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March 2016 WINES&VINES 59 WINE EAST GRAPEGROWING Richmond, Va., on Christmas Day 2015 was 75° F; on Jan. 5 the low in Winchester, Va., was 7.5° F, a change of almost 70° F. In Ithaca, N.Y., the weather was a balmy 64° F on Christmas Eve, with a low of 35° F; by Jan. 4, the high tempera- ture was 10° F with a low of 7° F. Now the major question is: Had grapevines from Virginia to New York acclimated to cold temperatures? Cold hardiness and dormancy In the article, "Questions from the Vineyard: Dormancy" in the De- cember 2015 issue of Viticulture Notes, professor Tony Wolf and Tremain Hatch, viticulture exten- sion research associate at Virginia Tech, said, "Vines have become reasonably cold hardy for this time of year." They noted, "Al- though we in Virginia are not cur- rently measuring grapevine cold hardiness, we've used a bud cold hardiness model developed at Washington State University that we have previously found to be fairly accurate in terms of predict- ing dormant bud cold hardiness at a given time of the fall, winter and early spring." After plugging in data about minimum daily temperatures in Winchester, Va., from Sept. 7 to Dec. 13, 2015, the duo predicted that Cabernet Sauvignon would be able to tolerate temperatures as low as 0° F. At the same time in 2014, Cabernet Sauvignon buds were estimated to be cold hardy to about -8° F. "Other varieties would not nec- essarily respond to ambient tem- peratures in the manner that Cabernet Sauvignon is predicted to do," they said. "Single-digit temperatures (or even tempera- tures much below freezing) have not been forecast for the remain- der of 2015." Of course, temperatures did drop into the single digits in Janu- ary, and some plants that weren't watching the calendar in late De- cember pushed a few flowers out. "Grapevines, fortunately, are a little smarter," Wolf and Hatch commented. "Multiple mecha- nisms help grapevine tissues sur- vive through the winter. For simplicity, let's lump these mecha- nisms into two categories: cold hardiness and dormancy. Both of these are dynamic processes that are dependent on the grape tissue and the temperature stimulus to which the tissue is exposed. Expe- rienced grapegrowers should be familiar with the U-shape of grapevine bud hardiness during the dormant period (see "Grape- vine Bud Hardiness in the North- ern Hemisphere"). Sharp vertical changes in the seasonal cold har- diness curve are due to the vine's physiology related to cold hardi- ness, in which the vine's tissues acclimate and deacclimate to cool- ing and warming temperatures." Wolf and Hatch continued, "Dormancy can be thought of as a protective feature that keeps grapevines from taking a miscue from warm periods in the fall. It can be separated into multiple Basic Hoe comes with a Hillup and a Takeaway Blade. Additional attachments include .3 Tooth Cultivator, Undercutter Blade, Rotary head, " NEW " Rolling Cultivator and "Vine Auger". The Green Hoe Company, Inc. 6645 West Main Road, Portland, NY 14769 PHONE (716) 792-9433 FAX (716) 792-9434 WWW.GREENHOECOMPANY.COM GREEN GRAPE HOE This profile of typical grapevine bud cold hardiness during the dormant season shows the acclimation, maximum hardiness and deacclimation stages. GRAPEVINE BUD HARDINESS IN THE NORTHERN HEMISPHERE 20 15 10 5 0 -5 -10 -15 -20 Median bud-freezing temperature LT50 (º F) Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. Maximum Hardiness Acclimation Deacclimation T. ZABADAL, ET AL. 2007. MICHIGAN STATE UNIVERSITY EASTERN WINE LABS Serving the Analytical needs of East Coast Wineries WWW.EASTERNWINELABS.COM Ph 609-859-4302 Cell 609-668-2854 chemist@easternwinelabs.com AOAC Member EasternWineLab_Mar09.qxp 1/22/09 9:47 AM Page 1