Late blight found in potato in Michigan’s St. Joseph County

Late blight was found in Michigan in three potato fields on July 25, 2016. Conditions remain conducive for late blight in irrigated potato crops.

Photo 1. Sporulating late blight lesion with white, velvety mycelial growth.

Photo 1. Sporulating late blight lesion with white, velvety mycelial growth.

Late blight was found in three more potato fields in Michigan’s St. Joseph County on Monday, July 25, 2016. Initial genotyping confirmed isolates as US-23 by GPI isomerase testing. Mating type and Ridomil sensitivity are underway. The source of the inoculum is volunteer potato plants in a sweet corn field (Photo 3).

Recommendations for late blight treatment remain the same as in previous reports posted at Michigan State University Extension, and include treating with one of the translaminar fungicides listed at the Michigan Late Blight Risk Monitoring website.

Conditions remain conducive for late blight in irrigated potato crops. Forecasts and disease severity value (DSV) accumulations can be checked daily at Michigan Late Blight Risk Monitoring website.

Late blight lesions.

Photo 2. Expanding brown-to-black lesions in the lower plant canopy.

Volunteer potato plants.

Photo 3. Volunteer potato plants growing among sweet corn.

Dr. Rosenzweig’s work is funded in part by MSU’s AgBioResearch.

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