Cool, overcast, rainy conditions during early soybean growth raise the risk of white mold problems. The mold also known as Sclerotinia stem rot can cause major yield losses in soybeans if left untreated. So growers are being urged to watch for white mold. Should a problem be spotted, growers can use a fungicide to help control it. Proper timing is crucial.  

White mold is most severe in soybean varieties with dense, fast-closing canopies and in fields planted at a high seeding rate and/or with narrow-row spacing, Purdue Extension reports.

The disease first shows up in single plants. The leaves remain on the plant but the stem turns brown and then the whole plant dies. A bleached area is evident on the lower stem and when split open, will have small black structures in it. The black structures are from the fungus and are called sclerotia.

Sclerotia live in the soil for several years. Wind transports it from the soil surface to soybean plants where it infects them at any point. The worst location for an infection, though, is in the flower where the sclerotia eat nutrients and eventually cripple and kill the plant. Because the sclerotia are similar to the size and density of soybeans, they end up in the grain bin or back in the soil with crop residue. Growers with a white mold problem in a soybean field need to clean out combines after harvesting that field.

During the growing season, there are fungicides that may be used to treat white mold, such as Proline from Bayer CropScience. Proline may be applied for preventive treatment at the R1 (flowering) growth stage and a second application at R3. A third application is allowed. There is a required 21-day preharvest interval.

MANA Crop Protection sells Incognito fungicide that is effective against white mold when applied in the early bloom state. A second application is recommended 7 to 14 days later if the weather is favorable for more white mold pressure. 

SipcamAdvan offers the fungicide Contans WG for white mold control. The company says that it “stops white mold at the source — prior to infection. Contans can be applied in the spring, giving growers a head start against yield robbing white mold."

Purdue Extension posts an online bulletin about white mold at www.extension.purdue.edu/extmedia/BP/BP-43-W.pdf.