorded in thepyrazosulfuron-treated plots in both seasons

The number of spikelets panicleminus1 was consistent acrossthe herbicide-treated plots in the boro season but it sig-nificantly differed in the aman season (Tables 10 and 11)

Herbicide-treated plots always had a higher number ofspikelets panicleminus1 (5ndash26 higher) than the partial weedyplots and always had a lower number than the weed-free plots(3ndash21 lower)

Grain yieldwas strongly influenced byweed control treat-ments (Tables 10 and 11) The highest yield (476ndash498 t haminus1)was obtained in the weed-free plots Herbicide-treated plotsalways yielded more than the partial weedy plots Amongthe herbicide treatments the highest yield was recorded inthe plots treated with oxadiargyl followed by ethoxysulfuron(413 t haminus1) in the boro season and oxadiargyl followed aone-timeHW(41 t haminus1) in the aman season Pendimethalin-treated plots produced a similar grain yield (41 t haminus1) Theplots treated with pyrazosulfuron produced the lowest yieldin both seasons Compared with the control treatmentherbicide-treated plots produced a 20ndash62higher yieldwhentreated with both pre- and postemergence herbicides thesevalues were 30ndash41 when plots received only preemergenceherbicide and a one-timeHWAlthough herbicide treatmentsresulted in a yield advantage over the control treatment noneof the herbicide treatments reached the yield levels fromthe weed-free plots Grain yield from the best-performingherbicide treatment was 13ndash18 lower than that from theweed-free plots suggesting that there is a considerable scopeto increase yield with improved weed control practices inDSR In the boro season yield was higher in the plots treatedwith preemergence followed by postemergence herbicidesbut the results were not consistent in both seasons In theaman season vegetative growth started early In the plots thatreceived preemergence herbicide followed by a one-timeHWcanopy closure occurred fast which suppressed weed growthat the later stages These results suggest that in the amanseason application of preemergence herbicide followed byHW was better than applying both preemergence and poste-mergence herbicides However these results also depend onothers factors such as efficacy of the postemergence herbicide

8 The Scientific World Journal

Table6Eff

ecto

fweedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

theb

oroseason

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

1267(161)

866

(748)

503

(25)

576

(327)

436

(188)

739(563)

304

(115

)868

(781)

438

(188)

2180(4773)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

856

(729)

773(604)

426

(188)

071

(00)

235

(104)

071

(00)

240

(55)

071

(00)

1298(1679)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

937(896

)70

3(49)

466

(215

)071

(00)

393

(156)

071

(00)

222

(47)

278

(94)

1378(1897)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

1014

(105)

779(604)

486

(240)

071

(00)

509

(260)

071

(00)

071

(00)

071

(00)

1458(2156)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

846

(729)

707(542)

642

(417

)233

(63)

652

(438)

448

(208)

071

(00)

291

(8)

1575(2476)

Oxadiargylfb

1HW

at35

DAS

595

(354)

834

(704)

709(50)

463

(302)

071

(00)

249

(58)

071

(00)

599

(375

)071

(00)

1514

(2293)

Pend

imethalin

fb1H

Wat35

DAS

424

(181)

1154(133)

571

(323)

424

(177

)071

(00)

179(33)

071

(00)

591

(354)

288

(83)

1546(2384)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

563

(313

)1035

(109)

619

(385)

460

(292

)071

(00)

399

(167)

071

(00)

492

(240)

071

(00)

1577(2489)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

636

(435)

643

(458)

650

(427)

374

(135)

747(678

)312

(94)

510

(257)

312

(94)

1593(2578)

LSD

005

107

249

NS

NS

091

367

136

171

124

284

119875value

lt0001

003

042

063

lt0001

0007

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 9

Table7Eff

ectofw

eedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

thea

man

season

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eind

icaGalinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

467

(217

)468

(240)

772(596

)255

(63)

1013

(102)

289

(81)

1062(117)

625

(398

)1945(3783)

Oxadiargylfb

etho

xysulfu

ron

211(40)

071

(00)

514

(260)

071

(00)

761(575)

071

(00)

343

(117

)396

(156)

1074

(1148)

Pend

imethalin

fbetho

xysulfu

ron

138(23)

071

(00)

601

(358)

071

(00)

654

(425)

294

(82)

575

(327)

514

(260)

1216

(1476

)Ac

etachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

597

(354)

295

(104)

905(817

)071

(00)

448

(210

)562

(313

)1342(1798)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

769(646)

252

(61)

1017

(104)

300

(87)

435

(203)

515

(273

)1519

(2307)

Oxadiargylfb

1HW

at35

DAS

281

(75)

279

(75)

468

(219

)071

(00)

460

(208)

071

(00)

1005(101)

438

(188)

1332

(1771)

Pend

imethalin

fb1H

Wat35

DAS

249

(73)

341

(115

)552

(300)

071

(00)

636

(400)

071

(00)

940(881)

475

(248)

1422(2017)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

260

(63)

363

(134)

465

(219

)200

(43)

945(906)

158(24)

991(983)

590

(354)

1650(2726)

Pyrazosulfu

ronfb

1HW

at35

DAS

255

(63)

397

(154)

325

(104)

192(42)

988(990

)232

(52)

910(833)

643

(415

)1630(2653)

LSD

005

134

147

216

147

170

077

242

NS

107

119875value

lt0001

lt0001

0029

001

lt0001

0001

lt0001

012

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

10 The Scientific World Journal

Table8Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )at

anthesisin

thebo

roseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Phyllanthu

sniruri

Galinsoga

ciliata

Totalw

eed

biom

ass

Partialw

eedy

710(52)

467

(217

)365

(129)

364

(13)

412

(19)

526

(27)

316

(13)

403

(16)

744(560)

1519

(2302)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

589

(353)

659

(429)

335

(111)

071

(00)

192(61)

071

(00)

071

(00)

285

(79)

1019

(1033)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

664

(443)

554

(303)

382

(145)

071

(00)

275

(78)

071

(00)

260

(81)

290

(81)

1066(1131)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

656

(437)

616

(375

)450

(203)

071

(00)

461

(21)

071

(00)

071

(00)

071

(00)

1106(1228)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

538

(277

)615

(417

)475

(221)

210

(49)

609

(39)

409

(17)

264

(65)

071

(00)

1262(1589)

Oxadiargylfb

1HW

at35

DAS

323

(101)

607

(364)

544

(291

)251

(74)

071

(00)

259

(62)

071

(00)

071

(00)

670

(444)

1158(1337)

Pend

imethalin

fb1H

Wat35

DAS

330

(11)

675

(453)

455

(206)

341

(113

)071

(00)

226

(48)

071

(00)

234

(56)

664

(441)

1196(14

27)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

392

(149)

618

(384)

486

(244)

373

(183)

071

(00)

299

(89)

071

(00)

071

(00)

530

(283)

1156(1332)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

503

(248)

531

(285)

561

(318

)370

(132)

598

(385)

362

(131)

257

(62)

628

(39)

1397(19

51)

LSD

005

111

190

NS

NS

123

245

134

130

155

124

119875value

lt0001

000

6015

011

lt0001

0001

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 11

Table9Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )atanthesisin

theam

anseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

biom

ass

Partialw

eedy

299

(86)

267

(73)

711(506)

178(28)

909(826)

201

(36)

712(511)

559

(313

)1543(2378)

Oxadiargylfb

etho

xysulfu

ron

224

(47)

071

(00)

537

(285)

071

(00)

800

(635)

071

(00)

259

(64)

328

(103)

1067(1135)

Pend

imethalin

fbetho

xysulfu

ron

185(36)

071

(00)

534

(2810)

071

(00)

676

(456)

206

(38)

429

(182)

494

(240)

1109(1231)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

454

(210

)228

(55)

946(896

)071

(00)

348

(129)

401

(162)

1204(14

52)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

688

(479

)19

8(35)

1008(1015)

212

(40)

418

(193

)388

(147)

1383(1908)

Oxadiargylfb

1HW

at35

DAS

221

(44)

165(23)

415

(171)

071

(00)

392

(153)

071

(00)

639

(405)

323

(102)

945(897

)Pend

imethalin

fb1H

Wat35

DAS

170(29)

197(36)

483

(232)

071

(00)

540

(287)

071

(00)

584

(337)

401

(171)

1046(1092)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

177(28)

194(340)

350

(118

)14

9(20)

719(515

)13

9(17)

569

(326)

489

(242)

1142(1301)

Pyrazosulfu

ronfb

1HW

at35

DAS

198(35)

195(33)

348

(116

)15

2(21)

825

(685)

162(24)

516

(264)

511(256)

1199(14

35)

LSD

005

089

076

133

087

139

055

188

146

130

119875value

0001

lt0001

lt0001

000

4lt0001

lt0001

0002

003

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

12 The Scientific World Journal

Table 10 Effect of weed control treatments on yield and yield components of rice in the boro season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 34700 8235 9352 1902 476Partial weedy 15967 5933 9279 1803 158Oxadiargyl fb ethoxysulfuron 31567 7838 9367 1870 413Pendimethalin fb ethoxysulfuron 30100 8025 9249 1854 408Acetachlor + bensulfuranmethyl fb ethoxysulfuron 30300 7793 9277 1861 401Pyrazosulfuron fb ethoxysulfuron 28167 7605 9174 1805 346Oxadiargyl fb 1HW at 35DAS 27833 7642 9167 1836 348Pendimethalin fb 1HW at 35DAS 26400 7612 9190 1823 338Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 27033 7662 9199 1890 342Pyrazosulfuron fb 1HW at 35DAS 24833 7547 9000 1862 322LSD005 2341 565 163 NS 028119875 value 119875 lt 0001 119875 lt 0001 0008 0074 119875 lt 0001

DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 11 Effect of weed control treatments on yield and yield components of rice in the aman season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 25333 12020 8871 1779 498Partial weedy 17233 9028 8893 1797 259Oxadiargyl fb ethoxysulfuron 23000 10230 9127 1755 353Pendimethalin fb ethoxysulfuron 21967 10252 8843 1774 343Acetachlor + bensulfuranmethyl fb ethoxysulfuron 18667 10057 8544 1719 307Pyrazosulfuron fb ethoxysulfuron 18033 9577 8953 1672 300Oxadiargyl fb 1HW at 35DAS 23633 11268 8663 1817 408Pendimethalin fb 1HW at 35DAS 23067 11363 8757 1828 405Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 21733 11070 8999 1707 395Pyrazosulfuron fb 1HW at 35DAS 20400 10797 8629 1700 385LSD005 1930 1071 255 NS 019119875 value lt0001 0001 0002 032 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

used weed flora in the field rice variety used and soil andclimatic conditions Information to support these results isnot available in the literature

Our study shows that even after the use of preemergencefollowed by postemergence herbicides at 21 DAS or preemer-gence followed by a one-time HW complete weed controlcannot be achieved In additionmanual weeding is becomingless popular due to high labor wages it will be difficult to findlabor for weeding in the futureTherefore additional researchneeds to be conducted on the performance of combinationsof different pre- and postemergence herbicides applicationtimings and herbicide doses across various seasons andenvironmental conditions

We found that some weed species emerged later in theseason (eg A arvensis P niruri and G ciliata) and thusescaped the postemergence herbicide application or the HWat 35 DAS Previous studies report that weeds emerging laterin the season may not reduce rice yield significantly but

add seeds to the soil seed bank and result in heavy weedinfestation in subsequent seasons [22 23] In both seasons wefound a significant and negative linear correlation betweengrain yield and weed biomass at anthesis (Figure 3) Therelationship was slightly stronger in the boro season (1198772 =075) than in the aman season (1198772 = 065) These resultsare supported by previous studies in India [10] and thePhilippines [18] both of which found that grain yield wasnegatively correlated with weed biomass

In conclusion it is clear that weeds are a serious problemin DSR production systems and herbicides are the essentialtool to control them However continuous use of a singleherbicide over a long period may cause the development ofherbicide-resistant weed biotypes Therefore it is crucial toevaluate herbicides and determine which are less harmfulto the crop and have the ability to control a wide rangeof weeds In addition when many effective herbicides areavailable farmers will have the option to rotate the use

The Scientific World Journal 13

Boro 2011-12

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

Gra

in y

ield

(t h

aminus1)

Gy = 579 minus 0016x

R2= 075

(a)

Aman 2012

Gy = 479 minus 0009x

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

R2= 065G

rain

yie

ld (t

haminus

1)

(b)

Figure 3 The relationship between grain yield and weed biomass

of different herbicides and will help reduce the risk ofresistance developing inweeds and shifts inweed flora towardproblematic weeds

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] GMahajan B S Chauhan J Timsina P P Singh and K SinghldquoCrop performance and water- and nitrogen-use efficiencies indry-seeded rice in response to irrigation and fertilizer amountsin northwest Indiardquo Field Crops Research vol 134 pp 59ndash702012

[2] B S Chauhan G Mahajan V Sardana J Timsina and M LJat ldquoProductivity and sustainability of the rice-wheat croppingsystem in the Indo-Gangetic Plains of the Indian subcontinentproblems opportunities and strategiesrdquoAdvances inAgronomyvol 117 pp 315ndash369 2012

[3] B A M Bouman and T P Tuong ldquoField water managementto save water and increase its productivity in irrigated lowlandricerdquo Agricultural and Water Management vol 49 no 1 pp 11ndash30 2001

[4] R Gopal R K Jat R K Malik et al ldquoDirect dry seeded riceproduction technology and weed management in rice basedsystemsrdquo Technical Bulletin International Maize and WheatImprovement Center New Delhi India 2010

[5] B S Chauhan and D E Johnson ldquoThe role of seed ecologyin improving weed management strategies in the tropicsrdquoAdvances in Agronomy vol 105 pp 221ndash262 2010

[6] G Mahajan and B S Chauhan ldquoEffects of planting pattern andcultivar on weed and crop growth in aerobic rice systemrdquoWeedTechnology vol 25 no 4 pp 521ndash525 2011

[7] S Singh J K Ladha R K Gupta et al ldquoEvaluation ofmulching intercropping with Sesbania and herbicide use forweed management in dry-seeded rice (Oryza sativa L)rdquo CropProtection vol 26 no 4 pp 518ndash524 2007

[8] S Singh L Bhushan J K Ladha R K Gupta A N Rao andB Sivaprasad ldquoWeed management in dry-seeded rice (Oryzasativa) cultivated in the furrow-irrigated raised-bed plantingsystemrdquo Crop Protection vol 25 no 5 pp 487ndash495 2006

[9] B S Chauhan and D E Johnson ldquoRow spacing and weedcontrol timing affect yield of aerobic ricerdquo Field Crops Researchvol 121 no 2 pp 226ndash231 2011

[10] B S Chauhan V P Singh A Kumar and D E JohnsonldquoRelations of rice seeding rates to crop and weed growth inaerobic ricerdquo Field Crops Research vol 121 no 1 pp 105ndash1152011

[11] B S Chauhan ldquoWeed ecology andweedmanagement strategiesfor dry-seeded rice in AsiardquoWeed Technology vol 26 no 1 pp1ndash13 2012

[12] B S Chauhan and JOpena ldquoWeedmanagement and grain yieldof rice sown at low seeding rates in mechanized dry-seededsystemsrdquo Field Crops Research vol 141 pp 9ndash15 2013

[13] L Bastiaans R Paolini and D T Baumann ldquoFocus on eco-logical weed management what is hindering adoptionrdquo WeedResearch vol 48 no 6 pp 481ndash491 2008

[14] G Mahajan B S Chauhan and D E Johnson ldquoWeed man-agement in aerobic rice in northwestern indo-gangetic plainsrdquoJournal of Crop Improvement vol 23 no 4 pp 366ndash382 2009

[15] D D Buhler M Liebman and J J Obrycki ldquoTheoretical andpractical challenges to an IPM approach to weed managementrdquoWeed Science vol 48 no 3 pp 274ndash280 2000

[16] S Ahmed M R Islam M M Alam M M Haque and A JM S Karim ldquoRice production and profitability as influencedby integrated crop and resources managementrdquo Eco-FriendlyAgriculture vol 11 pp 720ndash725 2011

[17] MHasanuzzamanO Islam and S Bapari ldquoEfficacy of differentherbicides over manual weeding in controlling weeds in trans-planted ricerdquoAustralian Journal of Crop Science vol 2 no 1 pp18ndash24 2008

[18] B S Chauhan and J Opena ldquoImplications of plant geometryand weed control options in designing a low-seeding seed-drillfor dry-seeded rice systemsrdquo Field Crops Research vol 144 pp225ndash231 2013

[19] D L Jordan P K Bollich A B Burns and D MWalker ldquoRice(Oryza sativa) response to clomazonerdquo Weed Science vol 46no 3 pp 374ndash380 1998

[20] J D Beaty B Guy and J Edmund ldquoBroadleaf weed control andcotton response with bensulfuron in ricerdquo in Proceedings of theSouthern Weed Science Society vol 46 pp 91ndash96 1993

[21] M Hess and R Rose ldquoHOE 095404 a new herbicide forbroadleaf weed and sedge control in ricerdquo in Proceedings of theBrighton Crop Protection ConferenceWeeds vol 2 pp 763ndash768Brighton UK 1995

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

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4 The Scientific World Journal

0

50

100

150

200

250

Boro 2011-12

LSD

Weed control treatments

Wee

d-fre

e

Part

ial w

eedy

Oxa

diar

gylfb

etho

xysu

lfuro

n

Pend

imet

halin

fbet

hoxy

sulfu

ron

Acet

achl

or+

bens

ulfu

ranm

ethy

l fb

etho

xysu

lfuro

n

Pyra

zosu

lfuro

nfb

etho

xysu

lfuro

n

Oxa

diar

gylfb

1H

W

at 3

5 D

AS

Pend

imet

halin

fb1

HW

at 3

5 D

AS

Acet

achl

or+

bens

ulfu

ranm

ethy

lfb

1 H

W at

35

DA

S

Pyra

zosu

lfuro

nfb

1H

W at

35

DA

S

Plan

t den

sity

(no

mminus2)

(a)

Aman 2012

LSD

Weed control treatments

Wee

d-fre

e

Part

ial w

eedy

Oxa

diar

gylfb

etho

xysu

lfuro

n

Pend

imet

halin

fbet

hoxy

sulfu

ron

Acet

achl

or+

bens

ulfu

ranm

ethy

l fb

etho

xysu

lfuro

n

Oxa

diar

gylfb

1H

W

at 3

5 D

AS

Pend

imet

halin

fb1

HW

at 3

5 D

AS

Acet

achl

or+

bens

ulfu

ranm

ethy

lfb

1 H

W at

35

DA

S

Pyra

zosu

lfuro

nfb

1H

W at

35

DA

S

0

50

100

150

200

250

Pyra

zosu

lfuro

nfb

etho

xysu

lfuro

n

Plan

t den

sity

(no

mminus2)

(b)

Figure 2 Effect of weed control treatment on rice plant density (number mminus2) at 14 days after sowing

Table 1 Effect of weed control treatments on weed density (number mminus2) at 20DAS (before application of post-emergence herbicide) Weeddensity data were subjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Grasses Broadleaf Sedges TotalPartial weedy 1368 (1875) 1541 (2385) 1010 (1021) 2298 (5281)Oxadiargyl 680 (458) 898 (802) 562 (313) 1256 (1573)Pendimethalin 504 (250) 1231 (1510) 915 (839) 1613 (2599)Acetachlor + bensulfuranmethyl 675 (453) 941 (885) 690 (474) 1348 (1812)Pyrazosulfuron 1300 (1688) 846 (714) 597 (354) 1662 (2756)LSD005 129 164 155 139119875 value lt0001 lt0001 0001 lt0001DAS days after sowing LSD least significant difference at 5 level of significance 119875 probability

present only in the boro season and Ageratum conyzoidesL was present only in the aman season Such variationsmight be the result of the seasonal adaptation of weeds Inaddition nonrice crops were grown before the start of theexperiment This may be another reason for the variation Inthe boro season temperatures were low up to 60 DAS but itlater increased (Figure 1) Because of low initial temperaturescrop and weed growth was slow However the growth ofsome species (eg Cyperus rotundus L Cynodon dactylonand Cleome rutidosperma) was unaffected by the low tem-peratures and severely suppressed crop growth at its earlystages in the boro season Another interesting observationwas that someweed species (egA arvensisGalinsoga ciliateBlake and Phyllanthus niruri L) emerged later than usualwhich could be their strategy to ldquoescaperdquo the application ofpreemergence herbicides

The dominant weed species in the experiments wereCelosia argentea L Cyperus rotundusDactyloctenium aegyp-tium (L) Willd Digitaria ciliaris (Retz) Koel E colonaEleusine indica (L) GaertnG ciliate and P niruriThe appli-cation of preemergence herbicides significantly reducedweeddensity compared with the control plots (partial weedy)At 20 DAS (before application of postemergence herbicide)plots treated with preemergence herbicides had 45ndash70lower weed density than the partial weedy plots (Table 1)

Among the herbicide treatments oxadiargyl-treated plotshad the lowest total weed density (157 plants mminus2) followedby those treated with acetachlor + bensulfuranmethyl (181plants mminus2) The highest weed density was recorded in theplots treated with pyrazosulfuron In terms of weed groupsthe lowest grass density was recorded in the plots treated withpendimethalin (88 less than in the partial weedy check) and

The Scientific World Journal 5

Table 2 Effect of weed control treatments on weed density (number mminus2) at 35DAS in the boro season Weed density data were subjectedto square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Amaranthusspinosus

Celosiaargentea

Cleomerutidosperma

Cyperusrotundus

Cynodondactylon

Echinochloacolona

Total weeddensity

Partial weedy 544 (292) 906 (854) 622 (385) 886 (790) 383 (146) 877 (792) 1800 (3258)Oxadiargyl fbethoxysulfuron 071 (00) 071 (00) 071 (00) 532 (281) 255 (63) 256 (83) 650 (427)

Pendimethalin fbethoxysulfuron 071 (00) 426 (177) 071 (00) 607 (365) 215 (52) 197 (42) 797 (635)

Acetachlor +bensulfuranmethyl fbethoxysulfuron

071 (00) 563 (313) 456 (208) 690 (479) 174 (31) 197 (42) 1036 (1073)

Pyrazosulfuron fbethoxysulfuron 071 (00) 509 (260) 071 (00) 609 (375) 193 (63) 562 (313) 1007 (1010)

Oxadiargyl fb 1HW at35DAS 071 (00) 071 (00) 071 (00) 790 (635) 193 (63) 071 (00) 830 (698)

Pendimethalin fb 1HW at35DAS 071 (00) 524 (271) 071 (00) 940 (892) 152 (31) 071 (00) 1093 (1194)

Acetachlor +bensulfuraonmethyl fb1HW at 35DAS

372 (135) 582 (333) 353 (125) 707 (500) 151 (21) 371 (135) 1120 (1250)

Pyrazosulfuron fb 1HW at35DAS 367 (135) 614 (375) 071 (00) 754 (573) 396 (156) 747 (583) 1342 (1823)

LSD005 070 165 090 203 NS 214 208119875 value lt0001 lt0001 lt0001 0009 020 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

the highest was recorded in the plots treated with pyrazosul-furon (only 10 less than in the partial weedy check) Againstbroadleaved and sedges acetachlor + bensulfuraonmethyloxadiargyl and pyrazosulfuron performed well (63ndash70fewer broadleavedweeds and 54ndash70 fewer sedges comparedto the partial weedy check) while pendimethalin performedpoorly (suppressed only 37 and 18 of broadleaved andsedges resp) The observed effectiveness of pendimethalinin the control of grasses and its poor control of sedgesand broadleaved weeds are consistent with the findings ofprevious published studies [8 16 17 19]

At 35 DAS (after application of postemergence herbicidesand before HW) total weed density and weed biomass weregreatly affected by herbicide treatments Plots treated withpreemergence herbicides had 39ndash76 and 23ndash45 lowerweed densities (326 and 293 plants mminus2 in the boro andaman seasons resp) compared with the partial weedy check(Tables 2 and 3) However the values were 66ndash88 and 46ndash65 respectively when plots were treated with both pre- andpostemergence herbicides

Among the herbicide treatments oxadiargyl-treatedplots performed best followed by those treated withpendimethalin and acetachlor + bensulfuranmethyl Poorperformance was observed in the pyrazosulfuron-treatedplots A similar trend was found for total weed biomass(Tables 4 and 5) Plots that were treated with only preemer-gence herbicides had 50ndash66 and 29ndash57 less weed biomassthan the partial weedy plots in the boro and aman seasonsrespectively Plots that received both pre- and postemergence

herbicides had 70ndash80 and 44ndash67 less weed biomass in theboro and aman seasons respectively The effect of herbicideson individual weed density and biomass was significant inboth seasons except on C dactylon suggesting that applyingherbicidewas not effective against this weed species Oxadiar-gyl was superior to other herbicides in reducing weed densityand biomass of several individual weed species including Ecolona Ageratum conyzoides Amaranthus spinosus Cleomerutidosperma and Celosia argentea The next best treatmentwas pendimethalin which suppressed all weeds that weresuppressed by oxadiargyl except C argentea and P niruriHowever both herbicides were ineffective againstC rotundusin both seasons

Plots treated with both pre- and postemergence herbi-cides always had less total weed density and biomass thanthose that were treated with only preemergence herbicidesFor example the plots that received only preemergenceherbicides had a weed density range of 70ndash182 and 157ndash233plants mminus2 in the boro and aman seasons respectively In theplots that received both pre- and postemergence herbicidesweed density range was 43ndash107 and 84ndash152 plants mminus2respectively The same trend was observed in weed biomasswhich indicates that the postemergence herbicide ethoxy-sulfuron significantly lowered weed density and biomassEthoxysulfuron suppressed a range of broadleaved weedspecies (eg Ageratum conyzoides Amaranthus spinosusCleome rutidosperma Celosia argentea and P niruri) andsedges (eg C rotundus) but not grasses (eg E colona DciliarisandC dactylon) Ethoxysulfuron has been reported to

6 The Scientific World Journal

Table 3 Effect of weed control treatments on weed density (number mminus2) at 35DAS in the aman season Weed density data were subjectedto square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Ageratumconyzoides

Cyperusrotundus

Celosiaargentea

Digitariaciliaris

Echinochloacolona

Phyllanthusniruri

Total weeddensity

Partial weedy 585 (344) 736 (542) 419 (177) 1002 (102) 803 (642) 456 (208) 1712 (2933)Oxadiargyl fb ethoxysulfuron 071 (00) 37 (136) 111 (11) 663 (438) 469 (218) 071 (00) 920 (843)Pendimethalin fb ethoxysulfuron 071 (00) 360 (167) 412 (167) 599 (385) 486 (231) 388 (146) 1074 (1148)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 301 (115) 387 (146) 860 (74) 671 (458) 071 (00) 1209 (1458)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 215 (83) 111 (11) 900 (854) 760 (573) 071 (00) 1231 (1521)Oxadiargyl fb 1HW at 35DAS 235 (104) 738 (542) 174 (31) 727 (563) 581 (333) 071 (00) 1253 (1573)Pendimethalin fb 1HW at 35DAS 497 (25) 814 (667) 472 (219) 533 (282) 492 (240) 356 (125) 1334 (1781)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 181 (52) 572 (323) 544 (292) 834 (693) 826 (677) 071 (00) 1410 (1984)

Pyrazosulfuron fb 1HW at 35DAS 291 (104) 640 (417) 521 (271) 949 (904) 769 (615) 134 (21) 1513 (2331)LSD005 265 281 126 310 165 085 209119875 value 0005 0002 lt0001 005 0001 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 4 Effect of weed control treatments on weed biomass (gmminus2) at 35 days after sowing in the boro season Weed biomass data weresubjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Amaranthusspinosus

Celosiaargentea

Cleomerutidosperma

Cyperusrotundus

Cynodondactylon

Echinochloacolona

Total weedbiomass

Partial weedy 182 (28) 219 (46) 135 (14) 324 (101) 100 (05) 225 (47) 492 (241)Oxadiargyl fb ethoxysulfuron 071 (00) 071 (00) 071 (00) 219 (43) 086 (02) 089 (03) 231 (49)Pendimethalin fb ethoxysulfuron 071 (00) 119 (09) 071 (00) 236 (51) 092 (04) 079 (01) 265 (66)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 124 (10) 139 (15) 207 (38) 101 (06) 080 (01) 274 (70)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 123 (10) 071 (00) 185 (30) 109 (10) 115 (09) 251 (59)Oxadiargyl fb 1HW at 35DAS 071 (00) 071 (00) 071 (00) 301 (86) 103 (08) 071 (00) 313 (94)Pendimethalin fb 1HW at 35DAS 071 (00) 107 (06) 071 (00) 350 (119) 073 (00) 071 (00) 360 (126)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 122 (10) 140 (15) 084 (02) 242 (55) 076 (01) 096 (04) 302 (87)

Pyrazosulfuron fb 1HW at 35DAS 127 (11) 140 (15) 071 (00) 209 (39) 098 (05) 161 (23) 310 (93)LSD005 016 044 020 052 NS 040 063119875 value lt0001 lt0001 lt0001 lt0001 084 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

be effective in controlling a wide range of broadleaved weedsas well as sedges [20 21] Our results are also supported bya previous study on the furrow-irrigated raised-bed DSR inwhich ethoxysulfuron (18 g ai haminus1) applied at 21 DAS waseffective in controlling broadleaved weeds [8]

Weed density and biomass as affected by different weedcontrol treatments at anthesis are given in Tables 6ndash9 Fromthe data it is clear that all herbicide treatments resulted inlower weed density and biomass compared to the partialweedy plots (ie HW at 35 DAS) Similar with observationsmade at 35 DAS total weed density and biomass werealso greatly affected by weed control treatments at anthesisConsidering the total weed density plots treated with pre-followed by postemergence herbicides always had lower weeddensity than those treated with preemergence herbicides

followed by a one-time HW at 35 DAS (Tables 6 and 7)Weed biomass maintained a similar trend as weed densityin the boro season In the aman season however plots thatreceived preemergence herbicides followed by a one-timeHW had lower weed biomass than those that received pre-and postemergence herbicides (Tables 8 and 9)

In the aman season crop vegetative growth went very fastat the early growth stages Rice in the plots that received a one-time HW at 35 DAS suppressed weed growth at later stagesIn the boro season however rice growth was very poor up to65 DAS because of low temperatures Sequential applicationof pre- and postemergence herbicides reduced weed biomassby 31ndash55 and 20ndash52 in the boro and aman seasons respec-tively and preemergence herbicide application followed by aone-timeHWreduced biomass by 15ndash40and 40ndash62 in the

The Scientific World Journal 7

Table 5 Effect of weed control treatments on weed biomass (gmminus2) at 35 days after sowing in the aman season Weed biomass data weresubjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Ageratumconyzoides

Cyperusrotundus

Celosiaargentea

Digitariaciliaris

Echinochloacolona

Phyllanthusniruri

Total weedbiomass

Partial weedy 260 (63) 377 (138) 312 (93) 629 (391) 623 (384) 242 (56) 1063 (1124)Oxadiargyl fb ethoxysulfuron 100 (07) 203 (41) 142 (25) 353 (121 ) 369 (132) 071 (00) 574 (325)Pendimethalin fb ethoxysulfuron 114 (12) 212 (51) 304 (88) 374 (140) 342 (113) 201 (37) 667 (441)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 178 (33) 279 (73) 550 (306) 465 (213) 071 (00) 790 (625)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 145 (27) 127 (14) 577 (343) 503 (249) 071 (00) 797 (633)Oxadiargyl fb 1HW at 35DAS 129 (19) 403 (16) 127 (13) 387 (147) 392 (149) 071 (00) 701 (487)Pendimethalin fb 1HW at 35DAS 257 (64) 461 (209) 356 (122) 362 (130) 354 (125) 140 (15) 817 (663)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 071 (07) 324 (101) 449 (197) 536 (287) 545 (296) 071 (00) 941 (834)

Pyrazosulfuron fb 1HW at 35DAS 142 (18) 370 (133) 386 (145) 600 (357) 517 (279) 083 (02) 966 (801)LSD005 100 145 091 144 129 083 098119875 value 0003 0002 lt0001 0001 0003 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

respective seasons all compared with the partial weedy check(ie one-time HW)

Among the herbicide treatments plots treated with oxa-diargyl followed by ethoxysulfuron reduced total weed den-sity by 65ndash70 compared with the partial weedy plots (378ndash477 plants mminus2) (Tables 6 and 7) The next best treatmentswere pendimethalin followed by ethoxysulfuron (60ndash62reduction in weed density) and acetachlor + bensulfuran-methyl followed by ethoxysulfuron (52ndash55 reduction inweed density) Compared with the partial weedy plots thosetreated with pyrazosulfuron followed by ethoxysulfuron sup-pressed weed density by only 39ndash48

33 Effect of Weed Control Treatments on Yield and Yield-Contributing Parameters Yield and yield-contributingparameters except 1000-grain weight were highly influencedby weed control treatments and the results were consistent inboth seasons (Tables 10 and 11) The highest panicle numbers(253ndash347mminus2) were recorded in the weed-free plots Paniclenumber was always lower in the herbicide-treated plotsthan in the weed-free plots and always higher than in thepartial weedy plots In the boro season the highest paniclenumbers (281ndash316mminus2) were recorded in the plots thatreceived pre- followed by postemergence herbicides In theaman season these values (204ndash236 panicles mminus2) werehighest when the plots received preemergence herbicidesfollowed by a one-time HW Among herbicide treatmentsthe highest panicle numbers (230ndash315mminus2) were recordedin the oxadiargyl-treated plots The next best herbicidetreatment was pendimethalin with panicle numbers (230ndash301mminus2) comparable to that of the oxadiargyl-treatedplots The lowest panicle numbers were recorded in thepyrazosulfuron-treated plots in both seasons

The number of spikelets panicleminus1 was consistent acrossthe herbicide-treated plots in the boro season but it sig-nificantly differed in the aman season (Tables 10 and 11)

Herbicide-treated plots always had a higher number ofspikelets panicleminus1 (5ndash26 higher) than the partial weedyplots and always had a lower number than the weed-free plots(3ndash21 lower)

Grain yieldwas strongly influenced byweed control treat-ments (Tables 10 and 11) The highest yield (476ndash498 t haminus1)was obtained in the weed-free plots Herbicide-treated plotsalways yielded more than the partial weedy plots Amongthe herbicide treatments the highest yield was recorded inthe plots treated with oxadiargyl followed by ethoxysulfuron(413 t haminus1) in the boro season and oxadiargyl followed aone-timeHW(41 t haminus1) in the aman season Pendimethalin-treated plots produced a similar grain yield (41 t haminus1) Theplots treated with pyrazosulfuron produced the lowest yieldin both seasons Compared with the control treatmentherbicide-treated plots produced a 20ndash62higher yieldwhentreated with both pre- and postemergence herbicides thesevalues were 30ndash41 when plots received only preemergenceherbicide and a one-timeHWAlthough herbicide treatmentsresulted in a yield advantage over the control treatment noneof the herbicide treatments reached the yield levels fromthe weed-free plots Grain yield from the best-performingherbicide treatment was 13ndash18 lower than that from theweed-free plots suggesting that there is a considerable scopeto increase yield with improved weed control practices inDSR In the boro season yield was higher in the plots treatedwith preemergence followed by postemergence herbicidesbut the results were not consistent in both seasons In theaman season vegetative growth started early In the plots thatreceived preemergence herbicide followed by a one-timeHWcanopy closure occurred fast which suppressed weed growthat the later stages These results suggest that in the amanseason application of preemergence herbicide followed byHW was better than applying both preemergence and poste-mergence herbicides However these results also depend onothers factors such as efficacy of the postemergence herbicide

8 The Scientific World Journal

Table6Eff

ecto

fweedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

theb

oroseason

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

1267(161)

866

(748)

503

(25)

576

(327)

436

(188)

739(563)

304

(115

)868

(781)

438

(188)

2180(4773)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

856

(729)

773(604)

426

(188)

071

(00)

235

(104)

071

(00)

240

(55)

071

(00)

1298(1679)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

937(896

)70

3(49)

466

(215

)071

(00)

393

(156)

071

(00)

222

(47)

278

(94)

1378(1897)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

1014

(105)

779(604)

486

(240)

071

(00)

509

(260)

071

(00)

071

(00)

071

(00)

1458(2156)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

846

(729)

707(542)

642

(417

)233

(63)

652

(438)

448

(208)

071

(00)

291

(8)

1575(2476)

Oxadiargylfb

1HW

at35

DAS

595

(354)

834

(704)

709(50)

463

(302)

071

(00)

249

(58)

071

(00)

599

(375

)071

(00)

1514

(2293)

Pend

imethalin

fb1H

Wat35

DAS

424

(181)

1154(133)

571

(323)

424

(177

)071

(00)

179(33)

071

(00)

591

(354)

288

(83)

1546(2384)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

563

(313

)1035

(109)

619

(385)

460

(292

)071

(00)

399

(167)

071

(00)

492

(240)

071

(00)

1577(2489)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

636

(435)

643

(458)

650

(427)

374

(135)

747(678

)312

(94)

510

(257)

312

(94)

1593(2578)

LSD

005

107

249

NS

NS

091

367

136

171

124

284

119875value

lt0001

003

042

063

lt0001

0007

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 9

Table7Eff

ectofw

eedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

thea

man

season

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eind

icaGalinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

467

(217

)468

(240)

772(596

)255

(63)

1013

(102)

289

(81)

1062(117)

625

(398

)1945(3783)

Oxadiargylfb

etho

xysulfu

ron

211(40)

071

(00)

514

(260)

071

(00)

761(575)

071

(00)

343

(117

)396

(156)

1074

(1148)

Pend

imethalin

fbetho

xysulfu

ron

138(23)

071

(00)

601

(358)

071

(00)

654

(425)

294

(82)

575

(327)

514

(260)

1216

(1476

)Ac

etachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

597

(354)

295

(104)

905(817

)071

(00)

448

(210

)562

(313

)1342(1798)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

769(646)

252

(61)

1017

(104)

300

(87)

435

(203)

515

(273

)1519

(2307)

Oxadiargylfb

1HW

at35

DAS

281

(75)

279

(75)

468

(219

)071

(00)

460

(208)

071

(00)

1005(101)

438

(188)

1332

(1771)

Pend

imethalin

fb1H

Wat35

DAS

249

(73)

341

(115

)552

(300)

071

(00)

636

(400)

071

(00)

940(881)

475

(248)

1422(2017)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

260

(63)

363

(134)

465

(219

)200

(43)

945(906)

158(24)

991(983)

590

(354)

1650(2726)

Pyrazosulfu

ronfb

1HW

at35

DAS

255

(63)

397

(154)

325

(104)

192(42)

988(990

)232

(52)

910(833)

643

(415

)1630(2653)

LSD

005

134

147

216

147

170

077

242

NS

107

119875value

lt0001

lt0001

0029

001

lt0001

0001

lt0001

012

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

10 The Scientific World Journal

Table8Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )at

anthesisin

thebo

roseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Phyllanthu

sniruri

Galinsoga

ciliata

Totalw

eed

biom

ass

Partialw

eedy

710(52)

467

(217

)365

(129)

364

(13)

412

(19)

526

(27)

316

(13)

403

(16)

744(560)

1519

(2302)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

589

(353)

659

(429)

335

(111)

071

(00)

192(61)

071

(00)

071

(00)

285

(79)

1019

(1033)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

664

(443)

554

(303)

382

(145)

071

(00)

275

(78)

071

(00)

260

(81)

290

(81)

1066(1131)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

656

(437)

616

(375

)450

(203)

071

(00)

461

(21)

071

(00)

071

(00)

071

(00)

1106(1228)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

538

(277

)615

(417

)475

(221)

210

(49)

609

(39)

409

(17)

264

(65)

071

(00)

1262(1589)

Oxadiargylfb

1HW

at35

DAS

323

(101)

607

(364)

544

(291

)251

(74)

071

(00)

259

(62)

071

(00)

071

(00)

670

(444)

1158(1337)

Pend

imethalin

fb1H

Wat35

DAS

330

(11)

675

(453)

455

(206)

341

(113

)071

(00)

226

(48)

071

(00)

234

(56)

664

(441)

1196(14

27)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

392

(149)

618

(384)

486

(244)

373

(183)

071

(00)

299

(89)

071

(00)

071

(00)

530

(283)

1156(1332)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

503

(248)

531

(285)

561

(318

)370

(132)

598

(385)

362

(131)

257

(62)

628

(39)

1397(19

51)

LSD

005

111

190

NS

NS

123

245

134

130

155

124

119875value

lt0001

000

6015

011

lt0001

0001

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 11

Table9Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )atanthesisin

theam

anseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

biom

ass

Partialw

eedy

299

(86)

267

(73)

711(506)

178(28)

909(826)

201

(36)

712(511)

559

(313

)1543(2378)

Oxadiargylfb

etho

xysulfu

ron

224

(47)

071

(00)

537

(285)

071

(00)

800

(635)

071

(00)

259

(64)

328

(103)

1067(1135)

Pend

imethalin

fbetho

xysulfu

ron

185(36)

071

(00)

534

(2810)

071

(00)

676

(456)

206

(38)

429

(182)

494

(240)

1109(1231)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

454

(210

)228

(55)

946(896

)071

(00)

348

(129)

401

(162)

1204(14

52)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

688

(479

)19

8(35)

1008(1015)

212

(40)

418

(193

)388

(147)

1383(1908)

Oxadiargylfb

1HW

at35

DAS

221

(44)

165(23)

415

(171)

071

(00)

392

(153)

071

(00)

639

(405)

323

(102)

945(897

)Pend

imethalin

fb1H

Wat35

DAS

170(29)

197(36)

483

(232)

071

(00)

540

(287)

071

(00)

584

(337)

401

(171)

1046(1092)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

177(28)

194(340)

350

(118

)14

9(20)

719(515

)13

9(17)

569

(326)

489

(242)

1142(1301)

Pyrazosulfu

ronfb

1HW

at35

DAS

198(35)

195(33)

348

(116

)15

2(21)

825

(685)

162(24)

516

(264)

511(256)

1199(14

35)

LSD

005

089

076

133

087

139

055

188

146

130

119875value

0001

lt0001

lt0001

000

4lt0001

lt0001

0002

003

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

12 The Scientific World Journal

Table 10 Effect of weed control treatments on yield and yield components of rice in the boro season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 34700 8235 9352 1902 476Partial weedy 15967 5933 9279 1803 158Oxadiargyl fb ethoxysulfuron 31567 7838 9367 1870 413Pendimethalin fb ethoxysulfuron 30100 8025 9249 1854 408Acetachlor + bensulfuranmethyl fb ethoxysulfuron 30300 7793 9277 1861 401Pyrazosulfuron fb ethoxysulfuron 28167 7605 9174 1805 346Oxadiargyl fb 1HW at 35DAS 27833 7642 9167 1836 348Pendimethalin fb 1HW at 35DAS 26400 7612 9190 1823 338Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 27033 7662 9199 1890 342Pyrazosulfuron fb 1HW at 35DAS 24833 7547 9000 1862 322LSD005 2341 565 163 NS 028119875 value 119875 lt 0001 119875 lt 0001 0008 0074 119875 lt 0001

DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 11 Effect of weed control treatments on yield and yield components of rice in the aman season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 25333 12020 8871 1779 498Partial weedy 17233 9028 8893 1797 259Oxadiargyl fb ethoxysulfuron 23000 10230 9127 1755 353Pendimethalin fb ethoxysulfuron 21967 10252 8843 1774 343Acetachlor + bensulfuranmethyl fb ethoxysulfuron 18667 10057 8544 1719 307Pyrazosulfuron fb ethoxysulfuron 18033 9577 8953 1672 300Oxadiargyl fb 1HW at 35DAS 23633 11268 8663 1817 408Pendimethalin fb 1HW at 35DAS 23067 11363 8757 1828 405Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 21733 11070 8999 1707 395Pyrazosulfuron fb 1HW at 35DAS 20400 10797 8629 1700 385LSD005 1930 1071 255 NS 019119875 value lt0001 0001 0002 032 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

used weed flora in the field rice variety used and soil andclimatic conditions Information to support these results isnot available in the literature

Our study shows that even after the use of preemergencefollowed by postemergence herbicides at 21 DAS or preemer-gence followed by a one-time HW complete weed controlcannot be achieved In additionmanual weeding is becomingless popular due to high labor wages it will be difficult to findlabor for weeding in the futureTherefore additional researchneeds to be conducted on the performance of combinationsof different pre- and postemergence herbicides applicationtimings and herbicide doses across various seasons andenvironmental conditions

We found that some weed species emerged later in theseason (eg A arvensis P niruri and G ciliata) and thusescaped the postemergence herbicide application or the HWat 35 DAS Previous studies report that weeds emerging laterin the season may not reduce rice yield significantly but

add seeds to the soil seed bank and result in heavy weedinfestation in subsequent seasons [22 23] In both seasons wefound a significant and negative linear correlation betweengrain yield and weed biomass at anthesis (Figure 3) Therelationship was slightly stronger in the boro season (1198772 =075) than in the aman season (1198772 = 065) These resultsare supported by previous studies in India [10] and thePhilippines [18] both of which found that grain yield wasnegatively correlated with weed biomass

In conclusion it is clear that weeds are a serious problemin DSR production systems and herbicides are the essentialtool to control them However continuous use of a singleherbicide over a long period may cause the development ofherbicide-resistant weed biotypes Therefore it is crucial toevaluate herbicides and determine which are less harmfulto the crop and have the ability to control a wide rangeof weeds In addition when many effective herbicides areavailable farmers will have the option to rotate the use

The Scientific World Journal 13

Boro 2011-12

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

Gra

in y

ield

(t h

aminus1)

Gy = 579 minus 0016x

R2= 075

(a)

Aman 2012

Gy = 479 minus 0009x

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

R2= 065G

rain

yie

ld (t

haminus

1)

(b)

Figure 3 The relationship between grain yield and weed biomass

of different herbicides and will help reduce the risk ofresistance developing inweeds and shifts inweed flora towardproblematic weeds

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] GMahajan B S Chauhan J Timsina P P Singh and K SinghldquoCrop performance and water- and nitrogen-use efficiencies indry-seeded rice in response to irrigation and fertilizer amountsin northwest Indiardquo Field Crops Research vol 134 pp 59ndash702012

[2] B S Chauhan G Mahajan V Sardana J Timsina and M LJat ldquoProductivity and sustainability of the rice-wheat croppingsystem in the Indo-Gangetic Plains of the Indian subcontinentproblems opportunities and strategiesrdquoAdvances inAgronomyvol 117 pp 315ndash369 2012

[3] B A M Bouman and T P Tuong ldquoField water managementto save water and increase its productivity in irrigated lowlandricerdquo Agricultural and Water Management vol 49 no 1 pp 11ndash30 2001

[4] R Gopal R K Jat R K Malik et al ldquoDirect dry seeded riceproduction technology and weed management in rice basedsystemsrdquo Technical Bulletin International Maize and WheatImprovement Center New Delhi India 2010

[5] B S Chauhan and D E Johnson ldquoThe role of seed ecologyin improving weed management strategies in the tropicsrdquoAdvances in Agronomy vol 105 pp 221ndash262 2010

[6] G Mahajan and B S Chauhan ldquoEffects of planting pattern andcultivar on weed and crop growth in aerobic rice systemrdquoWeedTechnology vol 25 no 4 pp 521ndash525 2011

[7] S Singh J K Ladha R K Gupta et al ldquoEvaluation ofmulching intercropping with Sesbania and herbicide use forweed management in dry-seeded rice (Oryza sativa L)rdquo CropProtection vol 26 no 4 pp 518ndash524 2007

[8] S Singh L Bhushan J K Ladha R K Gupta A N Rao andB Sivaprasad ldquoWeed management in dry-seeded rice (Oryzasativa) cultivated in the furrow-irrigated raised-bed plantingsystemrdquo Crop Protection vol 25 no 5 pp 487ndash495 2006

[9] B S Chauhan and D E Johnson ldquoRow spacing and weedcontrol timing affect yield of aerobic ricerdquo Field Crops Researchvol 121 no 2 pp 226ndash231 2011

[10] B S Chauhan V P Singh A Kumar and D E JohnsonldquoRelations of rice seeding rates to crop and weed growth inaerobic ricerdquo Field Crops Research vol 121 no 1 pp 105ndash1152011

[11] B S Chauhan ldquoWeed ecology andweedmanagement strategiesfor dry-seeded rice in AsiardquoWeed Technology vol 26 no 1 pp1ndash13 2012

[12] B S Chauhan and JOpena ldquoWeedmanagement and grain yieldof rice sown at low seeding rates in mechanized dry-seededsystemsrdquo Field Crops Research vol 141 pp 9ndash15 2013

[13] L Bastiaans R Paolini and D T Baumann ldquoFocus on eco-logical weed management what is hindering adoptionrdquo WeedResearch vol 48 no 6 pp 481ndash491 2008

[14] G Mahajan B S Chauhan and D E Johnson ldquoWeed man-agement in aerobic rice in northwestern indo-gangetic plainsrdquoJournal of Crop Improvement vol 23 no 4 pp 366ndash382 2009

[15] D D Buhler M Liebman and J J Obrycki ldquoTheoretical andpractical challenges to an IPM approach to weed managementrdquoWeed Science vol 48 no 3 pp 274ndash280 2000

[16] S Ahmed M R Islam M M Alam M M Haque and A JM S Karim ldquoRice production and profitability as influencedby integrated crop and resources managementrdquo Eco-FriendlyAgriculture vol 11 pp 720ndash725 2011

[17] MHasanuzzamanO Islam and S Bapari ldquoEfficacy of differentherbicides over manual weeding in controlling weeds in trans-planted ricerdquoAustralian Journal of Crop Science vol 2 no 1 pp18ndash24 2008

[18] B S Chauhan and J Opena ldquoImplications of plant geometryand weed control options in designing a low-seeding seed-drillfor dry-seeded rice systemsrdquo Field Crops Research vol 144 pp225ndash231 2013

[19] D L Jordan P K Bollich A B Burns and D MWalker ldquoRice(Oryza sativa) response to clomazonerdquo Weed Science vol 46no 3 pp 374ndash380 1998

[20] J D Beaty B Guy and J Edmund ldquoBroadleaf weed control andcotton response with bensulfuron in ricerdquo in Proceedings of theSouthern Weed Science Society vol 46 pp 91ndash96 1993

[21] M Hess and R Rose ldquoHOE 095404 a new herbicide forbroadleaf weed and sedge control in ricerdquo in Proceedings of theBrighton Crop Protection ConferenceWeeds vol 2 pp 763ndash768Brighton UK 1995

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

Nutrition and Metabolism

Journal of

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Food ScienceInternational Journal of

Agronomy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

AgricultureAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BiodiversityInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Plant GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biotechnology Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Forestry ResearchInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of BotanyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Cell BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World Journal 5

Table 2 Effect of weed control treatments on weed density (number mminus2) at 35DAS in the boro season Weed density data were subjectedto square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Amaranthusspinosus

Celosiaargentea

Cleomerutidosperma

Cyperusrotundus

Cynodondactylon

Echinochloacolona

Total weeddensity

Partial weedy 544 (292) 906 (854) 622 (385) 886 (790) 383 (146) 877 (792) 1800 (3258)Oxadiargyl fbethoxysulfuron 071 (00) 071 (00) 071 (00) 532 (281) 255 (63) 256 (83) 650 (427)

Pendimethalin fbethoxysulfuron 071 (00) 426 (177) 071 (00) 607 (365) 215 (52) 197 (42) 797 (635)

Acetachlor +bensulfuranmethyl fbethoxysulfuron

071 (00) 563 (313) 456 (208) 690 (479) 174 (31) 197 (42) 1036 (1073)

Pyrazosulfuron fbethoxysulfuron 071 (00) 509 (260) 071 (00) 609 (375) 193 (63) 562 (313) 1007 (1010)

Oxadiargyl fb 1HW at35DAS 071 (00) 071 (00) 071 (00) 790 (635) 193 (63) 071 (00) 830 (698)

Pendimethalin fb 1HW at35DAS 071 (00) 524 (271) 071 (00) 940 (892) 152 (31) 071 (00) 1093 (1194)

Acetachlor +bensulfuraonmethyl fb1HW at 35DAS

372 (135) 582 (333) 353 (125) 707 (500) 151 (21) 371 (135) 1120 (1250)

Pyrazosulfuron fb 1HW at35DAS 367 (135) 614 (375) 071 (00) 754 (573) 396 (156) 747 (583) 1342 (1823)

LSD005 070 165 090 203 NS 214 208119875 value lt0001 lt0001 lt0001 0009 020 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

the highest was recorded in the plots treated with pyrazosul-furon (only 10 less than in the partial weedy check) Againstbroadleaved and sedges acetachlor + bensulfuraonmethyloxadiargyl and pyrazosulfuron performed well (63ndash70fewer broadleavedweeds and 54ndash70 fewer sedges comparedto the partial weedy check) while pendimethalin performedpoorly (suppressed only 37 and 18 of broadleaved andsedges resp) The observed effectiveness of pendimethalinin the control of grasses and its poor control of sedgesand broadleaved weeds are consistent with the findings ofprevious published studies [8 16 17 19]

At 35 DAS (after application of postemergence herbicidesand before HW) total weed density and weed biomass weregreatly affected by herbicide treatments Plots treated withpreemergence herbicides had 39ndash76 and 23ndash45 lowerweed densities (326 and 293 plants mminus2 in the boro andaman seasons resp) compared with the partial weedy check(Tables 2 and 3) However the values were 66ndash88 and 46ndash65 respectively when plots were treated with both pre- andpostemergence herbicides

Among the herbicide treatments oxadiargyl-treatedplots performed best followed by those treated withpendimethalin and acetachlor + bensulfuranmethyl Poorperformance was observed in the pyrazosulfuron-treatedplots A similar trend was found for total weed biomass(Tables 4 and 5) Plots that were treated with only preemer-gence herbicides had 50ndash66 and 29ndash57 less weed biomassthan the partial weedy plots in the boro and aman seasonsrespectively Plots that received both pre- and postemergence

herbicides had 70ndash80 and 44ndash67 less weed biomass in theboro and aman seasons respectively The effect of herbicideson individual weed density and biomass was significant inboth seasons except on C dactylon suggesting that applyingherbicidewas not effective against this weed species Oxadiar-gyl was superior to other herbicides in reducing weed densityand biomass of several individual weed species including Ecolona Ageratum conyzoides Amaranthus spinosus Cleomerutidosperma and Celosia argentea The next best treatmentwas pendimethalin which suppressed all weeds that weresuppressed by oxadiargyl except C argentea and P niruriHowever both herbicides were ineffective againstC rotundusin both seasons

Plots treated with both pre- and postemergence herbi-cides always had less total weed density and biomass thanthose that were treated with only preemergence herbicidesFor example the plots that received only preemergenceherbicides had a weed density range of 70ndash182 and 157ndash233plants mminus2 in the boro and aman seasons respectively In theplots that received both pre- and postemergence herbicidesweed density range was 43ndash107 and 84ndash152 plants mminus2respectively The same trend was observed in weed biomasswhich indicates that the postemergence herbicide ethoxy-sulfuron significantly lowered weed density and biomassEthoxysulfuron suppressed a range of broadleaved weedspecies (eg Ageratum conyzoides Amaranthus spinosusCleome rutidosperma Celosia argentea and P niruri) andsedges (eg C rotundus) but not grasses (eg E colona DciliarisandC dactylon) Ethoxysulfuron has been reported to

6 The Scientific World Journal

Table 3 Effect of weed control treatments on weed density (number mminus2) at 35DAS in the aman season Weed density data were subjectedto square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Ageratumconyzoides

Cyperusrotundus

Celosiaargentea

Digitariaciliaris

Echinochloacolona

Phyllanthusniruri

Total weeddensity

Partial weedy 585 (344) 736 (542) 419 (177) 1002 (102) 803 (642) 456 (208) 1712 (2933)Oxadiargyl fb ethoxysulfuron 071 (00) 37 (136) 111 (11) 663 (438) 469 (218) 071 (00) 920 (843)Pendimethalin fb ethoxysulfuron 071 (00) 360 (167) 412 (167) 599 (385) 486 (231) 388 (146) 1074 (1148)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 301 (115) 387 (146) 860 (74) 671 (458) 071 (00) 1209 (1458)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 215 (83) 111 (11) 900 (854) 760 (573) 071 (00) 1231 (1521)Oxadiargyl fb 1HW at 35DAS 235 (104) 738 (542) 174 (31) 727 (563) 581 (333) 071 (00) 1253 (1573)Pendimethalin fb 1HW at 35DAS 497 (25) 814 (667) 472 (219) 533 (282) 492 (240) 356 (125) 1334 (1781)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 181 (52) 572 (323) 544 (292) 834 (693) 826 (677) 071 (00) 1410 (1984)

Pyrazosulfuron fb 1HW at 35DAS 291 (104) 640 (417) 521 (271) 949 (904) 769 (615) 134 (21) 1513 (2331)LSD005 265 281 126 310 165 085 209119875 value 0005 0002 lt0001 005 0001 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 4 Effect of weed control treatments on weed biomass (gmminus2) at 35 days after sowing in the boro season Weed biomass data weresubjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Amaranthusspinosus

Celosiaargentea

Cleomerutidosperma

Cyperusrotundus

Cynodondactylon

Echinochloacolona

Total weedbiomass

Partial weedy 182 (28) 219 (46) 135 (14) 324 (101) 100 (05) 225 (47) 492 (241)Oxadiargyl fb ethoxysulfuron 071 (00) 071 (00) 071 (00) 219 (43) 086 (02) 089 (03) 231 (49)Pendimethalin fb ethoxysulfuron 071 (00) 119 (09) 071 (00) 236 (51) 092 (04) 079 (01) 265 (66)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 124 (10) 139 (15) 207 (38) 101 (06) 080 (01) 274 (70)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 123 (10) 071 (00) 185 (30) 109 (10) 115 (09) 251 (59)Oxadiargyl fb 1HW at 35DAS 071 (00) 071 (00) 071 (00) 301 (86) 103 (08) 071 (00) 313 (94)Pendimethalin fb 1HW at 35DAS 071 (00) 107 (06) 071 (00) 350 (119) 073 (00) 071 (00) 360 (126)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 122 (10) 140 (15) 084 (02) 242 (55) 076 (01) 096 (04) 302 (87)

Pyrazosulfuron fb 1HW at 35DAS 127 (11) 140 (15) 071 (00) 209 (39) 098 (05) 161 (23) 310 (93)LSD005 016 044 020 052 NS 040 063119875 value lt0001 lt0001 lt0001 lt0001 084 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

be effective in controlling a wide range of broadleaved weedsas well as sedges [20 21] Our results are also supported bya previous study on the furrow-irrigated raised-bed DSR inwhich ethoxysulfuron (18 g ai haminus1) applied at 21 DAS waseffective in controlling broadleaved weeds [8]

Weed density and biomass as affected by different weedcontrol treatments at anthesis are given in Tables 6ndash9 Fromthe data it is clear that all herbicide treatments resulted inlower weed density and biomass compared to the partialweedy plots (ie HW at 35 DAS) Similar with observationsmade at 35 DAS total weed density and biomass werealso greatly affected by weed control treatments at anthesisConsidering the total weed density plots treated with pre-followed by postemergence herbicides always had lower weeddensity than those treated with preemergence herbicides

followed by a one-time HW at 35 DAS (Tables 6 and 7)Weed biomass maintained a similar trend as weed densityin the boro season In the aman season however plots thatreceived preemergence herbicides followed by a one-timeHW had lower weed biomass than those that received pre-and postemergence herbicides (Tables 8 and 9)

In the aman season crop vegetative growth went very fastat the early growth stages Rice in the plots that received a one-time HW at 35 DAS suppressed weed growth at later stagesIn the boro season however rice growth was very poor up to65 DAS because of low temperatures Sequential applicationof pre- and postemergence herbicides reduced weed biomassby 31ndash55 and 20ndash52 in the boro and aman seasons respec-tively and preemergence herbicide application followed by aone-timeHWreduced biomass by 15ndash40and 40ndash62 in the

The Scientific World Journal 7

Table 5 Effect of weed control treatments on weed biomass (gmminus2) at 35 days after sowing in the aman season Weed biomass data weresubjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Ageratumconyzoides

Cyperusrotundus

Celosiaargentea

Digitariaciliaris

Echinochloacolona

Phyllanthusniruri

Total weedbiomass

Partial weedy 260 (63) 377 (138) 312 (93) 629 (391) 623 (384) 242 (56) 1063 (1124)Oxadiargyl fb ethoxysulfuron 100 (07) 203 (41) 142 (25) 353 (121 ) 369 (132) 071 (00) 574 (325)Pendimethalin fb ethoxysulfuron 114 (12) 212 (51) 304 (88) 374 (140) 342 (113) 201 (37) 667 (441)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 178 (33) 279 (73) 550 (306) 465 (213) 071 (00) 790 (625)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 145 (27) 127 (14) 577 (343) 503 (249) 071 (00) 797 (633)Oxadiargyl fb 1HW at 35DAS 129 (19) 403 (16) 127 (13) 387 (147) 392 (149) 071 (00) 701 (487)Pendimethalin fb 1HW at 35DAS 257 (64) 461 (209) 356 (122) 362 (130) 354 (125) 140 (15) 817 (663)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 071 (07) 324 (101) 449 (197) 536 (287) 545 (296) 071 (00) 941 (834)

Pyrazosulfuron fb 1HW at 35DAS 142 (18) 370 (133) 386 (145) 600 (357) 517 (279) 083 (02) 966 (801)LSD005 100 145 091 144 129 083 098119875 value 0003 0002 lt0001 0001 0003 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

respective seasons all compared with the partial weedy check(ie one-time HW)

Among the herbicide treatments plots treated with oxa-diargyl followed by ethoxysulfuron reduced total weed den-sity by 65ndash70 compared with the partial weedy plots (378ndash477 plants mminus2) (Tables 6 and 7) The next best treatmentswere pendimethalin followed by ethoxysulfuron (60ndash62reduction in weed density) and acetachlor + bensulfuran-methyl followed by ethoxysulfuron (52ndash55 reduction inweed density) Compared with the partial weedy plots thosetreated with pyrazosulfuron followed by ethoxysulfuron sup-pressed weed density by only 39ndash48

33 Effect of Weed Control Treatments on Yield and Yield-Contributing Parameters Yield and yield-contributingparameters except 1000-grain weight were highly influencedby weed control treatments and the results were consistent inboth seasons (Tables 10 and 11) The highest panicle numbers(253ndash347mminus2) were recorded in the weed-free plots Paniclenumber was always lower in the herbicide-treated plotsthan in the weed-free plots and always higher than in thepartial weedy plots In the boro season the highest paniclenumbers (281ndash316mminus2) were recorded in the plots thatreceived pre- followed by postemergence herbicides In theaman season these values (204ndash236 panicles mminus2) werehighest when the plots received preemergence herbicidesfollowed by a one-time HW Among herbicide treatmentsthe highest panicle numbers (230ndash315mminus2) were recordedin the oxadiargyl-treated plots The next best herbicidetreatment was pendimethalin with panicle numbers (230ndash301mminus2) comparable to that of the oxadiargyl-treatedplots The lowest panicle numbers were recorded in thepyrazosulfuron-treated plots in both seasons

The number of spikelets panicleminus1 was consistent acrossthe herbicide-treated plots in the boro season but it sig-nificantly differed in the aman season (Tables 10 and 11)

Herbicide-treated plots always had a higher number ofspikelets panicleminus1 (5ndash26 higher) than the partial weedyplots and always had a lower number than the weed-free plots(3ndash21 lower)

Grain yieldwas strongly influenced byweed control treat-ments (Tables 10 and 11) The highest yield (476ndash498 t haminus1)was obtained in the weed-free plots Herbicide-treated plotsalways yielded more than the partial weedy plots Amongthe herbicide treatments the highest yield was recorded inthe plots treated with oxadiargyl followed by ethoxysulfuron(413 t haminus1) in the boro season and oxadiargyl followed aone-timeHW(41 t haminus1) in the aman season Pendimethalin-treated plots produced a similar grain yield (41 t haminus1) Theplots treated with pyrazosulfuron produced the lowest yieldin both seasons Compared with the control treatmentherbicide-treated plots produced a 20ndash62higher yieldwhentreated with both pre- and postemergence herbicides thesevalues were 30ndash41 when plots received only preemergenceherbicide and a one-timeHWAlthough herbicide treatmentsresulted in a yield advantage over the control treatment noneof the herbicide treatments reached the yield levels fromthe weed-free plots Grain yield from the best-performingherbicide treatment was 13ndash18 lower than that from theweed-free plots suggesting that there is a considerable scopeto increase yield with improved weed control practices inDSR In the boro season yield was higher in the plots treatedwith preemergence followed by postemergence herbicidesbut the results were not consistent in both seasons In theaman season vegetative growth started early In the plots thatreceived preemergence herbicide followed by a one-timeHWcanopy closure occurred fast which suppressed weed growthat the later stages These results suggest that in the amanseason application of preemergence herbicide followed byHW was better than applying both preemergence and poste-mergence herbicides However these results also depend onothers factors such as efficacy of the postemergence herbicide

8 The Scientific World Journal

Table6Eff

ecto

fweedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

theb

oroseason

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

1267(161)

866

(748)

503

(25)

576

(327)

436

(188)

739(563)

304

(115

)868

(781)

438

(188)

2180(4773)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

856

(729)

773(604)

426

(188)

071

(00)

235

(104)

071

(00)

240

(55)

071

(00)

1298(1679)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

937(896

)70

3(49)

466

(215

)071

(00)

393

(156)

071

(00)

222

(47)

278

(94)

1378(1897)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

1014

(105)

779(604)

486

(240)

071

(00)

509

(260)

071

(00)

071

(00)

071

(00)

1458(2156)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

846

(729)

707(542)

642

(417

)233

(63)

652

(438)

448

(208)

071

(00)

291

(8)

1575(2476)

Oxadiargylfb

1HW

at35

DAS

595

(354)

834

(704)

709(50)

463

(302)

071

(00)

249

(58)

071

(00)

599

(375

)071

(00)

1514

(2293)

Pend

imethalin

fb1H

Wat35

DAS

424

(181)

1154(133)

571

(323)

424

(177

)071

(00)

179(33)

071

(00)

591

(354)

288

(83)

1546(2384)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

563

(313

)1035

(109)

619

(385)

460

(292

)071

(00)

399

(167)

071

(00)

492

(240)

071

(00)

1577(2489)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

636

(435)

643

(458)

650

(427)

374

(135)

747(678

)312

(94)

510

(257)

312

(94)

1593(2578)

LSD

005

107

249

NS

NS

091

367

136

171

124

284

119875value

lt0001

003

042

063

lt0001

0007

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 9

Table7Eff

ectofw

eedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

thea

man

season

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eind

icaGalinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

467

(217

)468

(240)

772(596

)255

(63)

1013

(102)

289

(81)

1062(117)

625

(398

)1945(3783)

Oxadiargylfb

etho

xysulfu

ron

211(40)

071

(00)

514

(260)

071

(00)

761(575)

071

(00)

343

(117

)396

(156)

1074

(1148)

Pend

imethalin

fbetho

xysulfu

ron

138(23)

071

(00)

601

(358)

071

(00)

654

(425)

294

(82)

575

(327)

514

(260)

1216

(1476

)Ac

etachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

597

(354)

295

(104)

905(817

)071

(00)

448

(210

)562

(313

)1342(1798)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

769(646)

252

(61)

1017

(104)

300

(87)

435

(203)

515

(273

)1519

(2307)

Oxadiargylfb

1HW

at35

DAS

281

(75)

279

(75)

468

(219

)071

(00)

460

(208)

071

(00)

1005(101)

438

(188)

1332

(1771)

Pend

imethalin

fb1H

Wat35

DAS

249

(73)

341

(115

)552

(300)

071

(00)

636

(400)

071

(00)

940(881)

475

(248)

1422(2017)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

260

(63)

363

(134)

465

(219

)200

(43)

945(906)

158(24)

991(983)

590

(354)

1650(2726)

Pyrazosulfu

ronfb

1HW

at35

DAS

255

(63)

397

(154)

325

(104)

192(42)

988(990

)232

(52)

910(833)

643

(415

)1630(2653)

LSD

005

134

147

216

147

170

077

242

NS

107

119875value

lt0001

lt0001

0029

001

lt0001

0001

lt0001

012

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

10 The Scientific World Journal

Table8Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )at

anthesisin

thebo

roseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Phyllanthu

sniruri

Galinsoga

ciliata

Totalw

eed

biom

ass

Partialw

eedy

710(52)

467

(217

)365

(129)

364

(13)

412

(19)

526

(27)

316

(13)

403

(16)

744(560)

1519

(2302)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

589

(353)

659

(429)

335

(111)

071

(00)

192(61)

071

(00)

071

(00)

285

(79)

1019

(1033)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

664

(443)

554

(303)

382

(145)

071

(00)

275

(78)

071

(00)

260

(81)

290

(81)

1066(1131)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

656

(437)

616

(375

)450

(203)

071

(00)

461

(21)

071

(00)

071

(00)

071

(00)

1106(1228)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

538

(277

)615

(417

)475

(221)

210

(49)

609

(39)

409

(17)

264

(65)

071

(00)

1262(1589)

Oxadiargylfb

1HW

at35

DAS

323

(101)

607

(364)

544

(291

)251

(74)

071

(00)

259

(62)

071

(00)

071

(00)

670

(444)

1158(1337)

Pend

imethalin

fb1H

Wat35

DAS

330

(11)

675

(453)

455

(206)

341

(113

)071

(00)

226

(48)

071

(00)

234

(56)

664

(441)

1196(14

27)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

392

(149)

618

(384)

486

(244)

373

(183)

071

(00)

299

(89)

071

(00)

071

(00)

530

(283)

1156(1332)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

503

(248)

531

(285)

561

(318

)370

(132)

598

(385)

362

(131)

257

(62)

628

(39)

1397(19

51)

LSD

005

111

190

NS

NS

123

245

134

130

155

124

119875value

lt0001

000

6015

011

lt0001

0001

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 11

Table9Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )atanthesisin

theam

anseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

biom

ass

Partialw

eedy

299

(86)

267

(73)

711(506)

178(28)

909(826)

201

(36)

712(511)

559

(313

)1543(2378)

Oxadiargylfb

etho

xysulfu

ron

224

(47)

071

(00)

537

(285)

071

(00)

800

(635)

071

(00)

259

(64)

328

(103)

1067(1135)

Pend

imethalin

fbetho

xysulfu

ron

185(36)

071

(00)

534

(2810)

071

(00)

676

(456)

206

(38)

429

(182)

494

(240)

1109(1231)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

454

(210

)228

(55)

946(896

)071

(00)

348

(129)

401

(162)

1204(14

52)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

688

(479

)19

8(35)

1008(1015)

212

(40)

418

(193

)388

(147)

1383(1908)

Oxadiargylfb

1HW

at35

DAS

221

(44)

165(23)

415

(171)

071

(00)

392

(153)

071

(00)

639

(405)

323

(102)

945(897

)Pend

imethalin

fb1H

Wat35

DAS

170(29)

197(36)

483

(232)

071

(00)

540

(287)

071

(00)

584

(337)

401

(171)

1046(1092)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

177(28)

194(340)

350

(118

)14

9(20)

719(515

)13

9(17)

569

(326)

489

(242)

1142(1301)

Pyrazosulfu

ronfb

1HW

at35

DAS

198(35)

195(33)

348

(116

)15

2(21)

825

(685)

162(24)

516

(264)

511(256)

1199(14

35)

LSD

005

089

076

133

087

139

055

188

146

130

119875value

0001

lt0001

lt0001

000

4lt0001

lt0001

0002

003

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

12 The Scientific World Journal

Table 10 Effect of weed control treatments on yield and yield components of rice in the boro season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 34700 8235 9352 1902 476Partial weedy 15967 5933 9279 1803 158Oxadiargyl fb ethoxysulfuron 31567 7838 9367 1870 413Pendimethalin fb ethoxysulfuron 30100 8025 9249 1854 408Acetachlor + bensulfuranmethyl fb ethoxysulfuron 30300 7793 9277 1861 401Pyrazosulfuron fb ethoxysulfuron 28167 7605 9174 1805 346Oxadiargyl fb 1HW at 35DAS 27833 7642 9167 1836 348Pendimethalin fb 1HW at 35DAS 26400 7612 9190 1823 338Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 27033 7662 9199 1890 342Pyrazosulfuron fb 1HW at 35DAS 24833 7547 9000 1862 322LSD005 2341 565 163 NS 028119875 value 119875 lt 0001 119875 lt 0001 0008 0074 119875 lt 0001

DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 11 Effect of weed control treatments on yield and yield components of rice in the aman season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 25333 12020 8871 1779 498Partial weedy 17233 9028 8893 1797 259Oxadiargyl fb ethoxysulfuron 23000 10230 9127 1755 353Pendimethalin fb ethoxysulfuron 21967 10252 8843 1774 343Acetachlor + bensulfuranmethyl fb ethoxysulfuron 18667 10057 8544 1719 307Pyrazosulfuron fb ethoxysulfuron 18033 9577 8953 1672 300Oxadiargyl fb 1HW at 35DAS 23633 11268 8663 1817 408Pendimethalin fb 1HW at 35DAS 23067 11363 8757 1828 405Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 21733 11070 8999 1707 395Pyrazosulfuron fb 1HW at 35DAS 20400 10797 8629 1700 385LSD005 1930 1071 255 NS 019119875 value lt0001 0001 0002 032 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

used weed flora in the field rice variety used and soil andclimatic conditions Information to support these results isnot available in the literature

Our study shows that even after the use of preemergencefollowed by postemergence herbicides at 21 DAS or preemer-gence followed by a one-time HW complete weed controlcannot be achieved In additionmanual weeding is becomingless popular due to high labor wages it will be difficult to findlabor for weeding in the futureTherefore additional researchneeds to be conducted on the performance of combinationsof different pre- and postemergence herbicides applicationtimings and herbicide doses across various seasons andenvironmental conditions

We found that some weed species emerged later in theseason (eg A arvensis P niruri and G ciliata) and thusescaped the postemergence herbicide application or the HWat 35 DAS Previous studies report that weeds emerging laterin the season may not reduce rice yield significantly but

add seeds to the soil seed bank and result in heavy weedinfestation in subsequent seasons [22 23] In both seasons wefound a significant and negative linear correlation betweengrain yield and weed biomass at anthesis (Figure 3) Therelationship was slightly stronger in the boro season (1198772 =075) than in the aman season (1198772 = 065) These resultsare supported by previous studies in India [10] and thePhilippines [18] both of which found that grain yield wasnegatively correlated with weed biomass

In conclusion it is clear that weeds are a serious problemin DSR production systems and herbicides are the essentialtool to control them However continuous use of a singleherbicide over a long period may cause the development ofherbicide-resistant weed biotypes Therefore it is crucial toevaluate herbicides and determine which are less harmfulto the crop and have the ability to control a wide rangeof weeds In addition when many effective herbicides areavailable farmers will have the option to rotate the use

The Scientific World Journal 13

Boro 2011-12

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

Gra

in y

ield

(t h

aminus1)

Gy = 579 minus 0016x

R2= 075

(a)

Aman 2012

Gy = 479 minus 0009x

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

R2= 065G

rain

yie

ld (t

haminus

1)

(b)

Figure 3 The relationship between grain yield and weed biomass

of different herbicides and will help reduce the risk ofresistance developing inweeds and shifts inweed flora towardproblematic weeds

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] GMahajan B S Chauhan J Timsina P P Singh and K SinghldquoCrop performance and water- and nitrogen-use efficiencies indry-seeded rice in response to irrigation and fertilizer amountsin northwest Indiardquo Field Crops Research vol 134 pp 59ndash702012

[2] B S Chauhan G Mahajan V Sardana J Timsina and M LJat ldquoProductivity and sustainability of the rice-wheat croppingsystem in the Indo-Gangetic Plains of the Indian subcontinentproblems opportunities and strategiesrdquoAdvances inAgronomyvol 117 pp 315ndash369 2012

[3] B A M Bouman and T P Tuong ldquoField water managementto save water and increase its productivity in irrigated lowlandricerdquo Agricultural and Water Management vol 49 no 1 pp 11ndash30 2001

[4] R Gopal R K Jat R K Malik et al ldquoDirect dry seeded riceproduction technology and weed management in rice basedsystemsrdquo Technical Bulletin International Maize and WheatImprovement Center New Delhi India 2010

[5] B S Chauhan and D E Johnson ldquoThe role of seed ecologyin improving weed management strategies in the tropicsrdquoAdvances in Agronomy vol 105 pp 221ndash262 2010

[6] G Mahajan and B S Chauhan ldquoEffects of planting pattern andcultivar on weed and crop growth in aerobic rice systemrdquoWeedTechnology vol 25 no 4 pp 521ndash525 2011

[7] S Singh J K Ladha R K Gupta et al ldquoEvaluation ofmulching intercropping with Sesbania and herbicide use forweed management in dry-seeded rice (Oryza sativa L)rdquo CropProtection vol 26 no 4 pp 518ndash524 2007

[8] S Singh L Bhushan J K Ladha R K Gupta A N Rao andB Sivaprasad ldquoWeed management in dry-seeded rice (Oryzasativa) cultivated in the furrow-irrigated raised-bed plantingsystemrdquo Crop Protection vol 25 no 5 pp 487ndash495 2006

[9] B S Chauhan and D E Johnson ldquoRow spacing and weedcontrol timing affect yield of aerobic ricerdquo Field Crops Researchvol 121 no 2 pp 226ndash231 2011

[10] B S Chauhan V P Singh A Kumar and D E JohnsonldquoRelations of rice seeding rates to crop and weed growth inaerobic ricerdquo Field Crops Research vol 121 no 1 pp 105ndash1152011

[11] B S Chauhan ldquoWeed ecology andweedmanagement strategiesfor dry-seeded rice in AsiardquoWeed Technology vol 26 no 1 pp1ndash13 2012

[12] B S Chauhan and JOpena ldquoWeedmanagement and grain yieldof rice sown at low seeding rates in mechanized dry-seededsystemsrdquo Field Crops Research vol 141 pp 9ndash15 2013

[13] L Bastiaans R Paolini and D T Baumann ldquoFocus on eco-logical weed management what is hindering adoptionrdquo WeedResearch vol 48 no 6 pp 481ndash491 2008

[14] G Mahajan B S Chauhan and D E Johnson ldquoWeed man-agement in aerobic rice in northwestern indo-gangetic plainsrdquoJournal of Crop Improvement vol 23 no 4 pp 366ndash382 2009

[15] D D Buhler M Liebman and J J Obrycki ldquoTheoretical andpractical challenges to an IPM approach to weed managementrdquoWeed Science vol 48 no 3 pp 274ndash280 2000

[16] S Ahmed M R Islam M M Alam M M Haque and A JM S Karim ldquoRice production and profitability as influencedby integrated crop and resources managementrdquo Eco-FriendlyAgriculture vol 11 pp 720ndash725 2011

[17] MHasanuzzamanO Islam and S Bapari ldquoEfficacy of differentherbicides over manual weeding in controlling weeds in trans-planted ricerdquoAustralian Journal of Crop Science vol 2 no 1 pp18ndash24 2008

[18] B S Chauhan and J Opena ldquoImplications of plant geometryand weed control options in designing a low-seeding seed-drillfor dry-seeded rice systemsrdquo Field Crops Research vol 144 pp225ndash231 2013

[19] D L Jordan P K Bollich A B Burns and D MWalker ldquoRice(Oryza sativa) response to clomazonerdquo Weed Science vol 46no 3 pp 374ndash380 1998

[20] J D Beaty B Guy and J Edmund ldquoBroadleaf weed control andcotton response with bensulfuron in ricerdquo in Proceedings of theSouthern Weed Science Society vol 46 pp 91ndash96 1993

[21] M Hess and R Rose ldquoHOE 095404 a new herbicide forbroadleaf weed and sedge control in ricerdquo in Proceedings of theBrighton Crop Protection ConferenceWeeds vol 2 pp 763ndash768Brighton UK 1995

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

Nutrition and Metabolism

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Food ScienceInternational Journal of

Agronomy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

AgricultureAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BiodiversityInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Plant GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biotechnology Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Forestry ResearchInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of BotanyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Cell BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

6 The Scientific World Journal

Table 3 Effect of weed control treatments on weed density (number mminus2) at 35DAS in the aman season Weed density data were subjectedto square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Ageratumconyzoides

Cyperusrotundus

Celosiaargentea

Digitariaciliaris

Echinochloacolona

Phyllanthusniruri

Total weeddensity

Partial weedy 585 (344) 736 (542) 419 (177) 1002 (102) 803 (642) 456 (208) 1712 (2933)Oxadiargyl fb ethoxysulfuron 071 (00) 37 (136) 111 (11) 663 (438) 469 (218) 071 (00) 920 (843)Pendimethalin fb ethoxysulfuron 071 (00) 360 (167) 412 (167) 599 (385) 486 (231) 388 (146) 1074 (1148)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 301 (115) 387 (146) 860 (74) 671 (458) 071 (00) 1209 (1458)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 215 (83) 111 (11) 900 (854) 760 (573) 071 (00) 1231 (1521)Oxadiargyl fb 1HW at 35DAS 235 (104) 738 (542) 174 (31) 727 (563) 581 (333) 071 (00) 1253 (1573)Pendimethalin fb 1HW at 35DAS 497 (25) 814 (667) 472 (219) 533 (282) 492 (240) 356 (125) 1334 (1781)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 181 (52) 572 (323) 544 (292) 834 (693) 826 (677) 071 (00) 1410 (1984)

Pyrazosulfuron fb 1HW at 35DAS 291 (104) 640 (417) 521 (271) 949 (904) 769 (615) 134 (21) 1513 (2331)LSD005 265 281 126 310 165 085 209119875 value 0005 0002 lt0001 005 0001 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 4 Effect of weed control treatments on weed biomass (gmminus2) at 35 days after sowing in the boro season Weed biomass data weresubjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Amaranthusspinosus

Celosiaargentea

Cleomerutidosperma

Cyperusrotundus

Cynodondactylon

Echinochloacolona

Total weedbiomass

Partial weedy 182 (28) 219 (46) 135 (14) 324 (101) 100 (05) 225 (47) 492 (241)Oxadiargyl fb ethoxysulfuron 071 (00) 071 (00) 071 (00) 219 (43) 086 (02) 089 (03) 231 (49)Pendimethalin fb ethoxysulfuron 071 (00) 119 (09) 071 (00) 236 (51) 092 (04) 079 (01) 265 (66)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 124 (10) 139 (15) 207 (38) 101 (06) 080 (01) 274 (70)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 123 (10) 071 (00) 185 (30) 109 (10) 115 (09) 251 (59)Oxadiargyl fb 1HW at 35DAS 071 (00) 071 (00) 071 (00) 301 (86) 103 (08) 071 (00) 313 (94)Pendimethalin fb 1HW at 35DAS 071 (00) 107 (06) 071 (00) 350 (119) 073 (00) 071 (00) 360 (126)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 122 (10) 140 (15) 084 (02) 242 (55) 076 (01) 096 (04) 302 (87)

Pyrazosulfuron fb 1HW at 35DAS 127 (11) 140 (15) 071 (00) 209 (39) 098 (05) 161 (23) 310 (93)LSD005 016 044 020 052 NS 040 063119875 value lt0001 lt0001 lt0001 lt0001 084 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

be effective in controlling a wide range of broadleaved weedsas well as sedges [20 21] Our results are also supported bya previous study on the furrow-irrigated raised-bed DSR inwhich ethoxysulfuron (18 g ai haminus1) applied at 21 DAS waseffective in controlling broadleaved weeds [8]

Weed density and biomass as affected by different weedcontrol treatments at anthesis are given in Tables 6ndash9 Fromthe data it is clear that all herbicide treatments resulted inlower weed density and biomass compared to the partialweedy plots (ie HW at 35 DAS) Similar with observationsmade at 35 DAS total weed density and biomass werealso greatly affected by weed control treatments at anthesisConsidering the total weed density plots treated with pre-followed by postemergence herbicides always had lower weeddensity than those treated with preemergence herbicides

followed by a one-time HW at 35 DAS (Tables 6 and 7)Weed biomass maintained a similar trend as weed densityin the boro season In the aman season however plots thatreceived preemergence herbicides followed by a one-timeHW had lower weed biomass than those that received pre-and postemergence herbicides (Tables 8 and 9)

In the aman season crop vegetative growth went very fastat the early growth stages Rice in the plots that received a one-time HW at 35 DAS suppressed weed growth at later stagesIn the boro season however rice growth was very poor up to65 DAS because of low temperatures Sequential applicationof pre- and postemergence herbicides reduced weed biomassby 31ndash55 and 20ndash52 in the boro and aman seasons respec-tively and preemergence herbicide application followed by aone-timeHWreduced biomass by 15ndash40and 40ndash62 in the

The Scientific World Journal 7

Table 5 Effect of weed control treatments on weed biomass (gmminus2) at 35 days after sowing in the aman season Weed biomass data weresubjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Ageratumconyzoides

Cyperusrotundus

Celosiaargentea

Digitariaciliaris

Echinochloacolona

Phyllanthusniruri

Total weedbiomass

Partial weedy 260 (63) 377 (138) 312 (93) 629 (391) 623 (384) 242 (56) 1063 (1124)Oxadiargyl fb ethoxysulfuron 100 (07) 203 (41) 142 (25) 353 (121 ) 369 (132) 071 (00) 574 (325)Pendimethalin fb ethoxysulfuron 114 (12) 212 (51) 304 (88) 374 (140) 342 (113) 201 (37) 667 (441)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 178 (33) 279 (73) 550 (306) 465 (213) 071 (00) 790 (625)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 145 (27) 127 (14) 577 (343) 503 (249) 071 (00) 797 (633)Oxadiargyl fb 1HW at 35DAS 129 (19) 403 (16) 127 (13) 387 (147) 392 (149) 071 (00) 701 (487)Pendimethalin fb 1HW at 35DAS 257 (64) 461 (209) 356 (122) 362 (130) 354 (125) 140 (15) 817 (663)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 071 (07) 324 (101) 449 (197) 536 (287) 545 (296) 071 (00) 941 (834)

Pyrazosulfuron fb 1HW at 35DAS 142 (18) 370 (133) 386 (145) 600 (357) 517 (279) 083 (02) 966 (801)LSD005 100 145 091 144 129 083 098119875 value 0003 0002 lt0001 0001 0003 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

respective seasons all compared with the partial weedy check(ie one-time HW)

Among the herbicide treatments plots treated with oxa-diargyl followed by ethoxysulfuron reduced total weed den-sity by 65ndash70 compared with the partial weedy plots (378ndash477 plants mminus2) (Tables 6 and 7) The next best treatmentswere pendimethalin followed by ethoxysulfuron (60ndash62reduction in weed density) and acetachlor + bensulfuran-methyl followed by ethoxysulfuron (52ndash55 reduction inweed density) Compared with the partial weedy plots thosetreated with pyrazosulfuron followed by ethoxysulfuron sup-pressed weed density by only 39ndash48

33 Effect of Weed Control Treatments on Yield and Yield-Contributing Parameters Yield and yield-contributingparameters except 1000-grain weight were highly influencedby weed control treatments and the results were consistent inboth seasons (Tables 10 and 11) The highest panicle numbers(253ndash347mminus2) were recorded in the weed-free plots Paniclenumber was always lower in the herbicide-treated plotsthan in the weed-free plots and always higher than in thepartial weedy plots In the boro season the highest paniclenumbers (281ndash316mminus2) were recorded in the plots thatreceived pre- followed by postemergence herbicides In theaman season these values (204ndash236 panicles mminus2) werehighest when the plots received preemergence herbicidesfollowed by a one-time HW Among herbicide treatmentsthe highest panicle numbers (230ndash315mminus2) were recordedin the oxadiargyl-treated plots The next best herbicidetreatment was pendimethalin with panicle numbers (230ndash301mminus2) comparable to that of the oxadiargyl-treatedplots The lowest panicle numbers were recorded in thepyrazosulfuron-treated plots in both seasons

The number of spikelets panicleminus1 was consistent acrossthe herbicide-treated plots in the boro season but it sig-nificantly differed in the aman season (Tables 10 and 11)

Herbicide-treated plots always had a higher number ofspikelets panicleminus1 (5ndash26 higher) than the partial weedyplots and always had a lower number than the weed-free plots(3ndash21 lower)

Grain yieldwas strongly influenced byweed control treat-ments (Tables 10 and 11) The highest yield (476ndash498 t haminus1)was obtained in the weed-free plots Herbicide-treated plotsalways yielded more than the partial weedy plots Amongthe herbicide treatments the highest yield was recorded inthe plots treated with oxadiargyl followed by ethoxysulfuron(413 t haminus1) in the boro season and oxadiargyl followed aone-timeHW(41 t haminus1) in the aman season Pendimethalin-treated plots produced a similar grain yield (41 t haminus1) Theplots treated with pyrazosulfuron produced the lowest yieldin both seasons Compared with the control treatmentherbicide-treated plots produced a 20ndash62higher yieldwhentreated with both pre- and postemergence herbicides thesevalues were 30ndash41 when plots received only preemergenceherbicide and a one-timeHWAlthough herbicide treatmentsresulted in a yield advantage over the control treatment noneof the herbicide treatments reached the yield levels fromthe weed-free plots Grain yield from the best-performingherbicide treatment was 13ndash18 lower than that from theweed-free plots suggesting that there is a considerable scopeto increase yield with improved weed control practices inDSR In the boro season yield was higher in the plots treatedwith preemergence followed by postemergence herbicidesbut the results were not consistent in both seasons In theaman season vegetative growth started early In the plots thatreceived preemergence herbicide followed by a one-timeHWcanopy closure occurred fast which suppressed weed growthat the later stages These results suggest that in the amanseason application of preemergence herbicide followed byHW was better than applying both preemergence and poste-mergence herbicides However these results also depend onothers factors such as efficacy of the postemergence herbicide

8 The Scientific World Journal

Table6Eff

ecto

fweedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

theb

oroseason

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

1267(161)

866

(748)

503

(25)

576

(327)

436

(188)

739(563)

304

(115

)868

(781)

438

(188)

2180(4773)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

856

(729)

773(604)

426

(188)

071

(00)

235

(104)

071

(00)

240

(55)

071

(00)

1298(1679)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

937(896

)70

3(49)

466

(215

)071

(00)

393

(156)

071

(00)

222

(47)

278

(94)

1378(1897)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

1014

(105)

779(604)

486

(240)

071

(00)

509

(260)

071

(00)

071

(00)

071

(00)

1458(2156)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

846

(729)

707(542)

642

(417

)233

(63)

652

(438)

448

(208)

071

(00)

291

(8)

1575(2476)

Oxadiargylfb

1HW

at35

DAS

595

(354)

834

(704)

709(50)

463

(302)

071

(00)

249

(58)

071

(00)

599

(375

)071

(00)

1514

(2293)

Pend

imethalin

fb1H

Wat35

DAS

424

(181)

1154(133)

571

(323)

424

(177

)071

(00)

179(33)

071

(00)

591

(354)

288

(83)

1546(2384)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

563

(313

)1035

(109)

619

(385)

460

(292

)071

(00)

399

(167)

071

(00)

492

(240)

071

(00)

1577(2489)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

636

(435)

643

(458)

650

(427)

374

(135)

747(678

)312

(94)

510

(257)

312

(94)

1593(2578)

LSD

005

107

249

NS

NS

091

367

136

171

124

284

119875value

lt0001

003

042

063

lt0001

0007

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 9

Table7Eff

ectofw

eedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

thea

man

season

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eind

icaGalinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

467

(217

)468

(240)

772(596

)255

(63)

1013

(102)

289

(81)

1062(117)

625

(398

)1945(3783)

Oxadiargylfb

etho

xysulfu

ron

211(40)

071

(00)

514

(260)

071

(00)

761(575)

071

(00)

343

(117

)396

(156)

1074

(1148)

Pend

imethalin

fbetho

xysulfu

ron

138(23)

071

(00)

601

(358)

071

(00)

654

(425)

294

(82)

575

(327)

514

(260)

1216

(1476

)Ac

etachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

597

(354)

295

(104)

905(817

)071

(00)

448

(210

)562

(313

)1342(1798)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

769(646)

252

(61)

1017

(104)

300

(87)

435

(203)

515

(273

)1519

(2307)

Oxadiargylfb

1HW

at35

DAS

281

(75)

279

(75)

468

(219

)071

(00)

460

(208)

071

(00)

1005(101)

438

(188)

1332

(1771)

Pend

imethalin

fb1H

Wat35

DAS

249

(73)

341

(115

)552

(300)

071

(00)

636

(400)

071

(00)

940(881)

475

(248)

1422(2017)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

260

(63)

363

(134)

465

(219

)200

(43)

945(906)

158(24)

991(983)

590

(354)

1650(2726)

Pyrazosulfu

ronfb

1HW

at35

DAS

255

(63)

397

(154)

325

(104)

192(42)

988(990

)232

(52)

910(833)

643

(415

)1630(2653)

LSD

005

134

147

216

147

170

077

242

NS

107

119875value

lt0001

lt0001

0029

001

lt0001

0001

lt0001

012

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

10 The Scientific World Journal

Table8Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )at

anthesisin

thebo

roseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Phyllanthu

sniruri

Galinsoga

ciliata

Totalw

eed

biom

ass

Partialw

eedy

710(52)

467

(217

)365

(129)

364

(13)

412

(19)

526

(27)

316

(13)

403

(16)

744(560)

1519

(2302)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

589

(353)

659

(429)

335

(111)

071

(00)

192(61)

071

(00)

071

(00)

285

(79)

1019

(1033)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

664

(443)

554

(303)

382

(145)

071

(00)

275

(78)

071

(00)

260

(81)

290

(81)

1066(1131)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

656

(437)

616

(375

)450

(203)

071

(00)

461

(21)

071

(00)

071

(00)

071

(00)

1106(1228)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

538

(277

)615

(417

)475

(221)

210

(49)

609

(39)

409

(17)

264

(65)

071

(00)

1262(1589)

Oxadiargylfb

1HW

at35

DAS

323

(101)

607

(364)

544

(291

)251

(74)

071

(00)

259

(62)

071

(00)

071

(00)

670

(444)

1158(1337)

Pend

imethalin

fb1H

Wat35

DAS

330

(11)

675

(453)

455

(206)

341

(113

)071

(00)

226

(48)

071

(00)

234

(56)

664

(441)

1196(14

27)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

392

(149)

618

(384)

486

(244)

373

(183)

071

(00)

299

(89)

071

(00)

071

(00)

530

(283)

1156(1332)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

503

(248)

531

(285)

561

(318

)370

(132)

598

(385)

362

(131)

257

(62)

628

(39)

1397(19

51)

LSD

005

111

190

NS

NS

123

245

134

130

155

124

119875value

lt0001

000

6015

011

lt0001

0001

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 11

Table9Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )atanthesisin

theam

anseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

biom

ass

Partialw

eedy

299

(86)

267

(73)

711(506)

178(28)

909(826)

201

(36)

712(511)

559

(313

)1543(2378)

Oxadiargylfb

etho

xysulfu

ron

224

(47)

071

(00)

537

(285)

071

(00)

800

(635)

071

(00)

259

(64)

328

(103)

1067(1135)

Pend

imethalin

fbetho

xysulfu

ron

185(36)

071

(00)

534

(2810)

071

(00)

676

(456)

206

(38)

429

(182)

494

(240)

1109(1231)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

454

(210

)228

(55)

946(896

)071

(00)

348

(129)

401

(162)

1204(14

52)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

688

(479

)19

8(35)

1008(1015)

212

(40)

418

(193

)388

(147)

1383(1908)

Oxadiargylfb

1HW

at35

DAS

221

(44)

165(23)

415

(171)

071

(00)

392

(153)

071

(00)

639

(405)

323

(102)

945(897

)Pend

imethalin

fb1H

Wat35

DAS

170(29)

197(36)

483

(232)

071

(00)

540

(287)

071

(00)

584

(337)

401

(171)

1046(1092)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

177(28)

194(340)

350

(118

)14

9(20)

719(515

)13

9(17)

569

(326)

489

(242)

1142(1301)

Pyrazosulfu

ronfb

1HW

at35

DAS

198(35)

195(33)

348

(116

)15

2(21)

825

(685)

162(24)

516

(264)

511(256)

1199(14

35)

LSD

005

089

076

133

087

139

055

188

146

130

119875value

0001

lt0001

lt0001

000

4lt0001

lt0001

0002

003

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

12 The Scientific World Journal

Table 10 Effect of weed control treatments on yield and yield components of rice in the boro season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 34700 8235 9352 1902 476Partial weedy 15967 5933 9279 1803 158Oxadiargyl fb ethoxysulfuron 31567 7838 9367 1870 413Pendimethalin fb ethoxysulfuron 30100 8025 9249 1854 408Acetachlor + bensulfuranmethyl fb ethoxysulfuron 30300 7793 9277 1861 401Pyrazosulfuron fb ethoxysulfuron 28167 7605 9174 1805 346Oxadiargyl fb 1HW at 35DAS 27833 7642 9167 1836 348Pendimethalin fb 1HW at 35DAS 26400 7612 9190 1823 338Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 27033 7662 9199 1890 342Pyrazosulfuron fb 1HW at 35DAS 24833 7547 9000 1862 322LSD005 2341 565 163 NS 028119875 value 119875 lt 0001 119875 lt 0001 0008 0074 119875 lt 0001

DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 11 Effect of weed control treatments on yield and yield components of rice in the aman season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 25333 12020 8871 1779 498Partial weedy 17233 9028 8893 1797 259Oxadiargyl fb ethoxysulfuron 23000 10230 9127 1755 353Pendimethalin fb ethoxysulfuron 21967 10252 8843 1774 343Acetachlor + bensulfuranmethyl fb ethoxysulfuron 18667 10057 8544 1719 307Pyrazosulfuron fb ethoxysulfuron 18033 9577 8953 1672 300Oxadiargyl fb 1HW at 35DAS 23633 11268 8663 1817 408Pendimethalin fb 1HW at 35DAS 23067 11363 8757 1828 405Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 21733 11070 8999 1707 395Pyrazosulfuron fb 1HW at 35DAS 20400 10797 8629 1700 385LSD005 1930 1071 255 NS 019119875 value lt0001 0001 0002 032 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

used weed flora in the field rice variety used and soil andclimatic conditions Information to support these results isnot available in the literature

Our study shows that even after the use of preemergencefollowed by postemergence herbicides at 21 DAS or preemer-gence followed by a one-time HW complete weed controlcannot be achieved In additionmanual weeding is becomingless popular due to high labor wages it will be difficult to findlabor for weeding in the futureTherefore additional researchneeds to be conducted on the performance of combinationsof different pre- and postemergence herbicides applicationtimings and herbicide doses across various seasons andenvironmental conditions

We found that some weed species emerged later in theseason (eg A arvensis P niruri and G ciliata) and thusescaped the postemergence herbicide application or the HWat 35 DAS Previous studies report that weeds emerging laterin the season may not reduce rice yield significantly but

add seeds to the soil seed bank and result in heavy weedinfestation in subsequent seasons [22 23] In both seasons wefound a significant and negative linear correlation betweengrain yield and weed biomass at anthesis (Figure 3) Therelationship was slightly stronger in the boro season (1198772 =075) than in the aman season (1198772 = 065) These resultsare supported by previous studies in India [10] and thePhilippines [18] both of which found that grain yield wasnegatively correlated with weed biomass

In conclusion it is clear that weeds are a serious problemin DSR production systems and herbicides are the essentialtool to control them However continuous use of a singleherbicide over a long period may cause the development ofherbicide-resistant weed biotypes Therefore it is crucial toevaluate herbicides and determine which are less harmfulto the crop and have the ability to control a wide rangeof weeds In addition when many effective herbicides areavailable farmers will have the option to rotate the use

The Scientific World Journal 13

Boro 2011-12

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

Gra

in y

ield

(t h

aminus1)

Gy = 579 minus 0016x

R2= 075

(a)

Aman 2012

Gy = 479 minus 0009x

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

R2= 065G

rain

yie

ld (t

haminus

1)

(b)

Figure 3 The relationship between grain yield and weed biomass

of different herbicides and will help reduce the risk ofresistance developing inweeds and shifts inweed flora towardproblematic weeds

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] GMahajan B S Chauhan J Timsina P P Singh and K SinghldquoCrop performance and water- and nitrogen-use efficiencies indry-seeded rice in response to irrigation and fertilizer amountsin northwest Indiardquo Field Crops Research vol 134 pp 59ndash702012

[2] B S Chauhan G Mahajan V Sardana J Timsina and M LJat ldquoProductivity and sustainability of the rice-wheat croppingsystem in the Indo-Gangetic Plains of the Indian subcontinentproblems opportunities and strategiesrdquoAdvances inAgronomyvol 117 pp 315ndash369 2012

[3] B A M Bouman and T P Tuong ldquoField water managementto save water and increase its productivity in irrigated lowlandricerdquo Agricultural and Water Management vol 49 no 1 pp 11ndash30 2001

[4] R Gopal R K Jat R K Malik et al ldquoDirect dry seeded riceproduction technology and weed management in rice basedsystemsrdquo Technical Bulletin International Maize and WheatImprovement Center New Delhi India 2010

[5] B S Chauhan and D E Johnson ldquoThe role of seed ecologyin improving weed management strategies in the tropicsrdquoAdvances in Agronomy vol 105 pp 221ndash262 2010

[6] G Mahajan and B S Chauhan ldquoEffects of planting pattern andcultivar on weed and crop growth in aerobic rice systemrdquoWeedTechnology vol 25 no 4 pp 521ndash525 2011

[7] S Singh J K Ladha R K Gupta et al ldquoEvaluation ofmulching intercropping with Sesbania and herbicide use forweed management in dry-seeded rice (Oryza sativa L)rdquo CropProtection vol 26 no 4 pp 518ndash524 2007

[8] S Singh L Bhushan J K Ladha R K Gupta A N Rao andB Sivaprasad ldquoWeed management in dry-seeded rice (Oryzasativa) cultivated in the furrow-irrigated raised-bed plantingsystemrdquo Crop Protection vol 25 no 5 pp 487ndash495 2006

[9] B S Chauhan and D E Johnson ldquoRow spacing and weedcontrol timing affect yield of aerobic ricerdquo Field Crops Researchvol 121 no 2 pp 226ndash231 2011

[10] B S Chauhan V P Singh A Kumar and D E JohnsonldquoRelations of rice seeding rates to crop and weed growth inaerobic ricerdquo Field Crops Research vol 121 no 1 pp 105ndash1152011

[11] B S Chauhan ldquoWeed ecology andweedmanagement strategiesfor dry-seeded rice in AsiardquoWeed Technology vol 26 no 1 pp1ndash13 2012

[12] B S Chauhan and JOpena ldquoWeedmanagement and grain yieldof rice sown at low seeding rates in mechanized dry-seededsystemsrdquo Field Crops Research vol 141 pp 9ndash15 2013

[13] L Bastiaans R Paolini and D T Baumann ldquoFocus on eco-logical weed management what is hindering adoptionrdquo WeedResearch vol 48 no 6 pp 481ndash491 2008

[14] G Mahajan B S Chauhan and D E Johnson ldquoWeed man-agement in aerobic rice in northwestern indo-gangetic plainsrdquoJournal of Crop Improvement vol 23 no 4 pp 366ndash382 2009

[15] D D Buhler M Liebman and J J Obrycki ldquoTheoretical andpractical challenges to an IPM approach to weed managementrdquoWeed Science vol 48 no 3 pp 274ndash280 2000

[16] S Ahmed M R Islam M M Alam M M Haque and A JM S Karim ldquoRice production and profitability as influencedby integrated crop and resources managementrdquo Eco-FriendlyAgriculture vol 11 pp 720ndash725 2011

[17] MHasanuzzamanO Islam and S Bapari ldquoEfficacy of differentherbicides over manual weeding in controlling weeds in trans-planted ricerdquoAustralian Journal of Crop Science vol 2 no 1 pp18ndash24 2008

[18] B S Chauhan and J Opena ldquoImplications of plant geometryand weed control options in designing a low-seeding seed-drillfor dry-seeded rice systemsrdquo Field Crops Research vol 144 pp225ndash231 2013

[19] D L Jordan P K Bollich A B Burns and D MWalker ldquoRice(Oryza sativa) response to clomazonerdquo Weed Science vol 46no 3 pp 374ndash380 1998

[20] J D Beaty B Guy and J Edmund ldquoBroadleaf weed control andcotton response with bensulfuron in ricerdquo in Proceedings of theSouthern Weed Science Society vol 46 pp 91ndash96 1993

[21] M Hess and R Rose ldquoHOE 095404 a new herbicide forbroadleaf weed and sedge control in ricerdquo in Proceedings of theBrighton Crop Protection ConferenceWeeds vol 2 pp 763ndash768Brighton UK 1995

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

Nutrition and Metabolism

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Food ScienceInternational Journal of

Agronomy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

AgricultureAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BiodiversityInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Plant GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biotechnology Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Forestry ResearchInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of BotanyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Cell BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World Journal 7

Table 5 Effect of weed control treatments on weed biomass (gmminus2) at 35 days after sowing in the aman season Weed biomass data weresubjected to square-root (radic[119909 + 05]) transformation before analysis original values are shown in parentheses

Weed control treatments Ageratumconyzoides

Cyperusrotundus

Celosiaargentea

Digitariaciliaris

Echinochloacolona

Phyllanthusniruri

Total weedbiomass

Partial weedy 260 (63) 377 (138) 312 (93) 629 (391) 623 (384) 242 (56) 1063 (1124)Oxadiargyl fb ethoxysulfuron 100 (07) 203 (41) 142 (25) 353 (121 ) 369 (132) 071 (00) 574 (325)Pendimethalin fb ethoxysulfuron 114 (12) 212 (51) 304 (88) 374 (140) 342 (113) 201 (37) 667 (441)Acetachlor + bensulfuranmethyl fbethoxysulfuron 071 (00) 178 (33) 279 (73) 550 (306) 465 (213) 071 (00) 790 (625)

Pyrazosulfuron fb ethoxysulfuron 071 (00) 145 (27) 127 (14) 577 (343) 503 (249) 071 (00) 797 (633)Oxadiargyl fb 1HW at 35DAS 129 (19) 403 (16) 127 (13) 387 (147) 392 (149) 071 (00) 701 (487)Pendimethalin fb 1HW at 35DAS 257 (64) 461 (209) 356 (122) 362 (130) 354 (125) 140 (15) 817 (663)Acetachlor + bensulfuraonmethylfb 1HW at 35DAS 071 (07) 324 (101) 449 (197) 536 (287) 545 (296) 071 (00) 941 (834)

Pyrazosulfuron fb 1HW at 35DAS 142 (18) 370 (133) 386 (145) 600 (357) 517 (279) 083 (02) 966 (801)LSD005 100 145 091 144 129 083 098119875 value 0003 0002 lt0001 0001 0003 lt0001 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

respective seasons all compared with the partial weedy check(ie one-time HW)

Among the herbicide treatments plots treated with oxa-diargyl followed by ethoxysulfuron reduced total weed den-sity by 65ndash70 compared with the partial weedy plots (378ndash477 plants mminus2) (Tables 6 and 7) The next best treatmentswere pendimethalin followed by ethoxysulfuron (60ndash62reduction in weed density) and acetachlor + bensulfuran-methyl followed by ethoxysulfuron (52ndash55 reduction inweed density) Compared with the partial weedy plots thosetreated with pyrazosulfuron followed by ethoxysulfuron sup-pressed weed density by only 39ndash48

33 Effect of Weed Control Treatments on Yield and Yield-Contributing Parameters Yield and yield-contributingparameters except 1000-grain weight were highly influencedby weed control treatments and the results were consistent inboth seasons (Tables 10 and 11) The highest panicle numbers(253ndash347mminus2) were recorded in the weed-free plots Paniclenumber was always lower in the herbicide-treated plotsthan in the weed-free plots and always higher than in thepartial weedy plots In the boro season the highest paniclenumbers (281ndash316mminus2) were recorded in the plots thatreceived pre- followed by postemergence herbicides In theaman season these values (204ndash236 panicles mminus2) werehighest when the plots received preemergence herbicidesfollowed by a one-time HW Among herbicide treatmentsthe highest panicle numbers (230ndash315mminus2) were recordedin the oxadiargyl-treated plots The next best herbicidetreatment was pendimethalin with panicle numbers (230ndash301mminus2) comparable to that of the oxadiargyl-treatedplots The lowest panicle numbers were recorded in thepyrazosulfuron-treated plots in both seasons

The number of spikelets panicleminus1 was consistent acrossthe herbicide-treated plots in the boro season but it sig-nificantly differed in the aman season (Tables 10 and 11)

Herbicide-treated plots always had a higher number ofspikelets panicleminus1 (5ndash26 higher) than the partial weedyplots and always had a lower number than the weed-free plots(3ndash21 lower)

Grain yieldwas strongly influenced byweed control treat-ments (Tables 10 and 11) The highest yield (476ndash498 t haminus1)was obtained in the weed-free plots Herbicide-treated plotsalways yielded more than the partial weedy plots Amongthe herbicide treatments the highest yield was recorded inthe plots treated with oxadiargyl followed by ethoxysulfuron(413 t haminus1) in the boro season and oxadiargyl followed aone-timeHW(41 t haminus1) in the aman season Pendimethalin-treated plots produced a similar grain yield (41 t haminus1) Theplots treated with pyrazosulfuron produced the lowest yieldin both seasons Compared with the control treatmentherbicide-treated plots produced a 20ndash62higher yieldwhentreated with both pre- and postemergence herbicides thesevalues were 30ndash41 when plots received only preemergenceherbicide and a one-timeHWAlthough herbicide treatmentsresulted in a yield advantage over the control treatment noneof the herbicide treatments reached the yield levels fromthe weed-free plots Grain yield from the best-performingherbicide treatment was 13ndash18 lower than that from theweed-free plots suggesting that there is a considerable scopeto increase yield with improved weed control practices inDSR In the boro season yield was higher in the plots treatedwith preemergence followed by postemergence herbicidesbut the results were not consistent in both seasons In theaman season vegetative growth started early In the plots thatreceived preemergence herbicide followed by a one-timeHWcanopy closure occurred fast which suppressed weed growthat the later stages These results suggest that in the amanseason application of preemergence herbicide followed byHW was better than applying both preemergence and poste-mergence herbicides However these results also depend onothers factors such as efficacy of the postemergence herbicide

8 The Scientific World Journal

Table6Eff

ecto

fweedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

theb

oroseason

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

1267(161)

866

(748)

503

(25)

576

(327)

436

(188)

739(563)

304

(115

)868

(781)

438

(188)

2180(4773)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

856

(729)

773(604)

426

(188)

071

(00)

235

(104)

071

(00)

240

(55)

071

(00)

1298(1679)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

937(896

)70

3(49)

466

(215

)071

(00)

393

(156)

071

(00)

222

(47)

278

(94)

1378(1897)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

1014

(105)

779(604)

486

(240)

071

(00)

509

(260)

071

(00)

071

(00)

071

(00)

1458(2156)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

846

(729)

707(542)

642

(417

)233

(63)

652

(438)

448

(208)

071

(00)

291

(8)

1575(2476)

Oxadiargylfb

1HW

at35

DAS

595

(354)

834

(704)

709(50)

463

(302)

071

(00)

249

(58)

071

(00)

599

(375

)071

(00)

1514

(2293)

Pend

imethalin

fb1H

Wat35

DAS

424

(181)

1154(133)

571

(323)

424

(177

)071

(00)

179(33)

071

(00)

591

(354)

288

(83)

1546(2384)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

563

(313

)1035

(109)

619

(385)

460

(292

)071

(00)

399

(167)

071

(00)

492

(240)

071

(00)

1577(2489)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

636

(435)

643

(458)

650

(427)

374

(135)

747(678

)312

(94)

510

(257)

312

(94)

1593(2578)

LSD

005

107

249

NS

NS

091

367

136

171

124

284

119875value

lt0001

003

042

063

lt0001

0007

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 9

Table7Eff

ectofw

eedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

thea

man

season

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eind

icaGalinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

467

(217

)468

(240)

772(596

)255

(63)

1013

(102)

289

(81)

1062(117)

625

(398

)1945(3783)

Oxadiargylfb

etho

xysulfu

ron

211(40)

071

(00)

514

(260)

071

(00)

761(575)

071

(00)

343

(117

)396

(156)

1074

(1148)

Pend

imethalin

fbetho

xysulfu

ron

138(23)

071

(00)

601

(358)

071

(00)

654

(425)

294

(82)

575

(327)

514

(260)

1216

(1476

)Ac

etachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

597

(354)

295

(104)

905(817

)071

(00)

448

(210

)562

(313

)1342(1798)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

769(646)

252

(61)

1017

(104)

300

(87)

435

(203)

515

(273

)1519

(2307)

Oxadiargylfb

1HW

at35

DAS

281

(75)

279

(75)

468

(219

)071

(00)

460

(208)

071

(00)

1005(101)

438

(188)

1332

(1771)

Pend

imethalin

fb1H

Wat35

DAS

249

(73)

341

(115

)552

(300)

071

(00)

636

(400)

071

(00)

940(881)

475

(248)

1422(2017)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

260

(63)

363

(134)

465

(219

)200

(43)

945(906)

158(24)

991(983)

590

(354)

1650(2726)

Pyrazosulfu

ronfb

1HW

at35

DAS

255

(63)

397

(154)

325

(104)

192(42)

988(990

)232

(52)

910(833)

643

(415

)1630(2653)

LSD

005

134

147

216

147

170

077

242

NS

107

119875value

lt0001

lt0001

0029

001

lt0001

0001

lt0001

012

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

10 The Scientific World Journal

Table8Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )at

anthesisin

thebo

roseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Phyllanthu

sniruri

Galinsoga

ciliata

Totalw

eed

biom

ass

Partialw

eedy

710(52)

467

(217

)365

(129)

364

(13)

412

(19)

526

(27)

316

(13)

403

(16)

744(560)

1519

(2302)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

589

(353)

659

(429)

335

(111)

071

(00)

192(61)

071

(00)

071

(00)

285

(79)

1019

(1033)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

664

(443)

554

(303)

382

(145)

071

(00)

275

(78)

071

(00)

260

(81)

290

(81)

1066(1131)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

656

(437)

616

(375

)450

(203)

071

(00)

461

(21)

071

(00)

071

(00)

071

(00)

1106(1228)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

538

(277

)615

(417

)475

(221)

210

(49)

609

(39)

409

(17)

264

(65)

071

(00)

1262(1589)

Oxadiargylfb

1HW

at35

DAS

323

(101)

607

(364)

544

(291

)251

(74)

071

(00)

259

(62)

071

(00)

071

(00)

670

(444)

1158(1337)

Pend

imethalin

fb1H

Wat35

DAS

330

(11)

675

(453)

455

(206)

341

(113

)071

(00)

226

(48)

071

(00)

234

(56)

664

(441)

1196(14

27)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

392

(149)

618

(384)

486

(244)

373

(183)

071

(00)

299

(89)

071

(00)

071

(00)

530

(283)

1156(1332)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

503

(248)

531

(285)

561

(318

)370

(132)

598

(385)

362

(131)

257

(62)

628

(39)

1397(19

51)

LSD

005

111

190

NS

NS

123

245

134

130

155

124

119875value

lt0001

000

6015

011

lt0001

0001

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 11

Table9Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )atanthesisin

theam

anseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

biom

ass

Partialw

eedy

299

(86)

267

(73)

711(506)

178(28)

909(826)

201

(36)

712(511)

559

(313

)1543(2378)

Oxadiargylfb

etho

xysulfu

ron

224

(47)

071

(00)

537

(285)

071

(00)

800

(635)

071

(00)

259

(64)

328

(103)

1067(1135)

Pend

imethalin

fbetho

xysulfu

ron

185(36)

071

(00)

534

(2810)

071

(00)

676

(456)

206

(38)

429

(182)

494

(240)

1109(1231)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

454

(210

)228

(55)

946(896

)071

(00)

348

(129)

401

(162)

1204(14

52)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

688

(479

)19

8(35)

1008(1015)

212

(40)

418

(193

)388

(147)

1383(1908)

Oxadiargylfb

1HW

at35

DAS

221

(44)

165(23)

415

(171)

071

(00)

392

(153)

071

(00)

639

(405)

323

(102)

945(897

)Pend

imethalin

fb1H

Wat35

DAS

170(29)

197(36)

483

(232)

071

(00)

540

(287)

071

(00)

584

(337)

401

(171)

1046(1092)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

177(28)

194(340)

350

(118

)14

9(20)

719(515

)13

9(17)

569

(326)

489

(242)

1142(1301)

Pyrazosulfu

ronfb

1HW

at35

DAS

198(35)

195(33)

348

(116

)15

2(21)

825

(685)

162(24)

516

(264)

511(256)

1199(14

35)

LSD

005

089

076

133

087

139

055

188

146

130

119875value

0001

lt0001

lt0001

000

4lt0001

lt0001

0002

003

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

12 The Scientific World Journal

Table 10 Effect of weed control treatments on yield and yield components of rice in the boro season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 34700 8235 9352 1902 476Partial weedy 15967 5933 9279 1803 158Oxadiargyl fb ethoxysulfuron 31567 7838 9367 1870 413Pendimethalin fb ethoxysulfuron 30100 8025 9249 1854 408Acetachlor + bensulfuranmethyl fb ethoxysulfuron 30300 7793 9277 1861 401Pyrazosulfuron fb ethoxysulfuron 28167 7605 9174 1805 346Oxadiargyl fb 1HW at 35DAS 27833 7642 9167 1836 348Pendimethalin fb 1HW at 35DAS 26400 7612 9190 1823 338Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 27033 7662 9199 1890 342Pyrazosulfuron fb 1HW at 35DAS 24833 7547 9000 1862 322LSD005 2341 565 163 NS 028119875 value 119875 lt 0001 119875 lt 0001 0008 0074 119875 lt 0001

DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 11 Effect of weed control treatments on yield and yield components of rice in the aman season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 25333 12020 8871 1779 498Partial weedy 17233 9028 8893 1797 259Oxadiargyl fb ethoxysulfuron 23000 10230 9127 1755 353Pendimethalin fb ethoxysulfuron 21967 10252 8843 1774 343Acetachlor + bensulfuranmethyl fb ethoxysulfuron 18667 10057 8544 1719 307Pyrazosulfuron fb ethoxysulfuron 18033 9577 8953 1672 300Oxadiargyl fb 1HW at 35DAS 23633 11268 8663 1817 408Pendimethalin fb 1HW at 35DAS 23067 11363 8757 1828 405Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 21733 11070 8999 1707 395Pyrazosulfuron fb 1HW at 35DAS 20400 10797 8629 1700 385LSD005 1930 1071 255 NS 019119875 value lt0001 0001 0002 032 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

used weed flora in the field rice variety used and soil andclimatic conditions Information to support these results isnot available in the literature

Our study shows that even after the use of preemergencefollowed by postemergence herbicides at 21 DAS or preemer-gence followed by a one-time HW complete weed controlcannot be achieved In additionmanual weeding is becomingless popular due to high labor wages it will be difficult to findlabor for weeding in the futureTherefore additional researchneeds to be conducted on the performance of combinationsof different pre- and postemergence herbicides applicationtimings and herbicide doses across various seasons andenvironmental conditions

We found that some weed species emerged later in theseason (eg A arvensis P niruri and G ciliata) and thusescaped the postemergence herbicide application or the HWat 35 DAS Previous studies report that weeds emerging laterin the season may not reduce rice yield significantly but

add seeds to the soil seed bank and result in heavy weedinfestation in subsequent seasons [22 23] In both seasons wefound a significant and negative linear correlation betweengrain yield and weed biomass at anthesis (Figure 3) Therelationship was slightly stronger in the boro season (1198772 =075) than in the aman season (1198772 = 065) These resultsare supported by previous studies in India [10] and thePhilippines [18] both of which found that grain yield wasnegatively correlated with weed biomass

In conclusion it is clear that weeds are a serious problemin DSR production systems and herbicides are the essentialtool to control them However continuous use of a singleherbicide over a long period may cause the development ofherbicide-resistant weed biotypes Therefore it is crucial toevaluate herbicides and determine which are less harmfulto the crop and have the ability to control a wide rangeof weeds In addition when many effective herbicides areavailable farmers will have the option to rotate the use

The Scientific World Journal 13

Boro 2011-12

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

Gra

in y

ield

(t h

aminus1)

Gy = 579 minus 0016x

R2= 075

(a)

Aman 2012

Gy = 479 minus 0009x

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

R2= 065G

rain

yie

ld (t

haminus

1)

(b)

Figure 3 The relationship between grain yield and weed biomass

of different herbicides and will help reduce the risk ofresistance developing inweeds and shifts inweed flora towardproblematic weeds

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] GMahajan B S Chauhan J Timsina P P Singh and K SinghldquoCrop performance and water- and nitrogen-use efficiencies indry-seeded rice in response to irrigation and fertilizer amountsin northwest Indiardquo Field Crops Research vol 134 pp 59ndash702012

[2] B S Chauhan G Mahajan V Sardana J Timsina and M LJat ldquoProductivity and sustainability of the rice-wheat croppingsystem in the Indo-Gangetic Plains of the Indian subcontinentproblems opportunities and strategiesrdquoAdvances inAgronomyvol 117 pp 315ndash369 2012

[3] B A M Bouman and T P Tuong ldquoField water managementto save water and increase its productivity in irrigated lowlandricerdquo Agricultural and Water Management vol 49 no 1 pp 11ndash30 2001

[4] R Gopal R K Jat R K Malik et al ldquoDirect dry seeded riceproduction technology and weed management in rice basedsystemsrdquo Technical Bulletin International Maize and WheatImprovement Center New Delhi India 2010

[5] B S Chauhan and D E Johnson ldquoThe role of seed ecologyin improving weed management strategies in the tropicsrdquoAdvances in Agronomy vol 105 pp 221ndash262 2010

[6] G Mahajan and B S Chauhan ldquoEffects of planting pattern andcultivar on weed and crop growth in aerobic rice systemrdquoWeedTechnology vol 25 no 4 pp 521ndash525 2011

[7] S Singh J K Ladha R K Gupta et al ldquoEvaluation ofmulching intercropping with Sesbania and herbicide use forweed management in dry-seeded rice (Oryza sativa L)rdquo CropProtection vol 26 no 4 pp 518ndash524 2007

[8] S Singh L Bhushan J K Ladha R K Gupta A N Rao andB Sivaprasad ldquoWeed management in dry-seeded rice (Oryzasativa) cultivated in the furrow-irrigated raised-bed plantingsystemrdquo Crop Protection vol 25 no 5 pp 487ndash495 2006

[9] B S Chauhan and D E Johnson ldquoRow spacing and weedcontrol timing affect yield of aerobic ricerdquo Field Crops Researchvol 121 no 2 pp 226ndash231 2011

[10] B S Chauhan V P Singh A Kumar and D E JohnsonldquoRelations of rice seeding rates to crop and weed growth inaerobic ricerdquo Field Crops Research vol 121 no 1 pp 105ndash1152011

[11] B S Chauhan ldquoWeed ecology andweedmanagement strategiesfor dry-seeded rice in AsiardquoWeed Technology vol 26 no 1 pp1ndash13 2012

[12] B S Chauhan and JOpena ldquoWeedmanagement and grain yieldof rice sown at low seeding rates in mechanized dry-seededsystemsrdquo Field Crops Research vol 141 pp 9ndash15 2013

[13] L Bastiaans R Paolini and D T Baumann ldquoFocus on eco-logical weed management what is hindering adoptionrdquo WeedResearch vol 48 no 6 pp 481ndash491 2008

[14] G Mahajan B S Chauhan and D E Johnson ldquoWeed man-agement in aerobic rice in northwestern indo-gangetic plainsrdquoJournal of Crop Improvement vol 23 no 4 pp 366ndash382 2009

[15] D D Buhler M Liebman and J J Obrycki ldquoTheoretical andpractical challenges to an IPM approach to weed managementrdquoWeed Science vol 48 no 3 pp 274ndash280 2000

[16] S Ahmed M R Islam M M Alam M M Haque and A JM S Karim ldquoRice production and profitability as influencedby integrated crop and resources managementrdquo Eco-FriendlyAgriculture vol 11 pp 720ndash725 2011

[17] MHasanuzzamanO Islam and S Bapari ldquoEfficacy of differentherbicides over manual weeding in controlling weeds in trans-planted ricerdquoAustralian Journal of Crop Science vol 2 no 1 pp18ndash24 2008

[18] B S Chauhan and J Opena ldquoImplications of plant geometryand weed control options in designing a low-seeding seed-drillfor dry-seeded rice systemsrdquo Field Crops Research vol 144 pp225ndash231 2013

[19] D L Jordan P K Bollich A B Burns and D MWalker ldquoRice(Oryza sativa) response to clomazonerdquo Weed Science vol 46no 3 pp 374ndash380 1998

[20] J D Beaty B Guy and J Edmund ldquoBroadleaf weed control andcotton response with bensulfuron in ricerdquo in Proceedings of theSouthern Weed Science Society vol 46 pp 91ndash96 1993

[21] M Hess and R Rose ldquoHOE 095404 a new herbicide forbroadleaf weed and sedge control in ricerdquo in Proceedings of theBrighton Crop Protection ConferenceWeeds vol 2 pp 763ndash768Brighton UK 1995

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

Nutrition and Metabolism

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Food ScienceInternational Journal of

Agronomy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

AgricultureAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BiodiversityInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Plant GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biotechnology Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Forestry ResearchInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of BotanyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Cell BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

8 The Scientific World Journal

Table6Eff

ecto

fweedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

theb

oroseason

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

1267(161)

866

(748)

503

(25)

576

(327)

436

(188)

739(563)

304

(115

)868

(781)

438

(188)

2180(4773)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

856

(729)

773(604)

426

(188)

071

(00)

235

(104)

071

(00)

240

(55)

071

(00)

1298(1679)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

937(896

)70

3(49)

466

(215

)071

(00)

393

(156)

071

(00)

222

(47)

278

(94)

1378(1897)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

1014

(105)

779(604)

486

(240)

071

(00)

509

(260)

071

(00)

071

(00)

071

(00)

1458(2156)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

846

(729)

707(542)

642

(417

)233

(63)

652

(438)

448

(208)

071

(00)

291

(8)

1575(2476)

Oxadiargylfb

1HW

at35

DAS

595

(354)

834

(704)

709(50)

463

(302)

071

(00)

249

(58)

071

(00)

599

(375

)071

(00)

1514

(2293)

Pend

imethalin

fb1H

Wat35

DAS

424

(181)

1154(133)

571

(323)

424

(177

)071

(00)

179(33)

071

(00)

591

(354)

288

(83)

1546(2384)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

563

(313

)1035

(109)

619

(385)

460

(292

)071

(00)

399

(167)

071

(00)

492

(240)

071

(00)

1577(2489)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

636

(435)

643

(458)

650

(427)

374

(135)

747(678

)312

(94)

510

(257)

312

(94)

1593(2578)

LSD

005

107

249

NS

NS

091

367

136

171

124

284

119875value

lt0001

003

042

063

lt0001

0007

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 9

Table7Eff

ectofw

eedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

thea

man

season

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eind

icaGalinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

467

(217

)468

(240)

772(596

)255

(63)

1013

(102)

289

(81)

1062(117)

625

(398

)1945(3783)

Oxadiargylfb

etho

xysulfu

ron

211(40)

071

(00)

514

(260)

071

(00)

761(575)

071

(00)

343

(117

)396

(156)

1074

(1148)

Pend

imethalin

fbetho

xysulfu

ron

138(23)

071

(00)

601

(358)

071

(00)

654

(425)

294

(82)

575

(327)

514

(260)

1216

(1476

)Ac

etachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

597

(354)

295

(104)

905(817

)071

(00)

448

(210

)562

(313

)1342(1798)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

769(646)

252

(61)

1017

(104)

300

(87)

435

(203)

515

(273

)1519

(2307)

Oxadiargylfb

1HW

at35

DAS

281

(75)

279

(75)

468

(219

)071

(00)

460

(208)

071

(00)

1005(101)

438

(188)

1332

(1771)

Pend

imethalin

fb1H

Wat35

DAS

249

(73)

341

(115

)552

(300)

071

(00)

636

(400)

071

(00)

940(881)

475

(248)

1422(2017)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

260

(63)

363

(134)

465

(219

)200

(43)

945(906)

158(24)

991(983)

590

(354)

1650(2726)

Pyrazosulfu

ronfb

1HW

at35

DAS

255

(63)

397

(154)

325

(104)

192(42)

988(990

)232

(52)

910(833)

643

(415

)1630(2653)

LSD

005

134

147

216

147

170

077

242

NS

107

119875value

lt0001

lt0001

0029

001

lt0001

0001

lt0001

012

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

10 The Scientific World Journal

Table8Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )at

anthesisin

thebo

roseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Phyllanthu

sniruri

Galinsoga

ciliata

Totalw

eed

biom

ass

Partialw

eedy

710(52)

467

(217

)365

(129)

364

(13)

412

(19)

526

(27)

316

(13)

403

(16)

744(560)

1519

(2302)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

589

(353)

659

(429)

335

(111)

071

(00)

192(61)

071

(00)

071

(00)

285

(79)

1019

(1033)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

664

(443)

554

(303)

382

(145)

071

(00)

275

(78)

071

(00)

260

(81)

290

(81)

1066(1131)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

656

(437)

616

(375

)450

(203)

071

(00)

461

(21)

071

(00)

071

(00)

071

(00)

1106(1228)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

538

(277

)615

(417

)475

(221)

210

(49)

609

(39)

409

(17)

264

(65)

071

(00)

1262(1589)

Oxadiargylfb

1HW

at35

DAS

323

(101)

607

(364)

544

(291

)251

(74)

071

(00)

259

(62)

071

(00)

071

(00)

670

(444)

1158(1337)

Pend

imethalin

fb1H

Wat35

DAS

330

(11)

675

(453)

455

(206)

341

(113

)071

(00)

226

(48)

071

(00)

234

(56)

664

(441)

1196(14

27)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

392

(149)

618

(384)

486

(244)

373

(183)

071

(00)

299

(89)

071

(00)

071

(00)

530

(283)

1156(1332)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

503

(248)

531

(285)

561

(318

)370

(132)

598

(385)

362

(131)

257

(62)

628

(39)

1397(19

51)

LSD

005

111

190

NS

NS

123

245

134

130

155

124

119875value

lt0001

000

6015

011

lt0001

0001

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 11

Table9Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )atanthesisin

theam

anseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

biom

ass

Partialw

eedy

299

(86)

267

(73)

711(506)

178(28)

909(826)

201

(36)

712(511)

559

(313

)1543(2378)

Oxadiargylfb

etho

xysulfu

ron

224

(47)

071

(00)

537

(285)

071

(00)

800

(635)

071

(00)

259

(64)

328

(103)

1067(1135)

Pend

imethalin

fbetho

xysulfu

ron

185(36)

071

(00)

534

(2810)

071

(00)

676

(456)

206

(38)

429

(182)

494

(240)

1109(1231)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

454

(210

)228

(55)

946(896

)071

(00)

348

(129)

401

(162)

1204(14

52)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

688

(479

)19

8(35)

1008(1015)

212

(40)

418

(193

)388

(147)

1383(1908)

Oxadiargylfb

1HW

at35

DAS

221

(44)

165(23)

415

(171)

071

(00)

392

(153)

071

(00)

639

(405)

323

(102)

945(897

)Pend

imethalin

fb1H

Wat35

DAS

170(29)

197(36)

483

(232)

071

(00)

540

(287)

071

(00)

584

(337)

401

(171)

1046(1092)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

177(28)

194(340)

350

(118

)14

9(20)

719(515

)13

9(17)

569

(326)

489

(242)

1142(1301)

Pyrazosulfu

ronfb

1HW

at35

DAS

198(35)

195(33)

348

(116

)15

2(21)

825

(685)

162(24)

516

(264)

511(256)

1199(14

35)

LSD

005

089

076

133

087

139

055

188

146

130

119875value

0001

lt0001

lt0001

000

4lt0001

lt0001

0002

003

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

12 The Scientific World Journal

Table 10 Effect of weed control treatments on yield and yield components of rice in the boro season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 34700 8235 9352 1902 476Partial weedy 15967 5933 9279 1803 158Oxadiargyl fb ethoxysulfuron 31567 7838 9367 1870 413Pendimethalin fb ethoxysulfuron 30100 8025 9249 1854 408Acetachlor + bensulfuranmethyl fb ethoxysulfuron 30300 7793 9277 1861 401Pyrazosulfuron fb ethoxysulfuron 28167 7605 9174 1805 346Oxadiargyl fb 1HW at 35DAS 27833 7642 9167 1836 348Pendimethalin fb 1HW at 35DAS 26400 7612 9190 1823 338Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 27033 7662 9199 1890 342Pyrazosulfuron fb 1HW at 35DAS 24833 7547 9000 1862 322LSD005 2341 565 163 NS 028119875 value 119875 lt 0001 119875 lt 0001 0008 0074 119875 lt 0001

DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 11 Effect of weed control treatments on yield and yield components of rice in the aman season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 25333 12020 8871 1779 498Partial weedy 17233 9028 8893 1797 259Oxadiargyl fb ethoxysulfuron 23000 10230 9127 1755 353Pendimethalin fb ethoxysulfuron 21967 10252 8843 1774 343Acetachlor + bensulfuranmethyl fb ethoxysulfuron 18667 10057 8544 1719 307Pyrazosulfuron fb ethoxysulfuron 18033 9577 8953 1672 300Oxadiargyl fb 1HW at 35DAS 23633 11268 8663 1817 408Pendimethalin fb 1HW at 35DAS 23067 11363 8757 1828 405Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 21733 11070 8999 1707 395Pyrazosulfuron fb 1HW at 35DAS 20400 10797 8629 1700 385LSD005 1930 1071 255 NS 019119875 value lt0001 0001 0002 032 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

used weed flora in the field rice variety used and soil andclimatic conditions Information to support these results isnot available in the literature

Our study shows that even after the use of preemergencefollowed by postemergence herbicides at 21 DAS or preemer-gence followed by a one-time HW complete weed controlcannot be achieved In additionmanual weeding is becomingless popular due to high labor wages it will be difficult to findlabor for weeding in the futureTherefore additional researchneeds to be conducted on the performance of combinationsof different pre- and postemergence herbicides applicationtimings and herbicide doses across various seasons andenvironmental conditions

We found that some weed species emerged later in theseason (eg A arvensis P niruri and G ciliata) and thusescaped the postemergence herbicide application or the HWat 35 DAS Previous studies report that weeds emerging laterin the season may not reduce rice yield significantly but

add seeds to the soil seed bank and result in heavy weedinfestation in subsequent seasons [22 23] In both seasons wefound a significant and negative linear correlation betweengrain yield and weed biomass at anthesis (Figure 3) Therelationship was slightly stronger in the boro season (1198772 =075) than in the aman season (1198772 = 065) These resultsare supported by previous studies in India [10] and thePhilippines [18] both of which found that grain yield wasnegatively correlated with weed biomass

In conclusion it is clear that weeds are a serious problemin DSR production systems and herbicides are the essentialtool to control them However continuous use of a singleherbicide over a long period may cause the development ofherbicide-resistant weed biotypes Therefore it is crucial toevaluate herbicides and determine which are less harmfulto the crop and have the ability to control a wide rangeof weeds In addition when many effective herbicides areavailable farmers will have the option to rotate the use

The Scientific World Journal 13

Boro 2011-12

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

Gra

in y

ield

(t h

aminus1)

Gy = 579 minus 0016x

R2= 075

(a)

Aman 2012

Gy = 479 minus 0009x

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

R2= 065G

rain

yie

ld (t

haminus

1)

(b)

Figure 3 The relationship between grain yield and weed biomass

of different herbicides and will help reduce the risk ofresistance developing inweeds and shifts inweed flora towardproblematic weeds

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] GMahajan B S Chauhan J Timsina P P Singh and K SinghldquoCrop performance and water- and nitrogen-use efficiencies indry-seeded rice in response to irrigation and fertilizer amountsin northwest Indiardquo Field Crops Research vol 134 pp 59ndash702012

[2] B S Chauhan G Mahajan V Sardana J Timsina and M LJat ldquoProductivity and sustainability of the rice-wheat croppingsystem in the Indo-Gangetic Plains of the Indian subcontinentproblems opportunities and strategiesrdquoAdvances inAgronomyvol 117 pp 315ndash369 2012

[3] B A M Bouman and T P Tuong ldquoField water managementto save water and increase its productivity in irrigated lowlandricerdquo Agricultural and Water Management vol 49 no 1 pp 11ndash30 2001

[4] R Gopal R K Jat R K Malik et al ldquoDirect dry seeded riceproduction technology and weed management in rice basedsystemsrdquo Technical Bulletin International Maize and WheatImprovement Center New Delhi India 2010

[5] B S Chauhan and D E Johnson ldquoThe role of seed ecologyin improving weed management strategies in the tropicsrdquoAdvances in Agronomy vol 105 pp 221ndash262 2010

[6] G Mahajan and B S Chauhan ldquoEffects of planting pattern andcultivar on weed and crop growth in aerobic rice systemrdquoWeedTechnology vol 25 no 4 pp 521ndash525 2011

[7] S Singh J K Ladha R K Gupta et al ldquoEvaluation ofmulching intercropping with Sesbania and herbicide use forweed management in dry-seeded rice (Oryza sativa L)rdquo CropProtection vol 26 no 4 pp 518ndash524 2007

[8] S Singh L Bhushan J K Ladha R K Gupta A N Rao andB Sivaprasad ldquoWeed management in dry-seeded rice (Oryzasativa) cultivated in the furrow-irrigated raised-bed plantingsystemrdquo Crop Protection vol 25 no 5 pp 487ndash495 2006

[9] B S Chauhan and D E Johnson ldquoRow spacing and weedcontrol timing affect yield of aerobic ricerdquo Field Crops Researchvol 121 no 2 pp 226ndash231 2011

[10] B S Chauhan V P Singh A Kumar and D E JohnsonldquoRelations of rice seeding rates to crop and weed growth inaerobic ricerdquo Field Crops Research vol 121 no 1 pp 105ndash1152011

[11] B S Chauhan ldquoWeed ecology andweedmanagement strategiesfor dry-seeded rice in AsiardquoWeed Technology vol 26 no 1 pp1ndash13 2012

[12] B S Chauhan and JOpena ldquoWeedmanagement and grain yieldof rice sown at low seeding rates in mechanized dry-seededsystemsrdquo Field Crops Research vol 141 pp 9ndash15 2013

[13] L Bastiaans R Paolini and D T Baumann ldquoFocus on eco-logical weed management what is hindering adoptionrdquo WeedResearch vol 48 no 6 pp 481ndash491 2008

[14] G Mahajan B S Chauhan and D E Johnson ldquoWeed man-agement in aerobic rice in northwestern indo-gangetic plainsrdquoJournal of Crop Improvement vol 23 no 4 pp 366ndash382 2009

[15] D D Buhler M Liebman and J J Obrycki ldquoTheoretical andpractical challenges to an IPM approach to weed managementrdquoWeed Science vol 48 no 3 pp 274ndash280 2000

[16] S Ahmed M R Islam M M Alam M M Haque and A JM S Karim ldquoRice production and profitability as influencedby integrated crop and resources managementrdquo Eco-FriendlyAgriculture vol 11 pp 720ndash725 2011

[17] MHasanuzzamanO Islam and S Bapari ldquoEfficacy of differentherbicides over manual weeding in controlling weeds in trans-planted ricerdquoAustralian Journal of Crop Science vol 2 no 1 pp18ndash24 2008

[18] B S Chauhan and J Opena ldquoImplications of plant geometryand weed control options in designing a low-seeding seed-drillfor dry-seeded rice systemsrdquo Field Crops Research vol 144 pp225ndash231 2013

[19] D L Jordan P K Bollich A B Burns and D MWalker ldquoRice(Oryza sativa) response to clomazonerdquo Weed Science vol 46no 3 pp 374ndash380 1998

[20] J D Beaty B Guy and J Edmund ldquoBroadleaf weed control andcotton response with bensulfuron in ricerdquo in Proceedings of theSouthern Weed Science Society vol 46 pp 91ndash96 1993

[21] M Hess and R Rose ldquoHOE 095404 a new herbicide forbroadleaf weed and sedge control in ricerdquo in Proceedings of theBrighton Crop Protection ConferenceWeeds vol 2 pp 763ndash768Brighton UK 1995

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

Nutrition and Metabolism

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Food ScienceInternational Journal of

Agronomy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

AgricultureAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BiodiversityInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Plant GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biotechnology Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Forestry ResearchInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of BotanyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Cell BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World Journal 9

Table7Eff

ectofw

eedcontroltreatmentson

weeddensity

(num

bermminus2 )atanthesisin

thea

man

season

Weeddensity

dataweresub

jected

tosquare-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eind

icaGalinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

density

Partialw

eedy

467

(217

)468

(240)

772(596

)255

(63)

1013

(102)

289

(81)

1062(117)

625

(398

)1945(3783)

Oxadiargylfb

etho

xysulfu

ron

211(40)

071

(00)

514

(260)

071

(00)

761(575)

071

(00)

343

(117

)396

(156)

1074

(1148)

Pend

imethalin

fbetho

xysulfu

ron

138(23)

071

(00)

601

(358)

071

(00)

654

(425)

294

(82)

575

(327)

514

(260)

1216

(1476

)Ac

etachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

597

(354)

295

(104)

905(817

)071

(00)

448

(210

)562

(313

)1342(1798)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

769(646)

252

(61)

1017

(104)

300

(87)

435

(203)

515

(273

)1519

(2307)

Oxadiargylfb

1HW

at35

DAS

281

(75)

279

(75)

468

(219

)071

(00)

460

(208)

071

(00)

1005(101)

438

(188)

1332

(1771)

Pend

imethalin

fb1H

Wat35

DAS

249

(73)

341

(115

)552

(300)

071

(00)

636

(400)

071

(00)

940(881)

475

(248)

1422(2017)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

260

(63)

363

(134)

465

(219

)200

(43)

945(906)

158(24)

991(983)

590

(354)

1650(2726)

Pyrazosulfu

ronfb

1HW

at35

DAS

255

(63)

397

(154)

325

(104)

192(42)

988(990

)232

(52)

910(833)

643

(415

)1630(2653)

LSD

005

134

147

216

147

170

077

242

NS

107

119875value

lt0001

lt0001

0029

001

lt0001

0001

lt0001

012

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

10 The Scientific World Journal

Table8Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )at

anthesisin

thebo

roseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Phyllanthu

sniruri

Galinsoga

ciliata

Totalw

eed

biom

ass

Partialw

eedy

710(52)

467

(217

)365

(129)

364

(13)

412

(19)

526

(27)

316

(13)

403

(16)

744(560)

1519

(2302)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

589

(353)

659

(429)

335

(111)

071

(00)

192(61)

071

(00)

071

(00)

285

(79)

1019

(1033)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

664

(443)

554

(303)

382

(145)

071

(00)

275

(78)

071

(00)

260

(81)

290

(81)

1066(1131)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

656

(437)

616

(375

)450

(203)

071

(00)

461

(21)

071

(00)

071

(00)

071

(00)

1106(1228)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

538

(277

)615

(417

)475

(221)

210

(49)

609

(39)

409

(17)

264

(65)

071

(00)

1262(1589)

Oxadiargylfb

1HW

at35

DAS

323

(101)

607

(364)

544

(291

)251

(74)

071

(00)

259

(62)

071

(00)

071

(00)

670

(444)

1158(1337)

Pend

imethalin

fb1H

Wat35

DAS

330

(11)

675

(453)

455

(206)

341

(113

)071

(00)

226

(48)

071

(00)

234

(56)

664

(441)

1196(14

27)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

392

(149)

618

(384)

486

(244)

373

(183)

071

(00)

299

(89)

071

(00)

071

(00)

530

(283)

1156(1332)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

503

(248)

531

(285)

561

(318

)370

(132)

598

(385)

362

(131)

257

(62)

628

(39)

1397(19

51)

LSD

005

111

190

NS

NS

123

245

134

130

155

124

119875value

lt0001

000

6015

011

lt0001

0001

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 11

Table9Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )atanthesisin

theam

anseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

biom

ass

Partialw

eedy

299

(86)

267

(73)

711(506)

178(28)

909(826)

201

(36)

712(511)

559

(313

)1543(2378)

Oxadiargylfb

etho

xysulfu

ron

224

(47)

071

(00)

537

(285)

071

(00)

800

(635)

071

(00)

259

(64)

328

(103)

1067(1135)

Pend

imethalin

fbetho

xysulfu

ron

185(36)

071

(00)

534

(2810)

071

(00)

676

(456)

206

(38)

429

(182)

494

(240)

1109(1231)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

454

(210

)228

(55)

946(896

)071

(00)

348

(129)

401

(162)

1204(14

52)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

688

(479

)19

8(35)

1008(1015)

212

(40)

418

(193

)388

(147)

1383(1908)

Oxadiargylfb

1HW

at35

DAS

221

(44)

165(23)

415

(171)

071

(00)

392

(153)

071

(00)

639

(405)

323

(102)

945(897

)Pend

imethalin

fb1H

Wat35

DAS

170(29)

197(36)

483

(232)

071

(00)

540

(287)

071

(00)

584

(337)

401

(171)

1046(1092)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

177(28)

194(340)

350

(118

)14

9(20)

719(515

)13

9(17)

569

(326)

489

(242)

1142(1301)

Pyrazosulfu

ronfb

1HW

at35

DAS

198(35)

195(33)

348

(116

)15

2(21)

825

(685)

162(24)

516

(264)

511(256)

1199(14

35)

LSD

005

089

076

133

087

139

055

188

146

130

119875value

0001

lt0001

lt0001

000

4lt0001

lt0001

0002

003

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

12 The Scientific World Journal

Table 10 Effect of weed control treatments on yield and yield components of rice in the boro season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 34700 8235 9352 1902 476Partial weedy 15967 5933 9279 1803 158Oxadiargyl fb ethoxysulfuron 31567 7838 9367 1870 413Pendimethalin fb ethoxysulfuron 30100 8025 9249 1854 408Acetachlor + bensulfuranmethyl fb ethoxysulfuron 30300 7793 9277 1861 401Pyrazosulfuron fb ethoxysulfuron 28167 7605 9174 1805 346Oxadiargyl fb 1HW at 35DAS 27833 7642 9167 1836 348Pendimethalin fb 1HW at 35DAS 26400 7612 9190 1823 338Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 27033 7662 9199 1890 342Pyrazosulfuron fb 1HW at 35DAS 24833 7547 9000 1862 322LSD005 2341 565 163 NS 028119875 value 119875 lt 0001 119875 lt 0001 0008 0074 119875 lt 0001

DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 11 Effect of weed control treatments on yield and yield components of rice in the aman season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 25333 12020 8871 1779 498Partial weedy 17233 9028 8893 1797 259Oxadiargyl fb ethoxysulfuron 23000 10230 9127 1755 353Pendimethalin fb ethoxysulfuron 21967 10252 8843 1774 343Acetachlor + bensulfuranmethyl fb ethoxysulfuron 18667 10057 8544 1719 307Pyrazosulfuron fb ethoxysulfuron 18033 9577 8953 1672 300Oxadiargyl fb 1HW at 35DAS 23633 11268 8663 1817 408Pendimethalin fb 1HW at 35DAS 23067 11363 8757 1828 405Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 21733 11070 8999 1707 395Pyrazosulfuron fb 1HW at 35DAS 20400 10797 8629 1700 385LSD005 1930 1071 255 NS 019119875 value lt0001 0001 0002 032 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

used weed flora in the field rice variety used and soil andclimatic conditions Information to support these results isnot available in the literature

Our study shows that even after the use of preemergencefollowed by postemergence herbicides at 21 DAS or preemer-gence followed by a one-time HW complete weed controlcannot be achieved In additionmanual weeding is becomingless popular due to high labor wages it will be difficult to findlabor for weeding in the futureTherefore additional researchneeds to be conducted on the performance of combinationsof different pre- and postemergence herbicides applicationtimings and herbicide doses across various seasons andenvironmental conditions

We found that some weed species emerged later in theseason (eg A arvensis P niruri and G ciliata) and thusescaped the postemergence herbicide application or the HWat 35 DAS Previous studies report that weeds emerging laterin the season may not reduce rice yield significantly but

add seeds to the soil seed bank and result in heavy weedinfestation in subsequent seasons [22 23] In both seasons wefound a significant and negative linear correlation betweengrain yield and weed biomass at anthesis (Figure 3) Therelationship was slightly stronger in the boro season (1198772 =075) than in the aman season (1198772 = 065) These resultsare supported by previous studies in India [10] and thePhilippines [18] both of which found that grain yield wasnegatively correlated with weed biomass

In conclusion it is clear that weeds are a serious problemin DSR production systems and herbicides are the essentialtool to control them However continuous use of a singleherbicide over a long period may cause the development ofherbicide-resistant weed biotypes Therefore it is crucial toevaluate herbicides and determine which are less harmfulto the crop and have the ability to control a wide rangeof weeds In addition when many effective herbicides areavailable farmers will have the option to rotate the use

The Scientific World Journal 13

Boro 2011-12

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

Gra

in y

ield

(t h

aminus1)

Gy = 579 minus 0016x

R2= 075

(a)

Aman 2012

Gy = 479 minus 0009x

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

R2= 065G

rain

yie

ld (t

haminus

1)

(b)

Figure 3 The relationship between grain yield and weed biomass

of different herbicides and will help reduce the risk ofresistance developing inweeds and shifts inweed flora towardproblematic weeds

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] GMahajan B S Chauhan J Timsina P P Singh and K SinghldquoCrop performance and water- and nitrogen-use efficiencies indry-seeded rice in response to irrigation and fertilizer amountsin northwest Indiardquo Field Crops Research vol 134 pp 59ndash702012

[2] B S Chauhan G Mahajan V Sardana J Timsina and M LJat ldquoProductivity and sustainability of the rice-wheat croppingsystem in the Indo-Gangetic Plains of the Indian subcontinentproblems opportunities and strategiesrdquoAdvances inAgronomyvol 117 pp 315ndash369 2012

[3] B A M Bouman and T P Tuong ldquoField water managementto save water and increase its productivity in irrigated lowlandricerdquo Agricultural and Water Management vol 49 no 1 pp 11ndash30 2001

[4] R Gopal R K Jat R K Malik et al ldquoDirect dry seeded riceproduction technology and weed management in rice basedsystemsrdquo Technical Bulletin International Maize and WheatImprovement Center New Delhi India 2010

[5] B S Chauhan and D E Johnson ldquoThe role of seed ecologyin improving weed management strategies in the tropicsrdquoAdvances in Agronomy vol 105 pp 221ndash262 2010

[6] G Mahajan and B S Chauhan ldquoEffects of planting pattern andcultivar on weed and crop growth in aerobic rice systemrdquoWeedTechnology vol 25 no 4 pp 521ndash525 2011

[7] S Singh J K Ladha R K Gupta et al ldquoEvaluation ofmulching intercropping with Sesbania and herbicide use forweed management in dry-seeded rice (Oryza sativa L)rdquo CropProtection vol 26 no 4 pp 518ndash524 2007

[8] S Singh L Bhushan J K Ladha R K Gupta A N Rao andB Sivaprasad ldquoWeed management in dry-seeded rice (Oryzasativa) cultivated in the furrow-irrigated raised-bed plantingsystemrdquo Crop Protection vol 25 no 5 pp 487ndash495 2006

[9] B S Chauhan and D E Johnson ldquoRow spacing and weedcontrol timing affect yield of aerobic ricerdquo Field Crops Researchvol 121 no 2 pp 226ndash231 2011

[10] B S Chauhan V P Singh A Kumar and D E JohnsonldquoRelations of rice seeding rates to crop and weed growth inaerobic ricerdquo Field Crops Research vol 121 no 1 pp 105ndash1152011

[11] B S Chauhan ldquoWeed ecology andweedmanagement strategiesfor dry-seeded rice in AsiardquoWeed Technology vol 26 no 1 pp1ndash13 2012

[12] B S Chauhan and JOpena ldquoWeedmanagement and grain yieldof rice sown at low seeding rates in mechanized dry-seededsystemsrdquo Field Crops Research vol 141 pp 9ndash15 2013

[13] L Bastiaans R Paolini and D T Baumann ldquoFocus on eco-logical weed management what is hindering adoptionrdquo WeedResearch vol 48 no 6 pp 481ndash491 2008

[14] G Mahajan B S Chauhan and D E Johnson ldquoWeed man-agement in aerobic rice in northwestern indo-gangetic plainsrdquoJournal of Crop Improvement vol 23 no 4 pp 366ndash382 2009

[15] D D Buhler M Liebman and J J Obrycki ldquoTheoretical andpractical challenges to an IPM approach to weed managementrdquoWeed Science vol 48 no 3 pp 274ndash280 2000

[16] S Ahmed M R Islam M M Alam M M Haque and A JM S Karim ldquoRice production and profitability as influencedby integrated crop and resources managementrdquo Eco-FriendlyAgriculture vol 11 pp 720ndash725 2011

[17] MHasanuzzamanO Islam and S Bapari ldquoEfficacy of differentherbicides over manual weeding in controlling weeds in trans-planted ricerdquoAustralian Journal of Crop Science vol 2 no 1 pp18ndash24 2008

[18] B S Chauhan and J Opena ldquoImplications of plant geometryand weed control options in designing a low-seeding seed-drillfor dry-seeded rice systemsrdquo Field Crops Research vol 144 pp225ndash231 2013

[19] D L Jordan P K Bollich A B Burns and D MWalker ldquoRice(Oryza sativa) response to clomazonerdquo Weed Science vol 46no 3 pp 374ndash380 1998

[20] J D Beaty B Guy and J Edmund ldquoBroadleaf weed control andcotton response with bensulfuron in ricerdquo in Proceedings of theSouthern Weed Science Society vol 46 pp 91ndash96 1993

[21] M Hess and R Rose ldquoHOE 095404 a new herbicide forbroadleaf weed and sedge control in ricerdquo in Proceedings of theBrighton Crop Protection ConferenceWeeds vol 2 pp 763ndash768Brighton UK 1995

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

Nutrition and Metabolism

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Food ScienceInternational Journal of

Agronomy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

AgricultureAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BiodiversityInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Plant GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biotechnology Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Forestry ResearchInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of BotanyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Cell BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

10 The Scientific World Journal

Table8Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )at

anthesisin

thebo

roseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Anagalis

arvensis

Cyperus

rotund

usCy

nodon

dactylon

Digita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Phyllanthu

sniruri

Galinsoga

ciliata

Totalw

eed

biom

ass

Partialw

eedy

710(52)

467

(217

)365

(129)

364

(13)

412

(19)

526

(27)

316

(13)

403

(16)

744(560)

1519

(2302)

Oxadiargylfb

etho

xysulfu

ron

071

(00)

589

(353)

659

(429)

335

(111)

071

(00)

192(61)

071

(00)

071

(00)

285

(79)

1019

(1033)

Pend

imethalin

fbetho

xysulfu

ron

071

(00)

664

(443)

554

(303)

382

(145)

071

(00)

275

(78)

071

(00)

260

(81)

290

(81)

1066(1131)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

656

(437)

616

(375

)450

(203)

071

(00)

461

(21)

071

(00)

071

(00)

071

(00)

1106(1228)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

538

(277

)615

(417

)475

(221)

210

(49)

609

(39)

409

(17)

264

(65)

071

(00)

1262(1589)

Oxadiargylfb

1HW

at35

DAS

323

(101)

607

(364)

544

(291

)251

(74)

071

(00)

259

(62)

071

(00)

071

(00)

670

(444)

1158(1337)

Pend

imethalin

fb1H

Wat35

DAS

330

(11)

675

(453)

455

(206)

341

(113

)071

(00)

226

(48)

071

(00)

234

(56)

664

(441)

1196(14

27)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

392

(149)

618

(384)

486

(244)

373

(183)

071

(00)

299

(89)

071

(00)

071

(00)

530

(283)

1156(1332)

Pyrazosulfu

ronfb

1HW

at35

DAS

071

(00)

503

(248)

531

(285)

561

(318

)370

(132)

598

(385)

362

(131)

257

(62)

628

(39)

1397(19

51)

LSD

005

111

190

NS

NS

123

245

134

130

155

124

119875value

lt0001

000

6015

011

lt0001

0001

lt0001

lt0001

lt0001

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

The Scientific World Journal 11

Table9Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )atanthesisin

theam

anseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

biom

ass

Partialw

eedy

299

(86)

267

(73)

711(506)

178(28)

909(826)

201

(36)

712(511)

559

(313

)1543(2378)

Oxadiargylfb

etho

xysulfu

ron

224

(47)

071

(00)

537

(285)

071

(00)

800

(635)

071

(00)

259

(64)

328

(103)

1067(1135)

Pend

imethalin

fbetho

xysulfu

ron

185(36)

071

(00)

534

(2810)

071

(00)

676

(456)

206

(38)

429

(182)

494

(240)

1109(1231)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

454

(210

)228

(55)

946(896

)071

(00)

348

(129)

401

(162)

1204(14

52)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

688

(479

)19

8(35)

1008(1015)

212

(40)

418

(193

)388

(147)

1383(1908)

Oxadiargylfb

1HW

at35

DAS

221

(44)

165(23)

415

(171)

071

(00)

392

(153)

071

(00)

639

(405)

323

(102)

945(897

)Pend

imethalin

fb1H

Wat35

DAS

170(29)

197(36)

483

(232)

071

(00)

540

(287)

071

(00)

584

(337)

401

(171)

1046(1092)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

177(28)

194(340)

350

(118

)14

9(20)

719(515

)13

9(17)

569

(326)

489

(242)

1142(1301)

Pyrazosulfu

ronfb

1HW

at35

DAS

198(35)

195(33)

348

(116

)15

2(21)

825

(685)

162(24)

516

(264)

511(256)

1199(14

35)

LSD

005

089

076

133

087

139

055

188

146

130

119875value

0001

lt0001

lt0001

000

4lt0001

lt0001

0002

003

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

12 The Scientific World Journal

Table 10 Effect of weed control treatments on yield and yield components of rice in the boro season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 34700 8235 9352 1902 476Partial weedy 15967 5933 9279 1803 158Oxadiargyl fb ethoxysulfuron 31567 7838 9367 1870 413Pendimethalin fb ethoxysulfuron 30100 8025 9249 1854 408Acetachlor + bensulfuranmethyl fb ethoxysulfuron 30300 7793 9277 1861 401Pyrazosulfuron fb ethoxysulfuron 28167 7605 9174 1805 346Oxadiargyl fb 1HW at 35DAS 27833 7642 9167 1836 348Pendimethalin fb 1HW at 35DAS 26400 7612 9190 1823 338Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 27033 7662 9199 1890 342Pyrazosulfuron fb 1HW at 35DAS 24833 7547 9000 1862 322LSD005 2341 565 163 NS 028119875 value 119875 lt 0001 119875 lt 0001 0008 0074 119875 lt 0001

DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 11 Effect of weed control treatments on yield and yield components of rice in the aman season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 25333 12020 8871 1779 498Partial weedy 17233 9028 8893 1797 259Oxadiargyl fb ethoxysulfuron 23000 10230 9127 1755 353Pendimethalin fb ethoxysulfuron 21967 10252 8843 1774 343Acetachlor + bensulfuranmethyl fb ethoxysulfuron 18667 10057 8544 1719 307Pyrazosulfuron fb ethoxysulfuron 18033 9577 8953 1672 300Oxadiargyl fb 1HW at 35DAS 23633 11268 8663 1817 408Pendimethalin fb 1HW at 35DAS 23067 11363 8757 1828 405Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 21733 11070 8999 1707 395Pyrazosulfuron fb 1HW at 35DAS 20400 10797 8629 1700 385LSD005 1930 1071 255 NS 019119875 value lt0001 0001 0002 032 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

used weed flora in the field rice variety used and soil andclimatic conditions Information to support these results isnot available in the literature

Our study shows that even after the use of preemergencefollowed by postemergence herbicides at 21 DAS or preemer-gence followed by a one-time HW complete weed controlcannot be achieved In additionmanual weeding is becomingless popular due to high labor wages it will be difficult to findlabor for weeding in the futureTherefore additional researchneeds to be conducted on the performance of combinationsof different pre- and postemergence herbicides applicationtimings and herbicide doses across various seasons andenvironmental conditions

We found that some weed species emerged later in theseason (eg A arvensis P niruri and G ciliata) and thusescaped the postemergence herbicide application or the HWat 35 DAS Previous studies report that weeds emerging laterin the season may not reduce rice yield significantly but

add seeds to the soil seed bank and result in heavy weedinfestation in subsequent seasons [22 23] In both seasons wefound a significant and negative linear correlation betweengrain yield and weed biomass at anthesis (Figure 3) Therelationship was slightly stronger in the boro season (1198772 =075) than in the aman season (1198772 = 065) These resultsare supported by previous studies in India [10] and thePhilippines [18] both of which found that grain yield wasnegatively correlated with weed biomass

In conclusion it is clear that weeds are a serious problemin DSR production systems and herbicides are the essentialtool to control them However continuous use of a singleherbicide over a long period may cause the development ofherbicide-resistant weed biotypes Therefore it is crucial toevaluate herbicides and determine which are less harmfulto the crop and have the ability to control a wide rangeof weeds In addition when many effective herbicides areavailable farmers will have the option to rotate the use

The Scientific World Journal 13

Boro 2011-12

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

Gra

in y

ield

(t h

aminus1)

Gy = 579 minus 0016x

R2= 075

(a)

Aman 2012

Gy = 479 minus 0009x

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

R2= 065G

rain

yie

ld (t

haminus

1)

(b)

Figure 3 The relationship between grain yield and weed biomass

of different herbicides and will help reduce the risk ofresistance developing inweeds and shifts inweed flora towardproblematic weeds

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] GMahajan B S Chauhan J Timsina P P Singh and K SinghldquoCrop performance and water- and nitrogen-use efficiencies indry-seeded rice in response to irrigation and fertilizer amountsin northwest Indiardquo Field Crops Research vol 134 pp 59ndash702012

[2] B S Chauhan G Mahajan V Sardana J Timsina and M LJat ldquoProductivity and sustainability of the rice-wheat croppingsystem in the Indo-Gangetic Plains of the Indian subcontinentproblems opportunities and strategiesrdquoAdvances inAgronomyvol 117 pp 315ndash369 2012

[3] B A M Bouman and T P Tuong ldquoField water managementto save water and increase its productivity in irrigated lowlandricerdquo Agricultural and Water Management vol 49 no 1 pp 11ndash30 2001

[4] R Gopal R K Jat R K Malik et al ldquoDirect dry seeded riceproduction technology and weed management in rice basedsystemsrdquo Technical Bulletin International Maize and WheatImprovement Center New Delhi India 2010

[5] B S Chauhan and D E Johnson ldquoThe role of seed ecologyin improving weed management strategies in the tropicsrdquoAdvances in Agronomy vol 105 pp 221ndash262 2010

[6] G Mahajan and B S Chauhan ldquoEffects of planting pattern andcultivar on weed and crop growth in aerobic rice systemrdquoWeedTechnology vol 25 no 4 pp 521ndash525 2011

[7] S Singh J K Ladha R K Gupta et al ldquoEvaluation ofmulching intercropping with Sesbania and herbicide use forweed management in dry-seeded rice (Oryza sativa L)rdquo CropProtection vol 26 no 4 pp 518ndash524 2007

[8] S Singh L Bhushan J K Ladha R K Gupta A N Rao andB Sivaprasad ldquoWeed management in dry-seeded rice (Oryzasativa) cultivated in the furrow-irrigated raised-bed plantingsystemrdquo Crop Protection vol 25 no 5 pp 487ndash495 2006

[9] B S Chauhan and D E Johnson ldquoRow spacing and weedcontrol timing affect yield of aerobic ricerdquo Field Crops Researchvol 121 no 2 pp 226ndash231 2011

[10] B S Chauhan V P Singh A Kumar and D E JohnsonldquoRelations of rice seeding rates to crop and weed growth inaerobic ricerdquo Field Crops Research vol 121 no 1 pp 105ndash1152011

[11] B S Chauhan ldquoWeed ecology andweedmanagement strategiesfor dry-seeded rice in AsiardquoWeed Technology vol 26 no 1 pp1ndash13 2012

[12] B S Chauhan and JOpena ldquoWeedmanagement and grain yieldof rice sown at low seeding rates in mechanized dry-seededsystemsrdquo Field Crops Research vol 141 pp 9ndash15 2013

[13] L Bastiaans R Paolini and D T Baumann ldquoFocus on eco-logical weed management what is hindering adoptionrdquo WeedResearch vol 48 no 6 pp 481ndash491 2008

[14] G Mahajan B S Chauhan and D E Johnson ldquoWeed man-agement in aerobic rice in northwestern indo-gangetic plainsrdquoJournal of Crop Improvement vol 23 no 4 pp 366ndash382 2009

[15] D D Buhler M Liebman and J J Obrycki ldquoTheoretical andpractical challenges to an IPM approach to weed managementrdquoWeed Science vol 48 no 3 pp 274ndash280 2000

[16] S Ahmed M R Islam M M Alam M M Haque and A JM S Karim ldquoRice production and profitability as influencedby integrated crop and resources managementrdquo Eco-FriendlyAgriculture vol 11 pp 720ndash725 2011

[17] MHasanuzzamanO Islam and S Bapari ldquoEfficacy of differentherbicides over manual weeding in controlling weeds in trans-planted ricerdquoAustralian Journal of Crop Science vol 2 no 1 pp18ndash24 2008

[18] B S Chauhan and J Opena ldquoImplications of plant geometryand weed control options in designing a low-seeding seed-drillfor dry-seeded rice systemsrdquo Field Crops Research vol 144 pp225ndash231 2013

[19] D L Jordan P K Bollich A B Burns and D MWalker ldquoRice(Oryza sativa) response to clomazonerdquo Weed Science vol 46no 3 pp 374ndash380 1998

[20] J D Beaty B Guy and J Edmund ldquoBroadleaf weed control andcotton response with bensulfuron in ricerdquo in Proceedings of theSouthern Weed Science Society vol 46 pp 91ndash96 1993

[21] M Hess and R Rose ldquoHOE 095404 a new herbicide forbroadleaf weed and sedge control in ricerdquo in Proceedings of theBrighton Crop Protection ConferenceWeeds vol 2 pp 763ndash768Brighton UK 1995

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

Nutrition and Metabolism

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Food ScienceInternational Journal of

Agronomy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

AgricultureAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BiodiversityInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Plant GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biotechnology Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Forestry ResearchInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of BotanyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Cell BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World Journal 11

Table9Eff

ecto

fweedcontroltreatmentson

weedbiom

ass(gmminus2 )atanthesisin

theam

anseason

Weedbiom

assd

ataweresubjectedto

square-roo

t(radic[119909+05])transfo

rmationbefore

analysis

originalvalues

ares

hownin

parentheses

Weedcontroltreatments

Ageratum

conyzoides

Cyperus

rotund

usDigita

riaciliaris

Dactyloctenium

aegyptium

Echinochloa

colona

Eleusin

eindica

Galinsoga

ciliata

Phyllanthu

sniruri

Totalw

eed

biom

ass

Partialw

eedy

299

(86)

267

(73)

711(506)

178(28)

909(826)

201

(36)

712(511)

559

(313

)1543(2378)

Oxadiargylfb

etho

xysulfu

ron

224

(47)

071

(00)

537

(285)

071

(00)

800

(635)

071

(00)

259

(64)

328

(103)

1067(1135)

Pend

imethalin

fbetho

xysulfu

ron

185(36)

071

(00)

534

(2810)

071

(00)

676

(456)

206

(38)

429

(182)

494

(240)

1109(1231)

Acetachlor

+bensulfuranm

ethylfb

etho

xysulfu

ron

071

(00)

071

(00)

454

(210

)228

(55)

946(896

)071

(00)

348

(129)

401

(162)

1204(14

52)

Pyrazosulfu

ronfb

etho

xysulfu

ron

071

(00)

071

(00)

688

(479

)19

8(35)

1008(1015)

212

(40)

418

(193

)388

(147)

1383(1908)

Oxadiargylfb

1HW

at35

DAS

221

(44)

165(23)

415

(171)

071

(00)

392

(153)

071

(00)

639

(405)

323

(102)

945(897

)Pend

imethalin

fb1H

Wat35

DAS

170(29)

197(36)

483

(232)

071

(00)

540

(287)

071

(00)

584

(337)

401

(171)

1046(1092)

Acetachlor

+bensulfuraon

methyl

fb1H

Wat35

DAS

177(28)

194(340)

350

(118

)14

9(20)

719(515

)13

9(17)

569

(326)

489

(242)

1142(1301)

Pyrazosulfu

ronfb

1HW

at35

DAS

198(35)

195(33)

348

(116

)15

2(21)

825

(685)

162(24)

516

(264)

511(256)

1199(14

35)

LSD

005

089

076

133

087

139

055

188

146

130

119875value

0001

lt0001

lt0001

000

4lt0001

lt0001

0002

003

lt0001

DASdays

after

sowingfbfollowed

byH

Whandweeding

LSD

leastsig

nificantd

ifference

at5

levelofsignificance119875

probability

12 The Scientific World Journal

Table 10 Effect of weed control treatments on yield and yield components of rice in the boro season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 34700 8235 9352 1902 476Partial weedy 15967 5933 9279 1803 158Oxadiargyl fb ethoxysulfuron 31567 7838 9367 1870 413Pendimethalin fb ethoxysulfuron 30100 8025 9249 1854 408Acetachlor + bensulfuranmethyl fb ethoxysulfuron 30300 7793 9277 1861 401Pyrazosulfuron fb ethoxysulfuron 28167 7605 9174 1805 346Oxadiargyl fb 1HW at 35DAS 27833 7642 9167 1836 348Pendimethalin fb 1HW at 35DAS 26400 7612 9190 1823 338Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 27033 7662 9199 1890 342Pyrazosulfuron fb 1HW at 35DAS 24833 7547 9000 1862 322LSD005 2341 565 163 NS 028119875 value 119875 lt 0001 119875 lt 0001 0008 0074 119875 lt 0001

DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 11 Effect of weed control treatments on yield and yield components of rice in the aman season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 25333 12020 8871 1779 498Partial weedy 17233 9028 8893 1797 259Oxadiargyl fb ethoxysulfuron 23000 10230 9127 1755 353Pendimethalin fb ethoxysulfuron 21967 10252 8843 1774 343Acetachlor + bensulfuranmethyl fb ethoxysulfuron 18667 10057 8544 1719 307Pyrazosulfuron fb ethoxysulfuron 18033 9577 8953 1672 300Oxadiargyl fb 1HW at 35DAS 23633 11268 8663 1817 408Pendimethalin fb 1HW at 35DAS 23067 11363 8757 1828 405Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 21733 11070 8999 1707 395Pyrazosulfuron fb 1HW at 35DAS 20400 10797 8629 1700 385LSD005 1930 1071 255 NS 019119875 value lt0001 0001 0002 032 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

used weed flora in the field rice variety used and soil andclimatic conditions Information to support these results isnot available in the literature

Our study shows that even after the use of preemergencefollowed by postemergence herbicides at 21 DAS or preemer-gence followed by a one-time HW complete weed controlcannot be achieved In additionmanual weeding is becomingless popular due to high labor wages it will be difficult to findlabor for weeding in the futureTherefore additional researchneeds to be conducted on the performance of combinationsof different pre- and postemergence herbicides applicationtimings and herbicide doses across various seasons andenvironmental conditions

We found that some weed species emerged later in theseason (eg A arvensis P niruri and G ciliata) and thusescaped the postemergence herbicide application or the HWat 35 DAS Previous studies report that weeds emerging laterin the season may not reduce rice yield significantly but

add seeds to the soil seed bank and result in heavy weedinfestation in subsequent seasons [22 23] In both seasons wefound a significant and negative linear correlation betweengrain yield and weed biomass at anthesis (Figure 3) Therelationship was slightly stronger in the boro season (1198772 =075) than in the aman season (1198772 = 065) These resultsare supported by previous studies in India [10] and thePhilippines [18] both of which found that grain yield wasnegatively correlated with weed biomass

In conclusion it is clear that weeds are a serious problemin DSR production systems and herbicides are the essentialtool to control them However continuous use of a singleherbicide over a long period may cause the development ofherbicide-resistant weed biotypes Therefore it is crucial toevaluate herbicides and determine which are less harmfulto the crop and have the ability to control a wide rangeof weeds In addition when many effective herbicides areavailable farmers will have the option to rotate the use

The Scientific World Journal 13

Boro 2011-12

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

Gra

in y

ield

(t h

aminus1)

Gy = 579 minus 0016x

R2= 075

(a)

Aman 2012

Gy = 479 minus 0009x

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

R2= 065G

rain

yie

ld (t

haminus

1)

(b)

Figure 3 The relationship between grain yield and weed biomass

of different herbicides and will help reduce the risk ofresistance developing inweeds and shifts inweed flora towardproblematic weeds

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] GMahajan B S Chauhan J Timsina P P Singh and K SinghldquoCrop performance and water- and nitrogen-use efficiencies indry-seeded rice in response to irrigation and fertilizer amountsin northwest Indiardquo Field Crops Research vol 134 pp 59ndash702012

[2] B S Chauhan G Mahajan V Sardana J Timsina and M LJat ldquoProductivity and sustainability of the rice-wheat croppingsystem in the Indo-Gangetic Plains of the Indian subcontinentproblems opportunities and strategiesrdquoAdvances inAgronomyvol 117 pp 315ndash369 2012

[3] B A M Bouman and T P Tuong ldquoField water managementto save water and increase its productivity in irrigated lowlandricerdquo Agricultural and Water Management vol 49 no 1 pp 11ndash30 2001

[4] R Gopal R K Jat R K Malik et al ldquoDirect dry seeded riceproduction technology and weed management in rice basedsystemsrdquo Technical Bulletin International Maize and WheatImprovement Center New Delhi India 2010

[5] B S Chauhan and D E Johnson ldquoThe role of seed ecologyin improving weed management strategies in the tropicsrdquoAdvances in Agronomy vol 105 pp 221ndash262 2010

[6] G Mahajan and B S Chauhan ldquoEffects of planting pattern andcultivar on weed and crop growth in aerobic rice systemrdquoWeedTechnology vol 25 no 4 pp 521ndash525 2011

[7] S Singh J K Ladha R K Gupta et al ldquoEvaluation ofmulching intercropping with Sesbania and herbicide use forweed management in dry-seeded rice (Oryza sativa L)rdquo CropProtection vol 26 no 4 pp 518ndash524 2007

[8] S Singh L Bhushan J K Ladha R K Gupta A N Rao andB Sivaprasad ldquoWeed management in dry-seeded rice (Oryzasativa) cultivated in the furrow-irrigated raised-bed plantingsystemrdquo Crop Protection vol 25 no 5 pp 487ndash495 2006

[9] B S Chauhan and D E Johnson ldquoRow spacing and weedcontrol timing affect yield of aerobic ricerdquo Field Crops Researchvol 121 no 2 pp 226ndash231 2011

[10] B S Chauhan V P Singh A Kumar and D E JohnsonldquoRelations of rice seeding rates to crop and weed growth inaerobic ricerdquo Field Crops Research vol 121 no 1 pp 105ndash1152011

[11] B S Chauhan ldquoWeed ecology andweedmanagement strategiesfor dry-seeded rice in AsiardquoWeed Technology vol 26 no 1 pp1ndash13 2012

[12] B S Chauhan and JOpena ldquoWeedmanagement and grain yieldof rice sown at low seeding rates in mechanized dry-seededsystemsrdquo Field Crops Research vol 141 pp 9ndash15 2013

[13] L Bastiaans R Paolini and D T Baumann ldquoFocus on eco-logical weed management what is hindering adoptionrdquo WeedResearch vol 48 no 6 pp 481ndash491 2008

[14] G Mahajan B S Chauhan and D E Johnson ldquoWeed man-agement in aerobic rice in northwestern indo-gangetic plainsrdquoJournal of Crop Improvement vol 23 no 4 pp 366ndash382 2009

[15] D D Buhler M Liebman and J J Obrycki ldquoTheoretical andpractical challenges to an IPM approach to weed managementrdquoWeed Science vol 48 no 3 pp 274ndash280 2000

[16] S Ahmed M R Islam M M Alam M M Haque and A JM S Karim ldquoRice production and profitability as influencedby integrated crop and resources managementrdquo Eco-FriendlyAgriculture vol 11 pp 720ndash725 2011

[17] MHasanuzzamanO Islam and S Bapari ldquoEfficacy of differentherbicides over manual weeding in controlling weeds in trans-planted ricerdquoAustralian Journal of Crop Science vol 2 no 1 pp18ndash24 2008

[18] B S Chauhan and J Opena ldquoImplications of plant geometryand weed control options in designing a low-seeding seed-drillfor dry-seeded rice systemsrdquo Field Crops Research vol 144 pp225ndash231 2013

[19] D L Jordan P K Bollich A B Burns and D MWalker ldquoRice(Oryza sativa) response to clomazonerdquo Weed Science vol 46no 3 pp 374ndash380 1998

[20] J D Beaty B Guy and J Edmund ldquoBroadleaf weed control andcotton response with bensulfuron in ricerdquo in Proceedings of theSouthern Weed Science Society vol 46 pp 91ndash96 1993

[21] M Hess and R Rose ldquoHOE 095404 a new herbicide forbroadleaf weed and sedge control in ricerdquo in Proceedings of theBrighton Crop Protection ConferenceWeeds vol 2 pp 763ndash768Brighton UK 1995

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

Nutrition and Metabolism

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Food ScienceInternational Journal of

Agronomy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

AgricultureAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BiodiversityInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Plant GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biotechnology Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Forestry ResearchInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of BotanyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Cell BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

12 The Scientific World Journal

Table 10 Effect of weed control treatments on yield and yield components of rice in the boro season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 34700 8235 9352 1902 476Partial weedy 15967 5933 9279 1803 158Oxadiargyl fb ethoxysulfuron 31567 7838 9367 1870 413Pendimethalin fb ethoxysulfuron 30100 8025 9249 1854 408Acetachlor + bensulfuranmethyl fb ethoxysulfuron 30300 7793 9277 1861 401Pyrazosulfuron fb ethoxysulfuron 28167 7605 9174 1805 346Oxadiargyl fb 1HW at 35DAS 27833 7642 9167 1836 348Pendimethalin fb 1HW at 35DAS 26400 7612 9190 1823 338Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 27033 7662 9199 1890 342Pyrazosulfuron fb 1HW at 35DAS 24833 7547 9000 1862 322LSD005 2341 565 163 NS 028119875 value 119875 lt 0001 119875 lt 0001 0008 0074 119875 lt 0001

DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

Table 11 Effect of weed control treatments on yield and yield components of rice in the aman season

Weed control treatments Panicles(no mminus2)

Spikeletpanicleminus1

Spikelet fertility()

1000-grainweight (g)

Grain yield(t haminus1)

Weed-free 25333 12020 8871 1779 498Partial weedy 17233 9028 8893 1797 259Oxadiargyl fb ethoxysulfuron 23000 10230 9127 1755 353Pendimethalin fb ethoxysulfuron 21967 10252 8843 1774 343Acetachlor + bensulfuranmethyl fb ethoxysulfuron 18667 10057 8544 1719 307Pyrazosulfuron fb ethoxysulfuron 18033 9577 8953 1672 300Oxadiargyl fb 1HW at 35DAS 23633 11268 8663 1817 408Pendimethalin fb 1HW at 35DAS 23067 11363 8757 1828 405Acetachlor + bensulfuraonmethyl fb 1HW at 35DAS 21733 11070 8999 1707 395Pyrazosulfuron fb 1HW at 35DAS 20400 10797 8629 1700 385LSD005 1930 1071 255 NS 019119875 value lt0001 0001 0002 032 lt0001DAS days after sowing fb followed by HW hand weeding LSD least significant difference at 5 level of significance 119875 probability

used weed flora in the field rice variety used and soil andclimatic conditions Information to support these results isnot available in the literature

Our study shows that even after the use of preemergencefollowed by postemergence herbicides at 21 DAS or preemer-gence followed by a one-time HW complete weed controlcannot be achieved In additionmanual weeding is becomingless popular due to high labor wages it will be difficult to findlabor for weeding in the futureTherefore additional researchneeds to be conducted on the performance of combinationsof different pre- and postemergence herbicides applicationtimings and herbicide doses across various seasons andenvironmental conditions

We found that some weed species emerged later in theseason (eg A arvensis P niruri and G ciliata) and thusescaped the postemergence herbicide application or the HWat 35 DAS Previous studies report that weeds emerging laterin the season may not reduce rice yield significantly but

add seeds to the soil seed bank and result in heavy weedinfestation in subsequent seasons [22 23] In both seasons wefound a significant and negative linear correlation betweengrain yield and weed biomass at anthesis (Figure 3) Therelationship was slightly stronger in the boro season (1198772 =075) than in the aman season (1198772 = 065) These resultsare supported by previous studies in India [10] and thePhilippines [18] both of which found that grain yield wasnegatively correlated with weed biomass

In conclusion it is clear that weeds are a serious problemin DSR production systems and herbicides are the essentialtool to control them However continuous use of a singleherbicide over a long period may cause the development ofherbicide-resistant weed biotypes Therefore it is crucial toevaluate herbicides and determine which are less harmfulto the crop and have the ability to control a wide rangeof weeds In addition when many effective herbicides areavailable farmers will have the option to rotate the use

The Scientific World Journal 13

Boro 2011-12

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

Gra

in y

ield

(t h

aminus1)

Gy = 579 minus 0016x

R2= 075

(a)

Aman 2012

Gy = 479 minus 0009x

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

R2= 065G

rain

yie

ld (t

haminus

1)

(b)

Figure 3 The relationship between grain yield and weed biomass

of different herbicides and will help reduce the risk ofresistance developing inweeds and shifts inweed flora towardproblematic weeds

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] GMahajan B S Chauhan J Timsina P P Singh and K SinghldquoCrop performance and water- and nitrogen-use efficiencies indry-seeded rice in response to irrigation and fertilizer amountsin northwest Indiardquo Field Crops Research vol 134 pp 59ndash702012

[2] B S Chauhan G Mahajan V Sardana J Timsina and M LJat ldquoProductivity and sustainability of the rice-wheat croppingsystem in the Indo-Gangetic Plains of the Indian subcontinentproblems opportunities and strategiesrdquoAdvances inAgronomyvol 117 pp 315ndash369 2012

[3] B A M Bouman and T P Tuong ldquoField water managementto save water and increase its productivity in irrigated lowlandricerdquo Agricultural and Water Management vol 49 no 1 pp 11ndash30 2001

[4] R Gopal R K Jat R K Malik et al ldquoDirect dry seeded riceproduction technology and weed management in rice basedsystemsrdquo Technical Bulletin International Maize and WheatImprovement Center New Delhi India 2010

[5] B S Chauhan and D E Johnson ldquoThe role of seed ecologyin improving weed management strategies in the tropicsrdquoAdvances in Agronomy vol 105 pp 221ndash262 2010

[6] G Mahajan and B S Chauhan ldquoEffects of planting pattern andcultivar on weed and crop growth in aerobic rice systemrdquoWeedTechnology vol 25 no 4 pp 521ndash525 2011

[7] S Singh J K Ladha R K Gupta et al ldquoEvaluation ofmulching intercropping with Sesbania and herbicide use forweed management in dry-seeded rice (Oryza sativa L)rdquo CropProtection vol 26 no 4 pp 518ndash524 2007

[8] S Singh L Bhushan J K Ladha R K Gupta A N Rao andB Sivaprasad ldquoWeed management in dry-seeded rice (Oryzasativa) cultivated in the furrow-irrigated raised-bed plantingsystemrdquo Crop Protection vol 25 no 5 pp 487ndash495 2006

[9] B S Chauhan and D E Johnson ldquoRow spacing and weedcontrol timing affect yield of aerobic ricerdquo Field Crops Researchvol 121 no 2 pp 226ndash231 2011

[10] B S Chauhan V P Singh A Kumar and D E JohnsonldquoRelations of rice seeding rates to crop and weed growth inaerobic ricerdquo Field Crops Research vol 121 no 1 pp 105ndash1152011

[11] B S Chauhan ldquoWeed ecology andweedmanagement strategiesfor dry-seeded rice in AsiardquoWeed Technology vol 26 no 1 pp1ndash13 2012

[12] B S Chauhan and JOpena ldquoWeedmanagement and grain yieldof rice sown at low seeding rates in mechanized dry-seededsystemsrdquo Field Crops Research vol 141 pp 9ndash15 2013

[13] L Bastiaans R Paolini and D T Baumann ldquoFocus on eco-logical weed management what is hindering adoptionrdquo WeedResearch vol 48 no 6 pp 481ndash491 2008

[14] G Mahajan B S Chauhan and D E Johnson ldquoWeed man-agement in aerobic rice in northwestern indo-gangetic plainsrdquoJournal of Crop Improvement vol 23 no 4 pp 366ndash382 2009

[15] D D Buhler M Liebman and J J Obrycki ldquoTheoretical andpractical challenges to an IPM approach to weed managementrdquoWeed Science vol 48 no 3 pp 274ndash280 2000

[16] S Ahmed M R Islam M M Alam M M Haque and A JM S Karim ldquoRice production and profitability as influencedby integrated crop and resources managementrdquo Eco-FriendlyAgriculture vol 11 pp 720ndash725 2011

[17] MHasanuzzamanO Islam and S Bapari ldquoEfficacy of differentherbicides over manual weeding in controlling weeds in trans-planted ricerdquoAustralian Journal of Crop Science vol 2 no 1 pp18ndash24 2008

[18] B S Chauhan and J Opena ldquoImplications of plant geometryand weed control options in designing a low-seeding seed-drillfor dry-seeded rice systemsrdquo Field Crops Research vol 144 pp225ndash231 2013

[19] D L Jordan P K Bollich A B Burns and D MWalker ldquoRice(Oryza sativa) response to clomazonerdquo Weed Science vol 46no 3 pp 374ndash380 1998

[20] J D Beaty B Guy and J Edmund ldquoBroadleaf weed control andcotton response with bensulfuron in ricerdquo in Proceedings of theSouthern Weed Science Society vol 46 pp 91ndash96 1993

[21] M Hess and R Rose ldquoHOE 095404 a new herbicide forbroadleaf weed and sedge control in ricerdquo in Proceedings of theBrighton Crop Protection ConferenceWeeds vol 2 pp 763ndash768Brighton UK 1995

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

Nutrition and Metabolism

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Food ScienceInternational Journal of

Agronomy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

AgricultureAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BiodiversityInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Plant GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biotechnology Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Forestry ResearchInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of BotanyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Cell BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World Journal 13

Boro 2011-12

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

Gra

in y

ield

(t h

aminus1)

Gy = 579 minus 0016x

R2= 075

(a)

Aman 2012

Gy = 479 minus 0009x

0

1

2

3

4

5

0 50 100 150 200 250 300Weed biomass (gmminus2)

R2= 065G

rain

yie

ld (t

haminus

1)

(b)

Figure 3 The relationship between grain yield and weed biomass

of different herbicides and will help reduce the risk ofresistance developing inweeds and shifts inweed flora towardproblematic weeds

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] GMahajan B S Chauhan J Timsina P P Singh and K SinghldquoCrop performance and water- and nitrogen-use efficiencies indry-seeded rice in response to irrigation and fertilizer amountsin northwest Indiardquo Field Crops Research vol 134 pp 59ndash702012

[2] B S Chauhan G Mahajan V Sardana J Timsina and M LJat ldquoProductivity and sustainability of the rice-wheat croppingsystem in the Indo-Gangetic Plains of the Indian subcontinentproblems opportunities and strategiesrdquoAdvances inAgronomyvol 117 pp 315ndash369 2012

[3] B A M Bouman and T P Tuong ldquoField water managementto save water and increase its productivity in irrigated lowlandricerdquo Agricultural and Water Management vol 49 no 1 pp 11ndash30 2001

[4] R Gopal R K Jat R K Malik et al ldquoDirect dry seeded riceproduction technology and weed management in rice basedsystemsrdquo Technical Bulletin International Maize and WheatImprovement Center New Delhi India 2010

[5] B S Chauhan and D E Johnson ldquoThe role of seed ecologyin improving weed management strategies in the tropicsrdquoAdvances in Agronomy vol 105 pp 221ndash262 2010

[6] G Mahajan and B S Chauhan ldquoEffects of planting pattern andcultivar on weed and crop growth in aerobic rice systemrdquoWeedTechnology vol 25 no 4 pp 521ndash525 2011

[7] S Singh J K Ladha R K Gupta et al ldquoEvaluation ofmulching intercropping with Sesbania and herbicide use forweed management in dry-seeded rice (Oryza sativa L)rdquo CropProtection vol 26 no 4 pp 518ndash524 2007

[8] S Singh L Bhushan J K Ladha R K Gupta A N Rao andB Sivaprasad ldquoWeed management in dry-seeded rice (Oryzasativa) cultivated in the furrow-irrigated raised-bed plantingsystemrdquo Crop Protection vol 25 no 5 pp 487ndash495 2006

[9] B S Chauhan and D E Johnson ldquoRow spacing and weedcontrol timing affect yield of aerobic ricerdquo Field Crops Researchvol 121 no 2 pp 226ndash231 2011

[10] B S Chauhan V P Singh A Kumar and D E JohnsonldquoRelations of rice seeding rates to crop and weed growth inaerobic ricerdquo Field Crops Research vol 121 no 1 pp 105ndash1152011

[11] B S Chauhan ldquoWeed ecology andweedmanagement strategiesfor dry-seeded rice in AsiardquoWeed Technology vol 26 no 1 pp1ndash13 2012

[12] B S Chauhan and JOpena ldquoWeedmanagement and grain yieldof rice sown at low seeding rates in mechanized dry-seededsystemsrdquo Field Crops Research vol 141 pp 9ndash15 2013

[13] L Bastiaans R Paolini and D T Baumann ldquoFocus on eco-logical weed management what is hindering adoptionrdquo WeedResearch vol 48 no 6 pp 481ndash491 2008

[14] G Mahajan B S Chauhan and D E Johnson ldquoWeed man-agement in aerobic rice in northwestern indo-gangetic plainsrdquoJournal of Crop Improvement vol 23 no 4 pp 366ndash382 2009

[15] D D Buhler M Liebman and J J Obrycki ldquoTheoretical andpractical challenges to an IPM approach to weed managementrdquoWeed Science vol 48 no 3 pp 274ndash280 2000

[16] S Ahmed M R Islam M M Alam M M Haque and A JM S Karim ldquoRice production and profitability as influencedby integrated crop and resources managementrdquo Eco-FriendlyAgriculture vol 11 pp 720ndash725 2011

[17] MHasanuzzamanO Islam and S Bapari ldquoEfficacy of differentherbicides over manual weeding in controlling weeds in trans-planted ricerdquoAustralian Journal of Crop Science vol 2 no 1 pp18ndash24 2008

[18] B S Chauhan and J Opena ldquoImplications of plant geometryand weed control options in designing a low-seeding seed-drillfor dry-seeded rice systemsrdquo Field Crops Research vol 144 pp225ndash231 2013

[19] D L Jordan P K Bollich A B Burns and D MWalker ldquoRice(Oryza sativa) response to clomazonerdquo Weed Science vol 46no 3 pp 374ndash380 1998

[20] J D Beaty B Guy and J Edmund ldquoBroadleaf weed control andcotton response with bensulfuron in ricerdquo in Proceedings of theSouthern Weed Science Society vol 46 pp 91ndash96 1993

[21] M Hess and R Rose ldquoHOE 095404 a new herbicide forbroadleaf weed and sedge control in ricerdquo in Proceedings of theBrighton Crop Protection ConferenceWeeds vol 2 pp 763ndash768Brighton UK 1995

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

Nutrition and Metabolism

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Food ScienceInternational Journal of

Agronomy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

AgricultureAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BiodiversityInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Plant GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biotechnology Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Forestry ResearchInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of BotanyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Cell BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

14 The Scientific World Journal

[22] P Bridgemohan R A I Brathwaite and C R McDavidldquoSeed survival and patterns of seedling emergence studies ofRottboellia cochinchinensis (Lour) WD Clayton in cultivatedsoilsrdquoWeed Research vol 31 no 5 pp 265ndash272 1991

[23] B S Chauhan and J Opena ldquoEffect of tillage systems andherbicides on weed emergence weed growth and grain yieldin dry-seeded rice systemsrdquo Field Crops Research vol 137 pp56ndash69 2012

Submit your manuscripts athttpwwwhindawicom

Nutrition and Metabolism

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Food ScienceInternational Journal of

Agronomy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

AgricultureAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BiodiversityInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Plant GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biotechnology Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Forestry ResearchInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of BotanyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Cell BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Submit your manuscripts athttpwwwhindawicom

Nutrition and Metabolism

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Food ScienceInternational Journal of

Agronomy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

AgricultureAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BiodiversityInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Plant GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biotechnology Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Forestry ResearchInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of BotanyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Cell BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014