Potatoes in Canada

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More late blight found in Wisconsin, early blight attacks Ontario

August 21, 2020  By  Stephanie Gordon


Symptoms of late blight. Photo courtesy of Eugenia Banks.

A second outbreak of late blight was found in a tomato field in Pierce County, Wisconsin, according to the latest update from Eugenia Banks, potato specialist with the Ontario Potato Board.

The first outbreak was found on a potato field in Adams County, three hours west of Pierce County.

According to the University of Wisconsin-Madison, the infection is about one week old based on symptoms.

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Copper-containing fungicides are the most effective control available for organic growers. Banks says in Ontario, Parasol and Kocide are two registered copper fungicides that reduce late blight and blackleg incidence. Banks adds that Cueva is also registered but not as strong as Parasol or Kocide.

In Ontario, as of August 21, late blight spores have not been detected in spore traps across the province. Although there have been wet periods favourable to disease development, Banks continues, late blight has not been found because the inoculum is not present so far.

Early blight concerns

However, Banks adds that early blight is a concern for Ontario growers. On August 20, during a field visit Banks observed a lot of early blight in an area of a field that had not been irrigated.

“The infection was so severe that many stems had early blight lesions which can be confused with late blight lesions,” Banks says.

In a severe infection, early blight lesions can be confused with late blight lesions. Photos courtesy of Eugenia Banks.

“The field will be top killed tomorrow, [and] I will keep an eye on infected tubers,” Banks adds.

Scouting resources: You can download Eugenia Banks’ Scouting Guide and calendars to gain an understanding of general best practices for scouting potato fields and an in-depth look on specific issues, including insect threshold numbers.

 


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