Province keeps an eye out for late blight strains

Monday, June 20, 2011

by SUSAN MANN

Ontario’s agriculture ministry is participating in a survey to find out what new strains of late blight there are in Canada.

Agriculture Canada and the University of Manitoba are organizing and coordinating the survey.

Michael Celetti, Ontario agriculture ministry plant pathologist for horticultural crops, says late blight is a serious pathogen of tomatoes and potatoes. It caused significant problems in 2009 in the province and some difficulties last year, particularly in organic tomatoes. It was to the point “where guys were losing their crop,” he says.

Late blight is a fungus-like pathogen that can wipe out an entire crop. Celetti says he calls it a water mold. It causes a lesion on the leaves of potato or tomato plants. The lesion will expand fairly quickly and usually has a light green or yellow halo around it. As it expands, it takes the whole leaf. On the stems, it will make a chocolate brown lesion. On the underside of the leaf with the lesion, there will be a white, downy growth.

Under ideal conditions, which are cool and wet, late blight will wipe out a crop in seven to eight days.

Late blight can be splashed by water, blown around by wind or transported from infected areas by storms. It can also overwinter in potatoes from last year that were left in the field or be introduced on tomato seedlings for the home garden market. But Celetti says they aren’t aware of late blight being introduced in Ontario via tomato seedlings for the home garden market.

Celetti says they haven’t seen late blight in Ontario yet this year.

Some strains in previous years have been more resistant to certain fungicides. “That’s why we need to know,” what strains there are in Canada, he says, also noting some strains are more sensitive to a particular fungicide.

“That’s why you look at it and say there has been some mating going on here and that’s why you’re getting all those variants,” Celetti explains. 

Last year’s late blight survey was very limited but this year researchers want to do a more extensive survey.

Growers who spot late blight in their crop can contact Celetti at (519) 824-4120, extension 58910, or Janice LeBoeuf at (519) 674-1699. They will arrange to collect a sample. BF