He said that about 18,000 acres of Canadian potato farmland would not be harvested this year, adding that he had spent more than three decades in the potato industry and could recall only one year similar to this one: 2018.

“Last year was the first year we really experienced anything of this scale,” he said, adding that harvests were even worse in 2019, and that Manitoba and Alberta, the second- and third-highest potato-producing provinces, had been hardest hit. (The first, Prince Edward Island, a maritime province in the east, was doing a little better than it did last year.)

The weather was worse for fries than for other products, like fresh potatoes or chips, because the potatoes used for fries are often harvested a little bit later in the year and were more likely to be exposed to that fatal chill, Mr. MacIsaac said.

Potato production was down in the United States, too. The Department of Agriculture’s National Agricultural Statistics Service said in a report last month that American potato production in 2019 was forecast to be down 6 percent from last year.

The report said that farmers in Idaho reported losses because of freezing temperatures in September and October; growers in Washington State had quality concerns because of freeze damage; and prolonged wet conditions hampered the harvests in the Red River Valley of North Dakota.