Martin Chilvers, Janette Jacobs, Ray Hammerschmidt, Plant Pathology
Jan Byrne, Diagnostic Services

Now that flowering has begun and canopies are beginning to close, soybeans will be at risk to white mold. White mold is caused by the fungus Sclerotinia sclerotiorum. The fungus overwinters in crop debris or soil as sclerotia with an appearance similar to mouse droppings. During the growing season, apothecia (small mushrooms) are produced from the sclerotia which have the capacity to release millions of spores into the air (Figure 1). These spores are not thought to infect the plant directly, instead they land on and infect flower petals using them as a food source to initiate infection of the plant. Disease is favored by cool (less than 85ºF) temperatures and moisture. The university of Wisconsin-Madison has an excellent table and website with suggested management practices and further information.

http://www.plantpath.wisc.edu/soyhealth/wmmgmttab.htm

An irrigated pea crop was found last week in central Michigan with a heavy infestation of white mold. The lower canopy had a slimy appearance and on closer inspection areas of white cottony fungal mycelium (a.k.a. white mold) could be found on the crop canopy and apothecia on the soil surface. Pea pods with characteristic water-soaked lesions were also prevalent (Figure 2 & 3).


Figure 1. In this image, a sclerotium dug from
the soil can be seen hanging by the stalk that
connects it to the apothecium above the soil
surface.


Figure 2. White mold lesions on pea pods with
a water soaked appearance.


Figure 3. When pea pods are split open, white
fluffy mycelium is found within.