California Walnuts: 10 Key Management Points Ahead Of Harvest

Photo: California Walnut Board.

In July

#1. Examine how you’ll spend money.

Examine your IPM strategy for the season in light of lean prices. With crop value down, the damage level at which it “pays” to treat may increase. This article should provide insights.

#2. Watch for that third flight.

Monitor codling moth traps to set a biofix for the third flight, which comes 1100-1200 degree-days after the second biofix, on average. Based on our late walnut leafout, this will likely happen in early August for most varieties in the Sacramento Valley but could be in late July, depending on summer temperatures. Here is more information on timing and materials.

#3: Stay on top of husk fly.

Continue monitoring for walnut husk fly, checking traps at least weekly through the summer. Be sure traps are high in the tree on the north side to have meaningful trap information for your treatment decisions. There are about three weeks of protection after a spray application combined with the time needed for egg development in females. More info here.

#4. With mites, look for your allies.

Keep checking spider mites and their predators (sixspotted thrips and predator mites) through August. To cash in on biocontrol, allow subeconomic populations of spider mites and avoid broad-spectrum insecticides.

#5. Assess nutrients.

Take leaf samples to check on the effectiveness of your nitrogen management program, as well as potentially monitor for deficiencies in potassium and zinc, and toxicities in chloride and boron (depending on your site and orchard history). Sample four terminal leaflets from at least 29 trees, each at least 100 feet apart, on the same rootstock, scattered throughout the orchard.

#6. Avoid overwatering.

Ensure the lightest pellicle nuts possible by avoiding stress from too much water from mid- to late- summer. This can be achieved when using a pressure chamber for irrigation scheduling, by avoiding irrigation until stem water potential measurements show trees are 2 to 3 bars below baseline (more dry).

#7. Reduce disease inoculum levels.

Reduce botryosphaeria and phomopsis inoculum by pruning out dead blighted limbs. Burning prunings outside of the orchard, where permitted, provides the best inoculum reduction. However, chipping prunings in place is acceptable if disease levels are already high and being managed with an extensive spray program.

In August

#8. Assess potential for NOW damage.

As harvest approaches, monitor for navel orangeworm (NOW). Nuts that have not been damaged by sunburn, codling moth, etc., are generally not susceptible to NOW damage until hull split.

#9. Consider ethephon.

If you plan on using 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. For more, see: California Walnuts: Using Ethephon in a Year With Lean Prices, Straggled Leafout.

#10. Be aware of mold.

There have been increasing reports of mold in recent years. The main fungi involved in this damage are Fusarium and Alternaria species. New research has shown early indications that the application of a short preharvest interval fungicide during hull split can reduce mold infestations. Mold levels are also reduced with timely harvest, and same day pick up.

See related article: California Walnuts: More Mold, More Questions   6-27

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