Grape growers and winemakers in the Snake River Valley enjoyed a record vintage in 2012, but a string of days with single-digit temperatures has them worried about bud damage in 2013.

"We had temps down to minus 3 at our place for a week, so I am concerned," says Ron Bitner of Bitner Vineyards in Caldwell. "I am going to do bud samples next week."

Caldwell winemaker Martin Fujishin says another vineyard reported a low of minus 4.

"It's too early to tell exactly, but a rough guess could be that we might see a crop loss of 10 to 20 percent," Fujishin says.

Scott DeSeelhorst, owner of Snake River Winery and the 75-acre Arena Valley Vineyard in Parma, says this winter followed a nearly perfect year for the Idaho wine industry.

"It was single digits for two weeks, so I'm a little concerned about that," DeSeelhorst says. "We will know for sure at bud break, which is usually mid-to-late April for us, but I'm going to get some cuttings and put them in water, trying to force some buds to shoot. I'd like to have an idea before you start pruning."

Fujishin, a second-generation farmer in the Snake River Valley, says, "That's an old orchardist's trick, but it's a pretty good barometer."

Bitner, who began growing grapes soon after moving to the Sunnyslope area in 1980, has rated this as the coldest winter since 1991. At this point though, there's not a lot of widespread damage expected, according to Moya Shatz Dolsby, executive director for the Idaho Grape Growers and Wine Producers Commission in Boise.

"Since the vines are dormant, the risk to vine damage is much less than in spring and fall," she says. "The big concern will be if we warm up long enough for the vines to awake and then be hit with a late spring frost."

Fujishin works with a variety of vineyards for his own Fujishin Family Cellars and as the assistant winemaker for Greg Koenig. He says the bitter weather might be felt on several levels throughout Idaho's wine industry.

"It's the new blocks that I'm most worried about, because they might not be rooted down far enough yet," Fujishin says. "We found hard frost as deep as 14 inches."

Riesling has been largely bullet proof in the Snake River Valley and served as the backbone of the state's wine industry, but Treasure Valley winemakers have enjoyed recent success with newer plantings of less-winter-hardy varieties such as Petite Sirah, Sangiovese and Tempranillo.

"This is semi-alarming," Fujishin says. "We're operating in a grape shortage already with certain varietals. Now, we're looking at possible decrease in yields.

"In Idaho, we always live right on the edge - and some years we fall off," he adds with a smile.

••• Eric Degerman: eric@greatnorthwestwine.com