Downy Mildew detected in Michigan

First 2024 cucurbit downy mildew spores identified in air samples in Saginaw County

four views of infection on leaf

Photos 1, 2. Early symptoms of downy mildew on cucumber with the yellow-brown tissue bordered by the leaf veins. Photos 3, 4. The dark spores of the cucumber downy mildew pathogen can be seen on the underside of the leaf. These spores move via air currents and infect unprotected plants. Photos by David Perla, MSU.

Cucurbit downy mildew spores have been verified in air samples from Saginaw County in early June by the Hausbeck Vegetable Pathology Lab at MSU. Identification was made using a spore trap followed by qPCR molecular analysis and verification with microscopy. The cucurbit downy mildew pathogen does not overwinter in northern growing regions; the spores move from overwintering sites such as production greenhouses or the southern U.S. production regions via air currents. Growers, scouts, consultants and Extension educators are urged to monitor greenhouse cucumber production and early cucumber and melon field plantings.

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