Oct 24, 2022
Powdery mildew presses high tunnel winegrapes

Michigan State University researchers have found that grapes protected by high tunnels produce phenomenal yields compared to unprotected vines, but growers must be vigilant for powdery mildew.

Greg Lang, an MSU tree fruit specialist, told attendees of the 2022 Viticulture Field Day at MSU’s Southwest Michigan Research and Extension Center (SWMREC) in Benton Harbor, Michigan, that heat units under the tunnels give winegrape varieties a boost in the state’s lower temperatures. At the same time, growers must be prepared for diseases, just as with unprotected crops.

“What we’re seeing this year is powdery mildew Day at MSU’s Southwest Michigan Research and Extension Center (SWMREC) in Benton Harbor, Michigan, mildew came in with a vengeance, and got away from us,” Lang said. “I was out of town for 10 days, and they didn’t get checked on. I don’t know if we’re going to have any harvest in the tunnel. You can see we got a great crop, but we have a lot of mildew infection in that crop.”

Downy mildew loves a dry environment, he said, and “we went too long between sprays and it exploded on us. In the tunnel, the only water we’re going to give them is through the irrigation.

Last season, vines under high tunnels thrived, while vines outside the tunnels had leaf drop and other diseases.

“The grapes outside are exposed to so many different challenges,” Lang said. “Inside, they grow beautifully, except we have to worry about powdery mildew and spider mites. Those are the main issues under the tunnel.

This season’s grape crop outside the high tunnels is growing well.

“We’ll see how it ends up, but it might be close to the 2020 crop for in the tunnel,” he said. “This is 2022, so we’re looking at least two years behind compared with the grapes that were grown in the tunnel with their first crop. We’ll see how well we ripen them up and where the brix levels are.”

What’s the payoff?

Lang said the primary disadvantage of tunnel use for winegrapes is the cost, at $30,000-$35,000 an acre.

He believes the tunnels are a good investment for growers who meet the right criteria, primarily whether they have a market for such product.

“When you look at the differences in yields, so far we’ve been two years earlier with a good harvest, than if you were outside, so that starts paying off the tunnel,” he said. “The yields have been potentially 2-4 times the yields that you get outside, so that helps pay for it. The question is what’s that wine quality?”

The project has received minimal direct funding thus far, but Lang is hoping an enhanced grape team at SWMREC, which recently saw the addition of Russell Smithyman, (a viticulturalist, consultant and researcher with extensive experience in Washington state), will “get some grant proposals in and start to look at those kinds of questions, as well.”

High tunnels for winegrapes have been used previously in Michigan.

“Mari Vineyards, up on Old Mission Peninsula (near Traverse City) had at one time had some grapes under tunnels,” Lang said. “So, we said let’s get some (in southwest Michigan) with some long-season grapes and just start to see if they generate any industry interest. Certainly, last year there was a lot of interest and the grape industry wrote high tunnel grape research into their priorities. We know that they’re interested, now it’s just a matter of pulling the team together now that we have Russ.”

Tunnels can have a positive impact on pest management, Lang said.

“Generally, what we’ve seen in tunnels with the tree fruit research we’ve done for years is Japanese beetles don’t tend to go under the tunnels, and Japanese beetles love grapes. We’ve not seen any significant, if any, Japanese beetle damage in the vines under the tunnels.”

Lang would like to work with Tim Miles, from (MSU’s) pathology side, and Rufus Isaacs, from the entomology side, and for them to become involved in whatever grant proposal we have going forward.

How fast might the high-tunnel approach take hold in Michigan?

“I think every winery has its own marketing philosophy,” Lang said. “It’s perfectly valid to say we should grow what we grow best. Maybe it’s Pinot Noir, maybe it’s Riesling. Down here in southwest (Michigan) we can grow a lot more toward long season. We’ve got producers doing Cabernet and certainly we can do Merlot.

“The question I want to try to ask is are there wineries who have a clientele that would pay $50 a bottle for a Michigan Nebbiolo that was of good quality and not thin, red wine, but has all of the phenolics and all of the characteristics,” he said. “I think Mari Vineyards has shown that model can work for them. It depends on who your target market and consumer base is, what they’re looking for and what they’re willing to pay.”


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