CALIFORNIA
Vegetables A SPECIAL GROWERS’ REPORT OF AG ALERT ®
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Steam is applied to strawberry fields in the Butte Valley of Siskiyou County. A University of California Cooperative Extension researcher says steam may be an effective substitute for chemical fumigants.
Steam touted as remedy to treat strawberry diseases By Bob Johnson Years of painstaking progress have made it more viable than ever to manage soil- borne strawberry diseases without chemical fumigation. Fennimore said researchers are working on band steaming to treat the seed line for vegetables. For strawberries, he said, they are working with a machine that injects steam 12-inches deep, every 12 inches.
Researchers in Salinas are working with a Dutch company on the development of a self-propelled tractor that can band steam and shape beds for vegetable production. While a machine that could efficiently treat these spots to plant strawberries over an entire field has not yet been engineered, preliminary trials of the concept have been promising. Fennimore reported that steam reduced fusarium pathogens by more than 70% in a July trial in Ventura County. “There was no comparison in the amount of fruit per plant,” Fennimore said. “Steam worked.” Additional trials of spot steaming are underway in Salinas and at a Watsonville field infested with macrophomina charcoal rot. “We need to scale up to build a larger machine that can treat an entire field,” Fennimore said, noting that researchers are working with Soil Steam International in Norway. While steam shows promise against all the major strawberry diseases and weeds, See STEAM, Page 8
While these methods of reducing disease pathogens are of interest to organic growers who have few alternatives, conventional growers may also benefit as fumigants face increasing regulatory restrictions, researchers say. Steve Fennimore, University of California Cooperative Extension specialist based in Salinas, has studied steam as an alternative to soil fumigation since methyl bromide was first slated to be eliminated decades ago. While touting the usefulness of steam, he raised some thought-provoking questions. “What is the plan in case you can’t use fumigants in the future?” Fennimore asked. “How are we going to grow strawberries? How are we going to manage these difficult diseases?” He made his remarks during the 2023 UCCE Annual Strawberry Production Meeting in Watsonville in February, discussing the latest developments in adapting steam to manage diseases in strawberries. “Steam transfers heat from the flame to the soil,” he said. “It kills disease pathogens and weed seeds. There are no buffer zones, township caps or plastic tarps.” While he said steam can be as effective as chemical fumigants, it can be too expensive and time consuming to treat entire fields.
April 5, 2023 Ag Alert 7
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