As global temperatures and weather patterns change, a researcher from Michigan State University in East Lansing is working to protect Michigan’s wine grape crops. The state’s wine industry generates more than 27,000 jobs and $2 billion of economic activity annually, according to the Michigan Craft Beverage Council.
Wine grapes occupy more than 3,000 acres of Michigan farmland with nearly 150 commercial wineries producing 3 million gallons each year. Factors that can limit the success of the grapes include cool temperatures that create a shorter growing season, wet weather that creates conditions for diseases, and freezing temperatures and spring frost that can damage vines.
Growers are using equipment and techniques to improve fruit quality and manage disease.
“My research is very applied, so I’m in the field learning about the problems growers are dealing with,” says Paolo Sabbatini, associate professor in the department of horticulture. “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.”
One of the biggest issues facing growers is vine balance, in which vine shoot growth provides enough leaf area to properly mature fruit. Vineyards in other parts of the world tend to be naturally in balance due to an ideal climate.
Too many leaves on the vine prevents sunlight from reaching the grape clusters, lessening fruit quality. It also can prevent fungicides and pesticides from being applied 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 says. “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.”
Leaf removal also can be difficult and expensive. Doing it by hand has been best because leaf remover machines can damage fruit. A new tool that uses compressed air to remove leaves as opposed to a cutting tool, however, is gaining traction for its efficiency and ability to enhance the development of plant compounds necessary for fruit quality as compared to manual removal.
Sabbatini and researchers from the U.S. and Europe examined the timing and method of leaf removal in a cool-climate Pinot Grigio, a tightly clustered grape variety, in an October 2019 study published in the American Journal of Enology and Viticulture. They found that mechanized and manual techniques reduced gray mold, but only manual treatments lowered loss from a condition called sour rot. Researchers used pre- and post-bloom timings and found that only pre-bloom leaf removal improved fruit quality.
The results also indicate the need for reduced compactness of grape clusters to fight disease development, says Sabbatini.
“Both of these leaf removal methods are effective when applied pre-bloom,” he says. “If vines are managed properly, it’s a big step toward a productive growing season.”
The Michigan Craft Beverage Council matched funds from Project GREEEN (Generating Research and Extension to meet Economic and Environmental Needs) to support Sabbatini’s work.