Corn Tar Spot Update

Damon Smith, Extension Field Crops Pathologist, Department of Plant Pathology, University of Wisconsin-Madison, Roger Schmidt, Nutrient and Pest Management Program, University of Wisconsin-Madison

Grant and Columbia counties level first-detects of tar spot in Wisconsin are now on the national tar spot map. This week we are seeing more counties being added in Iowa, Illinois, Indiana, and Michigan.

Damon Smith has posted a new item, ‘Wisconsin Corn Tar Spot Update – July 23, 2020‘. Here is a short summary.

Tassels and silks are out in the southern portion of the state. We are now in the window of opportunity for a fungicide application if you feel the risk for disease, including tar spot, is warranted. While tar spot is slow to develop, we have seen gray leaf spot (GLS) developing in the lower canopy and moving up. Do some scouting and check weather reports.

Using a screenshot from the Tarspotter beta test smartphone app, you can see (figure 2) the present risk has declined overall for most of the state with exceptions for south-central and far Northwest Wisconsin.

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