Walnuts are one of the oldest tree nut crops in California, but that hasn’t kept growers from seeking out and adopting new management strategies.

Cover cropping, integrated pest management and attention to soil health all support regenerative walnut production. The California Walnut Board and Commission report that as part of the industry’s strategic plan, growers, processors and other industry stakeholders are working to define what sustainability means to the California walnut industry.

“Regenerative” is the current buzzword in sustainable agriculture, but California Walnut Conference panelists, speaking about a systems approach to orchard management, focused on actual management practices they tested and use in their orchards to benefit tree and soil health.

Mustard is one of the species included in a cover crop program used by Daniel Unruh of Unruh Walnut Farms. He wanted to determine if that plant species would help reduce nematode populations in the orchard soil.

Jocelyn Anderson of GSA Farms in Willows, Calif. said their regenerative efforts are focused on ‘climate-smart’ agriculture practices, including sensors to determine irrigation scheduling and water recycling using huller water. Anderson, who is on the Walnut Sustainability Working Group, said GSA used a SWEEP grant to install solar panels for the operation of orchard irrigation pumps.

Drew Cheney of Machado Family Farms in Linden, Calif. said in a search for practices that would work in their orchards, they discovered the benefits of sheep grazing the cover crops during dormancy. The first grazing experience was positive, Cheney said, and they increased the grazing program the next year after determining it supported their pest management program. Cheney said they were able to skip a leaf roller spray in the spring for the first time after grazing, as trap counts leveled off. Sheep in the orchards were the only change in management.

“These are all just tools that help us get where we want to be,” Cheney asserted. “We are looking for things that work in our orchards.”

Returns Per Acre Drive Management Decisions
Management decisions at Machado Family Farms come down to financial factors and returns per acre.

Cheney said water-holding capacity and early orchard access were primary reasons for planting the first cover crops for Machado. They started with one block and have since planted cover crops on all their walnut acres. Adding sheep grazing in the orchards in the winter and spring for consecutive years also made a difference, improving soil health. Besides adding organic matter, the managed sheep grazing kept cover crop roots in the soil, helping with crop quality and allowing for flexibility in water use.

A 2018 study by the UC Davis Gaudin Laboratory concluded that sheep integration in a mature orchard increased soil microbial biomass and diversity in the top 15 centimeters of soil and enhanced the amount of soil fungi recycling plant residues into soil organic matter.

“This is a systems approach where the trees and the soil watch out for each other,” Cheney said. “This is building resiliency in the orchard.”

Panel moderator Raquel Krach, project manager at Chico State’s Center for Regenerative Agriculture and Resilient Systems, noted cover crops and the water-holding capacity of orchard soils allow trees to compete for nutrients and water. Cover crop roots and soil microbes work synergistically, helping plants mine the soil for nutrients.

“It’s not just water-holding capacity that helps the soil; the cover crop also prevents erosion in orchards,”
Krach added.

With continued soil and leaf tissue sampling, she said, growers can fine-tune their management.

Systems Approach Gains Traction
Anderson said the implementation of new management practices and systems approaches by the industry is growing. The goal at GSA Farms, she said, is to start small with a new practice and determine if it is helping them reach their goal of improving production. Many long-time management practices are still being used, she said, but regulations and restrictions are pushing more growers to implement new methods in their orchards.

“It is hard to go into the unknown,” admitted Unruh.

When it comes to the adoption of new pest management tools, Unruh said it takes a level of faith and taking small steps at first. The use of puffers for the mating disruption of codling moths is proving successful for control. He is also using predator mites, purchased from an insectary, to control two-spotted spider mites in his orchards.

“We are turning nature against itself with these practices,” Unruh said. Cover crops planted in the orchards function to increase biodiversity of insects, providing resources to support natural enemies of insect pests.

Technical assistance is available, Krach said, for growers who want help implementing new practices in their walnut orchards.

“You don’t have to go into this alone,” she told growers.

Panelists discussed possible implications of some sustainable practices. The Produce Safety Rule in the Food Safety Modernization Act states that animals must be out of the orchard 120 days prior to harvest to prevent contamination of nuts. Cheney said it is important to inform handlers that precautions are being made to prevent any contamination at harvest. He also noted that in his case, he took soil and fecal samples from the orchard after grazing to a laboratory to test for salmonella. No pathogens were found in the samples, he said.

He stressed that it is important to work with shepherds to ensure healthy animals are brought in and that they understand the removal timing.

Soil compaction by the sheep has not been an issue, nor has damage to irrigation systems, Cheney said.

Unruh said his walnut production may currently be low due to the original nematode issues in the orchard, but he said soil and tissue analysis show improved nutrient cycling that allows him to reduce nitrogen inputs. He reported dropping the rate from 200 pounds N per acre to 80 pounds N. He said the increased water-holding capacity of the soil due to cover crops allows longer intervals between irrigations.

“It is a more forgiving system, not demanding,” Unruh said.