Orchard Origins

The staff from University of California Cooperative Extension (UCCE) have put together 10+ tips to help you as you get ready for harvest. Read about how to monitor for spider mites, guidelines for using ethephon and other useful information.

 

Walnut Orchard Management - July & August 2021

Evie Smith, UCCE Staff Research Associate, Southern Sacramento Valley

Katherine Jarvis-Shean, UCCE Orchard Advisor, Sacramento, Solano and Yolo Counties

Janine Hasey, UCCE Fram Advisor Emerita, Sutter, Yuba and 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 at sacvalleyorchards.com/manuals/stem-water-potential/pressure-chamber-advanced-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: sacvalleyorchards.com/walnuts/insects-mites-walnuts/walnut-husk-fly-biology-monitoring-and-spray-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 for spider mites in walnuts on the UC IPM site: ipm.ucanr.edu/agriculture/walnut/webspinning-spider-mites/

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: ipm.ucanr.edu/agriculture/walnut/codling-moth/

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: sacvalleyorchards.com/walnuts/diseases/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 on sacvalleyorchards.com

PM on a Budget: Cost Saving Strategies for Insect & Mite Management sacvalleyorchards.com/walnuts/cost-and-expense-considerations/cost-saving-strategies-for-insect-mite-management/

  • Maximizing Walnut Quality to Improve Value in a Low-Price Year: sacvalleyorchards.com/walnuts/cost-and-expense-considerations/maximizing-walnut-quality-to-improve-value-in-a-low-price-year/
  • Should You Use Ethephon in a Lean Price Year? sacvalleyorchards.com/walnuts/cost-and-expense-considerations/should-you-use-ethephon-in-a-lean-price-year
  • Navel Orangeworm (NOW): Begin monitoring for NOW in your orchard. Healthy walnuts are only susceptible to NOW at and after hull split. Consider pre harvest intervals and duration of residual activity when exploring treatment options. See the above article on IPM on a Budget for NOW control considerations in a lean price year.
  • Packing Tissue Brown (PTB): PTB will start developing in mid-August for early-season varieties like Serr and Solano. Start monitoring for PTB in your orchard about two weeks before expected. Sample once or twice a week by cutting open 100 nuts collected throughout your orchard. Nuts with completely brown packing tissue are at full PTB. When 100% of the nuts that you sample are at full PTB, it is safe to apply ethephon to accelerate harvest timing.
  • Ethephon: If you are applying ethephon in your orchard in August or September, use the following guidelines:
    • Apply 4-5 pints of product at a rate of 150-200 gallons per acre.
    • If you are applying from the ground, apply at a speed of 1.5-2.0 mph.
    • Avoid applications at temperatures greater than 90°F or if there are drying winds or rain forecasted.
    • For more information on ethephon use in walnuts, see Ethephon for Earlier Harvest.
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