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team of California State University, Fresno viticulture researchers is
seeking to develop a more accurate mathematical model for predicting
wine-grape crop yields.
The effort was spawned in part by recent, significant errors in
predicting statewide wine grape yields, said Dr. Robert Wample, director
of Fresno State’s Viticulture and Enology Research Center (VERC) and
leader of the project.
“The inability to accurately predict grape crop yield is a multimillion-dollar-a-year problem for the U.S. wine and grape industry, according to
industry experts,” Wample said. In 2005, for example, the official
wine-grape yield prediction was off by approximately 30 percent. More
recently, 30-50 percent errors in yield estimates have occurred,
according to industry reports.
Wample said, “For the grower, it results in not being able to accurately
and efficiently plan the harvesting process. For the winery, the problem
is in insuring sufficient fermenting capacity, chemicals, storage space,
including barrels and ultimately glass for bottling, and planning to
market the resulting wines.”
Conventional methods for estimating crop yield for grapes include
counting clusters from selected areas of the vineyard and recording the
number of berries and weight of each cluster. This data is then
extrapolated using formulas based on number of vines per acre, number of
acres and other information to obtain estimated yield per vineyard.
There are variations of this basic method, but most rely on what might
be a faulty assumption, Wample said.
“When sampling data such as grape clusters, which grow over time, the
use of competition models must be considered,” he said. “The usual
assumption is that neighboring measurements tend to be alike. In fact,
due to plant competition for nutrients and light, sizes of neighboring
clusters may be negatively correlated.”
“Our goal is to obtain yield estimates accurate to within five percent,”
Wample said. “Anticipated results are improved vineyard and winery
operations management. The yield model, once validated, could be used as
a computational engine in a simulation model to forecast yield for
various climatology and vineyard management scenarios.”
Potential commercial applications of the research include incorporation
of the yield model into existing vineyard-management software packages
and development of a stand-alone application program for use by growers
and wineries.”
For more information, contact Wample at
robert_wample@csufresno.edu.
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