A SPECIAL GROWERS’ REPORT OF AG ALERT ® CALIFORNIA Trees & Vines
Researchers advise on treatments for nut pest threats By Bob Johnson Growers of California nut crops, including pistachios, face a new threat from Carpophilus truncatus, a beetle species that University of California researchers say has been discovered in every county in the San Joaquin Valley.
UC researchers are working on guides to help nut growers identify Carpophilus beetles but have not begun work to establish management practices or treatment thresholds. The pest is not the only threat California researchers are targeting. Wilson is part of a team working on a trap for leaf-footed pests, which are usually out of the orchard before damage is visible. One of those insects, Gill’s mealybug, has been a familiar pest in pistachios for a quarter century. Mealybugs reduce yields in infested clusters. “The more mealybugs you have, the smaller your kernels because the mealybugs use carbohydrates that would have helped the nuts grow,” said David Haviland, UCCE farm advisor in Kern County. Management strategies are changing because buyers in the European market will not accept use of neonicotinoids, which can be harmful to bees. “Centaur is viable if your nuts are not going to the European Union,” he said. Haviland suggested a treatment threshold based on the expected yield and price, the cost of treatment and the number of mealybugs early in the season. He suggested if the expected yield is 3,000 pounds an acre at $2 per pound and spring monitoring shows one See PESTS, Page 7
Populations of an exotic insect that can drill through nut shells and lay eggs, producing larvae that feast on pistachio, almond and walnut kernels, are spreading throughout the San Joaquin Valley. “We have documented infestations in almonds, pistachios and walnuts, and in every county in the San Joaquin Valley,” said Houston Wilson, associate University of California Cooperative Extension specialist at UC Riverside. Wilson offered an overview on the challenge as nut crop researchers discussed insect pests during the Pistachio Industry Annual Conference in Monterey last month. The new beetle pest could prove particularly difficult to control. “Australians have been dealing with Carpophilus for 10 years,” Wilson said. “Chemical controls are difficult because of coverage issues.” The Carpophilus beetle is a known pest of almonds in Australia, where growers have been dealing with infestations for almost a decade. Other reports indicate similar Carpophilus beetles infesting walnuts in Argentina and Italy. Orchard sanitation is an important management tool, but Australian farmers found that Carpophilus beetles emerged even from mummies buried 3 feet below the orchard floor.
6 Ag Alert March 13, 2024
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