Pre-harvest Management Considerations

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

Monitor for navel orangeworm (NOW) to determine risk of damage. Walnuts that have made it through the season intact are most susceptible to damage when husks open. However, if this husk split timing does not overlap with female flight and egg laying, damage is unlikely. Third and fourth flight peaks come close together, often with overlap between generations. Treatment decisions thus need to take into account trap counts and husk split in each block, as well as pre-harvest intervals.

Optimize kernel quality with attention to water management. Not enough water this time of year can lead to stuck hulls and subsequently darkened pellicles. 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.

If you plan to use ethephon in a block, start monitoring for packing tissue brown about 35 days before the expected harvest date. With this year’s prolonged spring and possible differences in timing of maturity within a canopy, many growers may turn to ethephon to help tighten the window in which nuts in their orchard are ready to shake. Find more on ethephon use.

Start hardening off young trees by cutting off September irrigation until you see a terminal bud set. If there is no rain, irrigate 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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