A SPECIAL GROWERS’ REPORT OF AG ALERT ® CALIFORNIA Trees & Vines ®
Wet conditions, such as at this vineyard near Stockton, slows the emergence of weeds but limits opportunities for farmers to eradicate them with herbicides or grazing sheep due to soil compaction concerns. University of California Cooperative Extension researchers suggest pre-emergent herbicides that kill weeds before they become a problem.
Winter rains complicate weed control for vineyards By Vicky Boyd
The vineyard owner receives vegetation management and nutrient recycling while the flock owner has pasture for the animals. But Roncoroni said running sheep through some vineyards this winter may cause soil compaction because of unusually wet conditions. In addition, sheep like to graze on tender grapevine vegetation. With bud break im- minent, a “180-pound ewe could wipe out this year’s harvest,” he said. Mechanical cultivation, which involves running a modified plow, flexible fingers or sets of blades in the soil around grapevine trunks, also carries compaction concerns. “The last thing you want to do is get in with a cultivator when the soil is wet,” Roncoroni said. “Not only does it mess up the soil structure, but it doesn’t do a very good job on the weeds.” His comments came as part of the San Joaquin Valley Winegrowers Association’s 2023 grower education series. If growers opt for chemical weed control, Roncoroni recommended always reading herbicide labels beforehand since some have application restrictions after bud break. Others may allow use only on bearing or nonbearing vines or require hooded sprayers after bud break. See WEEDS, Page 8
While winter rains have delivered much-needed drought relief, they have also brought challenges for grape vineyard weed control by creating wet conditions and reducing management options. Bud break—where vines awaken from dormancy and leaves emerge—is beginning across the state, further limiting weed management choices, said John Roncoroni, University of California Cooperative Extension weed science advisor emeritus for Napa County. Joe Valente, a vineyard manager in the Lodi area, said he felt fortunate because he was able to apply herbicides to most of the vineyard ground between storm breaks. “We put ours on in mid-February after all of that rain in January,” he said. “We pretty much got it in. But this year, for whatever reason, it just seems like the weeds are slower growing because of the rain and the cold weather. On one ranch that was flooded, there’s virtually no weeds on the berms.” Vineyard weed management is typically focused on a band under vines to reduce competition, potential pest habitat and interference with air movement and harvest. Meanwhile, growers frequently plant cover crops or allow native vegetation to grow in the middle of rows during the winter and spring. A popular weed-management trend is to graze sheep in vineyards during the winter.
March 22, 2023 Ag Alert 7
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