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Serving: MI
Thomas Todaro, MSU viticulture educator, shows a sample of grapes that were allowed to stay on the vine to be frozen, harvested and processed into ice wine.
FROZEN ON PURPOSE: Thomas Todaro, MSU viticulture educator, shows a sample of grapes that were allowed to stay on the vine, purposely, to be frozen, harvested and processed into ice wine.

Polar vortex takes its toll in Michigan

Winegrapes take the brunt of cold weather in the southwest part of the state.

Michigan’s fruit growers worry about three things nature can throw at them — how low will the mercury go in winter, if a spring freeze will hit during bloom, and if favorable weather during bloom will provide good pollination. Each has the potential for disaster.

After January’s polar vortex that pushed temperatures to as low as −19 degrees F, grape growers are bracing for what the spring will reveal.

Certain varieties, including the most cold-tender vinifera varieties used for winemaking, are expected to be close to a total loss in southwest Michigan.

Michigan is a big state, and logically, the assumption would be the farther north, the colder it would be and the more extensive the damage.

Not so, as northwest Michigan was shielded by Michigan’s unique lake effect that provided insulation.

“While southwest Michigan was enduring −19-degree temperatures, Leelanau [northwest] got down to around −5, and Old Mission was the warmest,” explains Thomas Todaro, a Michigan State University viticulture educator out of Leelanau. “We can expect severe damage in the southwest and relatively minimal in northwest.”

After a mild December, Michigan experienced two extreme cold events in January.

The first was a pulse of cold, dry air Jan. 18-22. The second was a more extreme polar vortex event Jan. 30-31.

The name polar vortex was introduced during the 2013-14 and 2014-15 winters, describing a mass of frigid polar air that plunged south into the U.S.

As was the case in those years, it has left a grim outlook for vinifera grapes — such as Riesling, Merlot and Chardonnay — in southwest Michigan.

Winter cold injury depends on many interrelated factors, Todaro says, including the site, varieties planted, snow level, temperatures before and during the event, duration of the cold event and conditions during the freeze.

The level of damage could be a significant blow to Michigan’s budding wine industry. Vineyard area from 1991 to 2016 has increased in the state from only
38 acres to 3,050 acres, while total grape acreage increased from 210 acres to 13,100 acres, according to USDA’s National Agricultural Statistics Service.

Michigan now ranks in the top 10 in winegrape production in the nation. The number of approved commercial wineries rose from 14 in 1991 to 148 in 2018. The total economic impact of the wine industry is $5.4 billion per year, says Karel Bush, executive director of the Michigan Craft Beverage Council.

She also notes that Michigan wineries receive 1.7 million visits each year and contribute more than $252 million in tourism spending.

Damage breakdown

Michigan has five federally approved American Viticulture Areas. In the northwest part of the state, near Traverse City, are the Leelanau Peninsula and the Old Mission Peninsula AVAs.

This is where about 55% of Michigan’s winegrapes grow. In the southwest part of the state are the Lake Michigan Shore and Fennville AVAs, producing about 40% of the state’s winegrapes. The newest AVA is the Tip of the Mitt, located in the northern tip of the Lower Peninsula.

Within these AVAs, growers are primarily tending four types of grapes, going from the most cold-tender to the hardiest — European, Interspecific hybrid cultivars, American and Super hardy interspecific hybrid cold climate cultivars.

According to Enviroweather data, Todaro says temperatures taken in the Lake Michigan Shore on Jan. 30-31 were between −14.1 and −15.7 degrees.

On Jan. 30 in Fennville, air temperatures were recorded between −11 and −14 degrees for 10 hours straight, and on
Jan. 31, temps were between −11 and −15 degrees for nine more hours.

“They were only separated by about three hours of slightly more than −11 F,” Todaro says. “For these cold-sensitive varieties, the threshold for damage ranges between  −5  to −11 degrees. We were below that for nearly 19 consecutive hours.”

Meanwhile, at the same time, the northwest was getting west-to-east winds, pulling in the warm lake air under the protection of cloudy skies.

“For the northwest, we expect only 10% to 25% primary bud damage, which is not out of the normal,” Todaro says.

On the other hand, the southwest had no wind, he says, except for a few blasts blowing up cold air from South Bend, Ind.

“There was no blanket of protection from the lake and not much cloud cover, meaning any heat was lost to the atmosphere,” he says. “There was some snow, which was good, insulating the vines below the snow line, but vinifera, as well as American Concord and Niagra (juice grapes), will have significant damage. However, we’re not expecting a lot of complete vine dieback.”

In short, Todaro predicts the southwest region to have about 35% primary bud damage on Concord and Niagra, and about 75% or more damage on vinifera.

That may be optimistic, as research from Ohio State University during the polar vortex of 2014 found 100% of vinifera cultivars sustained 100% primary bud damage after six to nine hours of exposure to −11 degrees. It’s estimated it cost Ohio growers
$12 million in crop and wine loss.

“In extreme situations like this, growers will have to rehabilitate,” Todaro advises. “We hope for a surviving portion of the vine below the snow level. The living buds at the base of vines will produce shoots that growers will have to retrain.”

Those shoots also may be fruitful at the base, especially from 1-year-old wood, he says. Depending on the number of buds, growers might expect between a half-ton and 1.5 tons per acre.

“The severity of the damage is really not yet known, but worst-case scenario, growers will need to replant, meaning two to three years to get back to production,” Todaro says.

The frustration is growing. “We expect these kinds of events once or twice in every quarter century, not three of them in six years,” Todaro says. “The cost of not being able to produce consistently, and the reduction of production and revenue on a yearly basis, is wearing on growers.”

Todaro has been and will continue to work with growers on matching grape species and cultivars to suitable sites, and how cultural practices affect success in vineyards exposed to extremely low winter temperatures.

Peach, blueberry outlook

Expect both peach and blueberry damage from the polar vortex, says Mark Longstroth, MSU Extension fruit educator, who says it was the coldest air since 1994 when it got down to −25 degrees.

“It likely killed flower buds on some peach trees, but not cold enough to hurt the tree,” he says, while noting that already weak or young trees may be the exception.

“In Berrien County, close to the lake, there will probably still be a peach crop. It’s not a complete wipeout,” he adds.

Blueberries will be hurt some, he predicts, but expects there to still be plenty of live buds.

“Blueberries could have injury in Van Buren County and not in Ottawa County,” he says. “The damage won’t be like it was in ’94, when it was widespread and growers had to get summer jobs.”

Peach growers still will have to spray to some extent for insect and disease, but will find some savings in not having to spray for insects that attack fruit and will save on labor costs, Longstroth notes.

He suggests that growers prune peaches hard anticipating them to come back in abundance the next year.

“Growers can also cut back on fertilizers, because the plant will be recycling nutrients,” he says.

For consumers, Longstroth says don’t worry. “It’s not the whole state of Michigan,” he says. “There will be plenty of peaches from different areas of the state.”

For growers, he advises to buy crop insurance, and unless you have a really good site, look at something more cold-hardy and diversify your crops so that a freeze or winterkill is not a complete loss.

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