Late blight reports in potatoes in northern United States

Two recent reports of late blight in potatoes were confirmed in Wisconsin. All areas in Michigan are now in the yellow zone for Disease Risk Severity.

No late blight has been reported yet in Michigan, although there are now two confirmed reports from Wisconsin by Amanda Gevens, University of Wisconsin. Late blight was confirmed in Adams County, Wisconsin, on Friday, June 28, 2013, on potatoes (US-23) and a second confirmed report on July 1 from Juneau County, Wisconsin, on potatoes. There were also reports of late blight on tomatoes in New Jersey and Kentucky over the last two weeks.

As of Monday, July 1, there remains variability in the Disease Risk Severity accumulations for late blight across the state, but all areas are now in the “yellow zone.” All crops should be at least on a seven-day schedule of protectant fungicide. Disease Risk Severity Values are updated daily and stations across Michigan can be compared on the Late Blight Risk Monitoring website. The accumulations were initiated on May 1. You can accumulate late blight risk based on emergence date at all Enviro-weather sites across the state.

Current recommendations for fungicides for late blight, early blight and brown leaf spot can be found on the Michigan State University Extension E312 bulletin “Insect, Disease and Nematode Control for Commercial Vegetables” on page 114. There are also links for recommended fungicides and application rates and intervals based on late blight risk. Clicking on the product link takes you directly to the TIRMS website and the product label.

Dr. Kirk's work is funded in part by MSU's AgBioResearch.

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