EFFECT OF PLASTIC MULCH, FLOATING ROW COVER AND MICROTUNNELS ON INSECT POPULATIONS AND YIELD OF MUSKMELON

J. Farias-Larios, M. Orazco-Santos1 and J. Perez Facultad de Ciencias Biológicas y Agropecuarias. Universidad de Colima

Apartado postal 36.28100 Tecomal, Colima, Mexico. E mail jferias@volcaaucolmx

Abstract This woik was conducted to evaluate the effect of clear (CP) and black polyethylene (BP) middies, floating row cover (FRC) and perforated plastic aixl IXJ perforated microtunnels on growth and yield of muskmelon; and to determine the effect of diese üeatments on population densities of aphids, sweetpotato whitefly and soil temperature. Treatments were: 1) CP+FRC, 2) CP+ polyethylene perforated microtunnel (MPP), 3) CP+ polyethylene not perforated microtunnel (MNPP), 4) BP+FRC, 5) CP alone, 6) BP alone, and 7) bare soil as the control. Pests were completely excluded by FRC in die plots covered Protected plants had 0 and 1 nymphs/cnr at 34 and 41 days after sowing, respectively, whereas the control showed 3 and 29 nymphs/an2 at the same dates. CP + FRC increased soil temperature, number of maiketable fruits (452 and 44.8% higher) with respect to BP + FRC aixl bare soil. Polyethylene microtunnels were found not recommended by its costs for cantaloupe production. It is proposed diat floating row cover should be selected for their effects on insects in addition to their effects on soil temperature and melon yield

Keywords: Cucumis meló L, aphids, sweetpotato whitefly, soil temperature, yield

Introduction

Cucurbits comprise the largest acreage of cash crops grown in western Mexico, and are also a major crop in the Mexico countiy. Of the cucurbits, the most important ciop is muskmelon, followed by watermelon and cucumber. Muskmelons and related melons sell for a high price, but many farmers are reluctant to grow them because of pest problems which frequently result in poor yields. The most important insect pest are: sweetpotato withefly (Bemisia (abaci Gennadius) and the aphids Aphis spiraecola (Patch), Uroleucon ambrosiae (Tilomas), Myzus persicae (Sulzer), A. gossypii (Glover) and Rhopalosiphum nrfiabdomimlis (Sasaki) (17). Both insect groups cause damage by feeding directly and indirectly through the excretion of lioneydew: They are vector of one or more viiuses affecting cucurbit crops (12,2).

Mich of the research documenting the effects of mulching systems on the colonization of selected insect pests has been conducted with reflective mulches. Such muidles liave been evaluated on cucurbit crops, particularly in relation to virus vectors (8, 6,4.7). However, die use and adoption of polyethylene or reflective mulches is limited by some of its disadvantages. Primarily, reflective mulches are relatively expensive compared with clear or black plastic mulch; and secondly, they result is reduced soil temperatures which can reduce their potential for use during winter muskmelon production

The use of clear and black plastic mulches has become a standard practice for many vegetable crops in western Mexico where it lias been demonstrated that it speeds crap development and enhances earliness (9,17). These polyethylene mulches are used by some fanners for weed control in melon, and it is suggested tliat these might also affected insect population. Finthennore, in recent years, die use of floating rowcovers lias been practiced with variable results on reducing insect pest populations, delaying virus diseases, increasing earliness and total yield of muskmelon (18).

1 INIFAP. Campo Experimental Tecomán. Apartado postal 88. 28100 Tecomán, Colima, México. E mail orozco@bciencias.ucol.mx

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Polyethylene mulch in combination with floating row covers show promise as a method for excluding insects, reducing viats diseases and increasing yield of cucurbit ciops (14,1,13,22,16). However, there is poor information on the development of the muskmelon crop grown under floating row cover and polyethylene microtunnels in tropical conditions. The objectives of this study were 1) to determine the effectiveness of clear and black polyethylene middies, used alone or combined with floating row cover and perforated plastic or no perforated microtunnels, on growth and yield of muskmelon; and 2) to determine the effect of these treatments on population densities of aphids, sweetpotato whitefly and effect on soil temperatures.

Methods and Materials

The field experiment was conducted at die Tecoman Expeiimental Station, located at Tecoman valley, western Mexico (18°51' N, 103°50' W) and 40 m above sea level, during die winter 19%. The soil at the site was clay with a pH of 6.5 and 3% organic matter. Soil was disked and bedded, then, plastic mulch (0.025 mm thick, 12 m wide, clear and black embossed) and drip irrigation tubing (020 mm thick, emission spacing 30 cm, flow rate of 1.5 liters/min. per 30 m of row at 55 kPa (Hi Tech Irrigation, Tecoman, Mexico) were applied using recommended commercial practices. Synthetic fertilizer treatments (113.5 N - 207 P and 225 Kgtia) were applied to the plots before mulching using urea, superphosphate of calcium triple and potassium nitrate. On 7 January, melon (Cucumis melo L Cv. Cniiser) was direct seeded at 25 cm intervals in the center of 1.78 m wide, and plots were watered with a drip irrigation system to piomote geimination. Each bed had an emitter tube with emission spacing of 0.50 m, and flow rate of 2.3 litech.

Seven treatments were evaluated: (1) clear polyediylene mulch (CP), (2) black polyethylene mulch (BP), (3) CP + floating row cover (FRC, spounbonded polypropylene fiber AGRJBON (weight 17 gem2), Bonlam S. A de C. V., Guadalajara, Mexico) removed at the vegetative stage (12 Maich, before staminated flowers appeared in die plants), (4) BP + FRC, (5) CP + microtunnel with perforated polyethylene (MPP), (6) BPM + miaotunnels with non-perforated polyethylene (MNPP), and (7) bare soil as control. Each treatment consisted of thiee 7.0 m-long beds replicated four times in a randomized complete block design Data were collected from the centre row. After seeding FRC, MPP and MNPP were set on the beds with both edges and ends of covers secured with soil. Weeds were removed manually. All plots, except in FRC and MNPP, standard applications of insecticides (endosul&i, imidacloprid, methamidoplios, diazinon and permethrin) were made at 5- to 7- day intervals. Fungi diseases were controlled by fosetyl-Al, mancozeb and methalaxyl applications. Supplemental fertilization was made with 163.3 N, 00 P and 89.6 K applied through die drip system Soil water status was measured with tensiometers at 15- and 30-cm depths, and water was applied when water potential at 15 cm reached-024 kPa

Yellow pan plastic traps for aphids (28x22x 12 cm) containing a mixture of water and detergent were placed in die middle of each plot and die number of aphids trapped were lecoided twice weekly to determine die effectiveness of each treatment in delaying aphid infestation. The nmiber of whitefly adults was detennined twice weekly on 20 randomly selected plants of each treatment (two leaves/plant). Early morning (07:00 - 08:00 h), before flight activity, the leaves were gently turned and adults visually counted (5). On 10 and 17 February (34 and 41 days after sowing, respectively), die number of whitefly nymphs on five leaflets of two tower leaves were counted from 10 randomly selected plants with the aid ofa lOx dissecting microscope.

During the entire experimental period, soil temperature at 10 cm deep was measured in each treatment Soil thermometers were installed next to plant roots and temperature leadings were taken three times a week during the morning (08:00 h), midday (12:00 h), and evening (18:00 h). Plots were harvested by hand on 20,28 April and 01 May. Weight and number of fruit were lecoided and marketable fruit (according to exporting regulation specifications) was sized into 9,12,15,18, and 23 melon/carton, weighing 18.0 - 18.5 kg on average for each box. Data were analyzed with analysis of variance and means of different treatments were compared with a Duncan's multiple range test procedure.

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Results and Discussion

3.1. Aphid populations Aphids were excluded completely from de melon plants growing under MPP and MPNP until the plastic was removed

during perfect flowering. Also, the plots with FRC had similar results (Fig 1). Winged aphids were not caughted in the treatments with row cover during the first five weeks after sowing However from the six to tenth weeks when the covers were removed, a reduced number of aphids (less than 50 aphids'trap) were trapped in the yellow pan plastic traps. Over the whole experimental period, plots with CP and BP mulches had lesser number of caughted aphids with relation to the bare soil plots (between 100 to 200 aphids/trap). On the bare soil plots the highest aphid populations were caught during the first six weeks after sowing.

W E E K S

Fig. 1. Winged aphids caughted in ysllowtraps at several times on melon crop.

32. Whitefly populations Colonization of whitefly nymphs on the plant foliage was reduced by all treatments, compared to the control (Table 1).

During the first 34 days alter sowing, populations of nymphs were excluded from the melon plants growing under FRC and microtunnels. Also, plastic mulches (black and clear) reduced the number of whitefly nymphs compared with bare soil beds. At 41 days after sowing, treatments that had FRC and microtunnels showed less nymphs populations, recording between 0.6 to 22 nymphsfcm2, while plots with clear and black mulches had 33 and 4.1 nymphs, respectively. In contrast, plants growing on bare soil plots had significantly greater numbers of whitefly nymphs at 34 days (2.4 nymphs) and 45 days (292 nymphs-fern2) after sowing

33. Soil temperature Soil temperatures at 10 cm depth on different hours of day, on selected dates, are shown in Fig. 2. Soil temperatures were

consistently highest under clear polyethylene mulch plus floating row cover treatment and lowest under bare soil at 8:00,12:00 and 18:00 h during all period

78

2 3

1 Q _ s 3 P 32

0 30 D 28

2 2« 0 a £ 22 <1>

20

Fig. 2. Effect of different plastics and floating rowcoveis on soil temperature registred at 8:00 (A), 13:00 (B) and 18:00 h (Q.

O 30 -CO

37

35 -

33 —

31 -

29 -

27 -

25 A 5

Weeks

3.4. Marketable fruit yield Clear polyethylene mulch plus floating row cover significantly increased (PO.Ol) export fruit number and export number

of cartons in plots of 28 nr in comparison of all treatments (Table 2 and 3). National fruit number and national number of cartons production were similar (P>0.05) between clear polyethylene mulch plus microtunnel perforated plastic and CP + FRC (Table 2 and 3). Fewer muskmelon for export production was found in clear polyethylene mulch plus microtunnel with non perforated polyethylene.

7 9

Table 1. Average number of whitefly nymphs counted on different treatments and times.

Number of nymphs/an2

Mulch type 34DAS2 41 DAS

Clear polyethylene 0.4 bP 33 b Black polyethylene 0.4 b 4.1b Clear+floating row cover 0.0 b 0.6 c Black + floating row cover 0.0 b 22 be Clear+microtunnel perforated 0.1b 0.8 c Clear+microtunnel no perforated 0.0 b 2.0 be Bare soil 2.4 a 292 a

7 DAS=days after sowing of muskmelon. y=Mean separation within columns by Duncan's Multiple Range Test, P < 0.05

Table 2. Effect of different plastic mulches on fruit number with commercial quality in plots of 28 m2.

• Fruits number

Mulch type Export National Total

Clear polyethylene 1925 bcy 5025 b 70 Black polyethylene 11.00 bed 49.75 b 61 Clear+floating row cover 47.50 a 65.50 ab 113 Black+floating row cover 21.50b 51.50b 73 Clear+microtunnel perforated 7.75 cd 8725 a 95 Clear+microtunnel no perforated 0.00 d 41.50 b 41 Bare soil 025 d 425 c 5

y" Mean separation within columns by Duncan's Multiple Range Test, P £ 0.05

The results extend findings by ourselves (9,17) and others that plastic mulches used alone (7) and floating row covers can improve productivity of muskmelon (3,19,18), tomato (20) or bell peppers sowing at high population densities (11,10,15). Yield was significantly increased by die mulch treatment, while die row cover treatments 5 yielded the least Average of number of cartons was also significantly increased by CP + PRC, over the bare soil and BP + FRC or clear and black polyethylene mulch used alone. Our results show that mulching muskmelon with CP + FRC has enhanced yield and reduce insect pest incidence during the first weeks of cultivation This is not consistent with results of other researchers such as Rubeiz and Freiwat (21) who found diat early production in tomato is enhanced by black plastic mulch, while the row cover used alone had a negative effect on yield. Also Jollife and Gaye (15) working with bell peppers found that die row covets depressed the efficiency of leaves in generating shoot diy matter, as expressed by unit leaf area

8 0

Table 3. Mean number of commercial picks of muskmelon and total number grown on different mulch type and row cover in plots of 28 m2.

Number of cartons

Mulch type Export National Total

Clear polyethylene Black polyethylene Clear + floating row cover Black+floating row cover Clear+microtunnel perforated Clear+microtunnel no perforated Bare soil

1.03 bcy

0.53 bed 2.45 a 1.10b 0.37 cd 0.00 d 0.01 d

231 be 221 be 2.96 ab 2.47 b 3.73 a 1.15cd 0.16d

3.34 2.74 5.41 3.57 4.10 1.15 0.17

y=Mean separation within columns by Duncan's Multiple Range Test, P < 0.05.

Our data show that air temperatures at 18:00 h under the row cover exceeded 35°Con many days. Rubeiz and Freiwat (21) found that such temperatines would become detrimental for tomato yield as it would lead to insufficient pollination blossom drop or fruit abortion Similar effects were obseived in our study in muskmelon plants grown under clear polyethylene mulch plus no perforated microtunnels.

Total yield was significantly increased by use of clear mulch alone and CP + FRC, while the BP + FRC, microtunnels, plastic mulch used alone and control treatments yielded least. However, average fruit weight of the total yield was similar among these treatments.

This work indicates that large muskmelon fruit yields can be attained with management practices, such as mulching and floating row covers, that result in vigorous growth and less harm due to pests. Also, this study indicates that clear polyethylene mulch plus floating row cover had a potential economic value for muskmelon production as they advanced muskmelon fiuit production and increased yield with less insecticide applications. Whereas, die polyethylene perforated and no perforated micratunnels had a detrimental effect on muskmelon pioduction when are used in die western Mexico. In muskmelon crop, floating row covers should be removed after flowering starts and before day temperature exceeds 35°C, to prevent excess lieat build-up which would affect pollination and fruit setting Further research is needed to determine the appropiate time of removal of the floating row cover and microtunnels, when used in conjunction with clear polyethylene mulch.

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Conclusions

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