A method for controlling phytopathogen Alternaria solani for substantially curing early blight disease in tomato comprises applying crude rhamnolipid biosurfactant, obtained from bacterial isolate Pseudomonas aeruginosa JS29, in concentrations varying between 0.75 g L-1 and 1.5 g L-1 by weight on tomato, grown in field condition, for a suitable duration to substantially control phytopathogen Alternaria solani - the causal organism of early blight disease in tomato. FIG 5
