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

Indian Phytopath. 52 (2) : 142-147 (1999) Efficacy of different fungicidal spray schedules in combating apple scab severity in Uttar Pradesh Himalayas K.P. SINGH and J. KUMAR Plant 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 apple scab in the disease prone Bhatwari fruit belt in Uttar Pradesh hills over three consecutive growing seasons. At this region, the ascospore maturity and discharge took place on first fortnight of May and corresponded to the petal fall stage of trees to its fruit development stage. Urea @ 5 per cent concentration had a significant effect on breaking of the life cycle of V. inaequa/is in overwintered leaves. All the spray schedules starting at the petal fall stage were effective in reducing primary (67.8 to 81.2%) and secondary (82.5 to 90.9%) infection on leaves and fruits, thus saving earlier sprays. Thiophanate methyl was most effective in checking primary infection on one year growth. The variables most useful in differentiating disease incidence at various tree growth stages were infection rate Irsl and area under the scab progress curve (AUSPC]. Key words: Spray schedules, Venturia inaequalis, antisporulant activity, disease index, infection rate, AUSPC Scab caused by Venturia inaequalis (Cooke) winter (anamorph Spilocia pomi Fr.) is one of the most destructive disease of apple (Malus domestica Borkh.) world wide (MacHardy, 1996), and leads to significant losses every season in India (Ann, 1998). Chemical control forms an effective component of the disease management in apple scab as non-chemical alternatives do not exist (Jones, 1995). Different management strategies have been developed to prevent the disease efficiently through scheduled application of fungicides in a protective spray programme (Gupta, 1985), besides, application of systemic and sterol-inhibiting (SB!) fungicides (Schwabe, 1980; Schwabe and Jones, 1983; Schwabe et al., 1984; Szkolnik, 1981; Thakur and Gupta, 1990, 1992). In U.P. hills, the incidence of apple scab in Bhatwari fruit belt over the past five years ranges from 47.92 to 74.33 per cent. There are reports on pre- leaf fall sprays of various chemicals, showing adverse effect on pseudothecial development in the fallen apple leaves (Gupta, 1989; Gadoury et al., 1989; Gupta, 1995; Sharma, 1995). Present study was, therefore, conducted to develop a spray schedule involving commonly available systemic and non-systemic fungicides to combat this disease. MATERIALS AND METHODS Experiments were conducted on 10 year old Red Delicious apple trees naturally infected with V. inaequalis at the farmers orchards in the Bhatwari fruit belt (village Jhalla, 2600 m.s.!.) over three consecutive (1993, 1994 and 1995) apple growing seasons. Treatments were arranged in a randomized complete block design with three blocks and three trees per replication. Six spray schedules (Table 1) comprising of non-systemic and systemic fungicides along with a pre- leaf fall urea spray (5%) were given at different phenological stages of the tree. In another set of experiment, fungicides and urea were sprayed at preleaf fall stage to assess their role in suppressing the discharge of V. inaequalis ascospore. These treatments were replicated three times in randomized block design with single- tree plots. After one week of spray in November, 100 leaves were picked from each treatment and placed in cheese cloth bags and the bags were left on the orchard floor during the winter 1993, 1994 and 1995 crop season. The replicate set of leaves from each treatment were brought to the laboratory by May end in 1994, 1995 and 1996, and observed for the pseudothecial development. Number of ascospores in 30 randomly chosen disk from each treatment were recorded. A microprocessor based apple scab predictor, RSS-412, that records data on temperature, rainfall, relative humidity and leaf wetness to a modified Mill's table to give the probability of apple scab occurrence (Mills, 1944), was used to monitor the occurence of infection periods during each of the

[VoL 52(2) 1999] study year (Fig. I). Simultaneously, maturity and discharge of ascoposre in the orchard was monitored at weekly intervals. Fungicides were sprayed with a foot sprayer at different phenological stage of the tree. Control trees were sprayed with water. After each spraying, scab incidence was assessed on 10 terminals and 30 fruits, respectively, using Croxall's key (Croxall et al., 1952 a,b). Final observations were recorded 15 days before harvest on 100 leaves and 30 fruits per replication. The per cent disease 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 observed x highest class rating Data were analyzed separately for each year because over all effect of spray schedule significantly differed. Area under scab progress curve (Tooley and Grau, 1984) for each treatment was calculated as follows: r = where XI= per cent disease index at tl ; x 2 = per cent disease index at t2 ; t2 - tl = time interval between two observation; In = natural log n-l AUSPC = E;'I {(X;+I+ Xy2}{t;~I} in which Xi = the cumulative disease incidence, expressed 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 fruit set stage of trees. Anti-sporulant activity of fungicides in each spray schedule was also determined as reported by Sharma (1995). RESULTS Spray schedule AND DISUCSSION All the five spray schedules provided reasonably good control of primary and secondary infection of scab. This suggested that fungicidal spray would provide a preventive measure to control the apple scab disease in those areas where it is being disseminated through airborne conidia. During all the three years, first ascopsore maturity was recorded at the petal fall stage of the tree, and the first spray in each of the treatment were given at this stage (Table 1). All the five spray schedules recorded significant disease reduction in leaves and fruits when compared to untreated checks (Table 2). Of all schedules, 2nd was the most effective in control of primary and secondary infection of scab. Carbendazim (0.05%) and thiophanate methyl (0.01%) given as first spray in the schedules I and II were able to mask the appearance of reddish-brown flecks in the leaves which, however, were observed after 17 and 18 days of spraying, which is consistent with the earlier reports of Hoch and Szkolnik (1979), Szkolnik (I 981) and Thakur and Gupta (1990, 1992) on pre-symptom activity of these fungicides. Thiophanate methyl and carbendazim also showed 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 V I. 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 Delan development methyl(o.1%) (0.04%) (0.075%) (0.30%) (0.075%) 5. 20-25 days Mancozeb Mancozeb Bitertanol Captan Mancozeb before 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 check Schedule 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 89.49 II 87.26 100.00 85.49 92.37 72.45 87.19 8\.22 90.91 III 70.69 84.64 71.82 87.43 62.36 77.96 67.82 82.47 IV 79.28 87.99 77.87 90.10 67.64 85.04 74.44 87.35 V 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 flecks 15 days after first spraying and the findings are supported by the results of Thakur and Gupta (1990, 1992). On the contrary, Schwabe et a/. (1984) showed that the effect of these fungicides suppressed the appearance of chlorotic spots. The results suggest that Ist spray of thiophanate methyl and carbendazim, during abscission of petal were more effective in controlling disease infection than other fungicides. Mancozeb, bitertanol and chlorothalonil as the first spray were less effective in the suppression of symptom development and allowed the production of sporulation on scab lesions. Sharma (1995) recently studied different spray schedule on the control of primary infection of scab and concluded that carbendazim does playa decisive role in controlling scab while applied at the petal fall stage of apple trees. The results presented in Table 2 reveal that 2nd spray schedule showed better protective activity over other schedules. This schedule recorded significant reduction in leaf (81.2 %) and fruit infection (90.98%) over untreated control, respectively. Spray schedule I also 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' 52.22 b 58.89 b 0.022 203.53 L 1.23' 2.69' 3.25' 4.47' 5.45' 0.018 210.08 F 1.48' 2.59' 3.94' 8.89-9.93-0.025 138.42 T 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' 0.017 214.38 F 1.78' 2.96' 5.02' 7.68" 8.37-0.016 141.03 T 14.34' 56.67< 61.10< 70.00 d 78.89 d 0.043 219.89 III L 2.45' 5.15" 6.48b 7.79<1 8.97 b 0.011 226.36 F 2.29' 8.\4" 12.21 b 13.32' 15.44' 0.021 202.58 T 16.67' 41.11b 43.33'b 55.56 b 66.74< 0.021 219.44 IV L 1.76" 3.68-1 4.29'b 5.09- b 7.36'b 0.012 220.27 F 2.74' 3.70' 5.10" 10.47-1 11.34' 0.020 179.35 T 21.11 b 43.33 b 53.22b< 63.34< 72.22< 0.019/ 225.48 V L 1.93b 3.97' 4.6 pb 6.71 be 8.81 b 0.013 211.52 F 2.82-4.73" 8.22- b 11.47' 12.07-0.016 185.38 T 44.22b 76.67 d 91.11 d 96.67' 100.00' 0.058 253.84 Control L 7.97 b 12.34 b 21.90< 29.92 d 30.38< 0.024 231.89 F 13.34 b 28.33 b 40.81< 53.38 b 65.96 b 0.034 204.18 *Pooled data of three years, 1993, 1994 and 1995. #FS, fruit set (pea size); FD, fruit development (walnut size); FD, fruit development (3,6 ern) and BH, before harvest, growth stage (26 days after each growth stage). **The simple interest infection rate obtained by rearessing the transformed value of In [1I(I-x)] of disease incidence on time. $Area under scab progress curve.

[Vol. 52(2) 1999] Indian Phytopathology 145 Table 4. Antisporulant activity of fungicides used in spray schedules against Venturia inaequalis on naturally infected Red Delecious apple trees Reduction in conidia number Spray Production# Germination$ schedule (%) I IT ill IV V 84.81 89.67 74.82 82.19 81.56 53.47 58.53 42.74 52.26 50.38 No. of viable conidia produced! lesion 2598 0945 1876 3688 5864 Pooled mean of observation of 1993, 1994 and 1995. #Reduction in conidia production of 5 mmvlesion are the means of 10 lesions per treatment. $Data are the percentage of 100 conidia observed. May June July AugustSept. Months CJ 19930 1994.1995 Fig. 1. Occurrence of apple scab infection periods in Bhatwari fruit belt of V.P. Himalayas and recorded 78.06 and 89.49 per cent reduction in leaf and fruit infection, respectively. Statistically, both the spray schedules appeared equally good in comparison to others, while the 3rd spray schedule was found least effective in protective activity. As regards summer progress of infection, 2nd spray schedule gave complete control of disease in terminal leaves as well as fruits throughout the season. The infection rate and AUSPC values of disease incidence for each year at different phenological stages of tree were 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, leaves and fruits (Table 3). Second spray schedule also proved highly effective in reducing disease incidence as it reduced the infection 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 per day during 1993, 1994 and 1995, respectively (Fig. 1). AUSPC was least in II spray schedule (Fig. 2). Spray Table 5. Effect of pre leaf fall spray of various fungicides and urea on the production of pseudothecia and discharge of ascospores of Venturia inaequalis Concentration Pseudothecial Ascospore em' ROC discharged! Treatment (%) (%) ern' ROC Carbendazim 0.05 5.39'b 90.37 715' 94.28 Fenarimol 0.04 23.79,r 59.10 4182< 66.56 Dodine 0.10 28.17 rl 51.57 6194 d 50.47 Thiophanate methyl 0.10 11.53 bc 80.18 2974 b 76.22 Mancozeb 0.30 18.18 00 ' 68.75 4290< 65.70 Bitertanol 0.075 21.42dcr 63.18 4140< 66.89 Dithianon 0.075 31.49& 45.86 9220' 26.28 Chlorothalonil 0.20 28.75 rl 50.57 6528 d 47.80 Captan 0.20 18.42 OOe 68.33 4558< 63.55 Urea 2.00 14.73 00 74.68 3278 b 73.79 Urea 5.00 3.15' 94.58 563' 95.50 Control 58.17 h 12507 r *Reduction over check.

146 Indian Phytopathology A 200 U S P C ~.---~~------------------~-----. ---1996 60... ;.. 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 the spray schedule schedule 1st and 2nd were rated at par in 4hecking the scab rate during each year. The data on tedtinal, leaves and fruit disease incidence also indicat~ that spray schedule 2nd gave least disease score followed by spray schedule 1st, 4th and 5th. Vanderplank (1963) suggested that under low disease severity (i.e. < 5%), the disease progresses logarithmically because the susceptible tissues (I-X) are not a limiting factor. In case of spray schedule I and II, the increase of disease (dx/dt) was very slow, even though the green area was not a limiting factor for infection. Consequently, the disease developed at logarithmic rate. Antisporulant activity of fungicides From Table 4, it is evident that in treatments only a few of the conidia were viable. Spray schedule 2nd had a deleterious effect on the conidia reduction and produced very less number of viable conidia (945/lesion), since fungicidal treatment of secondary inoculum virtually checked the spread of the disease. However, the fungicides were ineffective if it rained immediately after spray. Several worker reported the reduced production and germination of V inaequa/is conidia after postinoculation treatment of fungicides (O'Leary and Sutton, 1986; Kelley and Jones, 1881; Thakur and Gupta, 1990, 1992). Although, Sharma (1995) observed that application of Difolatan at green tip; Benlate at petal fall; hexacap at walnut size; mancozeb at 15-20 days before harvest and urea at pre-leaf fall stage of tree were effective schedule that reduced the number of viable conidia. Our results indicate that conidia produced from lesions after pre- and postsymptom application of fungicides (spray schedule, II) have reduction in germination (58.53%) and production (89.67%) of conidia number than the control conidia. Pre-leaf fall spray [Vol. 52(2) 1999] In orchard, the primary source of inoculum overwintered on infected leaves which could provide ascospores throughout the growing season; foliar fungicides alone may not give satisfactory control of the disease. Therefore, the present investigation recorded that an application of urea at 5% level of concentration before abscission of leaves provided highest (94.58%) inhibition of pseudothecial development and suppression of ascospore productivity (95.50%), whereas at 2% level, it gave 74.68 and 73.79 per cent reduction. Carbendazim also exhibited 94.28 per cent reduction but dithianon, chlorothalonil and dodine showed least pseudothecial inhibitory action (Table 5). Ascospore productivity was also reduced by the application of 0.05 per cent of carbendazim. Five per cent urea spray not only suppressed the ascospore production completely in the fallen apple leaves but also helped in the early decomposition of the leaves by increasing the microbial activity of fallen leaves. The efficacy of urea and fungicides has also been worked (Gupta, 1989, Gupta and Lele, 1980; Gupta, 1995). Efficacy of thiophanate-methyl, bitertanol, dodine, chlorothalonil and captan was observed here as well and confirmed earlier reports (Gupta and Lele, 1980; Gupta, 1989; O'Leary and Suttan, 1986; Gadoury et al., 1989). Experiments showed that the five sprays of fungicides available with Plant Protection Department, Govt. of Uttar Pradesh and pre-leaf fall urea, spray can be rated as a safe treatment for scab control on Red Delicious apples. While it was recommended that thiophanate methyl is more benefical at the petal fall for primary infection, dodine, baycor, rubigan and Indofil M-45 were sufficient to control the secondary infections. ACKNOWLEDGEMENT Authors are grateful to the apple growers of village Jhala for providing orchards for conducting present study. Research support grant was provided by the ICAR.. We thank Shri Ramesh Pal for technical assistance. REFERENCES Anonymous (1998). Epidemiology and integrated management of apple scab. In: Final Report of AICRP on Apple Scab. Dr. Y.S. Parmar University of Horticulture and Forestry, Solan. pp. 166. Croxall, H.E., Gwyne, D.C. and Jenkins, J.E.E. (1952a). The rapid assessment of apple scab on leaves. Plant Path. 1: 39-41.

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