Recent Rainfall Pattern in Ontario Shows High Risk of Late Blight Incidence in Tomatoes and Potatoes

Dr. Rishi Burlakoti, Weather INnovations Consulting LP, Chatham ON

August 12, 2014

The 2014 weather pattern in Ontario, continuous and frequent rainfall occurred during the entire season in Ontario along with high humidity and cool to warm temperature, are very favourable for late blight development in potatoes and tomatoes. In the past seven days, late blight has been reported from 7 counties in Michigan (Fig. 1). The disease has already been reported in several counties in New York nearby bordering areas of Ontario.

Fig.1. Late blight incidence reports in neigbouring states of Ontario ((

Late blight has also been confirmed in Simcoe County in Ontario. Late blight has been also reported in Atlantic Canada, PEI and New Brunswick. Currently, high amount of rainfall has been occurring in Ontario (Fig. 2) and with more rain in the forecast this week. Our late blight prediction map also showing high risk as indicated by high disease severity values (DSVs) in Ontario (Fig. 3).

Fig. 2 Rainfall pattern in Ontario
Fig. 3 Late blight risk in Ontario

Since late blight has been already reported in Ontario as well as bordering states of USA and weather conditions are very favourable, it is suggested to take appropriate action to protect both tomato and potato plants from this devastating disease. To get the late blight risk map and management guideline, visit for Ontario Potato Growers and for Manitoba Potato Growers.

To get site-specific late blight advisory for tomatoes, login and register your field at

If you have any questions, please feel free to contact Dr. Rishi Burlakoti, Plant Pathologist at Weather Innovations (

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