October 2024 - 6

GRAPES
Trunk renewal essentials
D
Pruning approaches preserve
cold-damaged vineyards
BY GARY PULLANO
CONTRIBUTING WRITER
ealing with extreme low temperatures can keep
winegrape growers on edge, but some preliminary
research in Michigan pinpoints potential methods
of preserving a crop in the current freeze event year and
sustaining it into future seasons.
Mike de Schaaf, farm manager at Michigan State
University's (MSU) Southwest Michigan Research &
Extension Center in Benton Harbor, Michigan, shared
his research into pruning methods to adjust for winter
damage during his presentation at the 35th annual
Michigan Viticulture Field Day.
" This is our pruning strategy for post-freeze or frost
damage in the vineyard, " he told attendees. " We wanted
to take a look at how we could get more regenerative
growth down low at the graft union, especially for vines
that haven't been trunked or renewed in quite a while. "
The effort is in response to a changing climate. " It
wasn't necessarily the cold temperature that got us, it
was the quick drop in temperature because we weren't
cold enough for the cold, " de Schaaf said.
Mike Reinke, MSU Extension viticulture specialist, said
the cold snap occurred in January.
Chilling hours challenge
" Until Jan. 14, we were having the warmest winter on
record, " Reinke said. " We had no point here at the station
that got below 22º F. That was the case for the six weeks
before that point. Then, within two days, we went from
22º F to -8º F. "
Typically, at -8º F, if the vineyards had enough chilling
hours prior, de Schaaf explained that primary damage
will be seen, " but we'll have plenty of secondaries out
there. We'll have a crop. "
He shared that this year, when they were cutting buds,
observations weren't good.
" It's all site-specific, but some of the Chardonnay did
not fare well through the freeze. Cabernet Franc did not
do well. Riesling, on the other hand, came through with
flying colors, " de Schaaf said.
In several panels where pruning was done differently,
shoot counts varied.
Mike de Schaff, farm manager for Southwest Michigan
Research and Extension Center, discussed his research
of pruning methods. Photos by Gary Pullano
Interestingly, panels with the least amount of pruning
were the ones that pushed the most new shoots below,
de Schaaf said. He anticipated most new shoots would
have come from the vines that were most severely
pruned, but that wasn't the case.
" In Chardonnay, there were some differences, but in
Riesling, it didn't really matter in the shoots that were most
severely pruned, " de Schaaf. " It pushed the same number of
new shoots at the graft union no matter how we pruned it. "
He found that vines that weren't typically producing
new shoots from the base. Now, new shoots emerged at
the base after a frost.
While it is possible to crop after a frost, de Schaaf
cautioned growers that those cold temperatures damaged
the trunks' vascular systems, leading to degradation and
the need for replacement.
6 | OCTOBER 2024
October 2024

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