California Walnuts: Check List For Fall Orchard Management


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 here.

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. For more information, click here.


Timely harvest is important for nut quality. Delaying harvest can darken pellicles, and encourage mold development and navel orangeworm. Walnut color quality decreases most rapidly in the first nine hours, so try to pick up the same day that nuts are shaken.

Collect a representative IPM evaluation sample from across each orchard block at harvest to assess your IPM program. Grade sheets won’t always give the detail necessary to decipher the source of damage and what needs to be changed to improve an IPM program. Compare what you see with photos and descriptions.


If you are pruning this dormant season, prune as early in the fall as possible to avoid Botryosphaeria infections. Winter pruning resulted in infection in 78 to 99 percent of cut shoots, compared to only 28 to 75 percent in fall-pruned shoots. At minimum, avoid pruning cuts when wet conditions are in the forecast.

Consider applying either potassium sulfate or potassium chloride (KCl) if your leaf sample analysis indicates your orchard is potassium deficient. If you’re considering KCl to save money, be sure the chloride will be able to leach out of the root zone before spring leaf-out. Avoid where there is a perched water table, heavy clay and less than 8 inches of winter rainfall.

Scout for weeds to evaluate the success of this year’s weed management plan and revise your plan for next year. Here are weed identification tools and scouting templates.

If you’re removing an orchard, October is the time to kill roots with Garlon. It is critical to paint stumps with Garlon within five minutes of cutting trunks, and leave stumps for 60 days. See the article in this issue for more information.

Sanitize orchards to remove mummy nuts that can harbor overwintering NOW. Given the extended leaf- out this spring, the likelihood of leaving some nuts in the tree after harvest is high. Shake or pole remaining nuts out of trees, blow nuts into middles and flail mow. Clean out processing facilities that are adjacent to orchards.

If seeding a cover crop, try to get seed in the ground before leaf drop to get the best seed-soil contact.

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