Brown spot is a common disease which occurs frequently on young plants.
If warm moist weather conditions continue, infection, and defoliation progress from lower to upper leaves. Usually the hot dry weather of midseason arrests disease development, but the disease may become active again near maturity. If conditions favorable for disease development continue into the season or reoccur before maturity, the resulting defoliation can cause serious yield reductions. The pathogen overwinters on infected leaf and stem debris, and the disease is most severe when soybeans are grown continuously in the same field. Cotyledons, primary leaves, and lower trifoliolate leaves typically show brown spot symptoms.