C A L I F O R N I A
Vegetables A SPECIAL GROWERS’ REPORT OF AG ALERT ®
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Advisors seek practical use of steam in weed control ByBob Johnson After testing steam treatments in three Salinas Valley trials this year, UC Cooperative Extension specialists say they believe the technique can significantly reduce weed pressure in lettuce and spin- ach fields, and can cut hand-weeding time.
an organically approved compound that helps spread the heat. In one of the trials, the steamreduced hairy nightshade and shepherd’s purseweeds by 80% to 90%, and littlemallowby 70%with the hydrogen peroxide and 42%without. The researchers saidbanded steamshowed similar efficacy in the second lettuce trial, reducing nightshade and shepherd’s purse by 75% to 90%, and significantly reducing little mallowwhen the hydrogen peroxide was added to the steam. The steam treatment reduced hand-weeding time by 20% to 40%, and reduced let- tuce-drop damage by 54% to 67%, they said. Another set of Salinas Valley vegetable trials showed the promise of GPS-controlled, autonomous weeders that cultivate without a driver, outside and within the seed line. “This project comes down to labor,” said ElizabethMosqueda, weed science profes- sor at California State University, Monterey Bay. “It takes a lot of manpower to remove weeds from one lettuce field. How can we decrease labor costs in leafy green produc- tion? The other part of this is the number of herbicides available; the last formulation for lettuce was introduced in 2014.” Mosqueda tested two autonomous weeders in Salinas-area commercial lettuce fields: the relatively small DINO weeder from France and the larger Farmwise Titan robotic weeder. “Both of these companies want to get to the point that one operator can be in the fieldwithmultiplemachines,”Mosqueda said. “But autonomous weeders can already
Steam-treating a shallow band of soil within the seed line before plantingmay offer, when combined with advanced cultivators, an economical weed control option for organic farmers and conventional growers looking to reduce herbicide use. University of California specialists said their research inSalinas Valley vegetable fields this year showed the technique can significantly reduceweedpressure andhand-weed- ing time, and even produce larger andmore vigorous lettuce plants. “We’re reducing the hand-weeding time,” UCCooperative Extensionweed specialist Steve Fennimore said. “The plants were larger, significantly larger.” Fennimore, who has been studying steam as a way to control weeds and soil dis- eases since strawberry growers first faced the loss of the fumigant methyl bromide, presented his latest research during the UC Online 2020 Pest Management Series in early November. Steamworks aswell as fumigation in reducingweeds and soil-bornediseasepressure, he said, but previous efforts have shown that treating the entirebedcanbe tooexpensive and time-consuming to be practical inmost situations. “With banded steam, you treat less of the bed,” Fennimore said. “Our target would be to heat the soil to about 150 degrees Fahrenheit; but youwould only need to steam2 or 3 inches deep. Then you could seed lettuce in the seed line and cultivate outside of it.” Fennimore and UC graduate research fellow Nelly Guerra tested steam this year in three Salinas Valley trials—two on lettuce and the third on spinach—as they compared weed pressure after steam-treating the seed line with andwithout hydrogen peroxide,
See STEAM, Page 8
December 2, 2020 Ag Alert 7
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