Closing canopies, flowering soybeans, wet soils, cool temperatures = white mold risk

White mold fungus. The fungus that causes white mold of soybean is called Sclerotinia sclerotiorum. This fungus spends its life in the soil as hard, black structures called sclerotia. Sclerotia, which resemble mouse droppings, help the fungus survive over harsh winters and dry soil conditions. Under cool, wet, humid, and low-light conditions (conditions which are more likely to occur under a full soybean canopy) sclerotia germinate to produce small, cup-shaped mushrooms called apothecia (Figures). Apothecia release sexual spores called ascospores that can infect soybean. Soybean plants are susceptible to infection during flowering as ascospores use dead and dying flowers as a food source and then infect the soybean stem at nodes (where leaves meet the stem).

White mold disease in soybean. Symptoms of white mold are typically scattered in patches throughout the field and include lesions that start at stem nodes. Lesions initially have a water-soaked appearance and become bleached and stringy with time (Figure). The name "white mold" came about because sometimes, under very wet, humid conditions, a white, fluffy mold can be seen growing out of the lesions. Severe infections can result in plant wilt and death and significant yield loss.

Disease risk in 2014? The most recent USDA-NASS Crop Progress and Condition report released June 30th, stated that as of June 29, only 4% of the soybeans in the Western Illinois crop reporting district (which includes Monmouth and the NWIARDC) are blooming. According to the 2014 planting date study at the center, soybean fields planted earlier than May 22 may be susceptible to infection in the next several days for multiple reasons: 1) canopies are beginning to close, especially for soybean planted in 15 inch rows, 2) soybeans are flowering, and 3) we have wet soils due to recent rains and cool air temperatures are in the near-term forecast.

Dr. Carl Bradley, University of Illinois Plant Pathology Specialist, posted an article in 2013 in which he detailed the results of trials researching foliar fungicides for white mold management.


Additional resources:

Check out this NCSRP-Sponsored online publication White Mold in Soybean

Anyone who is interested in a hard-copy of the NCSRP publication Management of White Mold in Soybean is urged to either stop in to the Warren County Extension Office and pick up a copy or contact me to receive one through the mail.