White mold in soybeans a concern across Midwest
White mold, caused by the fungus Sclerotinia sclerotiorum, is not common every year in this region, but farmers that have battled the disease in the past will want to assess the risk of white mold development as soybeans approach flowering (growth stage R1 – plants have at least one open flower at any node).
“White mold development is favored by cool, cloudy, wet, humid weather at flowering,” says Damon Smith, assistant professor of plant pathology at the University of Wisconsin-Madison. “The disease is more problematic in soybeans in high-yield environments where high plant populations, narrow row spacing, and an early-closing canopy are commonly used.”
In the temperate north central soybean production areas of the United States, white mold can be a significant yield limiting disease. Yield can be reduced two-to-five bushels per acre for every 10 percent increment increase in white mold incidence in soybeans at the R7 growth stage. These impacts on yield are significant and make white mold one of the most important diseases of soybean in the north central United States.
White mold can survive for many years in soils; therefore it is difficult to use crop rotation to control it. In soybeans, infection occurs via flowers during bloom. Incidence of white mold can be sporadic from one year to the next, and one field to another, because of specific environmental requirements necessary for infection. White mold incidence is often greater in fields with high yield potential resulting in a dense canopy and in situations where plants are in narrow rows and at high population. In these instances, canopy humidity and wetness can be high thereby promoting increased incidence of white mold.
“Management of white mold can include reduced tillage, crop rotation, canopy management, irrigation management, weed control, and chemical control,” says Smith. “Chemical control of white mold is variable.”
There are fungicides available for in-season management of white mold, however not all commonly used fungicides are labeled for use against white mold in soybean. For information on which fungicides are labeled for disease control and recommendations on fungicide efficacy, visit fyi.uwex.edu/fieldcroppathology/files/2013/07/2014-Soybean-Fungicide-efficacy-table.pdf
Fungicide recommendations are developed by the NCERA-137 national soybean disease committee, and recommendations are based on replicated research data collected from university trials.
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