Influnce of weather parameters on the development of Alternaria leaf spot in cotton

摘要

The effect of weather factors on the development of Alternaria leaf spot in susceptible cotton variety Narasimha (NA 1325) was investigated during kharif 2012-2013 at Regional Agricultural Research Station, Lam Farm, Guntur. Weekly data on disease score at different phenological stages of the crop was recorded on randomly labeled plants and per cent disease intensity (PDI) was correlated with weather parameters. Alternaria leaf spot of cotton appeared during 37th meteorological week at the seedling stage and reached its peak (31.8%) during the 5th meteorological week at the boll maturity stage. Significant negative correlation was observed for maximum temperature and minimum temperature with per cent disease intensity, while morning relative humidity and sunshine hours were positive and significantly correlated. Multiple linear regression of PDI indicated that for every one per cent increase in morning relative humidity there was corresponding increase of 0.80 in per cent disease index of Alternaria leaf spot and suggests preventive and / or protective measures are to be taken up with recommended fungicides like mancozeb and propiconazole.