Good Fruit Grower

December 2011

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Grapes hardiness Cold A new cold hardiness model should help growers plan frost control and assess damage after cold events. by Melissa Hansen model represents two decades of work by Washington State University researchers who have annually collected cold hardiness data, making it available to growers. For years, WSU technician Lynn Mills and others would track critical temperatures and damage to 10, 50, and 90 per- cent of grapevine buds and phloem and xylem tissue, using a programmable freezer and data logger. Grape hardiness acclimation in the fall and deacclimation in the spring were also tracked. By linking the cold hardiness model with AgWeather- A Net, it now provides real-time data from any AgWeather- Net station, said Dr. Markus Keller, WSU viticulturist. "One of the biggest improvements is that the data will be more site specific for growers," he said, noting that in the past the values were only based on Prosser temperatures. Growers had to extrapolate the data and use it only as a rough reference point. Now, growers can use any of 135 weather stations that are tied to the AgWeatherNet grid. The majority are located in eastern Washington. The model, similar to other disease and pest models developed by WSU, is accessible through WSU's AgWeatherNet Web site ( cold hardiness of more than 20 varieties can be plotted on a chart, showing predicted damage to 10, 50, and 90 per- cent of the buds. Phloem and xylem damage prediction will be added later. Cold hardiness varies by site but also variety, with Cabernet Franc among the more cold hardy and Semillon among the more tender. Keller reminds growers that the numbers are estimates or simulated values—not measured values of actual cold hardiness (those can be found on WSU's cold hardiness Web site at weather/cold-hardiness/). But the model should help growers better predict where and when cold protection is needed, or not needed. Keller said the model could be useful for quickly check- ing site suitability for particular varieties. For example, checking the cold hardiness of Mourvèdre for the Wahluke Slope weather station during last year's November freeze showed no damage to the vines. But using the Moxee weather station for the same time period and variety resulted in 90 percent bud damage. To use the cold damage model, growers must be a reg- istered user of AgWeatherNet, which is free. Development of the cold hardy model was supported by a grant from the U.S. Department of Agriculture's Viticulture Consor- tium and WSU. Support to collect cold hardiness data at Prosser has come from the Washington Wine Industry Foundation and Washington State Concord Grape Research Council. • 62 DECEMBER 2011 GOOD FRUIT GROWER new cold hardiness tool is available just in time for winter for Washington State grape growers through AgWeatherNet, a statewide databank of weather and environmental information. The new grape cold hardiness computer

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