CALIFORNIA
Vegetables A SPECIAL GROWERS’ REPORT OF AG ALERT ®
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A spinach field at the University of California’s Desert Research and Extension Center was converted to drip irrigation from sprinklers to study whether the change could curb downey mildew disease.
Spinach drip trial cuts fungicide need, but not water By Vicky Boyd
“I think this is a game changer; it’s not all about water savings,” Montazar said. “There are still a lot of other benefits—less energy, less greenhouse gas.” Compared to sprinklers, buried drip irrigation requires less pumping pressure, which translates to less energy and reduced greenhouse gas emissions, Montazar said. Additionally, a Winterhaven-area grower cooperating in the trial found savings of $300 per acre. It included significantly fewer fungicide applications, improved fertilizer efficien- cy and eliminating water treatments. Current food safety best practices recommend growers who apply overhead irrigation from surface supplies to leafy greens first disinfect their water. Described by University of California scientists as the most widespread and destructive spinach disease in the state, downy mildew forms yellow spots on leaves that eventually become tan and dry. In addition to loss of quality, infected leaves may break down and begin to rot if packed or bagged. The first line of defense is to plant downy mildew-resistant varieties. Fungicides applied as protectants also can help manage the disease, although organic producers are severely restricted in the products they can use. Montazar said these limitations were another reason for his research. Jack Vessey, who grows leafy greens, including conventional and organic spinach in the
Subsurface or buried drip irrigation has long been touted for its potential to save water. But Ali Montazar, a University of California Cooperative Extension irrigation and water management advisor, wanted to see whether the technology also could be used to manage downy mildew fungal disease on spinach.
If so, that could bring savings on fungicide application costs. The theory was that by eliminating sprinkler-caused leaf wetting, which is conducive to fungal growth, buried drip irrigation would reduce disease pressure.
“We thought sprinkler irrigation was contributing to downy mil- dew, and 100% of spinach is sprinkler irrigated,” said Montazar, who serves Imperial, San Diego and Riverside counties. “For hours, the leaves stay wet. If the weather conditions are favorable, there could be disease issues.” He said impetus for the research came from the California Leafy Greens Research Board, which sought help with downy mildew management and supported his research. After four seasons of trials, Montazar saw no significant water savings, likely because baby spinach is a short-season crop only in the ground for about 40 days. But he did find savings of $200 per acre from reduced fungicide applications to conventionally grown plots and improved pumping efficiency compared to sprinklers.
See SPINACH, Page 8
October 5, 2022 Ag Alert 7
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