Researchers are gaining ground on some of most formidable challenges facing tree nut growers. Advances in sustainable pest management practices can help growers limit pesticide applications, giving them breathing room when it comes to export exclusions.
An update on sterile insect technique (SIT) to control navel orangeworm (NOW) by UCCE Specialist Houston Wilson showed progress of the California Pistachio Research Board (CPRB)-funded research. Wilson said the goal of SIT is to develop a competitive sterile moth and figure out how best to use it. The sterile insect technique is one of several NOW management approaches in tree nut orchards. This practice aims to limit NOW populations by delivering sterile moths to orchards where they mate with native moths but produce no new generations. Wilson and USDA Research Entomologist Chuck Burks have been working to determine overflooding ratio of sterile to native moths, delivery method, timing and location, and how to integrate SIT with existing integrated pest management tools.
“The key finding to date is sterile male NOW can fly, but just not that well,” Wilson told growers at an October American Pistachio Growers sustainable strategies event. They do now know sterile male and female NOW can find and attract mates. Wilson said transport and release does influence performance but noted drone delivery looks promising. Wilson said he is also involved in designing alternative rearing strategies for moths and alternative sterilization methods.
Wilson and his research team are also studying new traps and sensors for monitoring NOW in pistachio. Pistachio hull integrity is highly variable, Wilson said. Detection of volatiles, which draw in NOW females to lay eggs on hulls, can help with NOW risk monitoring, making predictive forecasts of risk of NOW infestation. The objectives of the CPRB-funded work will measure changes in egg deposition over time and characterize hull volatiles over time. The hull integrity and smart trap project, funded with a CDFA Specialty Crop Block Grant, will be determining accuracy of the new automated trap for NOW, evaluating field sensors to monitor hull integrity and develop a new online pest mapping tool.
Wilson also warned growers about a new pest that has spread through much of California pistachio production areas. The carpophilus beetle is the only insect species that feeds directly on pistachio kernels. Orchard sanitation is currently the only method of effective control as this pest overwinters in the orchard.
Sheep Favor Pistachio Nuts
Sheep grazing may provide another avenue for pest control. Johnny Etchamendy of Bakersfield operates a targeted grazing operation to help with sanitation and weed control in pistachio orchards. He said sheep in the orchard perform a couple tasks: They eat mummy nuts and weeds and their movement through the orchard breaks down dry matter.
“Sheep eat it all and recycle. The mummies are shaken to the ground and the sheep go for them. You can hear them crunching,” Etchamendy said. “The pistachios are one of the first things they eat.”
Research into sheep integration in an orchard system shows the benefits to the soil structure, pest control by destroying mummy nuts and savings on weed control materials. Impacts are greatest on whatever is most abundant on the orchard floor.
A CPRB-funded study done by Wilson, USDA Research Entomologist Joel Siegel and Etchamendy is going into its second year with the aim of exploring different stocking rates and grazing times as well as developing an economic analysis comparing grazing with conventional practices for sanitation, weed control and crop fertility.
Concerns about pesticide residues on harvested pistachios prompted a study by Fresno State Pomology Professor Gurreet Brar, who explained issues with systemic pesticides. Exceeding the maximum residue levels for pesticides can cause rejection in export markets.
Residue Research
Brar is conducting risk assessments based on terminal pesticide residues collected at harvest. He noted once systemic pesticides are taken up by the plant roots, they could be transported from roots to shoots and penetrate plant tissues. He said that systemic pesticides can enter through the peduncle and then gradually migrate to the top or can also infiltrate through the fruit exocarp.
Brar’s research in 2024 tested nut exocarp and kernel tissues for pesticides Intrepid, Assail, Admire and Sequoia CA after applications in mid-June, mid July 24 hours after each foliar application, three days after application and at harvest. Kernel and hulls and shells were analyzed separately. Brar said when results are available, data will be analyzed and a plan developed for next year’s trial.
Siegel also reported on his evaluation of the biological insecticide Spear Lep. This product, Siegel noted, is an interesting hybrid of Bacillus thuringiensis (Bt) that is used to disrupt the insect gut and a highly toxic venom. This product must be ingested to be effective, but Siegel noted adult activity and contact toxicity are not essential for efficacy. Timing and coverage and droplet size are important for this insecticide to be effective. The venom component of the product makes the Bt efficacy last longer, Siegel said. It can be a rotational partner to delay resistance to other materials.
One product that has been in use for more than 150 years, lime sulfur, is a new sustainable alternative for pistachio production. Zac Ellis, agronomy director with OFI, said this is not a traditional sulfur, but one that can be used for disease and insect control.
Pistachio, almond, walnut and pecan are all listed on the label for control of Gill’s mealybug, diseases, mites and aphids.
“The pH of this product is 0, and it can keep costs down and reduce MRL risk,” Ellis said.
