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How to Manage Pests

UC Pest Management Guidelines

Western tussock moth larva.


Western Tussock Moth

Scientific Name: Orgyia vetusta

(Reviewed 11/07, updated 11/07)

In this Guideline:


The western tussock moth is an occasional pest in coastal apricot orchards. A mature larva is 0.5 to 1 inch long with a gray background color and numerous red, blue, and yellow spots. Four white tufts of hair emerge from its back as well as two black tufts from its head and one from its tail end. Larvae emerge in March and mature in May. The wingless female moths mate in early summer and lay eggs in feltlike masses on old cocoons. Only one generation is produced each year.


The larvae are insignificant foliar feeders but may feed on the surface of fruit sufficiently in some years to warrant control measures. Feeding results in shallow, scabby, depressed areas at harvest.


Natural enemies usually keep tussock moth under control.

Biological Control
Biological control, including the egg parasite Telenomus californicus and naturally occurring diseases, usually restricts tussock moth to occasional outbreaks.

Organically Acceptable Methods
Bacillus thuringiensis sprays and sprays of the Entrust formulation of Spinosad are acceptable for use on organically grown apricots.

Monitoring and Treatment Decisions
Watch for tussock moth egg cases on old pupal cases attached to twigs as you monitor orchards in spring before and during bloom (late February through mid-March). Begin to look for larvae in March. Infestations can be controlled with Bacillus thuringiensis while larvae are small. You can control localized infestations by pruning them out and destroying them. Population buildups tend to be localized because the females are flightless.

Petal fall sprays to control other spring caterpillar problems will control this pest. Later instars are difficult to control. This pest is cyclic and often is controlled by parasitic wasps.

Common name Amount to Use** R.E.I.+ P.H.I.+
(trade name) (conc.) (dilute) (hours) (days)

Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and honey bees in order. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
  (Success) 4–8 fl oz 1–2 fl oz 4 14
  (Entrust)# 1.25–2.5 oz 0.3–0.6 oz 4 14
  COMMENTS: Most effective when applied at petal fall. This product is toxic to bees for 3 hours following treatment; apply in the late evening after bees have stopped foraging. Do not apply more than 29 fl oz/acre/year of Success or 9 oz/acre/year of Entrust.
  (various products) Label rates 4 0
  COMMENTS: Make two applications during bloom: the first between popcorn and the beginning of bloom and the second 7-10 days later, but no later than petal fall. Good coverage is essential. Ground application using a concentrate rate (80-100 gal water maximum) is preferred. If aerial applications must be made because conditions do not permit ground application, a concentrate rate (5 gal or less) is preferred. Fly material on at a height of about 20 ft over the canopy using appropriate nozzles to allow better deposition on the tree tops. Compatible with fungicide sprays, and can be tank mixed with them. For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum a.i. on any label when tank mixing products that contain the same a.i.
  (Intrepid) 2F 8–16 fl oz 2–4 fl oz 4 7
  COMMENTS: Do not apply more than 16 fl oz/acre/application or more than 64 fl oz/acre/season.
  (Imidan) 70WP 4.25 lb 1 lb 3 days 14
E. DIAZINON* 50WP 3 lb 1 lb 24 21
  COMMENTS: Avoid drift and tailwater runoff into surface waters. Where apricots are grown adjacent to waterways, do not use this material.
**  For concentrate applications, use the amount given in 80-100 gal water/acre or lower if the label allows; for dilute application, amount is per 100 gal water to be applied in 300-400 gal water/acre, according to label.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
# Acceptable for use on organically grown produce.
1 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 to help prevent development of resistance. 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 Group numbers are 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: Apricot
UC ANR Publication 3433
Insects and Mites
W. W. Coates, UC Cooperative Extension, San Benito County
R. A. Van Steenwyk, Insect Biology, UC Berkeley
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
K. R. Day, UC Cooperative Extension, Tulare County
K. A. Kelley, UC Cooperative Extension, Stanislaus County
J. L. Caprile, UC Cooperative Extension, Contra Costa County
Acknowledgment for contributions to Insects and Mites:
L. C. Hendricks, UC Cooperative Extension, Merced County

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