S T U D I E S ON THE E F F E C T S OF WEATHER P A R A M E T E R S ON I N C I D E N C E OF POWDERY M I L D E W ( U n c i n u l a necator ( S c h w . ) B u r r O N G R A P E S ( V i t i s vinifera L. )

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Date
1992-03-16
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MAHATMA PHULE KRSHI VIDYAPEETH Rahuri, Dist. Ahmednagar (Maharashtra, India)
Abstract
The experiment entitled, "Studies on the effects of weather parameters on incidence of powdery mildew (Uncinula necator (Schw.) Burr.) on grapes (Vitis vinifera L,)'\ was conducted during the post-monsoon season of the year 1990- 91. Five compartments, each consisting of nine vines, were erected with the help of transparent polythene sheet and wooden frame and were irrigated at an interval of 4, 8, 12, 16 and 20 d in order to create varying microclimatic conditions in these compartments. The temperatures, within the canopy of vines, in different compartments were recorded continuously by thermocouples and relati\ v humidity, within the canopy, was recorded by thermocouple psychrometer. Biological observations on per cent incidence of powdery mildew on berries (% IN), spore load on berries (SL)( and per cent disease intensity on leaves (PDI), were recorded at an interval of 3 d. Th*» disease incidence and multiplication was rapid in the months of December and January when the climate was cool and humid compared to the climate in the months of November and February. The vines suffered early and more from the attack of disease where irrigations were applied at shorter intervals than the vines irrigated at longer intervals. The most critical minimum and maximum temperature for rapid multiplication of powdery mildew ranged from 10.80 to 15.52"C and 25.33 to 32,39'C with an average of 12.87 ± 1.39'C and 28.26 ± 2.08*C, respectively. Similarly, the most critical relative humidity at 0730 h and 1430 h was ranged between 88.33 to 96.77% and 57.39 to 62.68% with an average of 92.76 ± 2.34% and 60.08 ± 2.22%, respectively. The most critical minimum and maximum temperature for zero rate of powdery mildew multiplication were 8.6'C and 34"C, respectively, while relative humidity at 0730 h and 1430 h were 100% and 47%, respectively. Thus, temperature in the range of 11 to 32"C and relative humidity greater than 57% favoured the development of powdery mildew on grapes. Below 8.6* C temperature and 47% relative humidity and above 34"C and 100% relative humidity, powdery mildew showed negative rate of multiplication which indicated that disease does not multiply below and above this range, however, it can exist out of this range.
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