Late blight control | Potato industry officials believe disease can be managed if gardeners grow resistant tomato varieties
EDMONTON — Controlling late blight in Alberta potato fields may lie in the hands of backyard gardeners.
Most commercial potato growers know about the dangers of the devastating disease.
But many backyard gardeners are unaware that their infected tomatoes and potatoes can spread disease for 100 kilometres on the wind and wipe out entire fields of commercial potatoes.
“A lot of inoculum originates from backyard gardens,” said Agriculture Canada pathologist Larry Kawchuk.
He said encouraging home gardeners to grow late blight resistant varieties of tomatoes will help commercial potato growers eliminate the disease.
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“In Alberta, we have a real opportunity to eradicate this pathogen from the province,” Kawchuk said during a late blight meeting hosted by Potato Growers of Alberta.
Late blight, which caused the Irish potato famine 150 years ago, has become a serious threat to Alberta potato growers, backyard gardeners and market gardens.
It was brought to the province in 2011 through infected tomato plants brought into box store garden centres from the United States.
“I am very confident (backyard gardens) are playing a role in this particular strain of late blight,” said Kawchuk, referring to US 23, a dominant strain of late blight in Canada and the United States.
Jeremy Carter, technical director for Potato Growers of Alberta, said they are hoping to work with garden centres and greenhouses to raise awareness of the disease and help reduce the spread of infection in potato fields.
He said late blight wiped out most of the tomatoes and potatoes in the small town of Barnwell last July, where he lives.
“The gardens just fell over by the end of July.”
The first sign of late blight is usually black lesions on the leaves and stems of tomato and potato plants. Eggplant, peppers, petunias and weeds such as nightshade are other sources of late blight.
Gardeners who don’t know what is wrong with their plants often leave them in the garden, hoping for a crop. The infected plants go into the compost pile at the end of the season, where the disease is allowed to continue as a source of infection.
Ron Pidskalny said his tomato plants “melted” in his Edmonton garden last summer.
“This is one of the worst diseases in the world, in the history of plants,” said Pidskalny, who wants pesticide labels changed to help protect plants from the disease.
Kawchuk said “melting” is an accurate description of what happens to the plants under ideal disease conditions with high moisture.
“You will look at the field in the evening and there will be a lot of the necrotic lesions, and you will say, ‘oh, I have a problem.’ You will go out the next day and there are sticks. There are no leaves left on the stem, just a black slime.”
The disease can melt a potato field in 24 hours in places like Prince Edward Island and parts of British Columbia where moisture levels are high.
“If it rained, rained, rained like it did in Ireland, we would be melting potato fields,” he said.
“We don’t have any cases like that. Alberta guys don’t know how lucky they are.”
Alberta’s generally drier weather conditions, along with fungicides, help slow and control the disease. Late blight requires a virulent pathogen, a susceptible host and a conducive environment to flourish.
The organism can also overwinter in seed potatoes, cull piles or volunteer plants growing in other crops.
Kawchuk plans to install air monitoring equipment this year in key locations around the province to detect late blight pathogens in the air. Once it is detected, he will use a combination of wind pattern analysis and hand-held detection equipment to locate the exact source of the spores.
He encourages gardeners to grow late blight resistant tomato varieties such as Defiant, Mountain Magic, Mountain Merit and Iron Lady.
There are no known resistant late blight genes in potatoes, although some older heirloom varieties, such as Stirling, have better resistance to late blight.
