Tomato late blight has now been confirmed in Niagara Region, Bruce County, Wellington County, Chatham-Kent, Essex, and Elgin Counties. Credible reports have been received from Norfolk County, as well. It is widespread across the Great Lakes region at this point.

OMAFRA has been collecting samples of tomato late blight for a research project by L. Kawchuk, Agriculture and Agri-Food Canada, Lethbridge, Alberta. He is able to isolate the pathogen (Phytophthora infestans) from the samples to look at their fungicide sensitivity and determine their genotype. Most of the samples in the Great Lakes region the last couple of years have been the genotype known as US-23. It becomes a concern when there is more than one genotype in an area and when new genotypes are found (the higher the number, the more recent the genotype has been identified). New genotypes, for example, could be more aggressive and better adapted to our growing conditions.

In Ontario, we have now identified two different genotypes present in 2015 – US-22 and US-23. They have both been found in Ontario before, but this is the first confirmation of them occurring in the same area.

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 Late blight update – August 11 for tomato late blight management recommendations and Tomato late blight photo gallery, to review the symptoms.

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

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