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Viticulture
Research Examines Extended Cool Growth for
Wine Grapes
Posted on Monday, September 26,
2011
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Research from California State
University, Fresno is exploring a
new approach
to wine-grape growing in the sizzling San Joaquin Valley
that could extend cool-season growth of certain
varieties producing higher-quality wine grapes.
Photo and Slideshow by JoAnne Green
The strategy involves a
“crop-forcing” practice employed in other places but not
in the Valley, – said research scientist Dr. Sanliang Gu,
a professor and the Ricchiuti Chair of Viticulture
Research at Fresno State’s Viticulture and
Enology Research Center (VERC).
“Wine grapes
produced in California’s warmer regions amount to 60
percent of tonnage, but only 25 percent of crop value,”
Gu said in outlining his research. “If the growing cycle
of wine grapes in warmer regions can be delayed or
shifted to the cooler period of the growing season,
fruit ripening will occur at lower temperatures, and
much improved fruit and wine quality should be
expected.”
Grapevines
have genetic ability to set and bear fruit multiple
times a year under certain conditions, Gu explained. It
does not occur under natural conditions, but will if
buds are forced out of dormancy soon after the berries
are set, he noted.
The method
involves buds being removed from newly-set berry
clusters, as well as pruning back shoots and removing
leaves and laterals. In some cases, leaves can be
retained to provide protection from sunburn.
When these
actions are taken, a second bud break quickly follows
and the whole developmental cycle starts anew, Gu said.
And since the new cycle starts up to several weeks
later, the fruit of the forced crop ripens later in the
season, generally under cooler temperatures, with
characteristics of cool-region, higher-value fruit.
In the
central San Joaquin Valley, harvest time of some
wine-grape varieties would be moved from the beginning
of September to the middle of November, Gu said.
Crop forcing
and even double-cropping of grapes have been employed in
Australia and in some tropical areas, respectively, Gu
noted. Since hand pruning is labor intensive and costly,
however, researchers have experimented with other
methods and have found some to be effective. Some of
those methods include spraying synthetic and/or natural
chemicals and extracts that prompt the vine to break new
buds.
Later-season
wine grape maturation in the Valley would mean crops
with smaller berries, higher acidity, lower pH, deeper
color, higher tannins and phenolics, and more intense
aroma and flavor – all characteristics that tend to
produce higher-quality wines, Gu said.
Since the
method is virtually untested in the Valley, many issues
must be addressed, Gu said. In other areas, such as
Australia, experiments have shown it can negatively
affect vine health, capacity and longevity.
However,
“with the knowledge we’ve gained and the advances we’ve
made during the past 30 years in vine physiology,
mechanization of cultural practices and chemical
defoliation or defruiting, we have the opportunity to
address these limitations,” he said.
Gu conducted
preliminary experiments in vineyard sites at Fresno
State and with industry partners in Madera County in
2009 and 2010. Partial funding was provided by the
California State University Agricultural Research
Institute.
Gu is
encouraged by initial results and seeks new funding to
continue the work. For more information, contact Gu at
sanliang@csufresno.edu.
(Source: Fresno State
University)
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