How to Manage Pests

UC Pest Management Guidelines

Walnut

Dormant Monitoring

(Reviewed 7/17, updated 7/17)

In this Guideline:


Monitor during the dormant period to determine the need for a spring sprays to manage populations of walnut scale, frosted scale, European fruit lecanium scale, San Jose scale, Italian pear scale, and European red mite.

How to monitor

  • Examine scaffolds, limbs, branches, and prunings for the following pests : walnut scale, San Jose scale, frosted scale nymphs, Italian pear scale, and European red mite eggs.
  • If they have been a problem in the past, monitor for European fruit lecanium scale.
  • Look for evidence of parasitization as characterized by emergence holes in the body of the dead, mature scale. A high level of parasitization may keep numbers down, thus eliminating the need for insecticide applications.
  • Map out areas of concern for spring monitoring and possible insecticide applications.

Treatment thresholds

These scale treatment thresholds are based on direct damage from scale; they do not reflect thresholds if Botryosphaeria is a concern in your orchard.

Walnut Scale

Natural enemies often cannot be relied on to keep walnut scale from causing damage. If scales are present but a high degree of parasitization is observed, insecticide applications probably are not needed.

Frosted Scale

If you find 5 or more nymphs per foot of last year's wood throughout the orchard and less than 90% parasitized nymphs, an insecticide application is warranted.

European Fruit Lecanium Scale

Same as frosted scale.

San Jose Scale

If you find 5 or more black caps per foot of last year's wood and less than 90% parasitism, an insecticide application is warranted.

Italian Pear Scale

No damage threshold levels are available to determine if an insecticide application is needed. The key to managing Italian pear scales is to control the lichens. Regular blight treatments in spring will provide control of moss and lichens.

European Red Mite

No damage threshold levels are available to determine if an insecticide application is needed. Avoid spraying low to moderate levels of European red mites because they can be important in maintaining predators of other mites.

IMPORTANT LINKS

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Walnut
UC ANR Publication 3471

General Information

J. A. Grant, UC Cooperative Extension, San Joaquin County (crop team leader)
E. J. Symmes, UC IPM Pro-gram, Butte County (IPM facilitator)
R. DeBiase, UC IPM Program (coordinator)
E. J. Fichtner, UC Cooperative Extension, Tulare County
J. A. Roncoroni, UC Cooperative Extension, Napa County and UC IPM Program
B. B. Westerdahl, Nematology, UC Davis

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