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Wisconsin soybean growers found purple seed stain, caused by Cercospora fungi, across the north-central region during the 2026 harvest. Warm temperatures, frequent rain and high humidity during seed fill favored infection.
The discoloration mainly affects grain quality rather than yield, but elevators are applying inconsistent discounts or rejecting affected beans.
Grade discounts on stained beans lower the effective price growers receive and can widen local basis for affected lots. The impact is regional and mostly on quality premiums rather than total supply, so it is a minor bearish factor for soybean prices.
farmprogress.comMindy WardNov 4, 2026After 50 past bearish disease events, Soybeans moved a median +0.5% over 5 sessions (58% higher; middle half -1.7% to +2.4%), and +0.0% over 20.
Moves of each commodity's benchmark from the last close before the event. Historical reads pool past events of the same kind; they describe what happened, not what will. Not investment advice.
