Pests Continued from Page 7
cans and hung in trees periodically emit puffs of pheromone. Devencenzi said the Pacific Biocontrol dispensers last all sea- son and are put out at a rate of one can for every acre. Rajkovich first began using codling moth mating disruption several years ago in his apples at Devencenzi’s recom- mendation. Eventually he expanded their use into the walnuts, which are upwind, to protect the apples. Mating disruption works best on larger blocks, but Jhalendra Rijal, University of California Cooperative Extension area IPM advisor for Merced, Stanislaus and San Joaquin counties, said they have seen success in orchards as small as 20 acres. On the five other farms, CAFF also is looking at mating disruption for an up-and- coming walnut pest, navel orangeworm. Considered the No. 1 insect pest of al- monds, NOW has begun to cause problems in some walnut and pistachio orchards. In addition, the group has codling moth and NOW larvae burrowing into nuts and feeding on the kernels, making them unmarketable. Codling moth lar- vae also may burrow into the hull to feed, which causes walnut shell staining that can’t be removed. These nuts are unsuit- able for inshell markets. Of all the major walnut pests, Devencenzi said, husk flies are the most
A sweeper gathers walnuts for hulling and drying. Well before the harvest, growers must deal with pests including the walnut husk fly, right. Its maggots feed in walnut husks and can render nuts unfit for market.
Photo/Whitney Cranshaw/Colorado State University
troublesome as he tries to balance pest control with maintaining viable benefi- cial insect populations. Females lay eggs in walnut husks. Larvae feed under the hull for 3 to 5 weeks, turning it soft and black. This causes irremovable staining and renders the nuts unmarketable for inshell sales. “Husk flies are a problem because we don’t have any products that aren’t dis- ruptive,” Devencenzi said. “The softest product is (the soil bacterium) spinosad, but it’s more expensive and more delicate because of the pH.” The standard go-to products, neon-
icotinoids and pyrethroids, knock out beneficials and allow pest populations to build. But growers and PCAs face a quandary: To slow insecticide resistance from developing, they also need to rotate to different modes of action. Chris Locke, a Lockeford-area walnut grower, is a longtime proponent of softer, more holistic approaches to farming. He also worked with UCCE farm advisor Joe Grant on pioneering codling moth mat- ing disruption research in the late-1990s and early 2000s. Locke continues to use mating dis- ruption and only occasionally has to spray an edge of an orchard because changing wind directions carried away the pheromone. “One of the reasons that sold us on it is you don’t have to spray,” said Locke, who also attended the BIOS demonstration field day. “We have the town of Lockeford as neighbors, so I have to be careful with my neighbors because I see them at the post office. Codling moths have been tak- en care of because of the puffers.”
As part of his low-impact approach, Locke has planted cover crops for years. In fact, a cover crop mix bears his name— the Locke Mix—comprising six different species of legumes, grasses and radishes. Since he began using the beneficial ground cover, he said he’s seen steady im- provement in soil health. Having evolved from sandy to more of a sandy loam, he said, his soil now contains about 6.5% or- ganic matter compared to 1% or less for typical sandy soils. “When you get heavy rains, your neigh- bor has standing water and you don’t,” Locke said of improved infiltration. When Rajkovich decided to move into cover crops several years ago, he first consulted with Locke. Rajkovich bought a no-till drill to plant his orchards and do custom cover-crop planting for nearby growers. Since then, he has bought an- other drill to keep up with demand and is considering purchasing a third because of the ever-increasing interest in cover crops. (Vicky Boyd is a reporter in Modesto. She may be contacted at vlboyd@att.net)
8 Ag Alert September 14, 2022
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