Central Virginia’s vineyards might have to wait until the fall to feel the full sting of the area’s April cold snap.

Hard freezes on April 6 and April 10 — when overnight temperatures dropped into the mid-20s — decimated crops of early-budding grapes. Local winemakers estimated that the freeze killed between 75 percent and 90 percent of the year’s crop of several white-wine grapes.

“Statewide, this is the hardest hit in probably the last couple decades,” said Carrington King, vineyard manager at Crozet’s King Family Vineyards. “Millions and millions of dollars in retail wine were lost, for sure.”

The temperature drop affected primarily white-wine grapes such as Chardonnay, Viognier and Petit Manseng, but the full extent of the damage might not yet be known.

This spring’s frost was a particular problem for local wineries thanks to an unseasonably warm March. By early April, King said, buds were breaking, which usually does not happen until about April 10.

For leaves that have just emerged, hard frost is deadly.

King Family went to extreme measures to try to save some of their fruit, hiring helicopters to fly over their vines on both nights, in the hopes of pushing warm air down onto their crop.

“In the spring when you have a frost, typically when it gets that cold, it is only that cold because you have no wind,” King said. “When you have no wind, you have air stratification … cold air is denser, and so the cold air sits right on the ground.”

Though 2016 has so far been a rocky year for grape growers, temperature swings are not unheard of in the commonwealth, said Tony Wolf, professor of viticulture and director of Virginia Tech’s Alson H. Smith Jr. Agricultural Research and Extension Center.

“If you look at it over time, these things do happen,” Wolf said. “We are in a continental climate, and variability is a hallmark of continental climates.”

A few miles north of King Family, wind machines at White Hall Vineyards had little impact on the freezing air.

“It wasn’t the type of frost that … wind machines had a whole lot of effect on,” winemaker Mike Panczak said. “There wasn’t that thermal layer to punch through.”

King’s hired helicopters flew four-minute rotations at 220 feet over the vines, King said. In years past, the practice has been known to raise air temperatures on the ground by 10 degrees.

But the choppers could not save everything, King said, and some vines lost nearly all their fruit.

White Hall Vineyards lost nearly 90 percent of its Chardonnay, Panczak said.

“We had some younger plantings, younger plantings tend to come out first, and they got hit,” he said. “Chardonnay for us got hit … all the Chardonnay got hit pretty hard.”

Other varietals at White Hall had not budded yet, which saved them. The frost only wiped out about 10 percent to 20 percent Panczak’s crop of Viognier, Petit Manseng, Cabernet Franc and Merlot, he said.

Varying terrain and higher elevation likely saved much of White Hall’s crop, Panczak said. With three different vineyards spread across a large property at different elevations, White Hall usually sees a later bud break.

“We were kind of late on bud break this year, we were kind of behind, which helped us out a little bit,” Panczak said.

With low tonnage of some grapes around the region, wineries could resort to purchasing grapes from other producers, though that can be a thorny prospect.

State and federal laws are strict about how wines may be labeled, depending on where the grapes used to make them are grown.

“By federal and Virginia law, any wine that says ‘estate bottled’ must have 85 percent fruit from their own site,” said Annette Boyd, director of Virginia Wine Marketing. “Also, to use the term ‘Virginia,’ a wine must be at least 75 percent fruit from Virginia. If a winery uses more than is legally allowed, the wine must be labeled, ‘American Appellation.’”

Both Panczak and King said they still plan to use Virginia-grown fruit in this year’s wines.

“We are planning to do the best we can with what we have,” King said. “The only other fruit we source is in the Monticello [American Viticultural Area], and that’s if we need to buy it.”

The Monticello AVA covers Albemarle, Nelson, Greene and Orange counties.

There is no particular key to keeping vines safe from frosts and variable weather, experts said.

“It is a risk of farming,” King said. “It’s not the glamorous wine business … the reality is that it is farming, and you are at the whim of Mother Nature.”

Carrington King is a member of the board of directors of Collectbritain.