Prediction of whitefly population and Okra yellow vein mosaic virus disease incidence in okra

Monthly sowing of okra and weekly record of the incidence of Okra yellow vein mosaic virus disease and the vector Bemisia tabaci were carried out for 12 months. Using important weather parameters, simple correlations and multiple regression analysis were worked out to identify the factors in predicting the whitefly population and the disease incidence at different stages of crop growth. The study revealed a significant, positive correlation between whitefly population and maximum temperature, minimum temperature and sunshine hours, whereas morning relative humidity, wind velocity and total rainfall had negative influence on whitefly population. Disease incidence also had a significant and positive correlation with whitefly population, minimum temperature and sunshine hours while morning relative humidity, evening relative humidity and wind velocity had a high negative association. Multiple regression analysis showed that in 6 weeks old crop, a unit increase in whitefly population, minimum temperature and sunshine hours caused a corresponding increase in the disease incidence by 2.7, 18.1 and 3.4 per cent, while there was reduction in disease incidence by 14.9, 3.5 and 2.0 per cent for every unit increase in maximum temperature, evening relative humidity and wind velocity, respectively.