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White Mold in Soybeans

Sclerotinia stem rot, also known as white mold, is an uncommon disease in soybean production in North Dakota.  Soybean is less susceptible to white mold as compared to dry beans, canola or sunflower.  However, fields with high disease pressure and ideal environmental conditions can develop white mold infection.  Also, hail injury to soybean plants can result in white mold.   

Crops are susceptible to white mold once they enter bloom.   Ascospores will colonize flower petals first.  After this occurs, the fungus will penetrate the rest of the plant and eventually, will cause the characteristic cream colored and shredded lesions. 

Environment & Disease Development

For white mold infection to occur, several environmental factors need to come together.  First, enough soil moisture must be present to allow sclerotia to germinate and produce ascospores.  Generally the minimum rainfall needed is 1 to 2 inches within 1 to 2 weeks of bloom.  Secondly, wet canopies (heavy dew, rain, etc), and cool to moderate temperatures during bloom are needed.  The white mold pathogen is much less of a threat when temperatures are above 85°F. 

Early infections at initial flowering are the most yield limiting.  These early infections are often lower on the plant and have the most time to develop and subsequently cause yield loss. Late infections are often on lateral branches, and have less time to develop lesions. 

Fungicide Application

For optimal control, apply fungicide at early flowering.  If the environment favorability continues, another subsequent application may be applied 7 to 14 days later.  Data suggests that once soybean reaches R3, fungicides for white mold are unlikely to impact yield under any temperature.  This is simply because the infections occurring after this crop stage are usually not yield- limiting.

The Carrington REC research data has shown a positive yield impact and disease reduction when Endura (Bayer) or Cobra (Valent) were applied singly, and with multiple applications of other chemicals.  Cobra will cause crop injury, and loss of yield from injury needs economic consideration.  In these extremely disease-laden experiments (over 90% of plants had white mold infections in no fungicide applied control plots), most fungicides were overwhelmed.  At the field-level and much lower infection rates, the need for a fungicide application is a rare event.

Resources and excerpts from: "White Mold in Soybeans", Crop and Pest Report 7/21/11, S. Markell

 2013 Soybean Sclerotinia Fungicide Efficacywebpage, M. Wunsch, CREC Plant Pathology

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