California Walnuts: Orchard Management – July & August

    Walnut orchard.


    • Drought Management Resources: 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. How-to information here. Additional considerations in the drought article in this newsletter.
    • 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. Details here.
    • Spider Mites: Monitor weekly in July and August for spider mites and their predators. Check 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. Details here.
    • 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. Details here.
    • Botryosphaeria (Bot) or Phomopsis: 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. Fungicide efficacy on page 72.
    • Lean Price Year Considerations: There are several management options to improve your profit margins:


    • Navel Orangeworm: Begin monitoring for NOW in your orchard. Healthy walnuts are only susceptible to NOW at and after hull split. Consider preharvest intervals and duration of residual activity when considering treatment options. See the above article on IPM on a Budget for NOW control considerations in a lean price year.
      Mold: While the current recommended control timing for mold is hull split, steps can be taken throughout the growing season to reduce mold at harvest. See the article in this newsletter to learn how to control mold in your walnut orchard this season.
    • Packing Tissue Brown (PTB): PTB will start developing in mid-August for early season varieties like Serr and Solano. If you’re considering using ethephon to remove more nuts at first shake or advance harvest timing, start monitoring for PTB in your orchard about two weeks before expected PTB. Sample once or twice a week by cutting open 100 nuts collected throughout your orchard. Application timing will vary depending on your goal. Apply at 100% PTB to advance harvest, but 5 to 7 days after 100% PTB to synch up maturity to remove more nuts at first shake. See “Ethephon for Earlier Harvest” for PTB photos and application guidelines.

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