Agriculture: Walnut Pest Management Guidelines

Nut Development (Fruit Set to Harvest)

This year-round IPM program covers the major pests of walnut in California.

About Nut Development (Fruit Set to Harvest)

What should you be doing during this time?

If conditions favor walnut blight development:

  • Manage according to the Pest Management Guidelines if rainy conditions continue beyond bloom.
  • Or use the Xanthocast model to determine the need for and timing of blight sprays.

Maintain a codling moth management program.

  • Check traps and keep records (example degree day monitoring formPDF).
  • If using sprayable mating disruptants, reapply according to the Pest Management Guidelines instructions.
  • Check traps and canopy nut counts to determine the need for supplemental sprays.
  • If not using mating disruptants, apply pesticides only if necessary according to the Pest Management Guidelines.

If dormant monitoring indicated infestations of walnut scale, monitor for crawlers.

  • Monitor for crawlers.
  • Manage if needed according to the Pest Management Guidelines.

Begin examining leaves for aphids.

  • Look for aphids, aphid mummies, and natural enemies.
  • Manage if needed according to the Pest Management Guidelines.

Take leaf samples in July for nutrition analysis.

Initiate fertilizer application and establish a nitrogen budget (PDF).

If Botryosphaeria and Phomopsis infection are a concern:

  • Manage if needed according to Pest Management Guidelines beginning in mid-May.
  • Look for dead and infected branches. Consider pruning for Botryosphaeria and Phomopsis cankers to reduce inoculum during dry summer months.

Start monitoring for webspinning mites when the weather warms up, once per week through August.

  • Keep records (example mite monitoring formPDF).
  • Manage if needed according to the Pest Management Guidelines.

Assess weeds in late spring and identify those not controlled by fall and winter treatments.

Manage weeds in tree rows with preemergence or postemergence herbicides or nonchemically in organic orchards. Manage weeds in row middles with mowing, cultivation or herbicides.

Monitor for walnut husk fly.

  • Set out supercharged walnut husk fly traps by June 1 and mid-May in coastal areas and check traps at least twice a week.
  • If using GF120 bait sprays, apply at first fly catch and use only in orchards with low numbers.
  • Keep records (example walnut husk fly monitoring formPDF).

If using insecticide and bait sprays:

  • Manage according to the Pest Management Guidelines when there is a sudden increase in trap catches, when the first flies are caught or when the first egg is detected.

Don't apply insecticides within 3 weeks of harvest.

Consider using the plant growth regulator ethephon to hasten husk split for early harvest if navel orangeworm is a problem. Consult with your pest control adviser (PCA) or crop consultant about the need for pre-harvest insecticide applications.

Bait ground squirrels, if needed, when vegetation begins to dry.

Other pests you may see:

  • Crown gall
  • Fall webworm
  • Ground squirrel
  • Phytophthora root and crown rot
  • Redhumped caterpillar
  • Tree squirrel
Text Updated: 07/17