White Mold (Sclerotinia Stem Rot)

A sign of white mold infection is white, fluffy mycelium as seen on this soybean stem. Click on image to view a larger version. Photo credit: Craig Grau, University of Wisconsin

White mold is caused by the fungus Sclerotinia sclerotiorum. The fungus is easily recognized by the presence of fluffy white mycelium (the vegetative body of the fungus) that is the source of the name white mold.

White mold has progressed from a sporadic disease to an annual threat to soybean production

White mold was discovered in central Illinois in 1948. Although it eventually became a chronic problem in Michigan, Minnesota, and Wisconsin, outbreaks were localized, and occurred where soybeans were grown in rotation with other susceptible crops.

Beginning in 1990, however, the occurrence of white mold became more widespread in the Great Lake states, and by 1992 was prevalent throughout all the North Central states.

Reasons for the sudden increase of white mold are not fully understood, but could be related to changes in cultural practices that promote a greater canopy density, changes in the genetic base of current soybean varieties, or changes in the white mold pathogen.

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