A group of Midwestern Extension crop disease specialists are warning 2014 could be a bad year for white mold (also called Sclerotinia stem rot) in soybeans. The disease is not common every year, but farmers who have battled the disease will want to assess the risk of white mold development as soybeans approach flowering (growth stage R1 — plants with at least one open flower at any node).
White mold development is favored by cool, cloudy, wet, humid weather at flowering. The disease is more of a problem where high plant populations, narrow row spacing and an early-closing canopy are used. No single management strategy is 100 percent effective at eliminating white mold, and in-season options for at-risk fields are limited.
Fungicides are available for in-season management of white mold; however, not all commonly used fungicides are labeled for use against white mold in soybeans.
Several products have been rated as “good” for white mold management, including Approach, Endura and Proline. Keep in mind that fungicides are most effective and economical when there is good distribution of the product through the canopy and when the fungicide is applied in a timely manner. Fungicides are effective at reducing the impact of white mold when applied at or close to growth stage R1.
Research at Wisconsin showed fungicides applied up to growth stage R3 (early pod — pods are 3/16-inch long at one of the four uppermost nodes) may be effective, but later applications will likely not reduce disease.
Once symptoms of white mold are found, fungicides will have no effect on reducing the disease. This is because fungicides are preventatives – not cures for 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, the 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. 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.
Several resources are available to help farmers and consultants manage white mold. A publication, titled “Management of White Mold in Soybean” is available at www.soybeanresearchinfo.com/pdf_docs/WhiteMold_NCSRP.pdf. If you do not have access to the Internet, please contact the Extension office so we can get you a copy of this publication.
Jeff Burbrink is an Extension educator in agriculture and natural resources. Write to him at 17746 E. C.R. 34, Goshen, IN 46528; call 533-0554; or fax 533-0254.