The rule of thumb
The strongest, most consistent fungicide response in both crops comes from a reproductive-stage application — around tasseling/silking (VT–R1) in corn and beginning bloom to beginning pod (R1–R3) in soybeans — when disease pressure is present. Spraying with no disease, or too early/late, usually doesn't pay.
Windows and responses summarize university extension guidance (e.g., Ohio State, Purdue, Iowa State, Univ. of Missouri, Penn State). Response is real but variable — scout first. See the ROI calculator to price a pass.
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