Lancaster, Pa.—Grapegrowers east of the Rockies often face cold winters. January 2014 has reinforced that understanding, as temperatures earlier this month dropped to lows not experienced for two decades across the Midwest and into the East. Those low temperatures, accompanied by strong winds, came from a large pocket of very cold air known as a polar vortex, which normally sits over the polar region.

How cold did it get? The Finger Lakes region of New York, with approximately 11,000 acres of grapes, had low temperatures between -3° and -11°F on the east side of Lake Seneca. Overall, New York has 350 wineries and 37,000 acres of grapes. In Pennsylvania, low temperatures ranged from -1°F in Lancaster County to -10°F in Tioga County in the north-central part of the state; Pennsylvania has a total of 13,600 vineyard acres and 172 wineries. The low temperatures in Ohio, with 1,900 acres of grapes and 144 wineries, varied from -6°F in the southeast to -16°F in the northwest.

Vines not as cold hardy
Dr. Imed Dami, associate professor of viticulture at Ohio State University Agricultural Research and Development Center, reported that temperatures in Ohio had been even colder in 2009, when the lows ranged between -7°F and -24°F. “The 2014 cold, however, was different (in a bad way),” he stated. “It was an advective freezing event, meaning a massive cold air (front) moved to our region with windy conditions. To make matters worse, the lowest temperatures lingered for hours. In 2009, the minimum temperatures were reached and stayed for a short time (minutes instead of hours) and resulted from a radiative freeze with calm conditions.”

In addition, Dami thinks that the vines were not as cold hardy prior to the temperature lows Jan. 6-7. “December was unusually mild, with temperature highs reaching the 60°s for several days,” Dami commented. “This was not unique to Ohio, but observed across the East and Midwest. Mild weather prompts grapes to lose hardiness, or ‘de-acclimate.’ There was large fluctuation of temperatures between highs and lows a few days before the temperature dipped Jan. 6-7. Freeze/thaw cycles in mid-winter are not desirable, as they lead to more damage.

“We did not experience this phenomenon in 2009. In fact, in 2009 air temperatures were below freezing for 10 days before the coldest temperature was reached. The weather pattern in 2009 caused grapes to reach maximum cold hardiness….Unfortunately, I doubt that the same varieties will have the same cold hardiness as in 2009 and will likely see more damage this year.”

Hans Walter-Peterson, viticultural extension specialist with the Finger Lakes Grape Program at Cornell University, noted in the “Finger Lakes Vineyard Update” that early bud examinations indicate 6% bud loss in Riesling and up to 26% (close to the lake) and 20% (uphill from the lake) in Merlot. The median bud freezing temperature range is -11° to -14°F for Cabernet Franc and -9°F to -13°F for Riesling.

According to Dr. Murli Dharmadikari, extension enologist at Iowa State University, growers in the upper Midwest know winters will be cold, and therefore they plant vineyards with cold-hardy Minnesota hybrids in Iowa, Minnesota and North and South Dakota. It’s only in regions where vinifera can be grown that unusually low temperatures are a problem.

Short of replanting their vineyards with Minnesota hybrids, what can grape growers do at this point? Mark Chien, viticulture extension educator at the Pennsylvania State University, stated in his “Wine Grape Information for Pennsylvania and the Region” newsletter: “Growers will certainly want to cut buds and make pruning adjustments. And given the way this season is going (cold), the timing and choice of pruning varieties is important (a blend of value of variety and cold tolerance), usually the Bordeaux reds would be pruned last. It’s hard for growers not to be in the vineyard, but it’s better to wait to the latest possible time to prune and still get it done before bud break. The good thing about the cold is that it should help to suppress disease and insect overwintering populations.”