Updates provided by Amanda J. Gevens, Chair, Associate Professor & Extension Specialist, UW-Madison, Dept. of Plant Pathology and Yi Wang, Assistant Professor & Extension Potato and Vegetable Production Specialist, UW-Madison, Dept. of Horticulture
Late blight on tomato has been confirmed in Pierce County Wisconsin (central western, bordering MN) today, August 20, 2020. The symptoms suggest an infection that is about one week old. Sporulation was evident in on symptomatic foliage. This is the second WI Co. with a confirmed late blight case this season. The first was 10 days ago on potato in Adams Co. It is critical to apply preventative fungicides to susceptible tomato and potato crops in the region surrounding Pierce Co.
Below is a link to the 2020 listing of fungicides for use in managing late blight in tomato in WI. For organic producers, copper-containing fungicides provide most effective management for preventative disease control.