UC IPM Online UC ANR home page UC IPM home page


SKIP navigation


How to Manage Pests

UC Pest Management Guidelines

Western tussock moth larva.


Western Tussock Moth

Scientific name: Orgyia vetusta

(Reviewed 2/07, updated 2/07)

In this Guideline:


Western tussock moth overwinters in the egg stage, and larvae begin emerging in March and April. Immature larvae are hairy and black. Mature western tussock moth larvae are large (almost 2 inches in length) caterpillars with numerous red and yellow spots and long tufts of hair. There are four white tufts of hair on the top of the first four abdominal segments, two black tufts on the head, and many grayish tufts over the body. Adult females are large, wingless, and predominantly gray. The males are winged moths. There is only one generation per year.


As the tree begins to leaf out, larvae feed on the foliage. Localized heavy populations can completely defoliate trees.


Visually search trees for black caterpillars feeding on terminal growth and look for cocoons on major scaffolds. Insecticides applied for plant bug control will reduce western tussock moth populations.

Organically Acceptable Methods
Sprays of Bacillus thuringiensis are acceptable for use in an organically managed orchard.

Common name Amount/Acre** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to impact on natural enemies and honey bees and environmental impact Not all registered pesticides are listed. Always read label of product being used.
  (various products) Label rates 4 0
  MODE OF ACTION: A microbial (Group 11.B2)1 insecticide.
**  Unless otherwise noted, apply with enough water to ensure adequate coverage.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment until harvest may occur. In some cases the R.E.I. exceeds the P.H.I. The longer of these two intervals is the minimum time that must elapse before harvest can take place.
# Acceptable for organically grown produce.
1 Modes of action are important in preventing the development of resistance to pesticides. Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action is assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Pistachio
UC ANR Publication 3461
Insects and Mites
W. J. Bentley, Kearney Agricultural Center, Parlier
R. H. Beede, UC Cooperative Extension, Kings County
K. M. Daane, Biological Control, UC Berkeley/Kearney Agricultural Center, Parlier
D. R. Haviland, UC Cooperative Extension, Kern County
Acknowledgment for contributions to Insects and Mites:
R. E. Rice, Kearney Agricultural Center, Parlier

Top of page

Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2014 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance.

Agriculture and Natural Resources, University of California

Accessibility   /PMG/r605300611.html revised: April 25, 2014. Contact webmaster.