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May frost caused selective damage to local vineyards

New buds at Alexis Bailly Vineyard suffered damage seemingly at random. In some cases, frost killed one new shoot within five inches of another that escaped unharmed. (Submitted photo)

A mid-May frost caused all sorts of trouble for regional vintners, causing some vineyards to lose a big percentage of this year’s grape crop.

According to an Associated Press article, the frost hit southern Wisconsin and southeastern Minnesota over the weekend of May 14-15, leaving several vineyards with less than 50 percent of their 2016 crop.

Locally, the frost made a big impact on the Alexis Bailly Vineyard.

“We got by with maybe, at the most, 50 percent loss,” said owner Nan Bailly.

That, she said, was good news.

“We’ve heard horror stories from other growers in the Midwest,” she said. “... We’re thinking that we got by pretty good.”

At Alexis Bailly Vineyards, the cold hit for three nights, but only did damage on one, the night of May 14. Temperatures dropped to 27 or 28 degrees at the vineyard, Bailly said, which is enough to kill a stem.

Bailly said that there was one thing she suspects played a part in saving many of her grapes. They had applied a particular fungicide/bactericide that has the convenient side effect of giving the plants a slight edge – 3 to 5 degrees, Bailly said – in cold tolerance.

Frost freezes the water within plant cells, causing the cell membranes to burst and the cell to die. An article published by the American Society for Horticultural Science notes that bacteria can also serve as a point of origin for frost formation; eliminating the bacteria can also reduce the chances a new shoot will succumb to frost.

Another factor, particularly for her Frontenac variety, was spring pruning that delayed those vines’ budding.

Vines at Alexis Bailly Vineyard started budding on April 30 and all but the Frontenacs had produced new buds before the frost hit.

Selective damage

What made the frost particularly odd was how selective it was. Normally, Bailly said, a frost will form in layers over the ground.

“When you have cold temperatures, they come in layers and they come in all sorts of different places,” she said.

The coldest layers are at ground level, and that’s where springtime frost typically forms. Plans about five feet above the ground, which is where the grapes’ fruit zone is, are typically safe from frost, she said. But the May 14 frost didn’t adhere to the normal rules.

“This was all over the board,” Bailly said.

Although her vineyards are on flat ground, the frost damage hit fresh shoots seemingly at random. Bailly said she had a shoot completely killed by the frost that was situated less than five inches away from another one that was unharmed.

“I’ve never actually seen anything like that,” she said.

The situation was much different just north of Hastings at Vinmark Estates.

“We actually did OK,” said owner Cynthia Bahr.

Bahr said damage to her vineyard was limited to less than 5 percent, although her nearby tomato and pepper plants took massive damage.

Her property is located a little higher, though, and the vines are situated on a slight slope with a low spot at one corner that allowed cold air to “drain” out of the vineyard. She also had heard of another nearby vineyard just south of hers that got hit hard by the frost.

“Placement of your grapes is key,” Bahr said.

Not a normal season

The best thing for farmers, Bailly said, is to have growing conditions stay normal. That’s not at all what they got this year. The spring was bizarre, Bailly said, with 50-degree days in March leading into a cool April and an average May.

“May 15 is our last average frost date,” she said. “It seems like an unusual year for us to have gotten such a late frost.”

The irregular temperatures make it difficult for plants to anticipate when they should start growing, and budding too early puts them at risk for cold damage.

Production impact

For Vinmark Estates, the damage won’t impact wine production too much. There will be a few less grapes to work with this year, so there will be some production loss, Bahr said.

At Alexis Bailly Vineyard, the impact will be more substantial.

“It will affect quite a bit of our production,” Bailly said, especially for wines produced from the vineyard’s Marquette grapes. That variety buds earlier than others, and sustained about 80 percent damage, Bailly said. In contrast, the Frontenac grapes buds late, so there Bailly expects a mere 5 percent loss.

Wines available this year, however, aren’t impacted at all, as those were produced last year.

“We’re always drinking last year’s wine,” Bailly said.

And, even with the smaller crop this year, she still expects “an adequate crop” of 2016 wine to be released in 2017. Bailly said she plans to supplement locally grown grapes with fruit grown elsewhere, most likely from New York or California.