Role of environmental factors on the progress of powdery mildew (Sphaerotheca pannosa var. rosae) of rose and its management under polyhouse conditions

Powdery mildew (Sphaerotheca pannosa var. rosae) of rose (Rosa species) appeared in the second fortnight of July under polyhouse conditions and attained the maximum level in August & September. Simple correlation coefficient between the disease severity and average relative humidity (0.873) was found to be highly significant and positive showing thereby consistent effect of relative humidity on disease development. However, correlation coefficients between disease severity and temperate (−0.737) and bligh (−0.623) were found to be significant and negative while partial correlation coefficient between disease severity and average relative humidity (0.743) was significant and positive. Coefficient of determination between disease severity and environmental factors explained 80.34 per cent change in the disease was due to environmental factors. Triadimefon reduced the disease severity to 6.25 per cent as compared to control (64.37%) and was significantly superior to all other treatments followed by triadimefon alternated with K₂HP0₄ and K₂HP0₄ with 23.12 and 23.75 per cent disease severity, respectively.