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Soybean White Mold Thoughts

By Joel DeJong

There have been reports of flowers in the earliest planted soybeans, and I observed them in NW Iowa late last week. That means these beans are entering the R-1 stage of development. If you have a history of white mold in your soybeans and are considering treatment for reducing the impact of this plant disease, check out the publication titled “RESEARCH UPDATE: Pesticide Impact on White Mold (Sclerotinia Stem Rot) and Soybean Yield.” The Crop Protection Network, a multi-state and provincial consortium of university extension specialists, published this Midwestern research summary last fall. ISU Extension Plant Pathologist Daren Mueller is one of the authors. It does not have the newest products on the market, but does summarize over 2000 plot level data points. The “Sporebuster” app developed in Wisconsin utilizes this data.

Another Wisconsin-developed app for white mold is called “Sporecaster.” This app uses your location, stage of growth, row spacing and local weather data to try to predict the risk of white mold appearing in your field. Last year, this model used to predict the risk seemed to work pretty well in Wisconsin and other areas, but not well at all in western Iowa. Data from several western Iowa fields that had white mold injury was shared with those researchers after the season. Some parts of the collected weather data have been tweaked, but the wind speeds we see in western Iowa seem to create shortfalls to the predictability of this model. Here is a suggestion from the lead developer, Damon Smith, UW Extension Field Crop Pathologist: If you use the “Sporecaster” app in 2020 and are in western Iowa, consider dropping the threshold level in the app down to 25%, instead of the standard 30%. In addition, if the level for your field(s) is creeping up above 20% around R-3/R-4, you might want to pull the trigger on a fungicide. If you use it, and do this, I would like to hear your results!

Source : iastate.edu