September Walnut Orchard Management Considerations

Dani Lightle, former UCCE Orchards Advisor, Glenn, Butte & Tehama Counties
Katherine Jarvis-Shean, UCCE Orchard Advisor, Sacramento, Solano and Yolo 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.

  • Water management: Keep an eye on your irrigation! Cutting it short on water during hull split can lead to hull tights and darkened kernels. Too much water this time of year can deprive nuts of carbohydrates, leading to bronze pellicles. Using a pressure chamber to keep trees at 2 to 3 bars below baseline (more dry) can help avoid tree stress. Profit margins are likely to be tight this year, so don’t sacrifice nut quality and value.
  • Nitrogen: You should be finished applying nitrogen by about now; walnuts don’t uptake much N during the fall. Adding N late in the season is like dumping your money into the groundwater supply.
  • Ethephon: Using ethephon can advance harvest. Earlier harvest helps maintain kernel color, and reduce navel orangeworm or mold damage. Beginning about 35 days before the expected harvest date, sample frequently for 100% packing tissue brown (PTB) to time the ethephon application properly.
  • Pest management: Collect harvest samples so that navel orangeworm or codling moth damage can be distinguished. Use a similar sampling protocol as described here for almonds to collect walnut harvest samples.
  • Pruning: Prune blighted branches and deadwood immediately after harvest (or earlier) to remove possible Botryosphaeria (Bot)/Phomopsis or branch wilt infected wood. It is easiest to tell dead, diseased from healthy wood when there are still leaves on the tree, rather than during dormant season. Additionally, pruning while the forecast is dry will help avoid infection of fresh pruning wounds.
  • Hardening off: Start hardening off young trees by cutting off September irrigation until you see a terminal bud set. If there is no rain, plan on irrigating by mid-to late October. Both young and mature trees should have some soil moisture by early November to better withstand an autumn freeze. Find more on preparing for an early freeze.

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