Late blight update – July 30

Tomato late blight has now been confirmed in Wellington County. Previous late blight confirmations this season have been in tomatoes in Chatham-Kent, Essex, and Elgin Counties and on potatoes in the Orangeville area.

Late blight reports are coming in from more states in the Great Lakes region, as well, including Michigan, New York, Pennsylvania, and Indiana. All US samples in the Great Lakes region reported so far have been US-23. In Ontario, US-23 has been found in the Orangeville area and US-22 in Essex County. Identifications of late blight genotypes for Ontario are provided by L. Kawchuk, AAFC Lethbridge, Alberta, Canada.

See the late blight post from June 24 for fungicide recommendations for tomatoes in Ontario. Information for potato growers can be found in the July 13 post.

Please contact me if you think you are finding late blight. If possible, samples can be taken to submit for genotyping* and research to help address this evolving disease issue. I can be reached at It’s helpful if you include photos of affected leaves (upper and lower surfaces), as well as stems and fruit if they are showing symptoms. See the tomato late blight photo gallery to review the symptoms.

Previous 2015 late blight posts: July 24, July 21, July 14, July 13, June 24

* Genotyping for Ontario samples is being conducted by L. Kawchuk, AAFC Lethbridge, AB Canada.

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