Amador County vineyards avoid major frost damage

Frost damage from recent cool temperatures should be at a minimum in Amador County vineyards, according to Scott Oneto, University of California Cooperative Extension Amador County Farm Advisor.

The recent chilly weather has been watched closely in Amador County, where temperatures dipped the past few days and delicate buds were on the vines.

For many of the grape growers, frost damage should be slight, he said. However, for those in frost-prone areas either at higher elevations, or in swales, damage may be more prevalent.

Frost injury to grapevines this time of year begins to occur at 31 degrees after about a half hour, Oneto said. The longer the lower temperature, the greater the damage.

Tuesday morning lows were in the 30s throughout much of the wine-growing region, Oneto said. Many of the higher elevation vineyards saw temperatures in the upper 20s, Oneto said in an e-mail.

Also, some of the vineyards planted in the the hollows between the hills, saw lower temperatures as cold air drained into the swales.

Charlie Havill, president of the Amador County Wine Grape Growers Association, said the daytime weather has been beautiful in the foothills.

"But the past week has been a little troublesome," he said. "Temperatures have dropped to 30-32 degrees. Those growers with wind machines have been well-protected."

Havill said there has not been significant frost damage.

"It's a normal spring for us -- we always get something happening in the weather this time of year," he said.

Amador County is noted for its zinfandel vines. Growth on those vines have not broken from the buds so there has been no damage to those plants.

"So far, so good," said Havill, owner of BellaGrace Vineyards. "It looks like it is going to be great the rest of the week. And it looks like rain coming in over the weekend."

Growers have appreciated the wet winter after some pretty dry years. The county has a lot of dry-farmed zinfandel vines, meaning they are not irrigated.

"The last two or three years it has been very difficult on the vines so production has not been as good," he said. "We like to have enough water so those older, dry-farmed zinfandel vines can make it through the season without any irrigation. There is enough moisture in the soil now that they will be fine through the summer."

Oneto said that growers have ways to minimize risk from cold. Most Amador County growers do this by managing cover crops or weeds between the rows of vines.

Disking the soil is detrimental to frost protection, said Oneto. Turning the soil reduces the heat capacity and removes heat from the soil.

Ground covers are beneficial so it is best to keep the ground cover short by mowing or use of chemicals, he said.

A few growers in the Shenandoah Valley rely on wind machines as another way to protect vines from frost. Wind machines provide protection by mixing warm air from above with colder air near the soil.

The National Weather Service forecast for Sacramento:

Today: Sunny, with a high near 73. North wind around 5 mph becoming calm.

Tonight: Mostly clear, with a low around 43. Calm wind becoming south around 6 mph.

Forecast for Plymouth, Amador County:

Today: Sunny, with a high near 68. East-southeast wind at 8 mph becoming southwest.

Tonight: Mostly clear, with a low around 43 degrees. Calm wind.