Technical Abstract: Sphenoclea zeyanica (gooseweed), a major weed of paddy rice in Southeast Asia, is one of the targets in a biological weed control research program in the Philippines. Afungal pathogen, Alternaria alternata f. sp. sphenocleae, is being evaluated as a biological control agent for this weed. The feasibility of solid substrate fermentation for the mass production of A. alternata f. sp. sphenocleae has been examined. Conidia production and virulence of A. alternata f. sp. sphenocleae were affected by temperature, light, and incubation period. Abundant conidia were produced under continuous light on seeds of sorghum, hard red spring wheat, and barley at 28 degrees C. The greatest number of conidia was produced on sorghum seed followed by barley and oats seeds at 28 degrees C exposed to near-ultraviolet (NUV). More conidia were produced at 28 degrees C under NUV light on sorghum, barley, oats, and hard red spring wheat seeds, cornmeal, and polished rice grains than on the other substrates. Less conidia were produced on these substrates under light. At 28 degrees C, large numbers of virulent conidia were produced on sorghum seeds after 4 weeks of incubation under either constant light or dark. A mix of equal quantities of sorghum seeds and water (w/v) maximized conidial production. Conidia produced on sorghum seeds had a shelf life of at least 12 months when stored in production flasks under room conditions (24+or-2 degrees C). The use of sorghum seeds as a solid substrate for production of A. alternata f. sp. sphenocleae could be a feasible method to produce conidia in a village co-operative or cottage industry type scenario in Southeast Asia.