Potatoes in Canada

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Late blight spores detected in Dufferin, Simcoe and Norfolk counties


July 24, 2019
By Stephanie Gordon


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Spores of late blight were detected in Dufferin, Simcoe, and Norfolk counties in Ontario, according to potato specialist Eugenia Banks.

The filters analyzed were from the period of July 18 to 22. Two days ago, high numbers of late blight spores were found in the filters of two spore traps placed near Delhi, Ont., and now reports have spread to include Dufferin and Simcoe counties.

This news comes after late blight was found on potatoes in Wisconsin earlier last week. At the time of the Wisconsin announcement, spore traps in Ontario had detected only low levels of late blight DNA. Spore traps for detecting late blight are placed in Shelburne, Alliston, and Simcoe-Delhi areas.

In 2018, late blight was not a serious issue in Ontario.

So far in 2019, the only report of late blight has been from St. Johns County in Florida on April 22. The pathogen strain was US-23, the newest and most common strain across 90 per cent of Canada and the United States.

However, there have been reports of outbreaks of Phytophthora nicotianae, a disease “cousin” of late blight, in eastern U.S. in places such as New York and Pennsylvania. Infected plants show symptoms very similar to late blight and at first glance, it can be difficult to distinguish between the two diseases. However, P.nicotianae does not spread as easily and can be controlled with fungicides that are also registered for late blight.

Regardless of the regional risk, late blight requires vigilance from growers. Eugenia Banks composed a list of early summer, mid-summer, and late summer practices that growers can do to protect against late blight in their fields. The summer checklist for late blight can be found online and includes achieving good spray coverage, scouting risky areas, and managing irrigation.