August 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

Please note that the following are general recommendations intended to help you keep track of regular practices in a busy time; the optimal timing for management practices may vary based on specific location and conditions.

  • 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: Walnut mold was a challenge at harvest last year. While mold infections usually occur at 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. 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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