A hard frost wrecked 75 percent of Wayne Geist’s apple crop last year and hail storms wrecked his entire crop in 2015 so he didn’t bat an eye when Mother Nature baked his trees and vines with sunshine and warm temperatures that were well above normal this month.
“It’s been kind of crazy. We keep trying to ride it out,” said Geist, owner of Bushel and a Peck Market in Chippewa Falls and the president of the Wisconsin Apple Growers Association.
Early warm weather is rarely a good thing for fruit growers in Wisconsin because it is usually followed by destructive cold temperatures after trees and vines have buds. That’s what happened at Geist’s orchard and at many others around the state last year when a hard frost covered the state in mid-May.
In 2012, apple production in the state was down 54 percent from the previous year and yields decreased more than three tons per acre because trees and vines bloomed prematurely after a March heat wave and many died when hard frost hit in April and May.
Fortunately, this month’s warm spell isn’t expected to harm the state’s apples, cherries and grapes because none of them have budded out and temperatures weren’t expected to drop too low, too fast, according to Amaya Atucha, an assistant professor in horticulture for UW-Madison and the state fruit specialist for UW Extension.
The biggest concern is whether the trees and vines adequately reacclimate themselves to the cold weather, she said.
“When temperatures get warm, they lose the ability to withstand cold temperatures,” Atucha said.
Plants can withstand sub-zero temperatures because they accumulate chilling units — or a plant’s version of a winter coat — as temperatures drop in late fall and early winter and the plant goes into dormancy, Atucha said. During dormancy, plants still have buds inside them and there are compressed flowers and leaves inside the buds that will produce the fruit for the following year.
When temperatures warm up and reach levels that covered the state this month, plants lose all their chilling units, Atucha said. That makes the buds susceptible to serious damage if temperatures drop too rapidly, or before the plant can accumulate more chilling units, according to Atucha.
“If temperatures drop dramatically into the low teens or single digits, that can produce damage even though we aren’t visually seeing anything happening or growing. Those (dormant) buds are damaged so when spring comes the buds and flowers will be damaged,” Atucha said.
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Plants will accumulate enough chilling units to reacclimate themselves to cold weather after a warm spell if temperatures drop slowly, which is what happened last week after much of the state had temperatures in the 60s through Wednesday, according to Atucha.
The lack of snow cover is not helping the fruit trees and vines because roots are susceptible to freezing and dying without snow insulating the ground, according to Atucha.
“The moment the buds break they need water from the roots but they won’t keep up because they were damaged from the freeze,” Atucha said.
Atucha blamed global warming for the wild temperature swings of the past few years.
“We’re going to see this more and more,” she said.
Her laboratory at UW-Madison is researching how to help plants and their buds withstand and cope with the rapid changes.
“Can we find one of those genes so we can breed for select varieties that won’t be so affected by these wild changes in temperatures,” she said.
Meantime, the warm weather allowed Geist to prune his trees this month in a T-shirt.
“It was nice to wear just T-shirts outside in February but I hope we won’t be doing it again very soon,” he said.