CARBERRY, Man. – Potato growers again felt the menacing effects of late blight this summer.
Ralph Oliver, a grower near Carberry, said he first noticed the fungus in late July. It forced him to step up his fungicide spray program from once a week to once every five days.
“The guys who had to cut their potatoes down early suffered horribly,” he said.
“It took some of the fields by surprise this year and wiped them right out.”
Growers forced to harvest their fields early because of the blight can expect lower yields. The tubers grow fastest in late summer and early fall.
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Frosts this month in Manitoba’s potato growing regions helped slow the spread of the blight, which appeared in Manitoba crops in 1994 following a 40-year hiatus. Frosts kill the plant foliage, where the spore first takes hold.
“We’re probably a little less concerned than we were before the frost,” said Bob Hyra of Midwest Food Products, a company at Carberry that processes potatoes into french fries.
But Hyra said frost doesn’t mean growers should let down their guard. The spores can filter into the tubers, causing problems once the potatoes are in storage.
Growers are advised to harvest only when the leaves and stems are dead. Suspect areas or wet areas should be harvested last.
“The risk is still there,” Hyra said. “It can attack you in so many different ways.”
The fungus can cause potatoes to rot in storage, setting the stage for other problems. Good air flow and proper temperature control can lessen the risk of rot.
Reg Curle, a Manitoba Agriculture potato agronomist, said late blight was found in all of Manitoba’s potato growing regions this year.
“We’ve had some pretty severe cases where the fields went down pretty quickly.”
Besides hampering yields and posing a risk to potatoes in storage, late blight is driving up production costs. It was not uncommon this year for growers to make 10 fungicide applications to their fields.
Curle believes growers have spent an average of $125 to $175 per acre to buy and apply fungicides aimed at late blight.
Manitoba Crop Insurance is monitoring potatoes as they go into storage. That can help tell insured growers whether it is worth harvesting a field.
“We’ve seen some fields that won’t be harvested because the problem is so bad,” said Roy Tufford of Manitoba Crop Insurance.
“A lot of the tubers are infected so badly they won’t keep.”
The coming months will show the depth of the problem. If blight is present in stored potatoes, it usually shows up before mid-December, Tufford said.
