Winter Injury to Grapevines and Methods of Protection (E2930)
Genotype determines a vine’s maximum cold hardiness potential. Environment — soil, weather, topography and pests — and grower management determine how much of that potential is realized.
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Winter injury to grapevines has challenged grape growers for centuries. The Romans burned prunings and other wastes to protect vineyards from cold. It is estimated that 5 to 15 percent of the world’s grape crop is lost to coldrelated damage in any given year. Preventing cold injury to vines is a key viticulture concern in many grape regions (Evans, 2000).
Grapevine tissues are susceptible to injury at temperatures as warm as 28 °F. Yet some grapevines, most notably cold-hardy Vitis riparia, can survive temperatures down to -40 °F (Howell, 2000). Winter injury to grapevines, particularly the cold-tender cultivars of Vitis vinifera, has many detrimental effects on wine growing in cold regions of the eastern and midwestern United States. As regional wines capture the imagination of consumers, wine production is expanding into areas that are considered high-risk for winter injury. Growers and consumers are especially interested in the classic European cultivars, which generally are susceptible to winter injury.
The effects of winter injury can be extensive, complex and devastating for vineyard businesses. For example, in the Finger Lakes region, almost half of the Vitis vinifera crop was lost in 2004 because of a single freeze event in January (Martinson and White, 2004). Winter injury can occur to all species of vines, but, ironically, there is often a direct correlation between the popularity of a grape, as judged by its wine quality, and its susceptibility to winter injury. Winter injury is also the major cause of crown gall disease development in vines. Injured or dead canes, trunks and buds cause crop losses or, worse, the need to replant vines with associated significant production loss and considerable expense. The economics of these losses to winter injury can be devastating to a vineyard business and are even more significant when valueadded in wine. The cost of establishing a Vitis vinifera vineyard can reach $25,000 per acre, with the vines being the single largest expense. Loss of vines affects a vineyard’s profitability for many years.
A shortage of grapes directly affects winery profitability. Wine markets are sensitive to shortages, and customers may be lost if supplies vary from year to year. Finally, there is the emotional cost to the grower, particularly to new grape growers who may be expecting their first crop, only to see vines die before they become productive.
Eastern and midwestern U.S. temperate growing conditions are challenging all year long, from spring freezes to hot, humid, wet summers to hurricanes and freezes in the fall. But it is the total loss of vines and/or crop due to winter injury that is the most difficult for a grower to endure. Fine wine grapes can be grown from Ontario to Georgia and from Michigan to Texas, but without control of winter injury to vines, the wines that are produced from these grapes will be at a severe economic and quality disadvantage to those from milder climates.
Research over the years in cold regions has revealed much about the anatomy and physiology of cold damage to grapevines. Practices such as hilling-up soil over graft unions and using wind machines to mix cold and warm air have been developed to reduce the severity of winter injury to grapevines. Careful site selection may be the most important decision a new grower can make. Cold-hardy cultivars are becoming increasingly available, and plant breeding programs continue to offer new hardy cultivars with good wine character. Although potentially controversial, genetic engineering may someday offer the best hope of a cold-hardy vine.
A grower plants a vineyard with the expectation of growing a quality product and creating a sustainable and successful farm business. Too often, winter injury prevents the achievement of these basic goals. The research and experience related to winter injury to grapevines had never been compiled into an easyto-reference publication. This bulletin fills this void and places in the hands of grape growers the information to understand winter injury, to prevent it and, if affected by it, to respond to it. This practical guide has the added value of numerous citations to more in-depth discussion of many topics. The authors have more than 100 years of collective experience in coldclimate viticulture. We have relied on scientific evidence and, in some cases, on reports that indicate a recurring documented experience. We identify those areas where further investigation would be helpful. This publication will lead the reader to a better understanding of winter injury to grapevines, will provide strategies for avoiding and dealing with winter injury to grapevines, and will provide a basis for advancing our knowledge of this topic.