We are getting questions about applying chlorothalonil to end our leaf spot spray programs and how much risk that creates for flaring Sclerotinia blight. One or two sprays during the season does not create a substantial risk for inducing more Sclerotinia blight above what is already present. We do caution that 3 or more sprays of chlorothalonil can set up a situation where Sclerotinia blight could increase relative to fungicide programs with less or no chlorothalonil.

At last year’s “Late-Season Disease and Harvest Tour” in late September at Lewiston-Woodville, we had a lot of Sclerotinia blight. We clearly saw more of this disease with the more intensive chlorothalonil spray programs. Dr. Langston at VT, and Dr. Lux and I, were in general agreement that one or two sprays of chlorothalonil is not catastrophic when it comes to Sclerotinia blight. I recall Dr. Shew making a similar statement.

This slide demonstrates this point. For more details, take a look at Peanut Notes No. 149 2024.