Agriculture: Citrus Pest Management Guidelines

Western Tussock Moth

  • Orgyia vetusta
  • Description of the Pest

    (View Caterpillar ID Key) (PDF)

    Western tussock moth has one generation a year. Overwintered eggs hatch about the time the spring growth flush is expanding. Larvae of the western tussock moth are distinctive: young larvae are black with long bristles; maturing larvae have numerous red and yellow spots and four median dorsal tufts of light gray hair. Mature larvae spin their cocoons and pupate mainly on scaffold branches and trunks.

    Adults emerge from late April through July and, after mating, wingless females lay 125 to 300 eggs each in a single egg mass—usually on the empty pupal case. Adult males are generally brownish and have wings that, when at rest and viewed from above, form a roughly triangular outline. The topsides of the male's forewings are darker with grayish areas and have two irregular darker markings that cross at one-third and two-thirds of their length.


    Western tussock moth infestations are occasionally a problem in Southern California and in foothill orchards in the San Joaquin Valley. A heavy infestation of this pest may destroy all new spring growth. The larva may also eat into newly set or young fruit. The damage is similar to that of katydids, grasshoppers, and citrus cutworm.


    Manage western tussock moth by monitoring in spring and applying an insecticide when necessary. Use selective (those listed with a narrow range of activity) insecticides to preserve natural enemies.

    Biological Control

    A dermestid egg predator, Trogoderma sternale, is common in some areas of Southern California as is a small parasitic wasp, Telenomus californicus.

    Organically Acceptable Methods

    Use biological control and sprays of Bacillus thuringiensis on organically certified citrus.

    Monitoring and Treatment Decisions

    Look for egg masses or larvae of western tussock moth in spring to determine moth numbers before damage occurs. If you find an average of one healthy egg mass per tree, economic loss may occur. Apply an insecticide after 90% of the eggs have hatched. If you monitor larvae, about 100 larvae an hour of search warrants an insecticide application.

    Common name Amount to use REI‡ PHI‡
    (Example trade name) (type of coverage)** (hours) (days)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.
    (various products) Label rates (OC) 4 0
    RANGE OF ACTIVITY: Pests: narrow (caterpillars); Natural enemies: none
    PERSISTENCE: Pests: short; Natural enemies: none
    COMMENTS: Can be used during bloom. Timing is important because of short residual period. Apply only during warm weather to control young, actively feeding worms. Use reduced wind velocity and drive 3 mph.
    (Prokil Cryolite 96) 8–20 lb/acre (OC) 12 15
    (Kryocide) 8–20 lb/acre (OC) 12 15
    RANGE OF ACTIVITY: Pests: intermediate (foliage feeders such as worms, katydids, and Fuller rose beetle); Natural enemies: few, if any
    PERSISTENCE: Pests: long, unless washed off by rain; Natural enemies: none to short
    COMMENTS: Check label for variety. Use higher rate for larger trees. Slow-acting stomach poison that may take several days of warm weather to kill worms. Use reduced wind velocity and a speed of 3 mph. Use of Prokil Cryolite 96 allowed under a supplemental label.
    (Sevin XLR Plus) 2–3 qt/acre (OC) 12 5
    RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
    PERSISTENCE: Pests: long; Natural enemies: long
    COMMENTS: For use on all varieties. During the bloom period, apply from 1 hour after sunset until 2 hours before sunrise. Check with your local county agricultural commissioner regarding application restrictions during the bloom period.
    D. NALED
    (Dibrom 8 Emulsive)* 1–2 pt/acre (OC) 48 7
    RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
    PERSISTENCE: Pests: short; Natural enemies: intermediate
    COMMENTS: For use on grapefruit, lemons, oranges, tangerines. This pesticide is hazardous to bees. Do not apply during bloom.
    (Lannate LV2.4) 1.5–3 pt/acre (OC or A) 72 (3 days) 1
    RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
    PERSISTENCE: Pests: short; Natural enemies: intermediate
    COMMENTS: For use on grapefruit, lemons, oranges, tangerines, and tangelos. Apply as needed, except during daylight hours of the bloom period.
    ** A - Aircraft applications 5 to 20 gal water/acre.
    OC - Outside coverage uses 100 to 250 gal water/acre.
    Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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 the 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 (un = unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee).
    Text Updated: 02/17
    Treatment Table Updated: 02/17