Good Fruit Grower

August 2014

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types of injury are more spotty and typ- ically found in habitually colder sites or sites that had heavy crops last year or stressed the plants, Longstroth reported. Other stresses that impact a plant's ability to withstand winter cold include lack of irrigation and drought stress in 2013 or too much irrigation or fertiliza- tion in 2013, resulting in late growth that did not acclimate well going into winter, he said. "We are continuing to see tree decline in older peach orchards in areas sub- jected to extreme low temperatures. Cuts made in pruning young trees with no crop reveal extensive damage to the wood in the trunk. These trees will begin to show real stress when they leaf out, and hot, dry weather puts a real stress on the water-conducting ability of dam- aged wood. Leaf yellowing and wilting will be symptoms of winter injury that will become more apparent as the season progresses." • by Richard Lehnert A cross Michigan, vinifera grapes were hammered by last winter's cold conditions, said Mark Longstroth, Michigan State University's tree fruit educator in Van Buren County in southwest Michigan. That statement was true across the Midwest and Northeast as growers and industry observers surveyed the damage after what is considered a "test winter." Regrowth this spring was from secondary and tertiary buds, Longstroth said. Primary buds were mostly dead. Most hybrid varieties and juice grapes were hurt if they were overcropped last year. "In 1994, we had vines collapsing in the summer and had to bring a lot of the vinif- era up from the snow line," Longstroth said. "This year we're telling growers to wait and see where the vine develops new shoots before doing anything drastic." Duke Elsner, the Michigan State Uni- versity fruit educator who works with wine grapes in northwest Michigan, reported that temperatures there were not quite as cold as further south in Longstroth's area but did dip to -20˚F one night and -10˚F on several nights. Elsner sampled grape buds in late March. "The results revealed good news and bad news, depending on the variety," he reported. "Riesling showed a solid 84 per- cent primary bud survival rate with Chardonnay not far behind at 74 percent. Each had over 90 percent of their secondary buds alive and well. "Pinot Gris and Gewürztraminer did not do as well, with just over 50 percent survival of primary buds. Pinot Noir and Cabernet Franc both came in at under 50 percent live primary buds, but each of these varieties showed decent survival rates for the secondary buds, so it should be possible to adjust prun- ing practices to achieve a typical crop load for the 2014 sea- son." A number of other varieties exhibited much greater bud mortality, he said. Pinot Blanc had only 37 percent and 45 percent survival of primary and secondary buds, respectively. Gruner Veltliner had under 5 percent of the primary and sec- ondary buds alive in his sample. Eight other promising Vitis vinifera wine varieties being tested at the Northwest Michigan Horticultural Research Cen- ter came in at under 30 percent primary bud survival. Muscat was also hard-hit by the cold. "As would be expected, hybrid varieties fared much better, as cold hardiness is one of the characteristics typically selected for in breeding programs," Elsner said. "Several hybrid varieties showed greater than 80 percent survival of primary buds." Ohio In Ohio, viticulturist Imed Dami reported near total losses of primary buds on vinifera varieties such as Riesling, Chardonnay, Pinot Noir, Cabernet Franc, Pinot Gris, and Cabernet Sauvignon. He pegged losses at 57 percent on hybrids such as Vidal Blanc, Chambourcin, Traminette, and Seyval, and 30 percent on the native varieties Concord, Catawba, and Niagara. Dami saw extensive damage to secondary and tertiary buds on the vines at grape research stations in Wooster and Kings- ville. He estimates that 20 percent of the grapevines in Ohio will be lost. As in Michigan, the growth of winemaking in Ohio has been fostered by a variety shift that began 40 years ago from native varieties to hybrids and then to vinifera in the 1990s. Evidence of increasingly mild winters spurred growers to plant tenderer varieties, but last winter's extreme cold showed that even in a warmer world, the risk of extreme weather hasn't lessened. Temperatures hit -14˚F in Ohio last winter—even as far south as southeastern Ohio. Disaster in New York In New York's Finger Lakes region, the U.S. Department of Agriculture declared 19 counties a disas- ter area. The declaration means the federal agency will provide financial assistance to grape growers to replant or rehabilitate their vines after months of frigid temperatures, with lows ranging from -7˚F to -18˚F. Cornell University researchers conducted tests suggesting that up to 50 percent of the region's Riesling, Gewürztraminer, Sau- vignon Blanc, Chardonnay, and Cabernet Franc vines revealed bud damage. Some vintners saw 100 per- cent of their vineyards damaged. The researchers say that at temperatures below -14˚F, even Riesling, the most cold-resistant of the Vitis vinifera cultivars, would sustain heavy damage. The deep freeze is particularly hard on the vines' primary buds, which carry most of the com- ing season's fruit. Riesling, the signature grape of the Finger Lakes region, experienced the worst year in a decade due to the subzero tem- peratures, Hans Walter-Peterson, a grape educator at Cornell University, told the Wall Street Journal. "This year knocks you for a loop," he said. Cold-hardy cultivars The cold winter may give new impetus to plantings of cold- hardy grapes like those developed by the University of Minne- sota. Four varieties—Frontenac, Frontenac Gris, La Crescent, and especially Marquette—all products of the University of Minnesota's grape-breeding program, survive temperatures well below -20˚F. The wine industry has, however, mostly used these new varieties to expand wine grape growing country beyond traditional areas. "I never dreamed that I'd be seeing any grapes produced in the Thousand Islands region of New York, where winter temperatures often drop into the -30s," Tim Martinson, senior Extension viticulture specialist with Cornell University, told the Minnesota Grape Growers Association at their meeting in February. "The cold-hardy Minnesota and Swenson hybrids made it possible to do so, and we now have a vibrant and growing win- ery industry both near Watertown and in the Lake Champlain region." New growers and wineries have expanded fast in the last two decades. Since the first University of Minnesota grape variety, Frontenac, was released in 1996, producers in 12 states have planted an estimated 5,400 acres of cold-hardy grapes, including 3,260 acres of the University of Minnesota varieties. The success of breeding for cold climates spurred the North- ern Grapes Project, funded by USDA's Specialty Crop Research Initiative. The idea is to encourage wine production in colder climates. States in the project are Connecticut, Illinois, Iowa, Maine, Massachusetts, Michigan, Minnesota, Nebraska, New Hampshire, New York, North Dakota, South Dakota, Vermont, and Wisconsin. • Above, empty Balaton tart cherry buds. Flowers were killed by winter cold and never developed. There was nothing in the buds when they opened. Rabbit damage in high-density Gala. Snow about two feet deep allowed rabbits to strip bark off these scaffold limbs. The primary buds on this Chardonnay vine were all killed, but secondary and tertiary buds stepped in to provide a partial crop. At some locations, the vine was killed to the snow line and a cordon will need to be developed. PHOTOS BY MARK LONGSTROTH Vinifera grapes hit hard "Hybrid varieties fared much better." —Duke Elsner Good Fruit Grower AUGUST 2014 13

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