Managing white mold in soybeans in Great Lakes region

Farmers in the Great Lakes region may be concerned about white mold in soybeans in 2014 and how to properly manage this disease.

Posted on July 1, 2014 by Martin Chilvers, Michigan State University Extension, Department of Plant, Soil and Microbial Sciences; Kiersten Wise, Purdue University; Damon Smith, University of Wisconsin; Carl Bradley, University of Illinois; and Daren Mueller, Iowa State University

White mold, also called Sclerotinia stem rot, is a disease caused by the fungus Sclerotinia sclerotiorum. It is not common every year in in the Great Lakes 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, or growth stage R1 – plants have at least one open flower at any node.

White mold development is favored by cool, cloudy, wet and humid weather at flowering. 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. No single management strategy is 100 percent effective at eliminating white mold, and in-season options for at-risk fields are limited.  

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 soybeans. For information on which fungicides are labeled for disease control and recommendations on fungicide efficacy, please see “Fungicide Efficacy for Control of Soybean Foliar Disease” by Purdue Extension. Fungicide recommendations are developed by the NCERA-137 National Soybean Disease Committee, and recommendations are based on replicated research data collected from university trials.

Several products have been rated as “good” for white mold management, including Aproach, Endura and Proline. If using fungicides for white mold management, keep in mind that efficacy may be based on the ability of the fungicide to penetrate into the canopy, and the timing of the fungicide application. Fungicides will be most effective at reducing the impact of white mold when applied at or close to growth stage R1. Wisconsin research data indicates that fungicides applied up to growth stage R3 or early pod – pods are 0.1875 inches long at one of the four uppermost nodes – may be effective, but later applications will likely not be effective at reducing disease. Once symptoms of white mold are evident, fungicides will have no effect on reducing the disease. Fungicide applications for white mold management may be most useful on fields where varieties rated as susceptible to white mold are planted in a field with a history of the disease.

If a soybean field is diagnosed with high levels of white mold, this field should be harvested last. This will help reduce the movement of the survival structures of the white mold fungus by harvesting equipment to fields that are not infested. Also, Michigan State University Extension reminds growers to be sure to clean all harvesting equipment thoroughly at the end of the season to avoid inadvertent infestation of fields. Rotations of two to three years between soybean crops can help reduce the level of the fungus causing white mold in fields. Using corn or small grains crops such as wheat, barley or oats in rotation with soybean is recommended.

There are several resources available to help farmers and agribusiness personnel manage white mold. Extension plant pathologists across the North Central Region have developed a publication, “Management of White Mold in Soybean,” in collaboration with the North Central Soybean Research Program to describe the disease and optimal management strategies.

This group also developed a management of white mold in soybeans podcast series to facilitate learning about white mold on-the-go.

This article was published by Michigan State University Extension. For more information, visit http://www.cnchemicals.com/. To contact an expert in your area, visit http://www.cnchemicals.com/, or call 888-MSUE4MI (888-678-3464).