White mold has become an annual threat to soybeans in northern states as farmers have adopted yield-boosting management techniques that accelerate canopy development. Looking to maximize yields with early planting, growers have unintentionally increased the risk of white mold as the establishment of early, dense canopies favors mold development. As we approach late June and early July, the typical timing of canopy closure in northern fields, farmers in risk areas should be scouting to look for signs of white mold.
Besides geographic location and early canopy closure, additional key risk factors to evaluate include seasonal climate conditions, field disease history and variety susceptibility. Farmers with previously infected fields should be finalizing treatment plans, as while mold is nearly impossible to eradicate. In cases of high disease risk or confirmed presence, a foliar application of a chemical product or a soil application of a biological product may help reduce disease severity and protect soybean yield.
“If you have a history of white mold in your fields, typically the two-pass system will be most effective,” said Mike Gronski, Pioneer Field Agronomist. “For that first application, you’re looking at the R1 growth stage, meaning the second pass will come at the R3 stage. For much of the upper Corn Belt, the R1 stage coincides with the first two weeks of July when the vegetative growth stage is typically about V7 to V10.”
To be effective, synthetic fungicides and lactofen must be applied before white mold is established on senescing flowers. Applications made just prior to pathogen invasion have helped reduce disease severity in some studies. Because soybeans normally flower for 30 days or more and fungicides for white mold control have maximum residual activity of about two weeks, a second application may become necessary if conditions for white mold development persist into mid-summer.