Rapeseed-mustard is one of the most important oilseed crop, grown both in tropical and subtropical regions of the world. It is plays a pivotal role in agricultural economy of the world. The oil of rapeseed-mustard serves as a very good cooking medium and dietary fat of the majority of populations. It is also most common medium of pickling and food preserving. Besides oil, the leaves of young plants are used as green vegetables and whole plant as green fodder. The seeds are highly nutritive containing 37.7-52.9% euric acid, 8.5-19.0% linoleic acid and 8.6-17.1% oleic acid. These crops are affected by several foliar diseases. Among them Downey mildew [Peronospora brassicae (Pers. ex. Fr.) Fr.], Alternaria blight [Alternaria brassicae (Berk) Sacc. and Alternaria brassicicola (Schwein) Wiltshire] and white rust [Albugo candida (Pers. ex Lev.) Kuntze] are most important in reducing the seed yield. These diseases also affect the seed size, seed quality and oil content.