White mold or Sclerotinia stem rot can be found in many soybean fields in northern Illinois. It is so named because the fungal caused disease produces white fluffy, cottony growth on the outside of the stem and on the pods. It is a relatively easy disease to identify.

Moist, cool weather (less than 80 degrees F) with heavy morning fog or dew favors the disease that occurs through the flowers. Dense soybean canopy and lack of air circulation in the row also are contributing factors.

In addition to the white fluffy growth mentioned above, the disease produces dark black, elongated cigar-shaped structures called sclerotia. These structures allow the fungal pathogen to survive for many years in the soil. Do not plant bin-run seed from infected fields since some of the sclerotia will be harvested with the seed.

Initial disease lesions develop at stem nodes during or after flowering. Infected plant parts will have a white, moldy growth. Infected stems become tan and eventually bleached. Leaves will turn gray to brown, wilt, and remain attached to the plant.

In fields where white mold has previously occurred, the sclerotia produce small mushroom-shaped structures that release the fungal spores into the air. Initial infection occurs during cool and moist weather conditions at time of flowering. If these airborne spores land on a soybean flower as the petals die, infection will occur.

White mold can spread from infected to healthy plants if they contact each other. Soybean seed can be infected with the disease causing pathogen.

Many soybean varieties are rated for resistance to white mold. This information can be found at the Variety Information Program for Soybeans (VIPS) web site, http://web.aces.uiuc.edu/VIPS/v2Home/VIPS2Home.cfm?VIPSbegin=yes Varieties with tolerance or partial resistance to white mold should be selected.

White mold may be more common in narrow row soybeans. The high yielding environment contributes to faster row closure and greater density of crop canopy. The effect of the closed canopy is cooler, wetter conditions that favor disease development.

Currently, it is too late to apply a fungicide. Topsin-M fungicide is registered to control white mold but it must be applied before infection and it must be directed into the lower canopy.

Since sclerotia can survive for many years, crop rotation is not effective for complete control of white mold. There are more than 300 plant hosts for the disease. Crop rotation with nonlegume crops should still be practiced. Corn and small grain are not affected by white mold. Certain broadleaf weeds may also serve as hosts.

Further information on white mold is available at University of Illinois Extension offices, at this University of Illinois web site, http://cropdisease.cropsci.uiuc.edu/ and at the Plant Health Initiative web site, http://www.planthealth.info/whitemold_basics.htm