How to Manage Pests

UC Pest Management Guidelines

Walnut

Dormant Monitoring

(Reviewed 12/07, updated 12/07)

In this Guideline:


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

PUBLICATION

[UC Peer Reviewed]

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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