Influence of Weather Parameters on the Development of Grey Mildew Disease in Cotton

A study was conducted at the Regional Agricultural Research Station in Warangal to investigate the impact of environmental factors on the development of grey mildew (Ramularia aerola Atk) in cotton. The research spanned from the Kharif season of 2019-20 to 2022-23 and focused on both Bt and non-Bt cotton genotypes grown in vertisols. Disease scores were recorded weekly on randomly selected labeled plants, and the percentage of disease intensity (PDI) was analyzed in relation to various weather parameters. Grey mildew was observed during the boll development stage up to the boll bursting stage, reaching its peak during the latter phase. Correlation analysis revealed significant negative associations between PDI and maximum temperature, minimum temperature, morning relative humidity, evening relative humidity, rainfall, and the number of rainy days. These findings indicate that these environmental factors influenced the development of the disease in both Bt and non-Bt genotypes. Furthermore, multiple linear regression analysis of PDI demonstrated that one percent increase in evening relative humidity led to a corresponding increase in the percent disease index of grey mildew. Specifically, in Bt (RCH 2 BG II) genotype, the increase was 0.38%, while in non-Bt (LRA-5166) genotype, it was 1.87%. Consequently, the study suggests the implementation of preventive and/or protective measures, such as the use of recommended fungicides like 0.3% wettable sulphur or 0.1% carbendazim.