UV-C Continued from Page 6
grape disease pressure. On the other hand, Oregon’s Willamette Valley, where USDA and Oregon State University are conduct- ing trials, has more moderate tempera- tures and higher humidity that promote powdery mildew. Since 2020, Moyers and her WSU group have compared a typical chemical fungi- cide program to applying UV-C light every other week, once per week and twice per week. UV-C light is a contact treatment, leaving no residue. As such, good coverage and having a direct line of sight to the target are king, Moyers said. After the 2022 season, the WSU re- searchers added leaf removal to their tri- als based on their results. The researchers want to determine whether it aids control by enhancing light contact on fruit and leaves much like it does with conventional fungicide applications. Both Brinkley and Peters said they al- ready pull leaves to increase air flow and improve fungicide spray deposition, so they didn’t have to change for the UV-C light applications. For producers who want to try the Thor- vald system, Thompson recommended they start with a small block and one ro- bot “because you’re changing a lot. You’re moving away from a tractor driver and chemicals to light.” Vicky Boyd is a reporter in Modesto. She can be reached at agalert@cfbf.com.
Mendocino County certified organic wine- grape producer also seeks practices that mesh with its regenerative philosophies. This season, it tested six UV-C light ro- bots on about 200 acres of chardonnay by the Russian River because the grape is one of the most mildew-susceptible vari- eties, and the environment is conducive to mildew. Bonterra’s typical mildew program consists of oil applications every 10 to 14 days beginning a few days after budbreak in April. Depending on the season and mildew pressure, the vineyard may also rotate with wettable or dusting sulfur until the berries reach about 13 degrees brix, or sugar content, sometime in July. After that time, the fruit doesn’t appear susceptible to mildew. This year in the test blocks, the vineyard was sprayed early in the season because of delays getting the machines deployed. It then continued with twice-a-week UV-C applications until veraison. Brinkley said he was “pleasantly surprised” by the re- sults. The blocks treated with UV-C had as good as or better mildew control than the blocks in which oil and sulfur were used. “This was such a challenging year for mildew,” he said. “This was one of the hardest mildew years that I can recall.” After using UV-C light to successfully treat fungal diseases in United Kingdom
With ultraviolet-C arrays on the sides and top, the Thorvald robot envelops vines in light. The units are typically run at night.
strawberries, Saga Robotics partnered with Cornell University’s AgriTech branch in 2020 to develop a commercial autono- mous UV-C system for winegrapes. The battery-powered Thorvald robot consists of a horse-shoe-shaped array of UV-C lights, which envelop the sides and tops of vines with light. It can run all night on one charge. Using sub-inch accurate real-time kine- matic GPS, Saga first maps the vineyard, including vine posts, vine spacing and other obstacles, to create what Thomp- son described as a digital robot highway. The platform can handle rows from 3 to 10 feet wide and most trellis systems with
crossarms up to 30 inches. Over the years, researchers have gained an understanding of how UV-C works on grapevine powdery mildew, said Michelle Moyers, a Washington State University professor and viticulture specialist. What she and fellow researchers at the U.S. Department of Agriculture and Oregon State University hope to determine with current field trials is how to best use the technology under local growing conditions. For example, the Prosser Irrigated Ag- riculture Research and Extension Center where Moyers is based is on Washington’s hot, arid eastern side and has relatively low
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October 7, 2026 Ag Alert 7
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