October 2022 - 15

PLANT & SOIL HEALTH
Powdery mildew presses high tunnel winegrapes
By Gary Pullano
Senior Correspondent
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
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
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
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. " FGN
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October 2022

Table of Contents for the Digital Edition of October 2022
