Soybean Scouting Tips for Sclerotinia Stem Rot

Weed seeds aren’t the only yield-robbers that can lurk below the soil surface and come back years later to haunt your fields. Sclerotia, which encapsulate and protect the White Mold fungus, can lay dormant for years and then grow when the conditions are suitable. Suitable conditions include cool, damp soils.

Cool and damp certainly is one way to explain this growing season, but weather isn’t the only factor affecting the likelihood of White Mold. Be sure to keep a close watch on fields with a history White Mold as it may be more severe this year with the current weather trend.

White Mold usually has a larger effect on a brand with a denser, faster-closing canopy.  Symptomsappear as single soybean plants within a generally healthy canopy thatwilt and die rapidly – usually in July and August – when plants are in the early reproductive stages. The fluffy white mycelium of the fungus then forms on the stem and/or pods, giving it the name White Mold.

Applying Foliar Fungicide

Foliar fungicides may be applied when you see White Mold starting to attack. Wisconsin research data indicates that fungicides applied up to growth stage R3 (early pod) may have some effect on White Mold severity, but later applications will likely not be as effective. Once symptoms of white mold are evident, fungicides will have no effect on reducing the disease.

Only fungal pathogens can be controlled with a fungicide, so it’s important to first scout and determine the type of disease or diseases present in a field. Scouting should be done prior to the R3 growth stage of the soybean plants, especially if weather has been rainy and/or humid as these conditions favor foliar diseases.

Please note that you can’t do anything for the plants already infected with the White Mold fungus. Keeping the fungus from spreading is really the most effective defense against White Mold.