Winegrape growers turn to higher trellises to beat heat
Science, that could influence future winegrape cultivation. Over several years, they compared the quality and yield of cabernet grapes grown on six different trellis systems at the UC Davis Oakville Research Station in Napa. The researchers found that vertical shoot position (VSP) trellises, favored for decades by North Coast growers, expose the grapes to too much direct sunlight and provide little pro- tection from solar radiation, especially when the ground reflects heat up into the clusters.
“We constantly see sunburn issues,” said Runze “Cliff” Yu, assistant profes- sor of viticulture and enology at Fresno State and co-author of the study. The researchers recommended cab- ernet growers in the North Coast switch to single high-wire trellises, which pro- duced the study’s best results. “The fruit maturity is decent, and the berry quality, in terms of the color and other flavonoids or compounds, are the most accumulating in this system,” said Yu,
By Caleb Hampton With its warm summers and mild win- ters, California’s North Coast produces some of the world’s best winegrapes. But as the region gets hotter, growers are navigating more obstacles to bring their grapes to maturity without losing their yield or quality. Cabernet sauvignon, Napa and Sonoma’s signature variety, needs sunlight, but excessive heat can dry out the fruit, costing growers thousands of pounds in weight per acre. It can also make the grapes too sugary. During fermentation, sugar turns into alcohol, and too much alcohol content masks the layered aromas that distinguish quality wines. “It was definitely a challenge,” said Napa County winegrape grower Peter Nissen, speaking about August and September heat waves that caused some growers to get their grapes rejected by wineries. “In all the years I’ve been farming, it was probably the worst heat event,” said Nissen, president of the Napa County Farm Bureau. Growers in Napa and Sonoma have tried various methods to mitigate the effects of heat on their grapes. Several years ago, a handful of Sonoma County farmers started growing cabernet grapes on high-wire trellises, a system more often seen in the Central Valley that shades the grape clusters with vine leaves. The technique also allows growers to cut labor costs due to the trellises’ com- patibility with machine pruning and oth- er mechanized maintenance. At the time, the decision to try the system was “purely economics,” said Duff Bevill, who owns Bevill Vineyard Management and has farmed winegrapes in Sonoma County for over four decades. Bevill manages roughly 1,300 acres of vineyards, including 100 acres of cabernet on high-wire trellises, the largest block in that style he knows of in the North Coast.
After employing the trellises, he said, he began noticing “dramatically less sun damage” to his grapes, particularly during intense heat waves. Now, researchers at the University of California, Davis, and California State University, Fresno, have found sim- ilar results in a study, published last month in the journal Frontiers in Plant
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