Functional relationship of sheath blight of rice with crop age and weather factors

Crop age was found as an important factor in sheath blight (Rhizoctonia solani Kuhn.) development Tillering to panicle emergence stages appeared most susceptible showing PDI of 30 to 80 during 2002 and 50.8 to 60 during 2003 while early crop stages were less susceptible where PDI varied between 3 to 20 and 2 to 28 during the two respective years. Temperature range of 20–30°C and relative humidity (RH) between 80 to 100 per cent were more favourable for disease development. Taking parameters like crop age (r = 0.763), minimum temperature (r = -0.542), number of rainy days (r = -0.504) which had significant correlation co-efficient along with maximum temperature (r = -0.320) were used to develop a multiple regression equation viz. Y = 169.910 + 0.0137 crop age -2.81 Tmax. - 2.36 Tmin -0.829 NORD for forecasting sheath blight of rice.