July Walnut Orchard Management Considerations

Evie Smith, UCCE Staff Research Associate, Southern Sacramento Valley
Katherine Jarvis-Shean, UCCE Orchard Advisor, Sacramento, Solano and Yolo Counties
Janine Hasey, UCCE Farm Advisor Emerita, Sutter, Yuba, Colusa Counties
Luke Milliron, UCCE Orchard Advisor, Butte, Glenn, and Tehama Counties

  • Drought Management Resources: This year is shaping up to be one of the driest years on record in California. See our article in this newsletter to learn more about water management options for maintaining your orchard health this year. Using the pressure chamber and waiting to irrigate until trees are 2 to 3 bars drier than the fully watered baseline remains the gold standard for deciding when to irrigate. Learn more from our article on Advanced Stem Water Potential Interpretation in Walnut.
  • Walnut Husk Fly (WHF): Use yellow sticky traps to monitor weekly for WHF in your orchard. Begin treatment as soon as you detect eggs in trapped females or when the number of WHF in your traps increases significantly. See our article on Walnut Husk Fly Biology, Monitoring, and Spray Timing for more about monitoring strategies and treatment options and timing.
  • Spider Mites: Monitor for spider mites and spider mite predators on a weekly basis throughout July and August. Check for spider mites on 10 leaflets (5 from higher branches), from 10 trees each time you monitor. If more than half of the leaflets with spider mites don’t also have predators, consider treatment. Learn more about treatment options on the UC IPM site for spider mites in walnuts.
  • Codling Moth: The third codling moth biofix occurs in late July or early August (about 1100-1200 degree days after the second). Monitor your traps to decide when to treat. See UC IPM for Codling Moth in Walnuts to learn more about treatment decisions and options.
  • Botryosphaeria (Bot) or Phomopsis: Severe freeze last November may have left your orchard with more dead limbs than usual this time of year, making it vulnerable to Bot and Phomopsis infection. Begin pruning dead limbs and removing them from your orchard this month to avoid severe infection. Also consider spraying for Bot in early July if your orchard has a history of Bot infection. For more information on Bot control, see our article on Botryosphaeria Canker & Blight.
  • Lean Price Year Considerations: When walnut prices are low, there are several management options that you can consider to improve your profit margins. Read our articles on walnut management during a lean price year:

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