Soybean Disease Shows in NW Missouri

Rare white mold can cause large yield losses

University of Missouri Extension agronomy specialist Wayne Flanary says about 160 acres of soybean in northwest Missouri show symptoms of sclerotina stem rot. MU Plant Diagnostic Clinic confirmed the disease..

Also known as white mold, the disease is rare in Missouri. It can cause large losses in fields with high yield potential.

The stem and root disease is usually found in the northern part of the soybean belt. MU Extension soybean specialist Bill Wiebold says he found it in Shelby County in northeastern Missouri as many as 10 years ago, but it is rare in Missouri.

In Integrated Pest Management’s Soybean Disease publication, retired MU plant pathologist Laura Sweet says the white mold first shows as a wilting of leaves in the upper canopy. Leaves may show a gray-green or off-color and wilted appearance. A white mold often grows on stems and leaves. The fungus may move to seeds and pods.

The disease is favored by moderate canopy temperatures (less than 82 degrees) and frequent rainfalls that cause high humidity in the canopy.

Research shows that sclerotina stem rot can remain in soil for years, Wiebold says. Seed can be contaminated with sclerotia, the fungus’s reproductive structures. Wiebold’s colleagues at Iowa State University say it may take up to two years for sclerotina to show up from infected seed.

Sclerotia needs exposed to cold temperatures to live. First season infection is unlikely. Therefore, Iowa researchers recommend planting two years of corn to reduce viable seeds, although there are no guarantees. Do not plant soybean after common bean, sunflower, canola or other susceptible crops, according to the MU IPM publication.

There are effective fungicides, but spray timing is critical to success. Apply fungicides during flowering (R1 and R2 stages of development), Wiebold says. Harvest infected fields last and clean out the combine to prevent spread. Select resistant varieties and maintain good weed control also, he says.

Wiebold also recommends using no-till production for three to four years to reduce the number of viable sclerotia near the soil surface.

Do not confuse this disease with one caused by with sclerotium rolfsii, a southern disease, Wiebold says. He advises against performing internet searches for “white mold” and suggests searching for sclerotina stem rot instead.

Learn more at http://extension.missouri.edu/explorepdf/agguides/pests/ipm1002.pdf.