Late blight forecasting in eastern plains based on blight favourable days

An improved forecasting system for potato late blight in eastern plains was developed on the basis of field trials conducted for 10 years at Patna during 1992–93 to 2001–02. It involved identification of 1st blight favourable period (BFP-1) of 2 consecutive days comprising average minimum temperature between 7° –15° C, av. max. temperature 22° –25° C (range 21.5° to < 26.0±1°C), RH > 75% and av. sunshine ≤ 5 hours per day. The disease was observed within 7–14 days when the crop canopy was dense after BFP-1 (crop age > 35 days) and within 15–21 days when the canopy was sparse (crop age < 30 days). The method predicted the disease accurately even during 1997–98 when the disease appeared early (Dec. 2nd week) suggesting that the method is reliable. The system was also validated using disease and weather data for the years 2002–03 and 2003–04.