A method is described to produce inoculum of Alternaria cassiae Jurair and Khan for biocontrol studies. Approximately 8 g of a conidial preparation containing 1 × 108 conidia/g were produced per liter of growth medium. In greenhouse studies the effectiveness of A. cassiae as a biocontrol agent for sicklepod (Cassia obtusifolia L.) was affected by dew-period temperature, dew-period duration, inoculum concentration, and the stage of growth of sicklepod seedlings at the time of inoculation. Optimum environmental conditions included at least 8 h of free moisture at 20 to 30C. Spray mixtures containing approximately 5 × 104 or more conidia/ml gave maximum control when sicklepod seedlings were sprayed to runoff. Sicklepod seedlings in the cotyledon to first-leaf stage were most susceptible to the pathogen.