Issue link: http://winesandvines.uberflip.com/i/643683
March 2016 WINES&VINES 61 WINE EAST GRAPEGROWING Tim Martinson, senior viticulture exten- sion associate in the department of horticul- ture at Cornell University, has also been tracking the cold-hardiness of grapevines. He told Wines & Vines, "We have been freezing buds from Geneva since early November. Basi- cally, bud hardiness to date is tracking what we saw last year: Riesling LT50 (median bud freezing temperature) is pretty much equiva- lent to last year (-10° F); Concord is more responsive, and LT50 seems to be down to -18° F or so. This suggests the vines are not any less hardy than last year at this time. That's good news." On the issue of chilling requirements, Mar- tinson commented, "We're ahead on 'chilling hours,' with enough to satisfy endodormancy, meaning that if temps rose well above freezing, time until bud burst would be the shortest possible, and responsive to ambient tempera- ture alone. So this may leave vines somewhat more at risk for early bud burst. The caveat is that we never worried about chilling hours in the past, so I'm not sure this is a 'real' issue. Bottom line: I'm not worried about any lasting impact from a warm December." Explaining how grapevines acquire cold hardiness In the February 2011 issue of Appellation Cor- nell, Martinson described how grapevines transi- tion from a cold-tender to a cold-hardy state in a process known as cold acclimation and then deacclimate, slowly, which leads to bud burst. This process allows vines to survive low winter temperatures. Martinson wrote: "It is a gradual process, which starts around veraíson in response to low tempera- tures and decreasing day length and contin- ues after leaf fall when temperatures are below freezing. As temperatures rise after mid-winter, grapevine tissues deacclimate in a gradual process, culminating in bud burst and active growth at the start of the growing season. How fast this process happens, and to what extent vine tissues survive extreme winter low temperatures, depends upon the cultivar (its genetic makeup), seasonal tem- peratures and how they vary, and the vine's condition as it enters the dormant season. "During the growing season, green, ac- tively growing vine tissue is composed mostly of water, which will form ice at freezing tem- peratures, expanding the cells and disrupting their integrity. In preparation for the dormant season, cells become resistant to lower tem- perature through two mechanisms: dehydra- t i o n t h r o u g h m o v e m e n t o f w a t e r t o intercellular spaces and accumulation of sug- ars and protein complexes that bind water and serve as cryoprotectants. These cryopro- tectants lower the freezing point of water and allow cell contents to supercool without form- ing damaging ice crystals. The acclimation process starts well before freezing tempera- tures occur, but buds continue to gain hardi- ness from the onset of freezing temperatures through the coldest part of midwinter. 251 Gambee Road, Geneva, NY 14456 Phone: 315-759-2118 Toll free: 888-234-6752 Fax: 315-789-1848 Email: cjennings@vancemetal.com Website: www.vancemetal.com Quality Rugged 12 gauge, Custom & Stock Stainless Tanks Catwalk Systems • Pump Over Carts • Custom Hoppers, Chutes & Bins PROUDLY MADE IN THE USA 2015-16 SEASON CONCORD - GENEVA 70 60 50 40 30 20 10 0 -10 -20 -30 Temperature max. and min. (º F) Oct Nov Dec Jan Feb Mar Apr Critical Temperatures (º F) 2015-16 SEASON RIESLING - GENEVA 70 60 50 40 30 20 10 0 -10 -20 -30 Temperature max. and min. (º F) Oct Nov Dec Jan Feb Mar Apr Critical Temperatures (º F) Bud freezing temperatures (black line) are compared with minimum and maximum daily temperatures during the 2015-16 winter season for Riesling and Concord at the New York State Agricultural Experiment Station in Geneva, N.Y. The blue line shows the measurements from 2014-15; the brown line is the predicted bud temperature based on a model out of Washington State (Keller & Ferguson, et al.). The predicted LT50 from min./max. temperatures alone predicted by model has converged by early January, after lagging behind in the fall. Note that LT50 temperatures are lower and change faster for Concord than for Riesling. This sug- gests that that the vines are not any less hardy than last year in early January. BUD10 BUD50 BUD90 2014-15: 50% Predicted 50% 2015-16: 50% BUD10 BUD50 BUD90 2014-15: 50% Predicted 50% 2015-16: 50%