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Being able to predict the cold hardiness of grapes could help growers know how to respond when severe freezes occur.

Researchers at Washington State University are developing a computer model for predicting grapevine cold hardiness that could be in place next winter. The model, currently being integrated with WSU’s AgWeatherNet, is being developed initially for two major wine grape cultivars, Chardonnay and Cabernet ­Sauvignon, and Concord juice grapes, though additional varieties soon will be included. The model, similar to other disease and pest models developed by WSU, will predict cold hardiness at any site that has a weather station.

For about 20 years, WSU has annually collected cold hardiness data on grapes and made it available to growers, WSU extension educator Gwen Hoheisel shared ­during a grape pruning workshop, but this has its ­limitations.

“Cold hardiness is based on what you do in the vineyard and where you are located. It varies by site,” she said. “Our [WSU’s] cold hardiness program is based on data from grapes at the Prosser research station. It has its limitations because it’s not localized for your conditions.”

The biggest advantage of the model will be for those growers with their own weather station or who use a nearby AgWeatherNet station, she said. “You’ll have site-specific information and can see your particular ­information and your cold hardiness prediction with the model. That’s something we can’t do now.”

Model applications

In the short term, the model will develop cold hardiness predictions for bud 10 and bud 90 LTE (low temperature exotherm). Bud LTE 10 is the temperature at which 10 percent of the primary buds will be killed; bud LTE 90 is the temperature when 90 percent of primary buds are killed. Later, the phloem and xylem tissue damage ­predictions will be added, as well as weather forecasts five to seven days out to warn of danger.

Hoheisel explained that the model will help growers predict where and when frost protection is needed or not needed and could be used to better match varieties to growing sites, using historical weather data or future ­climate predictions.

“It will help growers plan frost control, and after a cold event, guide where damage assessment should be done and if pruning practices should be adjusted,” she said.

The extensive data also show hardiness acclimation and deacclimation rates by varieties. Cabernet Sauvignon and Cabernet Franc are some of the hardiest red wine grape varieties. Chardonnay acclimates quickly in the fall to develop hardiness, but also deacclimates quickly in the spring and loses it.

Work to develop the model was supported by a grant from the U.S. Department of Agriculture and WSU. Collection of cold hardiness data has been partly funded by the Washington Wine Industry Foundation and the ­Washington State Concord Grape Research Council.