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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Western tussock moth larva.

Prune

Western Tussock Moth

Scientific Name: Orgyia vetusta

(Reviewed 6/06, updated 6/06)

In this Guideline:

DESCRIPTION OF THE PEST

The full-grown western tussock moth larva is 1.5 to 2 inches in length, generally gray in color with numerous colored spots, four prominent white tufts of hair on its body, and two black tufts on its head and one on its posterior end. The adult female moth is wingless and light silver-gray. Males are winged and also gray in color. Larvae appear in spring and become adults in May, June, and July. These adults produce caterpillars that feed for 40 to 60 days before they pupate. There are two generations of tussock moth in southern California, but only one in northern California.

DAMAGE

Western tussock moth caterpillars feed on foliage and young fruit, devouring large portions of leaves or entire leaves, and making irregular holes in the fruit.

MANAGEMENT

Natural enemies usually keep tussock moth under control.

Organically Acceptable Methods
Bacillus thuringiensis sprays and pruning out infestations are organically acceptable management tools.

Monitoring and Treatment Decisions
On small trees, remove infested twigs. Spray programs for other insects generally reduce populations. If insecticide treatments are required, localized treatments on individual trees and branches are generally all that is necessary. Treat when small caterpillars are first observed. (To identify caterpillars that are present during bloom, view photos.) The addition of a wetting agent to increase penetration of the webbing by the insecticide enhances control.

Common name Amount to Use** P.H.I.+
(trade name) (conc.) (dilute) (days)
When choosing a pesticide, consider information relating to impact on natural enemies and honey bees, impact of the timing on beneficials, and environmental impact.
 
A. BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various products) Label rates — 0
  MODE OF ACTION: A microbial (Group 11.B2)1 insecticide.
  COMMENTS: Most effective on small caterpillars. Does not destroy natural enemies.
 
 
** For dilute applications, rate is per 100 gal water to be applied in 300-500 gal water/acre, according to label; for concentrate applications, use 80-100 gal water/acre, or lower if the label allows.
+ Preharvest interval. Do not apply within this many days of harvest.
# Acceptable for use on organically grown produce.
—  Not recommended or not on label.
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/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Prune
UC ANR Publication 3464
Insects and Mites
C. Pickel, UC IPM Program, Sutter/Yuba counties
F. J. A. Niederholzer, UC Cooperative Extension, Sutter/Yuba counties
W. H. Olson, UC Cooperative Extension, Butte County
F. G. Zalom, Entomology, UC Davis
R. P. Buchner, UC Cooperative Extension, Tehama County
W. H. Krueger, UC Cooperative Extension Glenn County
Acknowledgment for contributions to the insects and mites section:
W. O. Reil, UC Cooperative Extension Solano/Yolo counties

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