White mold is caused by the fungus, Sclerotinia sclerotiorum and frequently results in significant damage to soybeans in the upper Midwest. The white mold fungus has a notoriously wide host range, which can result in large reservoirs of inoculum in and near soybean fields. The primary inoculum (ascospores) are born on cup-shaped structures called apothecia. These apothecia form when the weather conditions are cool and wet, the soybean canopy is dense, and flowers are present. The presence of a susceptible host (e.g., flowering soybeans), active pathogen (e.g., sporulating), and conducive weather has to happen at the same time, in the field to result in infection. This can be difficult for farmers to anticipate for predicting if they might have white mold, or if they want to implement an in-season management strategy (Willbur et al., 2019a). To take some of the guess-work out of managing white mold, soybean farmers have been interested in learning more about resistant soybean cultivars, what fungicides might be available for controlling white mold, whether it is economical to spray fungicide under certain conditions, how to anticipate favorable weather to better time fungicide applications, and cultural practices such as row-spacing and planting population that lead to less white mold, but don’t negatively affect yield. The Wisconsin Field Crops Pathology team in conjunction with the Wisconsin Soybean Team have been conducting research to address these questions.
Soil Science Extension
University of Wisconsin Madison