Walnut harvest is here, and the main goals for growers are clear: protect kernel quality, remove the crop quickly and continue preparing orchards for next season.

The decisions made during harvest can affect not only the quality and value of this year’s crop but also orchard health and production in the year ahead. Hardeep Singh and Luke Milliron with the University of California Cooperative Extension advise walnut growers to pay close attention to irrigation, pest activity, harvest timing and post-harvest evaluation.

Manage irrigation carefully during harvest

Proper irrigation management remains important as walnuts approach harvest. Applying too much water can keep hulls green for a longer period and increase the risk of mold. Excess moisture may also make orchard conditions more difficult during harvest.

However, growers should also avoid applying too little water. Insufficient irrigation can contribute to shriveled nuts, stuck hulls and darkened pellicles. The pellicle is the thin skin surrounding the walnut kernel, and its color can affect the appearance and marketability of the harvested crop.

The goal is to provide enough water to protect kernel quality without creating overly wet conditions or delaying hull maturity. Growers should continue monitoring orchard conditions and tree needs instead of making major irrigation changes based only on the arrival of harvest.

Begin preparing young trees for freezing temperatures

Freeze protection should also be part of fall orchard planning, especially in younger walnut blocks. Young trees may be more vulnerable to freezing temperatures if they continue producing tender new growth late in the season.

Growers should stop nitrogen applications on young trees and avoid practices that encourage new growth going into fall. Planning for freeze protection before temperatures drop gives growers more time to prepare and reduces the risk of being caught off guard by an early cold event.

Although harvest is the immediate priority, protecting young trees during the transition into dormancy can influence orchard health and future production.

Continue monitoring walnut pests

Pest monitoring does not end when harvest begins. Growers should continue watching for walnut husk fly, codling moth and navel orangeworm, particularly as walnut hulls begin to split.

Split hulls can leave nuts more exposed to pest damage. Continued monitoring can help growers understand which pests are active and where problems may be developing within the orchard.

Prompt harvest is one of the most important tools for limiting the amount of time nuts remain exposed to navel orangeworm. The longer mature nuts remain in the orchard, the more opportunity pests may have to damage the crop.

Pest management should continue after harvest as well. Removing mummy nuts left in the trees can help reduce the number of sites where pests may survive and contribute to next year’s population. Orchard sanitation after harvest can therefore become an important part of the following season’s pest-management program.

Harvest when the crop is ready

Growers should be prepared to begin harvest when more than 95% of the crop is hullable. Waiting too long after the crop reaches that point may reduce kernel quality and increase exposure to pests, mold and unfavorable weather.

Once shaking begins, speed becomes especially important. A significant amount of quality loss can occur within the first nine hours after walnuts are shaken from the tree.

Because of that narrow window, growers should only shake the amount of crop they can collect that same day. Nuts should be picked up promptly and delivered to the huller and dryer as quickly as possible.

Coordinating shaking, pickup, transportation, hulling and drying can help reduce the amount of time walnuts remain on the orchard floor. Harvest equipment and processing capacity should be considered when deciding how much of a block to shake at one time.

Moving quickly can help preserve kernel color and overall nut quality while reducing the risk associated with leaving the crop on the ground for an extended period.

Save a representative sample from each block

The work does not end when walnuts reach the huller and dryer. Growers should save a representative harvest sample from every orchard block.

These samples can provide useful information about the pest and disease problems that affected the crop. Examining samples from individual blocks may help growers identify patterns that were not obvious during the growing season.

The results can then guide pest-management, disease-control and orchard-management decisions for the following year. Keeping samples separated by block is important because conditions and pest pressure may differ across the same operation.

A representative sample turns the harvested crop into a useful diagnostic tool. Instead of waiting for the same problems to appear again, growers can use what they learn from this season to plan ahead.

Walnut harvest requires careful timing and coordination. Balanced irrigation can protect kernel development, continued pest monitoring can reduce damage and rapid pickup can preserve quality after shaking. Post-harvest sanitation and crop evaluation can also give growers a stronger starting point for next season.

Read the full article in the September issue of Pacific Nut Producer Magazine.