Southern Oregon vintners expect some damage from the recent cold snap, but they'll have to wait a bit to learn the extent.
Zero-degree lows sent vintner Herb Quady out to a Jackson County hillside Monday afternoon, searching for signs of potential damage.
Unless the single-digit temperatures persist beyond a few days, however, long-term damage will probably be minimal, vintners say.
The real danger involves new plantings and older vines that are vulnerable to splitting.
"Crops will be affected at least; young vines may be killed back," says Quady, who manages scores of acres. "Young, weak vines planted on rootstock this year could be killed back below the graft union and will need to be replanted. From what I saw at this location, there did not seem to be any damage to the vines, although I observed a fair amount of damage to the buds. The vines that were harvested first had the least damage because they had plenty of time to harden off."
In general, he says, older vines may see problems down the road from crown gall, a bacterial disease caused by the splitting of trunks.
Some of the varieties he inspected have 50 percent damage or more to the buds. He took samples for further study.
"Once I look at them under the microscope," he says, "I will know more."
The worst cold-weather years in modern Southern Oregon viticulture were in early 1989 and late 1990.
René Eichmann of Bridgeview Winery in Cave Junction, where his family first planted grapes in 1982, admits to paying far more attention to meteorological curiosities than most local residents.
"It's been really weird; it never really did get that cold (this week) in the Illinois Valley, but it got really cold in the Rogue Valley," says Eichmann, who now lives in Rogue River. "It was minus 1 in the Gold Hill area. The last really hard freeze that affected us in the Illinois Valley was in 1989, when it got down to single digits."
Such temperatures, he says, aren't good for chardonnay, riesling, cabernet sauvignon and franc grapes.
The difference between this icy winter and the one a quarter-century ago is magnitude.
"When it got cold in 1989, the grape industry was still in its infancy," Eichmann says. "Del Rio hadn't been planted yet, or a lot of the vineyards in Sams Valley, Ashland and Talent."
Another difference, he says, was that the 1989 freeze came in early February.
"Even though the plants don't show it then, there is an ever-slight amount of juice pushing up more moisture. If all of a sudden those vines dry up and freeze, that really goes to town."
The 1990 event came in December.
"Everyone said that 1989 was our 50-year frost, and then it happened again in 1990," Eichmann says. "The vines are about as dormant as they're going to get right now and that gives them a lot more resistance."
Most damage won't be visible until budding takes place.
"There are really three buds in each bud," Eichmann says. "The primary one that grows is fruitful and is what makes your crop. The second bud is kind of a fail-safe if something happens to the first one, and is almost as active as the first. The third one, if something happens to one and two, (produces) something green to prune for the next year, but there aren't going to be any grapes on there."
Outside White City, Eric Weisinger planted 2 acres of cabernet and tempranillo in 2011 to go with 15 acres put in during 2008.
Patrolling the rows after the mercury fell to minus 4 in the neighborhood, Weisinger remains hopeful.
"If you're getting temperatures in the teens for four or five days, maybe even a week, it could have some risk," Weisinger says. "A couple of things can happen to plants that were put in this year. One, if it gets really cold for any extended period of time, the cell walls can freeze and rupture, kind of like frostbite for a grapevine. Also, if it's freezing past a week or so, graft union can be endangered."
His experience in 2011 leads him to expect the best-case scenario.
"We put in 2,000 plants in 2011 and lost two," he says. "That's unheard of. Grapevines are almost like a weed in a sense, they're almost as tough as blackberries. There's going to be some damage; there always is. Weather is always factor in agriculture, and grapes are no different."