White mold, also called sclerotinia stem rot, is caused by the fungus Sclerotinia sclerotiorum. Sclerotia resume growth as mycelium, or as mushroom-like structures named apothecia. Apothecia are found on the soil surface and form from sclerotia when the soil is moist and dim light is filtered through the crop canopy. The number of apothecia is related to the number of sclerotia near the soil surface, soil moisture and temperature, and the timing and density of crop canopy closure. Apothecia will readily form under the canopy of a nonhost.
Spores form in apothecia and are ejected into the air and disseminated by wind to a host.
The white mold pathogen infects many broadleaf plants. Highly susceptible crops are soybean, dry beans, snap bean, lima bean, sunflowers, canola, carrots, and cabbage. Pea, potato, alfalfa, and read clover are hosts, but are examples of crops that are much less susceptible to the white mold pathogen. Examples of non-host crops are corn, small grains, and all forage grasses. Currently all forms of the pathogen are believed to be equally pathogenic to all hosts and varieties of soybean.