Abstract
The effect of weather factors on the development of alternaria leaf spot and grey mildew in Bt Cotton hybrid Jaadoo BG II was investigated at Regional Agricultural Research Station, Lam, Guntur during kharif 2013-2017. Maximum, minimum temperatures, evening relative humidity, rain fall, number of rainy days and wind speed were negatively correlated and significantly influenced the progress of alternaria leaf spot while number of sunshine hours showed positive significant influence. In case of grey mildew, minimum temperature, evening relative humidity, rain fall, number of rainy days, evaporation and wind speed were negatively correlated and significantly influenced the progress of disease. Multiple regression analysis of pooled data (2013-2016) showed that maximum, minimum temperatures, number of rainy days and wind speed significantly influenced the development of alternaria leaf spot (R2=0.984) where as minimum temperature and evaporation significantly influenced the development of grey mildew (R2=0.976). Validation of these regression equations during 2017-18 indicated the usefulness of these models for prediction of alternaia leaf spot and grey mildew in cotton under given environmental conditions.
Highlights
Cotton is an important commercial crop in India with a production of 377 lakh bales of 170 kg lint in 2017-2018 from an area of 122.35 lakh ha with a productivity of 524 kg ha-1, which is far behind the leading countries
Multiple regression analysis of pooled data (2013-2016) showed that maximum, minimum temperatures, number of rainy days and wind speed significantly influenced the development of alternaria leaf spot (R2=0.984) where as minimum temperature and evaporation significantly influenced the development of grey mildew (R2=0.976)
Alternaria leaf spot appeared during 36th to 38thstandard meteorological week (SMW) at vegetative stage and maximum Percent Disease Index (PDI) reached during 42nd to 49thSMW at boll formation and development.Grey mildew appeared during 43rd to 47thSMW(flowering to boll development stage) and maximum PDI reached during 51st to 4thSMW at boll development to boll bursting stage.Correlation analysis of pooled data (2013-2016) revealed that all the weather parameters except sunshine hours had negative and significant influence on the progress of alternaria leaf spot while number of sunshine hours showed positive significant influence (Table 1).In case of grey mildew, minimum temperature, evening relative humidity, rainfall, number of rainy days,evaporation and wind speed had negative and significant influence on the progress of the disease (Table 1)
Summary
Cotton is an important commercial crop in India with a production of 377 lakh bales of 170 kg lint in 2017-2018 from an area of 122.35 lakh ha with a productivity of 524 kg ha-1, which is far behind the leading countries. Andhra Pradesh stood 7th in area (5.44 lakh ha) but 5th in production (22.0 lakh bales) and 3rdin productivity (688 kg ha-1) during 2017-2018 (Anonymous, 2018).Cotton crop is affected by fungal, bacterial and viral diseases.In India, foliar diseases have been estimated to cause yield losses up to 20 to 30 per cent. Losses due toAlternaria leaf spot/blight were to the tune of 38.2 per cent in cotton (Bhattiprolu and Prasada Rao, 2009).Greymildew generally appears on older leaves as the plants reach maturity, in the form of irregularly angular, pale translucent spots with definite and irregular margin formed by the veins (called areolae). In view of the importance of alternaria leaf spot and grey mildew in cotton, an experiment was conducted to assess the progress of these diseases in relation to environmental factors along with phenological stage of the crop
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