UC IPM Online UC ANR home page UC IPM home page

UC IPM Home

Search

SKIP navigation
How to Manage Pests

Home & garden
Agriculture
Natural environments
Exotic & invasive

Weather data & products
Degree-days
Interactive tools & models

Educational Resources

Publications & more
Workshops and events
Training programs
Pesticide information

Research and IPM

Grants programs
Funded-project results

 
  Printer-friendly version

How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Western tussock moth larva.

Apple

Western Tussock Moth

Scientific name: Orgyia vetusta

(Reviewed 8/06, updated 8/06)

In this Guideline:

DESCRIPTION OF THE PEST

Western tussock moth has one generation a year. Wingless females lay 125 to 300 eggs in a single mass on the empty pupal case. Overwintering eggs hatch when spring growth is expanding. Young larvae are black caterpillars with long bristles; mature larvae have numerous red and yellow spots and four median dorsal tufts.

DAMAGE

A heavy infestation will destroy all spring growth. Larvae take shallow bites out of newly set, young fruit; these injured areas eventually scab over and russet. Infestations are spotty and may be isolated in certain areas of an orchard.

MANAGEMENT

Western tussock moth is common throughout California, especially in unsprayed orchards. Monitor for egg masses in winter and larvae in spring to determine need for treatment.

Organically Acceptable Methods
Sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are organically acceptable.

Monitoring and Treatment Decisions
During winter look for western tussock moth egg masses on props or tree trunks. Monitor during bloom by examining 100 fruit clusters for larvae. Spot-treat infested areas in the orchard. Applications made at night during bloom will minimize damage to bees. This insect is usually controlled by sprays for other pests.

Common name Amount to Use P.H.I.+
(trade name) (conc.) (dilute) (days)
When choosing a pesticide, consider information relating to the impact on natural enemies and honey bees and environmental impact.
 
A. BACILLUS THURINGIENSIS spp. KURSTAKI#
  (various products) Label rates — 0
  MODE OF ACTION: A microbial (Group 11.B2)1 insecticide.
  COMMENTS: Least harmful to beneficials. Bt is a stomach poison and must be consumed by the caterpillar; therefore, it is most effective when applied during warm, dry weather when larvae are actively feeding. Spray during bloom or when monitoring indicates a need. Most effective against young larvae. Requires more than 1 treatment; apply second application 7–10 days after first.
 
B. SPINOSAD
  (Entrust)# 2-3 oz 0.5-0.75 oz 7
  (Success) 6–10 oz 2–3.3 oz 7
  MODE OF ACTION: A microbial (Group 5)1 insecticide.
  COMMENTS: Apply at petal fall. To prevent the development of resistance to this product rotate to a material with a different mode of action after treating two consecutive generations.
 
 
**  For dilute application, 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.
* Permit required from county agricultural commissioner for purchase or use.
# 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: Apple
UC ANR Publication 3432
Insects and Mites
J. L. Caprile, UC Cooperative Extension, Contra Costa County
L. R. Wunderlich, UC Cooperative Extension, El Dorado County
P. M. Vossen, UC Cooperative Extension, Sonoma and Marin counties
W. W. Coates, UC Cooperative Extension, San Benito County
H. L. Andris, UC Cooperative Extension, Fresno County
L. G. Varela, UC IPM Program, Sonoma County
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgment for contributions to the insects and mites section:
C. Pickel, UC IPM Program, Sutter and Yuba counties

Top of page

Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2006 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 How to manage pests, or in the U.S., contact your local Cooperative Extension office for assistance. /PMG/r4301111.html revised: August 17, 2006. Contact webmaster.