EAST LANSING, Mich. — According to the Michigan Craft Beverage Council, the wine industry generates more than 27,000 jobs and $2 billion of annual economic activity throughout the state. Wine grapes occupy more than 3,000 acres of Michigan farmland, with nearly 150 commercial wineries producing 3 million gallons each year.
Despite the industry’s blossoming popularity, several factors can limit the success of wine grapes in Michigan’s climate. Paolo Sabbatini, an associate professor in the Michigan State University (MSU) Department of Horticulture, studies ways to mitigate damage.
Cool temperatures necessitate a shorter growing season, and wet weather creates ideal conditions for diseases such as powdery mildew and sour rot to infiltrate vineyards. During the winter months, freezing temperatures may severely damage vines, and spring frost events can be devastating.
But it’s clearly not all doom and gloom. Wine grape growers are using innovative equipment and techniques to improve fruit quality and manage disease issues. Sabbatini, who also has an appointment through MSU Extension, regularly connects with growers to share findings.
“My research is very applied, so I’m in the field learning about the problems growers are dealing with,” he said. “These challenges are constantly evolving, but we have a great industry with a young generation of growers who are deeply invested in research and eager to collaborate with MSU.”
To that end, the Michigan Craft Beverage Council has matched funds from Project GREEEN (Generating Research and Extension to meet Economic and Environmental Needs) to support Sabbatini’s work.
He describes vine balance — where vine shoot growth provides enough leaf area to properly mature fruit — as one of the most significant issues facing growers. Vineyards around the world tend to be naturally in balance due to ideal climatic conditions, but this isn’t always the case in Michigan.
Too many leaves on the vine prevent sunlight from reaching grape clusters, lessening fruit quality. Excess leaves may also prevent fungicides and insecticides from applying correctly. Getting rid of too many leaves, however, can result in sunburned fruit and delayed ripening.
“Timing is critical when it comes to leaf removal,” Sabbatini said. “In Michigan, more leaves benefit the plants by providing winter reserves once the leaves are dropped in the fall. But we have seen positive results from early removal to give fruit more sunlight and decrease disease likelihood, particularly in closely clustered varieties. It’s a delicate balance.”
In addition to timing, Sabbatini said that leaf-removal techniques have historically been difficult and costly.
“Leaf removal by hand is an effective-but-laborious process,” he said. “And if growers use the older machine leaf removers, they can damage fruit because they’re less precise than manual removal.”
While manual leaf removal is still preferred by many growers, a newer style of equipment has shown some advantages. Rather than a cutting tool used to sever leaves from the vine on older machines, the newer model uses compressed air. Sabbatini said the machine is extremely efficient and has enhanced the development of multiple plant compounds essential for fruit quality as compared to manual removal.
Sabbatini and a team of researchers from the U.S. and Europe examined both timing and method of leaf removal in cool-climate Pinot Grigio, a tightly clustered variety, in an October 2019 study published in the American Journal of Enology and Viticulture.
The group found that both mechanized and manual techniques reduced gray mold, but only manual treatments lowered loss from sour rot. Researchers used pre- and post-bloom timings and found that only pre-bloom leaf removal improved fruit quality.
He said these results confirm that early leaf removal enhances fruit quality and indicate the need for reduced compactness of grape clusters to fight disease development.
“Both of these leaf removal methods are effective when applied pre-bloom,” Sabbatini said. “If vines are managed properly, it’s a big step toward a productive growing season.”
This article was published in Futures, a magazine produced twice per year by Michigan State University AgBioResearch. To view past issues of Futures, visit www.futuresmagazine.msu.edu. For more information, email Holly Whetstone, editor, at firstname.lastname@example.org or call 517-355-0123.
— Cameron Rudolph, Michigan State University AgBioResearch
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