2014 Ontario weather pattern showing high risk of early and late blight of tomatoes

Dr. Rishi Burlakoti, Weather INnovations

Foliar fungal diseases including late blight, early blight, Septoria leaf spot and anthracnose often pose threat for tomato production in Ontario and other provinces in Canada. The late blight disease is caused by lower fungi or Oomycetes (Phytophthora infestans), whereas other three diseases are caused by higher fungi (Alternaria, Septoria, and Colletotrichum), which prefers relatively warmer temperature than the late blight pathogen. However, all these pathogens can cause disease epidemics in a wide range of temperature (13 to 29°C) if high humidity as well as heavy and frequent rainfall occurs during the tomato growing season.

Weather INnovations has been providing decision support tools to manage these foliar diseases of tomatoes to Ontario vegetable growers. TOMcast™, decision support tool for timing fungicide sprays to manage early blight, Septoria leaf spot, and anthracnose of tomatoes, has been delivering for Ontario Tomato Growers since early 2000. The new web portal ( was launched in 2012 and has now expanded to several diseases and pests advisories for all Ontario Vegetable Growers. The web portal includes TOMcast™, TOMblight™ (Late blight model) as well as advisories for purple blotch of Asparagus and foliar diseases of carrot and leafy vegetables. The web portal also has advisories to scout 12 different insects/pests for several vegetable crops. Vegetable growers can sign up to the site for free and get access to site-specific crop management advisories and weather data.

Fig. 1A. 2014 Late blight risk map in Ontario

The 2014 weather pattern in Ontario is very favorable for the development and epidemics of late blight as well as early blight and Septoria leaf spot of tomatoes. Both TOMcast™ (early blight model) and TOMblight™ (late blight model) show high risk of disease development and progress across Ontario (Figs. 1 & 2).

Fig. 2. 2014 Early blight (TOMcast™) risk map in Ontario

The accumulated rainfalls since May 15th as well as the recent 7-day total rainfall are very high across Ontario (Fig. 3). The accumulated disease severity values (DSVs) of both models have already crossed the first spray threshold for early blight and late blight (Figs. 1 & 2). Similarly, 7-day total DSVs across Ontario are also high. Most of the locations in Chatham-Kent and Essex Counties have relatively higher accumulated DSVs than other locations.

Recently, late blight has been reported in New Brunswick and Prince Edward Island during the last week of June. Since the last week of June to date, the disease has been also reported in several locations of New York, Pennsylvania, North Carolina as well as a few locations in Maryland and Indiana. Since late blight has been reported in both Canada and USA and recent weather conditions are very favourable for these diseases epidemics, growers are advised to take appropriate action to protect their crops. To get site specific advisories for late blight, early blight and other foliage diseases, growers are encouraged to sign up and register their fields at If you have any questions, please feel free to contact Dr. Rishi Burlakoti, Plant Pathologist at Weather Innovations (

Fig. 3. 2014 rainfall pattern in Ontario

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