Infected pods turn into a soft, watery mass. Following the watery stage, the affected tissues dry out and turn brown. Within a short time, the brown areas are covered with a dense, white fungal growth. With age, the white fungal growth turns gray and is dotted with small, hard black bodies called sclerotia. Some losses occur in shipping.
Infected beans tend to stick together.
The disease is favored by temperatures ranging between 60 and 70 F. Long periods of high humidity also favor development of white mold. Large plants with heavy vine growth encourage extended periods of high humidity, which favors disease development. Sclerotia fall to the ground at maturity where they lie dormant for as long as 10 years. When weather conditions are again favorable for fungal development, the sclerotia begin to grow again. The fungus enters beans directly as the plant parts come in contact with the developing fungus.