Indian Phytopath. 52 (2) : 142-147 (1999)

Efficacy of different fungicidal spray schedules in combatingapple scab severity in Uttar Pradesh Himalayas

K.P. SINGH and J. KUMARPlant Pathology Section, Hill Campus, G.B. Pant University of Agriculture and Technology, Ranichauri 249 199

ABSTRACT : Five spray schedules comprising of nonsystemic and systemic fungicides were evaluated against applescab in the disease prone Bhatwari fruit belt in Uttar Pradesh hills over three consecutive growing seasons. At thisregion, the ascospore maturity and discharge took place on first fortnight of May and corresponded to the petal fallstage of trees to its fruit development stage. Urea @ 5 per cent concentration had a significant effect on breaking ofthe life cycle of V. inaequa/is in overwintered leaves. All the spray schedules starting at the petal fall stage wereeffective in reducing primary (67.8 to 81.2%) and secondary (82.5 to 90.9%) infection on leaves and fruits, thus savingearlier sprays. Thiophanate methyl was most effective in checking primary infection on one year growth. The variablesmost useful in differentiating disease incidence at various tree growth stages were infection rate Irsl and area underthe scab progress curve (AUSPC].

Key words: Spray schedules, Venturia inaequalis, antisporulant activity, disease index, infection rate, AUSPC

Scab caused by Venturia inaequalis (Cooke) win-ter (anamorph Spilocia pomi Fr.) is one of the mostdestructive disease of apple (Malus domestica Borkh.)world wide (MacHardy, 1996), and leads to significantlosses every season in India (Ann, 1998). Chemicalcontrol forms an effective component of the diseasemanagement in apple scab as non-chemical alterna-tives do not exist (Jones, 1995). Different manage-ment strategies have been developed to prevent thedisease efficiently through scheduled application offungicides in a protective spray programme (Gupta,1985), besides, application of systemic and sterol-in-hibiting (SB!) fungicides (Schwabe, 1980; Schwabeand Jones, 1983; Schwabe et al., 1984; Szkolnik, 1981;Thakur and Gupta, 1990, 1992).

In U.P. hills, the incidence of apple scab inBhatwari fruit belt over the past five years ranges from47.92 to 74.33 per cent. There are reports on pre- leaffall sprays of various chemicals, showing adverse ef-fect on pseudothecial development in the fallen appleleaves (Gupta, 1989; Gadoury et al., 1989; Gupta,1995; Sharma, 1995). Present study was, therefore,conducted to develop a spray schedule involving com-monly available systemic and non-systemic fungicidesto combat this disease.

MATERIALS AND METHODS

Experiments were conducted on 10 year old RedDelicious apple trees naturally infected with V.

inaequalis at the farmers orchards in the Bhatwarifruit belt (village Jhalla, 2600 m.s.!.) over three con-secutive (1993, 1994 and 1995) apple growing sea-sons. Treatments were arranged in a randomized com-plete block design with three blocks and three treesper replication. Six spray schedules (Table 1) compris-ing of non-systemic and systemic fungicides along witha pre- leaf fall urea spray (5%) were given at differentphenological stages of the tree. In another set of ex-periment, fungicides and urea were sprayed at pre-leaf fall stage to assess their role in suppressing thedischarge of V. inaequalis ascospore. These treatmentswere replicated three times in randomized block de-sign with single- tree plots. After one week of spray inNovember, 100 leaves were picked from each treat-ment and placed in cheese cloth bags and the bagswere left on the orchard floor during the winter 1993,1994 and 1995 crop season. The replicate set of leavesfrom each treatment were brought to the laboratory byMay end in 1994, 1995 and 1996, and observed forthe pseudothecial development. Number of ascosporesin 30 randomly chosen disk from each treatment wererecorded.

A microprocessor based apple scab predictor,RSS-412, that records data on temperature, rainfall,relative humidity and leaf wetness to a modifiedMill's table to give the probability of apple scab oc-currence (Mills, 1944), was used to monitor theoccurence of infection periods during each of the

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study year (Fig. I). Simultaneously, maturity and dis-charge of ascoposre in the orchard was monitored atweekly intervals. Fungicides were sprayed with a footsprayer at different phenological stage of the tree.Control trees were sprayed with water.

After each spraying, scab incidence was assessedon 10 terminals and 30 fruits, respectively, usingCroxall's key (Croxall et al., 1952 a,b). Final obser-vations were recorded 15 days before harvest on 100leaves and 30 fruits per replication. The per cent dis-ease index (PDT) was calculated as follows :

Class rating x No. of leaves/Fruits in a particular class

Disease index (%) = --------------------------------- x 100

Total No. of leaves/Fruit observedx highest class rating

Data were analyzed separately for each year be-cause over all effect of spray schedule significantlydiffered. Area under scab progress curve (Tooley andGrau, 1984) for each treatment was calculated as fol-lows:

r =

where XI= per cent disease index at tl ; x2 = per centdisease index at t2 ; t2 - tl = time interval between twoobservation; In = natural log

n-l

AUSPC = E;'I {(X;+I+ Xy2}{t;~I}

in which Xi = the cumulative disease incidence, ex-pressed as a proportion at the ith observation; ti = time

Indian Phytopathology 143

(days after observation) at the ith observation; n =total number of observations.

Primary scab incidence was recorded at the fruitset stage of trees. Anti-sporulant activity of fungicidesin each spray schedule was also determined as re-ported by Sharma (1995).

RESULTS AND DISUCSSION

Spray schedule

All the five spray schedules provided reasonablygood control of primary and secondary infection ofscab. This suggested that fungicidal spray would pro-vide a preventive measure to control the apple scabdisease in those areas where it is being disseminatedthrough airborne conidia. During all the three years,first ascopsore maturity was recorded at the petal fallstage of the tree, and the first spray in each of thetreatment were given at this stage (Table 1).

All the five spray schedules recorded significantdisease reduction in leaves and fruits when comparedto untreated checks (Table 2). Of all schedules, 2ndwas the most effective in control of primary and sec-ondary infection of scab. Carbendazim (0.05%) andthiophanate methyl (0.01%) given as first spray in theschedules I and II were able to mask the appearanceof reddish-brown flecks in the leaves which, however,were observed after 17 and 18 days of spraying, whichis consistent with the earlier reports of Hoch andSzkolnik (1979), Szkolnik (I 981) and Thakur andGupta (1990, 1992) on pre-symptom activity of thesefungicides. Thiophanate methyl and carbendazim alsoshowed acute fungitoxicity to primary infection (ter-

Table 1. Spray schedule for the control of apple scab at Harsil fruit belt of Garhwal hills

Tree stage II III IV VI. Petal fall Carbendazim Thiophanate Mancozeb Bitertanol Chlorothalonil

(0.05%) methyl (0.1%) (0.30%) (0.075%) (0.20%)2. Fruit set Fenarimol Donine Captan Carbendazim Fenarimol

(pea size) (0.04%) (0.1%) (0.20%) (0.05%) (0.04%)3. Fruit Dodine Bitertanol Thiophanate Fenarimol Dodine

development (0.1%) (0.075%) methyl(O.1%) (0.04%) (0.1%)(walnut size)

4. Fruit Thiophanate Fenarimol Dithianon Mancozeb Delandevelopment methyl(O.1%) (0.04%) (0.075%) (0.30%) (0.075%)

5. 20-25 days Mancozeb Mancozeb Bitertanol Captan Mancozebbefore harvest (0.30%) (0.30%) (0.075%) (0.20%) (0.30%)

6. Pre-leaf fall Urea Urea Urea Urea Urea(5%) (5%) (5%) (5%) (5%)

Carbendazim(Bavistin WP); Fenarimol (Rubigan); Dodine (Sylit 65 WP); Thiophanate methyl (Topsin M 70 WP);Mancozeb (Indofil M-45); Bitertanol (Baycor 25 WP); Dithianon (Delan 75 WP); Chlorothalonil (Kavach 75 WP).

144 Indian Phytopathology [Vol. 52(2) 1999]

Table 2. Effectiveness of different fungicidal spray schedules against apple scab

Spray Reduction over checkSchedule 1993 1994 1995 Mean

L F L F L F L F

[ 82.39 97.46 83.92 90.99 69.85 86.13 78.06 89.49II 87.26 100.00 85.49 92.37 72.45 87.19 8\.22 90.91III 70.69 84.64 71.82 87.43 62.36 77.96 67.82 82.47IV 79.28 87.99 77.87 90.10 67.64 85.04 74.44 87.35V 75.87 83.37 74.24 89.21 64.48 83.66 71.08 85.73

Average of three replications, 100 leaves/30 fruits were assessed per replication. L, Per cent leaves; F, Per cent fruit.

minals, leaves and fruit) of V. inaequalis. Bitertanol(0.075%) produced reddish-brown to chlorotic flecks15 days after first spraying and the findings are sup-ported by the results of Thakur and Gupta (1990, 1992).On the contrary, Schwabe et a/. (1984) showed thatthe effect of these fungicides suppressed the appear-ance of chlorotic spots. The results suggest that Istspray of thiophanate methyl and carbendazim, duringabscission of petal were more effective in controllingdisease infection than other fungicides. Mancozeb,bitertanol and chlorothalonil as the first spray wereless effective in the suppression of symptom develop-

ment and allowed the production of sporulation onscab lesions. Sharma (1995) recently studied differentspray schedule on the control of primary infection ofscab and concluded that carbendazim does playa de-cisive role in controlling scab while applied at thepetal fall stage of apple trees.

The results presented in Table 2 reveal that 2ndspray schedule showed better protective activity overother schedules. This schedule recorded significant re-duction in leaf (81.2 %) and fruit infection (90.98%)over untreated control, respectively. Spray schedule Ialso exhibited good protective coverage to the crop

Table 3. Effect of different spray schedules on scab incidence, infection rate (r) and area under scab progress curve (AUSPC)at different phenological stage of Red Delecious apple trees*.

Disease incidence at phenological stages#Spray r.schedule FS FD FD FD BH (per day)** AUSPCs

T 13.33' 28.67' 35.56' 52.22b 58.89b 0.022 203.53L 1.23' 2.69' 3.25' 4.47' 5.45' 0.018 210.08F 1.48' 2.59' 3.94' 8.89- 9.93- 0.025 138.42T 13.34' 28.89' 34.54- 44.44' 51.11- 0.022 186.90

II L 1.16' 3.24' 3.36' 4.52- 4.91' 0.017 214.38F 1.78' 2.96' 5.02' 7.68" 8.37- 0.016 141.03T 14.34' 56.67< 61.10< 70.00d 78.89d 0.043 219.89

III L 2.45' 5.15" 6.48b 7.79

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Table 4. Antisporulant activity of fungicides used in sprayschedules against Venturia inaequalis on natu-rally infected Red Delecious apple trees

Reduction in conidia numberSpray Production# Germination$schedule (%)

No. of viableconidia produced!

lesion

IITillIVV

84.8189.6774.8282.1981.56

53.4758.5342.7452.2650.38

25980945187636885864

Pooled mean of observation of 1993, 1994 and 1995.#Reduction in conidia production of 5 mmvlesion are themeans of 10 lesions per treatment.$Data are the percentage of 100 conidia observed.

CJ 19930 1994 .1995

As regards summer progress of infection, 2nd sprayschedule gave complete control of disease in terminalleaves as well as fruits throughout the season. Theinfection rate and AUSPC values of disease incidencefor each year at different phenological stages of treewere analyzed separately to evaluate treatment effects.The unsprayed control plots had significantly higher r(0.058;0.024;0.034) and AUSPC values (253.84;231.89; 204.18) for disease incidence at terminal, leavesand fruits (Table 3).

Second spray schedule also proved highly effec-tive in reducing disease incidence as it reduced theinfection rate at the terminals (0.03, 0.03, 0.01), leaves(0.03, 0.02, 0.02) and fruits (0.01, 0.02) per unit perday during 1993, 1994 and 1995, respectively (Fig. 1).AUSPC was least in II spray schedule (Fig. 2). Spray

May June July AugustSept.

Months

Fig. 1. Occurrence of apple scab infection periods inBhatwari fruit belt of V.P. Himalayas

and recorded 78.06 and 89.49 per cent reduction inleaf and fruit infection, respectively. Statistically, boththe spray schedules appeared equally good in compari-son to others, while the 3rd spray schedule was foundleast effective in protective activity.

Table 5. Effect of pre leaf fall spray of various fungicides and urea on the production of pseudothecia and discharge ofascospores of Venturia inaequalis

Concentration Pseudothecial Ascosporeem' ROC discharged!

Treatment (%) (%) ern' ROC

Carbendazim 0.05 5.39'b 90.37 715' 94.28Fenarimol 0.04 23.79,r 59.10 4182< 66.56Dodine 0.10 28.17rl 51.57 6194d 50.47Thiophanate methyl 0.10 11.53bc 80.18 2974b 76.22Mancozeb 0.30 18.1800' 68.75 4290< 65.70Bitertanol 0.075 21.42dcr 63.18 4140< 66.89Dithianon 0.075 31.49& 45.86 9220' 26.28Chlorothalonil 0.20 28.75rl 50.57 6528d 47.80Captan 0.20 18.42OOe 68.33 4558< 63.55Urea 2.00 14.7300 74.68 3278b 73.79Urea 5.00 3.15' 94.58 563' 95.50Control 58.17h 12507r

*Reduction over check.

146 Indian Phytopathology

~.---~~------------------~-----.

A 200USPC

---199660 ... ;.. MEAN . r ,- .; ; ; ; .; ;

oL-~--------~~~~~~~~~~~I II III IV V VI I II III IV V VI I II III IV V VI

Terminal Leaves!I'er. Fruit

Fig. 2. Area under scab progress curves for each of thespray schedule

schedule 1st and 2nd were rated at par in 4hecking thescab rate during each year. The data on tedtinal, leavesand fruit disease incidence also indicat~ that sprayschedule 2nd gave least disease score followed by sprayschedule 1st, 4th and 5th. Vanderplank (1963) sug-gested that under low disease severity (i.e. < 5%), thedisease progresses logarithmically because the suscep-tible tissues (I-X) are not a limiting factor. In case ofspray schedule I and II, the increase of disease (dx/dt)was very slow, even though the green area was not alimiting factor for infection. Consequently, the diseasedeveloped at logarithmic rate.

Antisporulant activity of fungicides

From Table 4, it is evident that in treatments onlya few of the conidia were viable. Spray schedule 2ndhad a deleterious effect on the conidia reduction andproduced very less number of viable conidia (945/le-sion), since fungicidal treatment of secondary inocu-lum virtually checked the spread of the disease. How-ever, the fungicides were ineffective if it rained imme-diately after spray.

Several worker reported the reduced productionand germination of V inaequa/is conidia after post-inoculation treatment of fungicides (O'Leary andSutton, 1986; Kelley and Jones, 1881; Thakur andGupta, 1990, 1992). Although, Sharma (1995) ob-served that application of Difolatan at green tip;Benlate at petal fall; hexacap at walnut size; mancozebat 15-20 days before harvest and urea at pre-leaf fallstage of tree were effective schedule that reduced thenumber of viable conidia. Our results indicate thatconidia produced from lesions after pre- and post-symptom application of fungicides (spray schedule, II)have reduction in germination (58.53%) and produc-tion (89.67%) of conidia number than the controlconidia.

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Pre-leaf fall spray

In orchard, the primary source of inoculum over-wintered on infected leaves which could provide as-cospores throughout the growing season; foliar fungi-cides alone may not give satisfactory control of thedisease. Therefore, the present investigation recordedthat an application of urea at 5% level of concentra-tion before abscission of leaves provided highest(94.58%) inhibition of pseudothecial development andsuppression of ascospore productivity (95.50%),whereas at 2% level, it gave 74.68 and 73.79 per centreduction. Carbendazim also exhibited 94.28 per centreduction but dithianon, chlorothalonil and dodineshowed least pseudothecial inhibitory action (Table 5).Ascospore productivity was also reduced by the appli-cation of 0.05 per cent of carbendazim. Five per centurea spray not only suppressed the ascospore produc-tion completely in the fallen apple leaves but also helpedin the early decomposition of the leaves by increasingthe microbial activity of fallen leaves. The efficacy ofurea and fungicides has also been worked (Gupta, 1989,Gupta and Lele, 1980; Gupta, 1995). Efficacy ofthiophanate-methyl, bitertanol, dodine, chlorothaloniland captan was observed here as well and confirmedearlier reports (Gupta and Lele, 1980; Gupta, 1989;O'Leary and Suttan, 1986; Gadoury et al., 1989).

Experiments showed that the five sprays of fungi-cides available with Plant Protection Department, Govt.of Uttar Pradesh and pre-leaf fall urea, spray can berated as a safe treatment for scab control on Red De-licious apples. While it was recommended thatthiophanate methyl is more benefical at the petal fallfor primary infection, dodine, baycor, rubigan andIndofil M-45 were sufficient to control the secondaryinfections.

ACKNOWLEDGEMENTAuthors are grateful to the apple growers of vil-

lage Jhala for providing orchards for conducting presentstudy. Research support grant was provided by theICAR.. We thank Shri Ramesh Pal for technical assis-tance.

REFERENCES

Anonymous (1998). Epidemiology and integrated manage-ment of apple scab. In: Final Report of AICRP on AppleScab. Dr. Y.S. Parmar University of Horticulture andForestry, Solan. pp. 166.

Croxall, H.E., Gwyne, D.C. and Jenkins, J.E.E. (1952a).The rapid assessment of apple scab on leaves. PlantPath. 1: 39-41.

[Vol. 52(2) 1999]

Croxall, H.E., Gwyne, D.C. and Jenkins, J.E.E. (1952b).The rapid assessment of apple scab on fruit. Plant Path.I: 89-92.

Gadoury, D.M., MackHardy, W.E. and Rosenberger, D.A.(1989). Integration of pesticide application schedulesfor disease and insect control in apple orchards of theNortheastern United states. Plant Dis. 73: 98-105.

Gupta, G.K. (1985). Recent trends in forecasting and con-trol of apple scab (Venturia inaequalis (Cke.) Wint.).Pesticides 19: 19-31.

Gupta, G.K. (1989). Pre-leaf fall spray of chemicals andcow urine in suppression of ascospore. Pesticides 23:23-24.

Gupta, G.K. and Lele, V.c. (1980). Role of urea in sup-pression of ascigenous stage, and camparative in vitroefficacy offungicides against apple scab. Indian J agric.Sci. 50: 167-173.

Gupta, V.K. (1995). Status report 1987- 1994. Epidemiol-ogy and integrated management of apple scab. Dr. Y.S.Parmar University of Horticulture & Forestry, Solan,39 pp.

.Hoch, H.C. and Szkolnik, M. (1979). Viability of Venturiainaequalis in chlorotic flecks resulting from fungicideapplication to infected Ma Ius leaves. Phytopathology69: 456-462.

Jones, A.L. (1995). A stewardship program for using fun-gicides and antibiotics in apple disease managementprograms. Plant Dis. 79: 427432.

Kelley, R.D. and Jones, A.L. (1981). Evaluation of twotriazole fungicides for postinfection control of applescab. Phytopathology. 71: 737-742.

MacHardy, W.E. (1996). Apple Scab: Biology, Epidemiol-ogy and Management. American PhytopathologicalSociety. St. Paul. MN.

Mills, W.D. (1944). Efficient use of sulfur dusts and spraysduring rain to control apple scab. N.Y. Agric. Exp. Stn.Ithaca Bull. 630.

Indian Phytopathology 147

O'Leary, A.L. and Sutton, T.B. (1986). Effect of postinfection application of the ergosterol biosynthesis-in-hibiting fungicides on lesion formation and pseudothecialdevelopment of Venturia inaequalis. Phytopathology,76: 119-124.

Sharma, J.N. (1995). Efficacy of fungicidal spray schedulesfor the control of apple scab. Indian J. Mycol. PlantPathol., 25: 250-253.

Schwabe, W.F.S. (1980). Curative activity of fungicidesagainst apple leaf infection by Venturia inaequalis.Phytophylactica 12: 199-207.

Schwabe, W.F.S. and Jones, A.L. (1983). Apple scab con-trol with bitertanol as influenced by adjuvant addition.Plant Dis. 67: 1371-1373.

Schwabe, W.F.S., Jones, A.L. and Jonker, J.P. (1984).Greenhouse evaluation of the curative and protectiveaction of sterol-inhibiting fungicides against apple scab.Phytopathology 74: 249-252.

Szkolnik, M. (1981). Physical modes of action of sterolinhibiting fungicides against apple diseases. Plant Dis.65: 981985.

Thakur, V.S. and Gupta, G.K. (1990). Evaluation of pre-symptom activity of fungicides on symptom expression,conidia production and viability of Venturia inaequalis.Indian Phytopath. 43: 520-526.

Thakur, V.S. and Gupta, G.K. (1992). Post-infection fun-gicidal inhibition of apple scab (Venturia inaequalis)sporulation. Indian J agric. Sci. 62: 629-36.

Tooley, P.W. and Grau, P.R. (1984). Field characteriza-tion rate-reducing resistance to Phytophthoramegasperma f.sp. glycinea in soybean. Phytopathology74: 1201-1208.

Vanderplank, J.E. (1963). Plant Diseases: Epidemics andControl. Academic Press, New York. 349pp.

Received for publication September I, 1997