The worst spring frost in decades has taken its toll on Napa County, causing  more than a million dollars in crop damage, according to local growers.

 Many growers have been running wind machines at full tilt, but night temperatures dipping into the twenties have damaged some vineyards nonetheless.

“It’s been one of the worst frosts on record,” said Garrett Buckland, a viticulturist at Premiere Viticulture in Napa. He noted there have been 27 days of frost over the past month and a half.

Grape-growing mogul Andy Beckstoffer, chairman and CEO of Beckstoffer Vineyards, which owns 1,000 acres in Napa County, said this is the worst frost he’s witnessed since the early 1970s.

“Everybody’s talking about it,” said Beckstoffer, who does not yet know the extent of the damage to his vineyards. “We think it’s substantial.”

Julie Nord of Nord Vineyards owns or manages a total of 1,000 acres in Napa County. She estimated her company’s loss at about $1 million and crop insurance may only cover $350,000 of the losses.

A total of 60 acres are damaged at vineyards in Pope Valley, Carneros, Foss Valley and Yountville, Nord said.

Buckland said clients have lost about 20 acres of sauvignon blanc and cabernet sauvignon near Calistoga and Stags Leap district. Some may be forced to buy fruit to be able to make their traditional wines this year, he said.

Beckstoffer and others said the frost hit vineyards that are normally shielded from it.

For instance, Robert Biale, co-owner of Robert Biale Vineyards, reported that one acre of petite syrah was lost at his family’s vineyards off El Centro Avenue in north Napa. He said the nearness of residential neighborhoods has helped stave off frost in the past, but not this year.

Another 20 acres of zinfandel, where Biale does not have a wind machine or other device to keep vines from suffering in a cold snap, suffered light damage, he said.

Things were made worse this weekend, Buckland said, because cold temperatures made it harder for wind machines to pull the usually warmer air from about 40 feet above the vineyards. As a result, the machines blew cold air upon cold air.

Stephen Krebs, program coordinator and professor of viticulture at Napa Valley Community College, said the 6-acre student vineyard received some damage.In an e-mail, Krebs said the green shoots carry the crop. Once damaged, secondary buds grow out but these rarely produce fruit, he said.Biale said he and his staff are pinching off the frost-burned tips to allow the secondary buds to push through and save the vine for the next season.