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Start Fresh This Spring, Says Vegetable Expert

After last year’s late blight apocalypse, many home gardeners have spent a dreary winter opening tin cans instead of jars of their own delicious preserved tomatoes.

Added to that disheartening experience, was the sinking feeling one gets when reaching into the potato bin and pulling out the odd stinky, mushy tuber.

There are no guarantees for tillers of the soil, but generally good gardening practices and taking a few extra precautions this spring can help to boost the odds of avoiding another outbreak of the fungal pestilence, said Tom Gonsalves, a business development specialist for vegetable crops based in Souris.


That starts with a good garden cleanup.

“For potatoes or tomatoes, after a year when there was a fair bit of late blight, all the trash that’s left over should be removed from the area,” said Gonsalves, who has 30 years of experience with vegetable crops.

If it’s been laying on top of the ground, got totally frozen, and there’s no green material still showing signs of life, it can be raked up and thrown onto the compost pile or carted away.

But if there is any live tissue lingering, say potato tubers that may have been overlooked in last fall’s soggy harvest, that means the late blight pathogen could be lurking inside.

“As you are digging your garden this spring and you find, not just a rotten potato, but actual viable pieces, then if that’s an infected potato, that tuber could carry the disease,” he said.

Getting rid of all potentially infected living tissue is critical to preventing a future outbreak, he added, because once the weather starts to warm up, it could start churning out spore and infecting nearby plants.

Depending on how much high-risk material is left over, sealing it in garbage bags or wrapping it in a large sheet of plastic, sealing it with duct tape, and leaving it in the sun can isolate the fungus and kill it by heat.


Once that’s done, the organic gardener can cross his or her fingers and pray. With luck, the other three corners of the disease “triangle” won’t appear this growing season.

As plant pathology textbooks state, for a disease outbreak to occur there needs to be all three factors present: the pathogen, a host, and hot, humid weather.

The first element, the pathogen, is likely present in the soil. The second, the host, can be mitigated by rotating non-susceptible crop in that spot. That just leaves the third element that Prairie gardeners have no control over: the weather.

“Just because last year was a bad year for late blight does not predispose us 100 per cent to having a bad year for late blight this year,” said Gonsalves.

For those who got any tomatoes at all, at least enough for seed, can take heart that the late blight can’t survive on hard, dry seeds. But for potatoes, the best thing to do is eat them all and buy new certified, disease-free seed.

Grandma may have planted leftover spuds every year, but Gonsalves said that’s not a good idea because it can lead to a buildup of various potato diseases in the garden over time. Picking through the lot and planting only the good ones, is fraught with risk, because even though rot in stored potatoes might not be caused by late blight, it might have been caused by some other disease or secondary infection.

The Irish in the 1840s probably had no other choice, but that practice was likely an aggravating factor in the years of the great potato famine, he added.

“Start new with certified seed potatoes. Not just this year, but every year. There’s no 100 per cent guarantee no matter what you do, but that’s really the only way to have certainty that your potatoes have gone through an inspection process and were found to be free of disease.”

If blight does reappear this summer, there is still one or two last-ditch defence methods. Gonsalves said spraying copper sulphate products may work as a preventive measure when risk of infection is high, and those adverse to spraying can try aggressive culling of diseased plants to prevent further spread. Early detection is critical, however.


Norah Aagaard, who runs Aagaard Farms, a 27-member CSA and organic market garden just east of Brandon, was spared the scourge of late blight last year.

Unlike home gardeners, her 15-acre operation on sandy soil surrounded by windbreaks gives her ample space for rotating crops. She also avoids overwatering and overfertilizing, and uses lots of mulch and drip irrigation to prevent pathogens from being splashed up from the soil to the crop.

“We have pretty healthy, strong plants,” she said.

Growing some 25 varieties of potatoes, Aagaard has had good success with storing her potatoes in a 10 by 20-foot underground root cellar. She saves seed potatoes every year with the goal of developing seed stock that is optimized for her local conditions.

To prevent disease, she makes sure that her potatoes are clean and well dried before going into storage.

“A lot of small farmers and householders can’t rotate as much as we can. We have enough space that we can be well away from where we planted potatoes in other years.”

She follows potatoes, tomatoes and peppers with lettuce, chard, beans or squash in her rotation to break disease cycles.


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