The study demonstrate morphological and physiological variations in isolates of Alternaria brassicae and to evaluate the efficacy of fungicide (in vitro) on radial growth of the fungus and foliar sprays (field) against the disease severity on rapeseed-mustard. Morphological variations of A. brassicae obtained from various places were differed in their conidial size and septation. Physiological response of A. brassicae at varying temperatures, the fungus showed its maximum growth at 25øC followed 20øC and on different culture medium, maximum radial growth is on PDA. However, the fungus exhibited a descending trend in its growth at lower and higher regimes of temperature. Among the non systemic and systemic fungicides evaluated in vitro on radial growth inhibition of A. brassicae were found significantly most effective and reduced maximum radial growth at higher concentration. All fungicidal sprays applied under field conditions to manage the incidence of blight reduced significantly the severity of the disease and increased yield in comparison to untreated control. Ridomil-MZ proved to be most effective. Highest net profit as well as cost : benefit ratio was Bavistin + Indofil-Z 78.