(Wines&Vines) - By mid-May, most winemakers across the country aren’t worrying quite so much about spring frosts. During the weekend of May 14-15, however, grapegrowers in southern areas of Minnesota and Wisconsin had temperatures drop well below freezing. The cold temperatures started early on May 14 in western Minnesota, and by early on May 15 they had moved into Wisconsin as well.

At Wollersheim Winery in Prairie Du Sac, Wis. (just northwest of Madison), the temperature was 32° F at 1 a.m. on May 15; by 4:35 a.m. it had dropped to 27° F. The result was devastating. Philippe Coquard, owner (with his wife Julie) and winemaker at Wollersheim, told Wines & Vines that 75% of the red grapes and 25% of the white grapes were lost on their 30 acres of vineyard.

Coquard stated, “We know grapevines do better on slopes, and that was proven this time around. We lost 20% of the grapes on the slopes, and 70% to 80% on the flat.” Even some of the cold-hardy Minnesota varieties such as Frontenac Gris and Marquette were frozen, as they had four leaves out. St. Pepin and La Crosse, on the other hand, were two weeks behind the other earlier budding Minnesota varieties, and with one leaf out, suffered only a 10%-20% loss. Other grapes that came through included some 45-year-old Maréchal Foch planted on a slope that Coquard uses for his Domaine Reserve wine. “They did just fine,” he stated with some relief.

The winery, along with its sister winery Cedar Creek Winery in Cedarburg, Wis., produce more than 200,000 cases of wine each year. The wineries purchase some of their grapes from Washington and New York state, but as Coquard said, “You can’t go out and replace estate-grown grapes.”

When asked about the extent of the frost damage in Wisconsin, Steve Johnson, president of the Wisconsin Grape Growers Association and owner of Parallel 44 Vineyard and Winery in Kewaunee, Wis., told Wines & Vines, “It depends on where you are. We’re near Lake Michigan, and while we had frost damage in 2015, this year we lost nothing. If you’re west of Madison, it depends on the variety, but growers probably lost 40% to 90% of their grapes.”