Late blight and downy mildew


Sally Miller, Plant Pathology, OSU Extension and OARDC
(330) 263-3678

WOOSTER, Ohio — Late blight and downy mildew — diseases that attack tomatoes, potatoes and vine crops such as cucumbers and squash — have been confirmed in Ohio, threatening vegetable farms and backyard gardens across the state.

“What’s different this year is that both diseases have appeared in Ohio earlier than we have seen before,” said Sally Miller, a vegetable pathologist with Ohio State University Extension and the Ohio Agricultural Research and Development Center (OARDC).

If left unmanaged, both downy mildew and late blight — which are transmitted via spores — can result in complete destruction of crops. Recent rainy and stormy weather most likely created favorable conditions for these diseases to show up in Ohio, since their spores are carried by winds and they thrive in wet environments.

Downy mildew was found June 23 on cucumbers in Wayne and Holmes counties (northeast Ohio), following reports of the disease in Ontario, Canada, the previous week.

Late blight was confirmed around the same time on tomatoes on an organic farm in Harrison County (east-central Ohio). This follows confirmations of late blight in potatoes, tomatoes or both in Michigan, Pennsylvania, Kentucky and New York.

“People need to be on the alert for these diseases and prepare for their possible arrival on farms or gardens,” Miller said.

Detailed management recommendations for both diseases are available at

Ohio State fact sheets with photos of symptoms and additional disease information can be found at (downy mildew) and (late blight).

A video about late blight is available at


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