How to Manage Pests
UC Pest Management Guidelines
Western Tussock Moth
Scientific name: Orgyia vetusta
(Reviewed 8/06, updated 3/09, pesticides updated 10/15)
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.
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.
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.
UC IPM Pest Management Guidelines: Apple
Insects and Mites
L. R. Wunderlich, UC Cooperative Extension, El Dorado County
Acknowledgment for contributions to Insects and Mites:H. L. Andris, UC Cooperative Extension, Fresno County
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
W. W. Coates, UC Cooperative Extension, San Benito County
C. Pickel, UC IPM Program, Sutter/Yuba counties