Late Blight In Manitoba Potatoes Under Control

“It was going to be devastating if we had not talked about it (late blight) earlier.”


What could have been a late blight disaster this summer was averted by early detection and quick action on the part of potato farmers, a plant pathologist with Manitoba Agriculture and Food Initiatives says.

Late blight has been found in most, but not all, of Manitoba’s potato-growing areas, but it’s under control, said Vikram Bisht.

“It was going to be devastating if we had not talked about it (disease) earlier,” Bisht said in an interview July 13.

Still, some parts of fields, and even the odd entire field, has been worked down af ter becoming infected, said MAFRI potato specialist Brian Wilson.

Bisht just happened to discover tomatoes infected with late blight at a retail outlet in Brandon in early spring. Infected tomatoes were also found in Winnipeg.


Infected seedlings found in stores were destroyed and the public, including potato farmers, were warned to be on the lookout for the infamous disease, known for its role in the Irish Potato famine between 1845 and 1852.

Manitoba potato growers normally spray fungicides weekly to protect their crops from late blight and other fungal diseases, but many stepped up treatments to every five days in light of the increased risk, Bisht said. However, some potatoes still became infected, either through new foliage that hadn’t been sprayed or parts of a field that were missed because they were too close to shelter-belts or power lines, said Gary Sloik, manager of the Keystone Potato Producers Association.

“I think it is under control pretty well,” he said. “We’ve had late blight before and stored a crop. Sometimes growers and even the processors panic. It doesn’t mean we won’t have a decent crop.”


What it does mean, however, is higher production costs due to more fungicide applications, often with more expensive products, Sloik added.


EARLY WARNING: MAFRI plant pathologist Vikram Bisht says late blight in potatoes is under control and would have been much worse if farmers hadn’t been so quick to protect their crops with repeated fungicides applications.

Farmers with crops that still have good yield potential can handle it better than those with a poor crop, he said. Growers won’t be getting higher prices, despite their extra costs, because prices were set before seeding. And they’re lower than last year.

Late blight-infected potatoes have been found in western Manitoba, Carberry, Winkler, Carman, and near Winnipeg, Wilson said. As of last week the disease hadn’t been found in the Treherne or Portage la Prairie areas, but there’s enough inoculum around that all potato growers must stay vigilant until harvest, he added.

A dry harvest will help. It’s less likely then that late blight spores from potato foliage will come in contact with potato tubers as they’re being harvested, Sloik said.

Infected potatoes can be treated post-harvest to prevent them from rotting in storage, Bisht said.

As of last week, Sloik estimated about half this year’s processing potato crop still has excellent potential. Much of it was planted in April, which is earlier than normal.

About 30 per cent of the potatoes were planted in May, which is normally when they are planted. The rest were planted later.

Sloik said an estimated five per cent of processing potatoes and 15 per cent of table potatoes drowned.


Some fields were replanted but are in poor shape, he said.

Wilson estimates Manitoba farmers planted less than 70,000 acres of potatoes this spring, including for processing, table, chipping and seed.

The source of the late blight infection in tomatoes this spring has not been determined, Bisht said, but he suspects it was local – perhaps spores sucked into a greenhouse by giant cooling fans.

Manitoba has two main tomato seedling suppliers. Although only one had late blight-infected tomatoes, both had to take back plants from retailers after the disease was discovered and destroy them. Given the cost of that, Bisht said both operators are sure to take steps to prevent their seedlings from being infected next year.

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About the author


Allan Dawson

Allan Dawson is a reporter with the Manitoba Co-operator based near Miami, Man. Covering agriculture since 1980, Dawson has spent most of his career with the Co-operator except for several years with Farmers’ Independent Weekly and before that a Morden-Winkler area radio station.



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