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Janaury 2017 WINES&VINES 165 WINE EAST GRAPEGROWING among the most cold-hardy variet- ies with the lowest LT 50 values, while Tempranillo, Lagrein, Bar- bera and Durif were among the most cold-sensitive varieties with the highest LT 50 values. Also, this study showed that not all varieties acclimated, de-accli- mated or reached maximum hardi- ness at the same time and same level. "Cold Hardiness for Three Seasons" shows three varieties to illustrate this finding. Gamay Noir was the most cold-hardy variety (lowest LT 50 in mid-winter) and was the quickest (steepest slope) to cold acclimate in the fall. Tem- pranillo was the most cold sensitive (highest LT 50 in mid-winter) and was the quickest to deacclimate in late winter. Dolcetto acclimated the slowest in the fall and reached maximum cold hardiness later than Gamay and Tempranillo. Methods of assessing cold hardiness Standard method: Mid-winter bud cold hardiness (LT 50 ) is the most commonly used index to estimate a given variety's cold hardiness and has been reported as such by re- search institutions in several states conducting this type of work in the past 30 years. In Ohio, we found that mid-winter cold hardiness var- ied between LT 50 = -18.3° C (-0.9° F) and LT 50 = -24.8° C (-12.6° F). "Cold Hardiness Based on Stan- dard Method" shows that Gamay Noir was the most cold-hardy vari- ety, whereas Tempranillo was the most cold sensitive in this study. We also found that the standard method has a few drawbacks: a) the lowest LT 50 in mid-winter is generally based on a single LT 50 measurement; b) not all varieties reached their maximum cold hardi- ness on the same date; and c) wide variability of LT 50 within each cul- tivar made it difficult to distinguish cold hardiness between two variet- ies if the difference between their LT 50 was less than 3° C (5.4° F). During the polar vortex in January and February 2014, the research vineyard in Wooster ex- perienced successive low tempera- tures that dropped below the MATERIALS AND METHODS Varieties tested: Vitis vinifera—Arneis, Barbera, Cabernet Franc, Cabernet Sau- vignon, Carmenère, Chardonnay, Dol- cetto, Durif, Gamay Noir, Kerner, Lagrein, Malbec, Malvasia Bianca, Merlot, Pino- tage, Rotberger, Sangiovese, Sauvignon Blanc, Siegerrebe, Syrah, Tempranillo, Teroldego; and Vitis sp.—Regent (a Ger- man cross of Diana and Chambourcin) Rootstock: 101-14 Mgt. (V. riparia × V. rupestris) Location: OSU Research Vineyard at OARDC in Wooster, Ohio (lat. 40°44'16" N; long. 81°54'12" W) Elevation: 1,165 feet above sea level USDA Plant Hardiness Zone: Zone 6a (-10° F to -5° F). Spacing: 9 feet x 6 feet (row x vine) Training: Bilateral low cordon (40-inch height) with vertical shoot position (VSP) Pruning: Spur pruning to 30 buds per vine (two to three buds per spur) COLD HARDINESS FOR THREE SEASONS LT 50 (°C) 0 -5 -10 -15 -20 -25 252 287 312 341 3 46 82 Day of Year Cold hardiness changes of Gamay Noir, Dolcetto and Tempranillo in the Wooster research vineyard by day of year for three seasons. Plot points represent LT 50 (lethal temperature that kills 50% population) collected for three seasons. Note the U-shaped trend lines of cold hardiness in the three varieties. Gamay Noir Tempranillo Dolcetto