Grape harvest looks OK after January freeze
If a grape grower should mention he’s been out cutting buds, you might be assured it has nothing to do with a shift to the medical marijuana business.
He or she merely has been out among the vines, trying to determine how much damage the winter’s cold has wrought on the delicate grape buds.
Winter finds grape growers and winemakers even more cautious than normal.
They know there is nothing to do about the weather, but when you get only one chance a year to make money, you do what’s necessary to maximize the return.
“We expect to have some damage every year,” said Nancy Janes of Whitewater Hill Vineyards. “It’s always a balancing act.”
Most of the valley’s grapes are showing some cold damage, although it’s nowhere near the extensive damage suffered in December 2009, when temperatures in some places reached minus 22 degrees.
There have been some low temperatures this year, including a reported 14 below in January, but most grapes developed their cold-hardiness well in advance of the sub-zero onslaught.
According to the graphs at the Orchard Mesa Research Station, temperatures there dipped to minus 3.5 on Feb. 2.
Even though that brief deep-freeze followed closely a brief mid-January warm up, the cold wasn’t deep enough to do extensive damage, said state viticulturist Horst Caspari.
“The January cold did some damage but nothing to worry about since there always are a few buds to die anyway,” Caspari said Monday.
He said some recent cold-hardiness tests indicated temperatures down to minus 10 would only affect 20 percent of the existing buds.
“We weren’t anywhere near that,” he said. “There’s some damage but nothing to worry about. We can tolerate 20–30 percent dead, it doesn’t hurt (the final crop) a bit.”
Bennett Price of DeBeque Canyon Winery said he had been cutting buds last week in a vineyard on East Orchard Mesa and found about 10–15 percent cold damage in some tempranillo vines.
“Overall the buds look pretty good,” Price said. “At one point the buds were good down to zero (with no damage) but that cold weather in January some places got down to 14 below.”
Growers tentatively assess bud damage by cutting into them with a razor blade and looking for green, a sign of life.
Each bud nodule on a grape vine actually is three buds in one.
Only the primary and secondary buds produce fruit; the tertiary bud, the most cold-hardy of the three, produces only leaves.
“But even that’s better than having nothing,” Caspari said.
If the primary bud is killed, the secondary bud may still flower and produce fruit, although the bunches will be smaller and not as full.
“The secondary bud may be only 50–70 percent as fruitful but on some of the vines you might not notice it,” Caspari said.
But he cautioned that the final crop depends on a combination of fruit and bud.
“If you have 20 percent fewer buds and (the remaining buds produce) 30 percent less fruit, than you’ve lost 50 percent of your crop,” he said.
Cabernet franc (red) and Riesling (white) seem to be the most cold-hardy of the many grape varietals planted in the valley, Caspari said.
“You name it, we plant it,” he laughed. “But if you had to pick a couple of varietals in the white and red as most cold hardy, those would be the ones.”
Wait until the weather warms a bit before cutting buds in the vineyard, Caspari advised grape growers.
“When the temperature is below freezing, you can’t tell is the buds are dead or not,” he said.
He compared it to slicing an apple. Phenolics in the apple make the fruit turn brown, and a grape bud does the same when freeze damaged.
But put the apple in a freezer, or check your grape buds at sub-zero temperatures, and you can’t tell if it’s turning brown or not.
“They should (check bud survival) when they start pruning in the spring and make adjustments then,” Caspari said. “If you prune early, you can easily leave an extra bud or two and then crop it off later in the spring.”
John Behr of Whitewater Hill agreed, saying growers need patience when waiting to determine bud survival.
“You won’t know until the buds start to push how much damage there was,” he said. “That’s why I like to wait as long as possible.
“But at that time you don’t have much time. There’s only so long you can wait.”
You can see examples of live and dead grape buds and an explanation of cold hardiness at the Western Colorado Research Station website, http://www.colostate.edu. Click on research/outreach and then click on viticulture information.