Chilli (Capsicum annuum L.) powdery mildew incited by Leveillula taurica (Lev.) Arn. ( = Oidiopsis taurica (Lev.) Salmon.) is one of the most serious diseases in Tamil Nadu. The leaf extracts of Azadirachta indica A. Juss. (10%) and bulb extracts of Allium sativum L. and A. cepa L. (5%) were highly effective in inhibiting conidial germination of L. taurica under greenhouse and field conditions. Among the antagonistic microorganism screened, maximum reduction in conidial germination was recorded by the culture filtrates of T. viride Per. ex. S. F. Gray., T. harzianum Rifai. and P. fluorescens Migula. under greenhouse and field conditions. Spraying of dipotassium hydrogen orthophosphate and monopotassium phosphate were highly effective in reducing chilli powdery mildew under greenhouse and field conditions. Among the chemicals tested, dipotassium hydrogen orthophosphate significantly increased the protein, total phenol, phenylalanine ammonia lyase, polyphenol oxidase and peroxidase activity of the leaves. In an integrated disease management, foliar spraying with sulphur alternating with dipotassium hydrogen orthophosphate or plant extract Azadirachta indica was as effective as alternating with wettable sulphur fungicide.