How to Manage Pests

UC Pest Management Guidelines

Walnut

Dormant Monitoring

(Reviewed 12/07, updated 12/07)

Monitor during the dormant period to determine the need for a spring treatment to manage populations of walnut scale, frosted scale, European fruit lecanium scale, San Jose 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, 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 populations down, thus eliminating the need for treatment.
• Map out areas of concern for spring monitoring and possible treatments.

Treatment thresholds

Walnut scale: Natural enemies usually can be relied on to keep walnut scale from causing damage. If scales are present but a high degree of parasitization is observed, treatments will not be 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, treatment 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 years wood and less than 90% parasitism, treatment is warranted.

European red mite: No damage threshold levels are available to determine when to treat. Avoid treating low-to-moderate levels of European red mites because they can be important in maintaining predators of other mites.

IMPORTANT LINKS

• Photos of key pests
• Photos of natural enemies of scales

PUBLICATION

UC IPM Pest Management Guidelines: Walnut
UC ANR Publication 3471

General Information

C. Pickel (Crop Team Leader), UC IPM Program/UC Cooperative Extension, Sutter/Yuba counties
J. E. Adaskaveg, Plant Pathology, UC Riverside
J. A. Grant, UC Cooperative Extension, San Joaquin County
J. K. Hasey, UC Cooperative Extension, Sutter/Yuba counties
R. P. Buchner, UC Cooperative Extension, Tehama County
K. K. Anderson, UC Cooperative Extension, Stanislaus County
W. J. Bentley, UC IPM Program/ Kearney Agricultural Center, Parlier
W. W. Coates, UC Cooperative Extension, San Benito County
R. B. Elkins, UC Cooperative Extension, Lake County
W. H. Krueger, UC Cooperative Extension Glenn County
D. Light, USDA, Albany, CA
M. V. McKenry, Kearney Agricultural Center, Parlier
A. Shrestha, UC IPM Program/Kearney Agricultural Center, Parlier

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