AgronomyTargeting Late Blight in Canada

Targeting Late Blight in Canada


[deck]The National Late Blight Research Program is taking aim at late blight strains across Canada, helping producers manage this yield-robbing pathogen.[/deck]

This year’s weather conditions in potato-growing regions of Canada are very conducive to an onslaught of late blight, which is caused by the oomycete Phytophthora infestans, and is considered one of the most devastating diseases of potato- and tomato-growing regions in North America.

“If the weather continues to be warm and humid during the day and cool at night, chances are the disease will spread—it won’t stop. Once you have it in a province it continues spreading, even if farmers use all the management tools that they have,” says Khalil Al-Mughrabi, a pathologist with the Department of Agriculture, Aquaculture and Fisheries in New Brunswick. “With late blight, a field can look perfectly fine one day and overnight turns into a wilted mess.”

So far this season, late blight has been reported in British Columbia, Ontario and New Brunswick. If not properly addressed, in damp, rainy conditions late blight can infect plant foliage, and can cause tuber rot when the pathogen is washed down into the soil profile. “Late blight normally does not show in fields until approximately the second week of July, but we alerted growers in June to scout their fields daily and to narrow their spraying window if necessary,” says Al-Mughrabi. If the weather changes and there is less moisture, it could slow the disease down, he says. But for now, Al-Mughrabi is advising growers to spray every five days, and to keep scouting and roguing fields daily because if growers miss even one day or that window to spray, they may be out of luck, he says.

Al-Mughrabi helped form, and is also chair of, the National Potato Late Blight Working Group, an initiative aimed at gaining a greater understanding of the disease and reducing its impact on potato production in Canada. “The purpose of the working group is to determine what strains of late blight exist in the country, and with the cooperation of researchers across Canada we are coordinating this information to ensure all growers will have access to the same information,” says Al-Mughrabi. Strain identification is currently being carried out by researchers in Alberta, Prince Edward Island, Ontario and Manitoba. Through the program, Canadian scientists are working together to help producers determine effective management strategies for late blight in their fields.

It’s not an easy task for the producer or the researcher. For example, not all fungicides are effective; efficacy is dependent upon the type of late blight strain present in a particular area—in fact, some strains have become resistant to certain chemical applications. Determining the specific strain of late blight is also a tedious and time-consuming project to be 100 per cent accurate as new strains have entered Canada over the past decade.

National Research Shows Results

The National Late Blight Research Program in 2010 accepted late blight samples from all provinces, which were then processed so pure cultures of the pathogen could be obtained. Once the cultures were purified, subcultures were processed to identify the strains. The results revealed that the US8 strain is still predominant in Eastern Canada and US23 was the dominant genotype in Western Canada. These results indicate that the movement of new P. infestans genotypes have contributed to the increased incidence of late blight in the country.

National Program Determined to Grow

Al-Mughrabi added that, for the 2011 season, not only are researchers accepting potato samples, but they will also accept tomato and weed samples because they can be infected by late blight as well. “With this national approach we can help determine the proper form of protection that will be most effective in terms of control, and in the timing of applications.”

The National Late Blight Research Program has received funding for a three-pronged approach to its research:

  • Strain sample screening and identification across Canada.
  • Assessing the efficacy of new fungicides and fungicide combinations for late blight control.
  • Determining the function of phosphorous acid-related compounds on the suppression of late blight in potatoes.

Al-Mughrabi explains the first step is to determine the specific strain in a particular growing region, which can offer tremendous insight when choosing the fungicide products to apply for optimum control. “A product that works in one area may not necessarily have the same amount of control in another. With our research, we can tell if a strain has changed, spread or if other strains have infected the area.”

Producers may have to consider multiple modes of action for effective control of late blight—that is where continued research, such as the work being conducted by the National Late Blight Working Group, can help producers across Canada make the right application decisions at the right time—now and in the future.


Top Five Tips for Managing Late Blight

  • Plant disease-free seed and inspect tubers before planting.
  • Dispose of all cull piles—do not forget about them. Covering, composting or burial are effective.
  • Use weather-based forecasting models to initiate and maintain spray schedules. Protecting early crop development is essential to season-long success.
  • Scout regularly (daily) for symptoms of late blight. If symptoms are noted, take immediate action.  Do not delay.
  • Thoroughly kill all foliage two to three weeks prior to harvest.


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