Walnut

Year-Round IPM Program

(Reviewed 3/08, updated 3/08)

These practices are recommended for a monitoring-based IPM program that reduces water and air quality problems related to pesticide use. Links take you to information on how to monitor, forms to use, and management practices. Track your progress through the year with the annual checklist form. This program covers the major pests of walnuts; information on additional pests is included in the Walnut Pest Management Guidelines.

Water quality becomes impaired when pesticides move off-site and into water. Air quality becomes impaired when volatile organic compounds move into the atmosphere. Each time a pesticide application is considered, review the Pesticide Application Checklist at the bottom of this page for information on how to minimize air and water quality problems.

Dormancy

Why is this season important in an IPM program?

Special issues of concern related to environmental quality: none identified.

What should you be doing during this time?
Manage orchard floor vegetation.
  • Continue postharvest weed assessment in late fall to identify those that were not controlled by fall treatment.
  • Keep records (example winter weed survey form PDF).
Assess mummy nut levels on the ground and in trees for navel orangeworm management.
Look for scale pests and mites and evidence of parasitism.
  • Examine scaffolds, limbs, branches, spurs and prunings, for scale pests and European red mite eggs.
  • Note areas of concern for possible treatment.
Other pests you may see:

Delayed-dormancy

Why is this season important in an IPM program?

Special issues of concern related to environmental quality: none identified.

What should you be doing during this time?
If a significant number of mummy nuts are still on trees or on the ground at the end of February:
  • Remove mummy nuts from trees before mid-March.
  • Flail mow to destroy mummy nuts and remove huller waste materials.
Mow ground cover before bloom.
If dormant scale and mite monitoring indicated need, treat according to Walnut Pest Management Guideline:
Look for the following pests if they have been a problem in the past:

Treat if needed according to Walnut Pest Management Guidelines.

Manage squirrels before April, if needed.

Budbreak through bloom

Why is this season important in an IPM program?

Special issues of concern related to environmental quality: pesticide runoff.

What should you be doing during this time?
If conditions favor walnut blight, treat according to Walnut Pest Management Guidelines.
Place codling moth pheromone traps in mid-March to determine first moth emergence.
  • Check traps twice weekly until biofix, and weekly thereafter.
  • Use degree-days for monitoring pest development.
  • Keep records (example degree-day monitoring form PDF).
If using mating disruptants for codling moth, place them in orchards using female biofix according to the Walnut Pest Management Guidelines.
Initiate fertilizer application and establish a nitrogen budget (PDF).
Look for crown gall and manage if needed according to Walnut Pest Management Guidelines.
Keep records of other pests you may see:
  • Phytophthora root and crown rot
  • Armillaria (oak root fungus)
  • Gophers

In-season (nut development)

Why is this season important in an IPM program?

Special issues of concern related to environmental quality: pesticide runoff.

What should you be doing during this time?
If conditions favor walnut blight development:
  • Treat according to PMG if rainy conditions continue beyond bloom.
  • Or use the Xanthocast model to determine the need for and timing of blight sprays.
Maintain codling moth management program.
  • Check traps and keep records (example degree-day monitoring form PDF).
  • If using sprayable mating disruptants, reapply according to PMG instructions; check traps and canopy nut counts to determine the need for supplemental sprays.
  • If not using mating disruptants treat only if necessary according to Walnut Pest Management Guidelines.
If dormant monitoring indicated infestations of walnut scale, monitor for crawlers.
  • Manage if needed according to Walnut Pest Management Guidelines.
Begin examining leaves for aphids.
  • Look for aphids, aphid mummies, and natural enemies.
  • Manage if needed according to Walnut Pest Management Guidelines.
Take leaf samples in July for nutrition analysis.
Start monitoring for webspinning mites when the weather warms up, once per week through August.
  • Keep records.
  • Manage if needed according to Walnut Pest Management Guidelines.
Assess weeds in late spring and identify those not controlled by fall/winter treatment.
Manage weeds in rows with preemergent or postemergent herbicides or nonchemically in organic orchards. Manage weeds in row middles.
Monitor for walnut husk fly.
  • Set out supercharged walnut husk fly traps by June 1 in coastal areas and by June 15 in inland 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 populations.
  • Keep records (example walnut husk fly monitoring form—PDF).

If using insecticide and bait sprays:

  • Treat according to PMG when there is a sudden increase in trap catches, or when the first egg is detected.
  • Don't treat within 3 weeks of harvest.
Consider using a plant growth regulator to hasten husk split for early harvest if navel orangeworm is a problem.
Bait ground squirrels, if needed, when vegetation begins to dry.
Other pests you may see:
  • Phytophthora root and crown rot
  • Crown gall
  • Redhumped caterpillar
  • Fall webworm

Harvest

Why is this season important in an IPM program?

Special issues of concern related to environmental quality: none identified.

What should you be doing during this time?
Harvest nuts promptly to reduce potential for navel orangeworm damage and to preserve kernel quality.
Sample nuts at harvest to evaluate your pest management program.

Evaluate this season's management program and plan for the next season's management.

Postharvest

Why is this season important in an IPM program?

Special issues of concern related to environmental quality: herbicide runoff.

What should you be doing during this time?
Manage orchard floor vegetation.

Pesticide application checklist

When planning for possible pesticide applications in an IPM program, review and complete this checklist to consider practices that minimize environmental and efficacy problems.
  • Choose a pesticide from the UC IPM Pest Management Guidelines for the target pest considering:
  • Select an alternative chemical or nonchemical treatment when risk is high.
    • Choose sprayers and application procedures that keep pesticides on target.
    • Identify and take special care to protect sensitive areas (for example, waterways or riparian areas) surrounding your application site.
    • Review and follow label for pesticide handling, storage, and disposal guidelines.
    • Check and follow restricted entry intervals (REI) and preharvest intervals (PHI).
    • After an application is made, record application date, product used, rate, and location of application. Follow up to confirm that treatment was effective.
  • Consider water management practices (PDF) that reduce pesticide movement off-site:
    • Install an irrigation recirculation or storage and reuse system.
    • Use drip rather than sprinkler or flood irrigation.
    • Limit irrigation to amount required using soil moisture monitoring and evapotranspiration (ET).
    • Consider vegetative filter strips (PDF) or ditches.
    • Redesign inlets into tailwater ditches to reduce erosion.
  • Consider management practices that reduce air quality problems.
    • When possible, choose pesticides that are not in emulsifiable concentrate (EC) form which release volatile organic compounds (VOCs). VOCs react with sunlight to form ozone, a major air pollutant.

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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