Viticulture Advice For Warmest March Ever from MSU and UW Experts
According to Diane Brown at the Berrien County Michigan State University Extension, with the weather this warm this early, grape growers are in uncharted waters in terms of vineyard management practices. Brown, who is a Commercial Horticulture Educator at MSU, said that there has never been an earlier bud break in Michigan than 2012. The National Grape Cooperative officially set bud break for Concord and Niagara grapes on Wednesday, March 21. As of Friday morning, Berrien Springs, which is in the heart of Southwest Michigan’s fruit growing region, was at 220 growing degrees base 50, which is also a record. (The normal for March 23rd is 30.7 growing degrees base 50.)
The story is the same in Wisconsin where Tim Rehbein, University of Wisconsin Agent for Vernon County, has been feverishly communicating with area grape growers all week. Rehbein said that there is one historical precedent for the current March warm spell: 1910. That year, when the earth passed through the tail of Halley’s comet, remains the warmest March on record for La Crosse, Wisconsin. “If the final days of March 2012 trend back a little closer to normal, chances are the March 1910 record will stay intact,” Rehbein said.
And what happened to temperatures during April of 1910? The good news, according to Rehbein, is that April 1910 stayed above average. The bad news is that during April, 1910 the coldest nights were on April 16th, 17th, 18th and 23rd with temps of 27, 20,24,and 18 respectively. To add insult to injury, on May 3, 1910, the low in central Wisconsin was 28 degrees, said Rehbein.
The effect of the current warm weather is evident across the region, including Michigan, which by some estimates has 5,000 acres of wine grapes. Brown from MSU said that on Wednesday there were no dormant varieties at her research station. “Chardonnay at our site was the least advanced, but the buds were swelling. Most varieties were at least at early bud swell. Many were showing color. The most advanced was Marquette which was at bud burst. I suspect that if I went out today (Friday) I would find many more varieties at bud burst or beyond today,” Brown said.
Both Brown and Rehbein have practical advice regarding grape frost protection and protecting vines in these uncertain times.
“What I would propose is a version of double pruning to delay bud break,” according to Rehbein. “In a nutshell, there are only a couple of buds per shoot that are controlling all the other buds on that shoot. The controllers are usually towards the tip of the shoot. Most of the other buds closer to the fruiting cane usually break bud later than the controlling buds. The theory of double pruning is to go through your vineyard in spring when buds are just starting to swell and then cut off only half of the shoot. Do not prune all the way down the shoot to your final bud count yet.”
Rehbein went on to say that once the controller buds are pruned off, it can take as long as two weeks for the remaining buds to figure out that the controller buds are not there. When this occurs, some of the remaining buds have to change into controller buds, he said. After the cold weather has passed and the new controller buds are starting to swell, then it’s time to prune back more a more regular bud count. Once again, we are most likely taking off the controller buds and the remaining buds that we want to fruit will take another couple of weeks to get started, he added.
Double pruning does have limitations, Rehbein said. “If it stays warm both nights and days, there is no telling just how fast all the buds could start to swell and break. If you have open buds when you are still doing major pruning and brush removal, you have to be extremely careful not to break off the buds you want to keep.”
Brown at MSU said that if a radiation freeze occurs, wind machines or irrigation could be used for frost protection. She also advised leaving the canes long to help delay bud burst at basal nodes and provide some extra buds as insurance.
See related story: Frost Protection for the Small Grower
Brown also suggests keeping the grass mowed short and getting rid of weeds. Leaving the ground unplowed will also help build more heat in the soil during the day and maintain it at night, she said . “With development this early it is hard to say what would work; it all depends on how low temperatures go and when,” Brown said.
So what does future hold? “At the beginning of this week, the predictions for the first part of April were for bitter cold,” Rehbein said. “Well, that computer model prediction lasted only one day.” The weather service forecast for La Crosse indicates that early April will be is 5 — 10 degrees F above normal. “This should keep our night-time lows above freezing. The longer outlook could also trend above normal for temps,” Rehbein said.