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1. Role of environmental factors in epiphytotics 1. Temperature High temperature Powdery mildew of black gram / green gram – severe in summer Root rot is favoured by high temperature (30 to 35 C) Colletotrichum is favoured by a high temperature Yellow mosaic of pulses is severe in summer Bacterial leaf blight is severe when temperature is around 25-30 C

2. Low temperature Rice blast is favoured by low night temp (<20 C) Phytophthora infestans is serious in cold regions Puccinia graminis tritici infection cycle completes in 22 days at 5°C, 15 days at 10°C and 5-6 days at 23°C Verticillium wilt is also favoured by low temperature Loose smut of wheat is severe at temp 19 to 20 C Apple scab is severe when the temperature is 20 C Downy mildew of sorghum is severe when the temperature is 20-25 C Heavy shade favours powdery mildews, blister blight of tea, damping off & brown spot of rice

3. 2. Relative Humidity Generally high RH favours the severity of plant diseases High sporulation of Peronosclerospora sorghi at 100% RH High sporulation of Peronosclerospora sacchari at 86 to 90% RH Late blight of potato 10 C Temp & >75% RH for two days 12hrs >90% RH , temp 10 C & free moisture on leaf Night RH of about 95%

4. 3. Rain Frequent drizzling favours ergot of pearlmillet Drizzling favours rice blast Rainy weather favours BLB of rice Downy mildew of maize and brown spot of rice favours by rain 4. Dew Sorghum downy mildew ( Peronosclerospora philippiensis ) Blast of rice

5. 5. Light More sporangial production in S . graminicola when light duration increases Virus diseases Darkness / shade increases the incidence of tea blister blight & rice brown spot 6. Soil factors Soil moisture Low soil moisture favours potato scab, root rots and Verticillium wilt of cotton High soil moisture favours damping off and wet root rot Alkaline soil – Fusarium wilt of cotton & potato scab Acid soils – Club root, Plasmodiophora brassicae