Like an unwanted guest, white mold can stop a soybean crop in its tracks. And once it gets a hold, it’s a problem that might linger for seasons to come. Soybean growers, especially in the upper Midwest where white mold is prevalent, should monitor fields often for early impact.
Signs and Causes of White Mold
White mold is caused by Sclerotinia sclerotiorum, which thrives in cool, wet conditions (less than 85 °F) during soybean early reproductive stages when flower petals are abundant. Planting methods intended for high yields, such as narrow row spacing and dense early-closing canopy, can contribute to the spread of the infestation. In some cases, soybeans that experience hail injury have a higher risk for white mold.
Typically, white mold begins to appear in July and August, where single plants in a canopy wilt and die rapidly. Leaves turn brown but remain on the stem, and soybeans produce small or no pods. Over time, the infected stems will become light in color or “bleached” and stringy. Lesions can also start on stems, pods and sometimes leaves.
Infestations are often patchy within a field as the disease spreads. Other signs of infection include white, moldy growth inside or on the outer surface of stems and pods and sclerotia on infected plant tissues.
Take an Integrated Approach to Controlling White Mold
Early infestations of white mold will cause the most damage to soybean yields. For optimal results, apply fungicide at R1 or early flowering. When spraying, ensure the application achieves coverage deep into the soybean canopy where infestations start. Flat fan spray nozzles that produce fine to medium droplets work best. Follow manufacturer’s recommendations for spray volume and pay attention to environmental conditions such as wind speed, which influences spray coverage.
UPL recommends using ZOLERA® FX in preventative applications at R1. In UPL trials, soybeans treated with 5 fl oz/A of ZOLERA FX showed a 7.6-bushel yield increase when white mold infestations were present, compared to untreated soybeans.
The Lasting Effect of White Mold
Once white mold shows up, it can remain in the soil for several years. The sclerotia can also be spread through the combine at harvest. Growers need to scout diligently and record locations of disease incidence so they can properly manage disease populations in subsequent seasons. This might include selecting seed varieties that offer the best disease resistance available for the growing region, reducing plant populations, increasing row width, altering irrigation timing during flowering and rotating tillage practices.
Learn more about controlling disease in corn and soybeans:
