Southern blight is caused by a soil-born fungus, Sclerotium rolfsii .
Soybeans are susceptible to the southern blight fungus anytime from emergence through pod fill.
The disease, however, most commonly occurs in isolated plants in fields that are well into the reproductive stages of development. When this is the case, the disease is usually more of a curiosity than a concern. In some years, certain fields may develop southern blight in the early to mid vegetative stages. In these cases, the disease may spread rapidly, down rows, and cause serious losses. Leaves of affected plants turn brown, dry up, and usually remain attached to the plant.