Good Fruit Grower

January 15

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Grapes New approaches to frost control The height of the vines influences how they fare during cold weather. by Peter Mitham ight water supplies in California are driving research that promises to give wine grape growers a better understanding of the factors contributing to frost damage, and alternative approaches to reducing the risk of damage. Mark Battany, an advisor to growers in San Luis Obispo and Santa Barbara counties with University of California Cooperative Extension, presented the results of recent research to growers attending the annual B.C. Wine Grape Council meeting in Penticton, British Columbia, Canada, this summer. Battany discussed work regarding the strength of temperature inversions, the performance of wind machines as frost-control tools, and the importance of trellising in preventing frost damage. Speaking afterwards, Battany explained that showering the vines with water to create an insulating coat of ice has been a simple, but increasingly inefficient way of protecting California vineyards from winter damage. "Water was relatively available and cheap, so sprinkler frost protection was the default tool that they would use," he said. "But now we're starting to get a lot more competition for that water, or the water's simply not available. So, growers really have to look at what other options they can use." In order to make the right choices, growers need to understand a site's specific climate, how vines respond to it, and the management tools that will improve vine performance, Battany said. "[We're] helping to understand what the weather conditions are like during frost events, and those weather conditions will then tell growers how they need to respond to frost." His goal is to help people understand that the height of the vines has an impact on what the vines will experience during cold weather. T Site Wise site selection is the basic way for growers to manage climate risks such as the potential for frost damage. Robert Evans, recently retired from the USDA-ARS Northern Plains laboratory in Sidney, Montana, told Good Fruit Grower earlier this year that site selection was "the most effective passive risk avoidance strategy." A site with good air drainage allows cold air to flow out and prevents the inversions that occur when cold air pools, pushing warmer air (which rises) to higher altitudes. Those altitudes can be significant. "The size of the potential cold air pond will likely be four to five times greater than the height of a physical obstruction," Evans said. Sometimes, however, a particular site has many desirable traits, and growers want to find a way to work with local conditions to make use of the parcel. This is where trellis height can play a role, Battany said. Since cold air pools closer to the ground, a vineyard might be designed to raise the canopy to a level that protects sensitive tissues from frost damage in winter. "Knowing that, maybe we can design vineyards from the beginning to place the frost-tender tissues up higher to avoid frost damage in the first place," he said. On the other hand, in some cool-climate vineyards, those same tissues may need to be close to the ground to garner the maximum benefit from the reflective power of the earth in summer. He showed British Columbia growers a slide from Argentina where very short vines are trellised close to the ground to maximize exposure to heat units. "[Those growers] feel that in order to get the fruit to ripen, they need to plant the vines very low to the ground so that fruit and those vines are enjoying the warmest air possible," Battany said. "Of course now, that then predisposes those vines to spring frost damage, so in that vineyard they have sprinklers for frost protection." But with water supplies under pressure in California, alternatives are needed. Wind machines aren't always the answer, however, because temperature inversions are sometimes too weak or nonexistent because of factors such as wind that prevent inversions from forming. "If growers are going to make the shift, or if we're trying to encourage growers to make the shift, they need to have some data that yes, wind machines are going to Serving America's Landowners Since 1929 3035 Rickenbacher Drive Pasco, Washington 99301 Call us for your farm real estate needs! Flo Sayre, Managing Broker Accredited Land Consultant ABR, ALC, CNE, CRIS, TRC, REALTOR "2013 Washington Land Broker of the Year" Mobile: (509) 539-3161 Nat Cruzen, Broker Mobile: (509) 460-0526 Henry Johnson, Managing Broker Mobile: (509) 539-6678 Check out our website for exclusive listings! Real Estate • Auctions • Farm and Ranch Management Appraisals • Consultations • Insurance • Oil and Gas Management Lake Management • National Hunting Leases 32 JANUARY 15, 2014 GOOD FRUIT GROWER

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