Posted 21 September 2009. PMN Crop News.
White Mold in Soybeans
Source: University of Illinois Press Release. aces.illinois.edu
Urbana-Champaign, Illinois (August 27, 2009)--White mold or Sclerotinia stem rot has been found in 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. Symptoms also include wilted leaves and stems that appear to be "bleached", and shredding of the stem tissue. It is a relatively easy disease to identify.
Cool (temperatures less than 85 degrees F) and wet conditions especially when soybean plants are blooming favors the disease. Prolonged periods of fog and leaf wetness also favor the disease, especially during flowering. Dense soybean canopy, high plant populations, 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.
Once the symptoms are observed, there are no in-season management practices available. Foliar fungicides (currently Topsin M and Domark) must have been applied between R1 (beginning bloom) and R2 (full bloom) growth stages to protect the soybean flowers which are the site of the disease infection.
Management of white mold in soybean is difficult and requires the integration of multiple practices.
Even though there are no varieties completely resistant, some are less susceptible than others. Many soybean seed companies rate varieties for susceptibility to white mold. Information on varieties can be found at the Variety Information Program for Soybeans (VIPS) web site, www.vipsoybeans.org.
In areas where white mold is a severe problem year after year, wider rows (30-inch) may reduce the impact of the disease. It is also important to follow recommended seeding rates and to avoid high seeding rates which decrease the airflow through the canopy.
The white mold fungus can be seedborne, so do not plant bin-run seed.
Research trials evaluating several foliar fungicide products (including Topsin M and Domark) and a biological control product marketed as Contans WG are ongoing.
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.