West Lafayette, Ind.—A warm winter and even warmer spring has vines waking up a few weeks early across most of the central United States, and that is prompting growers to worry about the significant threat of a late spring freeze that could kill the tender buds and shoots.

“Unfortunately, we had a high of 84 yesterday and are forecast for 86 today,” Bruce Bordelon, a horticulture professor with Purdue University, said last week. “We haven’t had any low temperatures at all.”

Growers delayed pruning as long as they could in Indiana, but Bordelon said that with the balmy weather he expects to see bud break across much of the state's vineyard acreage. Leaving as many buds as possible is one method to mitigate frost damage. If killing temperatures do occur, apical buds are sacrificed to protect basal buds. If there is no swing to low temperatures this season, growers can go back through and trim off the excess growth.

The record high temperatures have some viticulturists comparing this spring to that of 2007, when a warm spell shattered historic highs only to be followed by a record-setting string of cold temperatures. The University of Missouri’s Institute for Continental Climate Viticulture & Enology, ICCVE, found that Columbia, Mo., saw its third-warmest period in 118 years for late March 2007, followed by the coldest period in 118 years.

The “Easter freeze” cost the United States $2 billion in crop damage, said Michael Hudson, the operations officer for the National Weather Service’s central region. He said the weather is similar to 2007, although the next month is predicted to continue to be warmer than normal.

However, there could be two to three days of freezing weather that could cause damage and yet not bring the average temperature down for the month. “We’re not out of the woods statistically for freezing temperatures,” he said. The weather service has weather outlooks from six to 10 days to three months at cpc.ncep.noaa.gov, which includes predictions for hazards.
 
Persistent warm pattern
The warm weather has been a persistent pattern throughout much of the United States all winter. Hudson added that there have been 41 different record highs in the north central U.S., and those temperatures broke records from as recently as 2011 to as far back as 1894.
 
Mark Hart, a grapevine breeder who owns Mt. Ashwabay Vineyard in Bayfield, Wis., said a killing freeze has been the common subject of conversation where he lives in the northern half of the state. He said most bud pressure in Wisconsin had been limited to the vineyards in the south, but he acknowledged his four acres of vines are still at risk.

He said many of the growers in Wisconsin are relatively new to the industry and might not have heard about the 2007 freeze. Those growers have most of their capital is in vineyard development, he said they don’t have burners, fans or overhead irrigation to protect against frost damage.

Speaking from the Leelanau Peninsula in Northern Michigan, Mark Johnson, the winemaker and vice president for Chateau Chantal described the weather as “weird” and “surreal.”

He said he plans to leave four or five buds per cane in the hopes that if a freeze occurs, he could stand to lose half. Chateau Chantal grows vines on 65 acres. Taking the optimistic view, Johnson said that if the weather stays warm it would bring an early ripening season that could mean harvesting some Merlot and Cabernet Franc he doesn’t get every year. “That would be fun, I’d look forward to that.”

Johnson said the peninsula can see wild temperature variations, and so he’s considering investing in a fan that he can attach to a tractor. Having a well-situated fan in a good location could protect several acres of vines from frost, he said.

R. Andrew Allen, extension viticulturist with the ICCVE, said many of Missouri’s vineyards have already gone through bud break, particularly in the southern part of the state. With temperatures expected to stay relatively high, and soils full of moisture, Allen expects vines to exhibit quite a bit of vegetative growth.

Unfortunately, Missouri has a history of late spring frosts from the end of April through the first week of May.

Most growers don’t have frost protection systems, and Allen said some would turn to helicopters or burning hay bales if needed. In the meantime, he said most would likely just pray that the mild weather holds out and they can ride out what could be an early season. “We’re all very nervous.”