Navel orangeworm, codling moth, and webspinning spider mites remain harmful pests facing walnut growers and require continual study toward better IPM management strategies. Equally important is for UC IPM to share research outcomes with growers to inspire the adoption of those strategies. This means academics and growers working together.
Jhalendra Rijal, UC IPM associate director for agricultural IPM and area IPM advisor, North San Joaquin Valley, has been doing just that in partnership with the Community Alliance with Family Farmers (CAFF) and UC IPM Collaborative Demonstration Project. The goal of this project is to “increase the adoption of innovative alternative practices to pest management in walnuts” by conducting applied research-cum-demonstration trials. Rijal’s work exemplifies the long history of UC IPM advisors collaborating with innovative growers and nonprofit organizations on research and on delivering practical IPM information to growers and other stakeholders—who in turn share best practices with others.
According to Rijal, “A critical UC IPM goal is outreach. By partnering with nonprofit organizations like CAFF, with their connections and power to coordinate events, I was able to engage with people outside of UC ANR. That’s how to develop multiplier effects. Growers really trust IPM practices they’ve learned from other growers. It was a win-win for both organizations in terms of making a positive impact on Californians.”
Rijal has contributed to the CAFF and UC IPM Collaborative Demonstration Project from the proposal stage—formulating research, engaging growers and pest control advisers—through execution—co-organizing field extension events, giving talks, advising committees, and consulting on the field data collection and summaries spearheaded by Dr. Hanna Kahl of CAFF. Kahl studied pest management in working orchards and demonstrated the resulting evidence-based management strategies onsite at CAFF’s Biologically Integrated Orchard System (BIOS) field days. BIOS is a whole-orchard approach that prioritizes protecting natural enemies and soil health and managing water efficiently.
Since 2020, over 300 people have attended BIOS field days at small-family walnut orchards. Rijal co-organized and CAFF hosted the 2022 BIOS field day “Effective IPM Strategies for Major Walnut Pests” at Blossom Farms in Stockton, featuring presentations by Rijal, Kahn, and Blossom Farms Pest Control Adviser Mike Devencenzi about mating disruption tools for navel orangeworm and codling moth; using cover crops to improve predator diversity, augment biomass in soil, and reduce soil compaction; releasing predatory mites to manage webspinning spider mites; and using pheromone traps.
This information drives change in the field. One walnut grower wrote, “I really appreciated the information from Jhalendra on the flatheaded borer... I had never noticed [flatheaded borer] damage in my orchard, but understanding how to identify damage helped me to notice early damage in my own trees. It also helped me consider new field management practices regarding pruning.”
What sets the project’s field days apart is that they are more than lectures and demos: they are also a place where growers exchange information with each other and share their experiences with UC IPM advisors. “It’s great to see people in three related yet sometimes separate disciplines—science, pest management, and farming—coming together around research and demonstrations. It takes a lot of organization, but it’s hard to find that exchange of knowledge anywhere else,” said Rijal.
At the field day, Dr. Hannah Kahl presented research with demonstration about the outcomes of project studies she led.
The first was a study of mating disruption of codling moth and navel orangeworm at six orchard sites totaling 30 to 40 acres in the San Joaquin Valley with varying pest pressures over two years, from 2021 to 2022. With mating disruption, all farms showed some reduction in numbers of either or both pests (except Blossom Farms, which had low numbers to begin with). “Our studies clearly showed the benefits of mating disruption in managing these two major lepidopteran pests as a part of the integrated pest management program,” said Rijal.
At the same time, another study in three of the six orchards looked at the role of cover crops to improve the diversity of predators in walnut orchards, and the effectiveness of releasing predatory mites to promote biological control of spider mites in orchards. About 10 acres were treated with either cover crops or predatory mite releases or both, using the grower standard as a control. The experiment was replicated three times over two years, from 2021 to 2022.
In one research field, cover crops combined with predatory mite releases increased predatory mites and sixspotted thrips (predatory thrips). Cover crops enhanced some key spider mite predators in two out of three farms. Most predatory mites found were not those released, suggesting that cover cropping increased habitat and survival for predatory mites overall.
According to Rijal, “In addition to the known benefits of cover crops in improving soil health and moisture retention, the cover crop also benefits farmers by improving predatory insects and mite populations, which are essential to maintaining a biological control system against pest mites in orchards.”
With research-based demonstrations on mating disruption - biological-based pest control method, cover crops, better monitoring, and more, California walnut growers can now implement important IPM practices in their orchards. The Rijal and CAFF partnership brings science-based research results directly to farmers and pest control advisers who are willing to try new things and who can spread the word on what works. Seemingly small steps such as augmenting habitat for general predators and better monitoring reduce the use of pesticides, which improves environmental health and the life of all Californians.
The Community Alliance with Family Farmers and UC IPM Collaborative Demonstration Project was funded by California Department of Food and Agriculture as a part of the Biologically Integrated Farming System (BIFS) funding.
