Photo: A grape cane shows cold-damaged tissue (brown) just under the bark.
University experts offer training to help growers deal with damage.
WOOSTER, Ohio -- This is not the type of cold that helps make your favorite ice wine.
The prolonged and extremely frigid temperatures experienced in Ohio earlier this year have destroyed a majority of the crop of popular wine grape varieties grown in the state, according to a survey recently conducted by Ohio State University’s Grape Team.
“Following the extreme minimum low temperatures experienced in January and February across Ohio, many vineyards were affected, and vines sustained extensive bud damage and likely trunk damage depending on the location and the variety grown,” said Imed Dami, associate professor and state viticulturist with the university’s College of Food, Agricultural, and Environmental Sciences.
“This is probably the worst grape damage on record in Ohio, even worse than the last bad one that took place in 1994.”
The survey was completed by 62 grape producers statewide representing 838 acres, 720 of which are occupied by wine grape varieties. The average coldest temperature recorded at these vineyards was -14 degrees F, with an unofficial low of -27 degrees F.
Growers reported 97 percent losses of vinifera (European) grape varieties such as Chardonnay, Cabernet Franc and Riesling, which are the most popular and profitable for wine production but also the most susceptible to cold weather, Dami said.
Hybrid grape varieties such as Vidal Blanc, Chambourcin and Traminette, which are more cold resistant than vinifera, experienced an average crop loss of 57 percent.
Finally, cold-hardy American grape varieties such as Concord and Catawba fared better, with reported losses estimated at 29 percent.
These losses amount to nearly $4 million, according to the survey. Total losses to Ohio grape producers (who also grow juice and table grapes) are much larger, considering that there are some 1,900 acres growing this crop in the state.
While these losses are substantial, Dami said potential damage to grapevine trunks and vine death is more worrisome, as it would impact growers over a longer period of time.
“When you lose the buds to cold, you lose one season’s production,” Dami explained. “With trunk damage, it takes one year to retrain new trunks and another year to resume full production. However, if the whole vine dies, you have to start from scratch, and it will take four years from replanting to have a full crop again.”
The extent of trunk damage and possible vine death can’t be assessed until later in the spring, but based on grower reports Dami estimates it may be around 20 to 30 percent of the state’s grapevines.
Dami said grape crop loss to cold is not uncommon in Ohio and grape growers understand the risks of farming this crop -- especially those producers who grow vinifera varieties, which have become more popular in the past 20 years as the wine industry has substantially expanded in the Buckeye state.
“If you lose a vinifera crop once every 10 years, that’s normal in this industry anywhere in the eastern U.S.,” he said. “Our industry has been fortunate to avoid a catastrophic loss in the past 20 years and has been producing high-quality wines from these varieties. Therefore, the cold events in 2014 should be seen as an exception rather than the rule because the impact of this winter’s polar vortex was more extreme and very different from past cold weather events.”
Dami said several factors made this year’s winter particularly damaging to grapevines. First, the coldest temperatures experienced in the state were frequent as a result of the polar vortex that descended into the United States. Second, extremely low temperatures that can kill buds and trunks usually only last a few minutes, while this year such temperatures lingered for hours, he said.
The most important factor, however, was that vine hardiness became compromised this winter due to warm weather in December that tricked vines into believing spring was coming, which Dami refers to as “de-acclimation.” Additionally, the coldest days of the season were preceded by relatively warm temperatures and basically took the vines by surprise.
“For example, in Wooster we recorded a low temperature of -11 degrees F during the polar vortex event,” Dami said. “The same temperature caused 50 percent bud damage to vinifera varieties in 2009, but this year it lasted much longer, and the day before, the temperature was 45 degrees, leading to nearly 100 percent bud damage. The mild temperature also melted the snow, which eliminated the extra protection it gives to the trunks.”
Additionally, Dami said, the growers who have wind machines that help protect grapevines from extreme cold could not use them this year because of the windy conditions that prevailed during the polar vortex.
To help producers deal with the aftermath of this year’s catastrophic weather, Ohio State’s Grape Team has conducted a series of hands-on workshops that address specific issues related to cold damage, and is planning to conduct more.
Between January and March, nearly 300 growers attended various workshops around the state focused on how to assess winter damage and how to prune affected vines, which according to Dami is different from normal pruning. “Many growers are new to the industry, and the survey showed that nearly half of them hadn’t experienced such weather issues before and didn’t know how to assess or manage cold damage,” he explained.
More training sessions are planned for the summer to teach growers how to manage affected vines, especially those that experienced trunk damage.
The 2014 Grape Winter Damage Survey Report is available by contacting Dami at firstname.lastname@example.org.