Aug 5, 2022
Cold tolerance is hot topic at Michigan Viticulture Field Day

Cold damage and the quest to predict it was among the featured presentations at the 2022 Viticulture Field Day at Michigan State University’s (MSU) Southwest Michigan Research and Extension Center in Benton Harbor, Michigan.

The July 27 event, co-presented with the Michigan Grape Society, featured research updates, new vineyard technology, wine tasting and networking.

Project updates focused on intelligent spray control for precision chemical applications, late-season vineyard pest and weed control, grape disease monitoring and management, techniques for successful vineyard establishment and replanting, using drones for chemical application in vineyards, weed control management and high tunnel warm season winegrape cultivar plantings.

Cold damage impacts

MSU tree fruit specialist Bill Shane, who has been working for several years to determine how growers can address cold hardiness in tree fruit crops, shared additional work that’s taking place in viticulture management.

“There are some projects here that have been focusing on cold hardiness in tree fruit,” he said. “Some aspects of the work we’ve been doing to understand cold hardiness in peaches and other tree fruit crops are very apropos to winegrapes.”

The work is supported by Michigan Tree Fruit Commission funds and AgBio Research, and the Michigan Grape Society helped secure funds from Michigan Department of Agriculture.

While Michigan is a great place to grow fruit, the downside is severe cold events, he said.

“I’ve catalogued, since 2000, the cold events that we’ve had here in southwest Michigan,” Shane said. “I’ve separated them into rapid late fall/early winter temperature drops, mid-winter low temperatures and spring low temperatures. You can see there are quite a few years where we are challenged. It depends on the type of crop that we’re dealing with regarding what the impact is on the crop.”

The southwest Michigan grape bud hardiness project is providing data for comparing varieties, model building and other purposes. Three grape varieties are looking good for southwest Michigan; more site-specific weather data may improve model performance, he said.

Preserving the primary bud is paramount.

“This study was set up to look at getting the equipment and techniques together to determine the critical temperatures that are efficient to kill fruit buds,” he said.

He said anticipating severe cold events is important for growers, insurers and those who determine labor needs for harvesting.

“In addition to monitoring what’s out there, it is predicting what will happen out there,” Shane said. “If we have a cold event, can we know in advance this is going to cause this type of damage to this crop? This becomes very important. There are predictive models that are being developed that are very helpful for us in starting to understand how to predict what kind of damage we will have.”

Taking steps to protect the crop when low temperatures are expected is also a concern for researchers.

Determining tolerance to low temperatures

To determine what buds are doing in vineyards, researchers gather shoots and place cut fruit buds in sample tins, which are put into a freezer.

“In the old days we would sneak the buds out of the chamber, cut them and see whether they were dead or not,” he said.

Now, devices measure the temperature inside the small tins, Shane said. Whenever a fruit bud dies, it gives off a small temperature spike.

“We don’t have to take buds out of the chamber to see whether they are dead or not, because they gave us their swan song by the temperature spike. It’s taken a little bit of time to work out the technique, but we have a pretty good system now to do that.”

Shane said that, with the trials, they use a lot of varieties and cooperators, including wineries, producers, vineyard staff  and others

The project included hybrid, vinifera and Concord grapes because all three groups are important in southwest Michigan.

With each grape type, researchers sought at least three sites so they would have an indication of what the behavior of that variety was. They sampled up to 16 different times during the growing season.

“Such as, 50% of the buds were killed at a temperature of -9˚ F,” Shane said. “As we went into the fall, we could see the temperatures that the fruit buds could take became greater. We got down to -20˚ F that Cabernet Franc could take.”

When a low temperature of -3.7˚ was logged on Feb. 17, 2001, for example, fewer than 10% of the buds died, giving researchers an indication the variety wouldn’t be in danger.

Sauvignon blanc buds at a Lemon Creek location on Mountain Road during the same temperature drop, however, behaved differently. Researchers predicted a bud mortality of at least 10%.

“The difference between killing 10% and 50% is pretty narrow, by just a couple degrees,” Shane said. “The difference between 50% and 90% is equally narrow.

“You can see that having fairly accurate information is very important,” Shane said. “It’s very important to know the temperature in order to know what’s going on in that vineyard. Each variety is its own particular situation.”

In a look at Merlot, information was shown for a 50% kill at three different locations. In general, the trend is that by late January around -7˚ F was around the 50% kill point.

What determines that hardiness is of interest, whether location, cultural practices, vine or rootstock DNA  or other variables.

“There’s a lot of things that can impact the questions that come out of this. It gives us a tool to be able to figure out what’s going on with the crop,” he said. “Each year the picture is a little bit different.”

Shane emphasized the need for a predictive model to determine what is taking place in the vineyard.

Modeling cold hardiness

Shane said research has been conducted, primarily at Washington State University, with the Ferguson model for hardiness of grapes.

“The models have been developed for that area,” Shane said. “The big question is how useful are they for us in Michigan?”

MSU has been collaborating with researchers from Cornell University and the University of Wisconsin, which have developed models to predict cold hardiness responses of grapevines. The Kovaleski & Londo model uses temperature oscillations to predict budbreak. The models are specific for cold hardiness impacts in the eastern U.S.

The Wisconsin and Cornell model initially used Concord, Cabernet Sauvigon and Riesling. The model has added 28 other cultivars. A web portal for predicting cold hardiness is based on the NEWA/MSU weather station sites.

“This is good news,” Shane said. “With information we can plug into any weather station model we can come up with a prediction of hardiness.”

Shane said the proliferation of micro-sprinkers, wind machines and plant-based dispersions that are being used in the tree fruit industry also has applications to vineyard freeze management techniques. Bud hardiness information also is useful for testing cold-mitigation techniques such as plant-based cryoprotectants.

— Gary Pullano, FGN Senior Correspondent

Top photo: Southwest Michigan Research and Extension Center station coordinator Bill Shane presents findings regarding cold damage in viticulture crops. Photo: Gary Pullano

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