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164 WINES&VINES January 2017 GRAPEGROWING WINE EAST Determining the Best Cold Hardiness Measurement Nearly two-dozen grape varieties tested for ability to withstand below-freezing temperatures By Imed Dami G rapes contribute more than $5 billion per year to the economy of the eastern United States, and the grape and wine industries have been expanding rapidly in those regions. However, the sustainability of profitable yet cold-sensitive cultivars is limited by climatic constraints, primarily lethal freez- ing temperatures that can drop well below 0° F. The severe economic losses that result from freezing injury continue to be a major setback for the continuous growth of the grape and wine industries in this region. In 2014, the polar vortex caused temperatures to drop to critical levels for grape survival and resulted in widespread damage and crop losses across the Midwest and eastern United States. Ohio experienced the worst damage and crop loss in 20 years (valued at $12 million). This problem was exacerbated with whole-vine loss of cold- sensitive species V. vinifera, which have dominated new plantings in the past 15 years in Ohio. Therefore, the limitation imposed by the sensitivity of the vinifera species has an im- pact on the sustainable growth of the indus- try, and it is critical for growers to know the cold hardiness (CH) of the newly introduced varieties, in addition to the standard viticul- tural and enological characteristics. Sub- freezing temperatures below -20° C (-4° F), often damage V. vinifera, which is mostly adapted to a Mediterranean-type climate. Nonetheless, information about the CH of the newly introduced vinifera varieties has not been available. Ohio's cold-hardiness study The purpose of the study at the Ohio Agricultural Research and Development Center in Wooster was to determine the cold hardiness of 23 variet- ies of recently introduced V. vinifera grapes so that grapegrowers and nurseries would have a better understanding of the ability of those variet- ies to survive the harsh winter conditions in the Midwest and northeastern United States. Re- searchers also investigated whether there are better ways to estimate the CH of vines. Buds were collected from each variety bi- weekly between September and March for three dormant seasons (2011-14) and placed in a freeze chamber. The freeze chamber was set up indoors to conduct freezing tests that would simulate cold damage in the vineyard. Cold hardiness was determined by thermal analysis and expressed by the lethal temperature that kills 50% of the bud population, or LT 50 . We evaluated three methods to express cold hardiness: 1) Standard method: computing mid-winter hardiness based on a single and lowest LT 50 value; 2) Modified standard method: computing mid-winter hardiness based on multiple lowest LT 50 values; 3) Annual freezing tolerance (AFT, or an- nual cold hardiness): computing LT 50 not only during mid-winter, but also during fall acclimation and spring deacclimation. Cold hardiness of 23 varieties As expected, all 23 varieties behaved similarly and followed the typical U-shaped pattern of bud cold hardiness, which consists of three stages: fall cold acclimation (September to December), followed by maximum hardiness in mid-winter (January to February) and deac- climation in late winter and early spring. However, there were differences of cold hardiness among varieties. Gamay Noir, Rot- berger, Pinotage and Regent were generally KEY POINTS The Ohio State University's OARDC tested the cold hardiness of 23 varieties newly introduced in Mid- west and northeastern vineyards using three methods of testing: the standard method of indexing mid-winter bud cold hardiness (LT 50 ); a modified standard method based on regression analysis; and researchers developed a new cold hardiness index, the relative annual freezing tolerance (RAFT), which compares annual freezing tolerances of these varieties with that of a benchmark variety. These 23 varieties can be grouped into two distinct groups of most cold hardy (Gamay Noir, Chardon- nay, Pinotage, Regent and Rotberger) and most cold sensitive (Barbera, Durif, Lagrein, Sangiovese, Syrah, Tempranilllo and Teroldego). The remaining 11 varieties fall in the gray area, and their CH may shift one way or another depending on other factors such as weather and cultural practices The findings of this study provide research-based information for nurseries and on cold hardiness of new varieties they sell. They will also guide growers making decisions on suitable varieties for sites where winter damage is a concern. A variety trial plot (shown here before the polar vortex of 2014) helped researchers understand each variety's cold tolerance.