Michigan potato late blight update – Oct. 2, 2019

Potato late blight has been reported in Michigan’s Clinton County, with continued confirmed reports in neighboring areas.

Potato late blight symptoms on leaf
Photo 1. Potato late blight samples from Clinton County, Michigan. Typical water-soaked lesions (left) with gray-white, fuzzy growth on the underside (right). Photos by Jaime Willbur, MSU.

Potato late blight has been confirmed in Clinton County, Michigan, in a home garden plot. Symptoms were first detected Sept. 20, 2019. Samples were submitted to the Michigan State University Potato and Sugar Beet Pathology on Oct. 1. Typical water-soaked lesions with gray, fuzzy undersides were observed (Photo 1) and Phytophthora infestans sporangia were confirmed (Photo 2). Genotype testing is in progress.

In Michigan, most commercial potato fields are either undergoing harvest or have been vine-killed to prepare for harvest. However, late-planted fields with green canopies may still be at risk for infection.

Phytophthora infestans sporangia and sporangiophores
Photo 2. Typical Phytophthora infestans sporangia and sporangiophores collected from underside of symptomatic potato leaves. Photo by Jaime Willbur, MSU.

This summer, late blight was confirmed in several neighboring areas, including 14 counties in Wisconsin, 10 counties in New York and nine counties in Pennsylvania. All tested isolates were determined to be the US-23 genotype of P. infestans. Late blight was also reported in Tennessee, North Carolina, Florida and Washington. Visit the USA Blight Outbreak Map for more details.

Please contact MSU Potato and Sugar Beet Pathology at 517-355-3863 to report potential late blight detections or visit our website for more information.

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