By Tim Martinson, senior extension associate
Horticultural Sciences, New York State Agricultural Experiment Station
Cornell College of Agriculture and Life Sciences
Groups of 30 buds cut from canes collected every two weeks are placed on sensitive thermocouples and placed in a temperature-controlled freezer. When they freeze, they release a small amount of heat, which allows measurement of the precise bud freezing temperatures.
Growers and wineries in New York can now turn to the internet for the latest information on winter temperatures and bud hardiness, thanks to a Cornell project funded by the Viticulture Consortium East and the New York Wine and Grape Foundation
The project, led by senior extension associates Tim Martinson and Stephen Hoying, funded collection of dormant buds and canes from 28 New York vineyards in the Finger Lakes, Lake Erie, and Hudson Valley regions. Bud freezing temperatures were measured at one to two-week intervals from December 2009 through March 2010 for four representative grape varieties (Concord, Cayuga White, Riesling and Cabernet franc). The bud freezing temperatures were overlaid with daily minimum and maximum temperatures to provide growers with an easy, graphical look at the risk of winter injury to buds. Cornell Cooperative Extension's Finger Lakes and Lake Erie Grape Programs disseminated the information to growers through their electronic Crop Updates.
This winter, mild temperatures during the critical December to February period stayed well above the critical lows that would have caused winter injury. Bud examinations in early March revealed low levels of dead buds—ranging from 2% to 8%—well below the threshold growers use to adjust the number of buds they leave on vines after pruning.
Winter injury to buds and trunks is an ongoing concern for grape growers in New York. Periodic winter low temperature events can damage buds and trunks—particularly those of cold-sensitive varieties, including most high-quality V. vinifera cultivars such as Riesling, Pinot Noir, Chardonnay, and Cabernet Franc. The most recent serious freeze in 2004 resulted in 300 acres of dead vines, reduced the crop by 30% overall, and cost the industry an estimated $11 million in lost vineyard income and an additional $50 million in lost potential wine value.
Because of the threat that winter injury poses to production, growers routinely evaluate bud injury by examining dormant buds before pruning. If they observe high levels of bud injury (typically >20%) in their vineyards, they can adjust by leaving extra buds to compensate for the dead buds they observe.
Cornell's cold hardiness information provides growers with a quick way to evaluate the risk of winter injury. As Lodi grower John Wagner, of Wagner Vineyards commented, "The bud hardiness graph is excellent. If the actual temperature line dropped down where it overlapped into the danger zone, I think it would be a real easy way for growers to realize that they had potential for damaged buds and really needed to check their individual blocks carefully. Great job."
Martinson wants to continue collecting bud hardiness information over the next several years. "We have a long history of evaluating bud hardiness for research programs, but the information hasn't been consistent from year to year. Collecting consistent information over several years will provide insights on what weather conditions lead to serious bud injury, and this will help New York growers make better decisions about managing their vineyards to compensate for winter injury—a 'given' in our climate."