By SEAN ELLIS

Capital Press

CALDWELL, Idaho -- Grape growers and wineries in the state's main wine region are starting to get a little concerned about an extended period of unusually low temperatures.

"Any time the mean temperature stays real low for an extended period of time, there is always concern about bud damage," said winemaker Martin Fujishin, who teaches viticulture at Treasure Valley Community College. "I think we're getting close to that point where people start to get concerned."

A winter inversion in the Treasure Valley in southwestern Idaho caused low temperatures in Caldwell to remain in the single digits for more than a week. The mercury dipped to 0 degrees Fahrenheit Jan. 4 and 1 degree Jan. 5, about 20 degrees below normal.

Though temperatures began to rise on Jan. 6, they have flirted with the point where there begins to be real concern about plant damage.

"If it starts getting down below zero, your awareness is heightened," said Gregg Alger, owner of Huston Vineyards in Caldwell. "I'm not too worried this year, so far."

For now, Idaho's wine producers aren't overly concerned about significant bud damage but the low temperatures have gotten their attention, says Maurine Johnson, winemaker for Ste. Chapelle, the state's largest winery, which purchases grapes from several vineyards in the area.

"I'm keeping an eye on it," she said.

On Jan. 4, temperatures in the Treasure Valley area reached their lowest point since Nov. 25, 2010. That year, there was significant damage to grape vines because the plants didn't have enough time to shut down and acclimate to the cold, Alger says.

Grape vines become more cold hardy throughout the winter as they adjust to the cold.

"We had just got done with harvest that year and the plants weren't fully to that level yet," Alger said. "I had some pretty serious winter damage that particular year."

But this year is a different story because the unusually low temperatures have come later in the year and vine grapes are more cold hardy, said professor Essie Fallahi, University of Idaho's project leader on fruit crops.

Fallahi said he has checked some vines during the cold snap and they look OK.

"We are OK so far because the cold is coming in early January, when the vines and other plants have been acclimating gradually," he said.

The recent cold snap evoked faint memories of the winter of 1990-91, when temperatures in the valley fell well below zero and stayed there for three weeks. Temperatures that low can kill grape vines all the way to the ground and it can take three years before they produce at normal levels again.

"It pretty much killed everything to the ground that year," Johnson said.