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Sclerotinia (White Mold)
Sclerotinia or white mold is not as common or damaging on soybeans as it is on dry beans. Long periods of wet weather at flowering, however, favor infection. Severe sclerotinia outbreaks can occur when rainfall at flowering is high.
Sclerotinia spores infect the dead blossoms, in much the same way as they infect dry beans. Infections are favored by wet weather prior to flowering and during flowering. Infected plants develop bleached stems that become shredded and contain hard black fungal bodies called sclerotia. During wet weather a white mold may grow on the surface of infected tissues.
Sclerotia survive for up five or six years in the soil. When the surface soil is wet for 10-14 days, sclerotia from previous susceptible crops germinate to produce tiny mushroom-like bodies that liberate millions of airborne spores. These spores infect the blossoms during wet weather.
Sclerotinia is not usually a serious problem on soybean. Crop rotation is usually adequate to avoid serious damage: avoid rotating soybean with highly susceptible crops such as sunflower, dry bean or canola. Bury infected crop residue. Topsin M is registered for control of Sclerotinia on soybean, with application at early bloom. Research in Wisconsin indicates that Topsin M will help suppress Sclerotinia if used at early bloom. The 16 oz rate would be more effective than lower rates, but this is an expensive treatment. Treatment may be justified if Sclerotinia has been severe in nearly fields in recent years and if wet weather persists from 2 weeks before bloom into early bloom.
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