Strong winds sweeping across Saskatchewan and Alberta this week have scattered swaths of canola and wheat, causing significant yield losses.

Winds blew across central and southern Alberta on Monday, rolling swaths of canola, wheat and barley into neighbouring fields and damaging crops that were still standing.

"For canola especially, a lot of swaths have been rolled into balls the size of a pickup," said Brian Tainsh, provincial adjusting manager with Agriculture Financial Services Corp., Alberta's crop insurance company.

"It was a very significant wind."

Damage is especially serious for canola. Winds can cause canola's pods to break open, scattering the seeds that farmers sell to produce vegetable oil and meal.

The harvest in southern Alberta is furthest advanced in the province, minimizing damage, while only one-fifth of crops in central Alberta were off the field as of Sept. 4.

Winds, reported up to 100 km/h, caused widespread damage around Saskatoon, said Curtis Rempel, vice-president of crop production at the Canola Council of Canada.

The impact on yields is unclear, but it appears to be significant, Rempel said.

"Swaths along the whole length of the field have moved significantly, it's not just 20 feet here and 20 feet there, and then swaths have come apart in some instances," he said.

"I think growers are going to able to salvage some, but nothing about this is easy."

Canada was expected to produce a record-large canola crop this year, but some analysts have lowered their estimates as yields came in disappointingly low due to summer heat and crop disease.

As of Monday, just over half of Saskatchewan's canola crop was harvested, and safe from wind damage, according to the provincial government.

Strong winds blew through Manitoba last weekend, but there have been few if any reports of crop damage, said Pam de Rocquigny, who co-ordinates the weekly crop report for the provincial agriculture department.

Farmers have finished harvesting Manitoba's cereal crops and have almost all of their canola off their fields as well.

-- Rod Nickel writes for Reuters from Winnipeg.