Agriculture: Cherry Pest Management Guidelines

Western Tussock Moth

  • Orgyia vetusta
  • Description of the Pest

    The western tussock moth is an occasional pest in coastal cherry orchards. Tussock moths survive the winter as fuzzy egg masses that female moths cement to their old pupal cases and cover with hairs. Mature larvae are gray caterpillars with numerous red, blue, and yellow spots and four white tufts of hair on their backs, two black tufts on their heads, and one on their tail ends. Larvae emerge in March and mature in May; when mature they are 0.5 to 1 inch long. Adults are active from May through July. Males are gray moths; females are grayish white and lack wings. Only one generation is produced each year.


    Larvae are usually 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

    Natural enemies, including larval parasites (Hyposoter exiguae, H. fugitivus, Dibrachys sp.) and a predatory beetle (Trogoderma sternale), usually keep tussock moth under control.

    Cultural Control

    Localized infestations can be pruned out and destroyed. Population buildups tend to be localized because the females are flightless.

    Organically Acceptable Methods

    Biological and cultural controls and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are acceptable for use on an organically certified crop.

    Monitoring and Treatment Decisions

    Watch for tussock moth egg cases on leaves and twigs as you monitor orchards in spring before and during bloom. (For more information, see MONITORING PESTS AT BLOOM.) Begin to look for larvae in March. Infestations can be controlled with Bacillus thuringiensis while larvae are small. Petal fall sprays to control other worm problems generally control this pest. Later instars are difficult to control. Localized infestations can be pruned out and destroyed. This pest is cyclic and often controlled by parasitic wasps.

    Common name Amount to use** REI‡ PHI‡
    (Example trade name) (conc.) (dilute) (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 4 0
      COMMENTS: Is not harmful to beneficial insects. Apply when larvae are small. Make 2 applications during bloom: the first at early bloom and the second 7–10 days later, but no later than petal fall. Compatible with fungicide sprays. Good coverage is essential.
      (Entrust)# 1.25–2.5 oz 0.42–0.83 oz 4 7
      COMMENTS: Most effective when applied at petal fall. Apply when larvae are small. This product is toxic to bees for 3 hours following treatment; apply in late evening after bees have stopped foraging. Do not apply more than 29 oz/acre per year of Success or 9 oz/acre per year of Entrust.
      (Delegate WG) 4.5–7 oz/acre 4 7
      COMMENTS: Apply when larvae are small. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
      (Diazinon 50W) 1 lb/100 gal water 96 (4 days) 21
      COMMENTS: Apply when larvae are small. Avoid drift and tailwater runoff into surface waters. Where cherries are grown adjacent to waterways, do not use this material. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
      (Sevin XLR PLUS) 3–4 qt/acre 12 1
      COMMENTS: Apply when larvae are small. May cause increased spider mite problems. Do not apply more than 14 qt XLR PLUS/acre per season. The XLR PLUS formulation is less hazardous to honey bees than other formulations if applied from late evening to early morning when bees are not foraging. May cause mite flare ups.
    ** For concentrate applications, use the amount given in 80–100 gal water/acre, or lower if the label allows; for dilute applications, amount is per 100 gal water to be applied in 300–400 gal water/acre, according to label.
    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.
    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).
    # Acceptable for use on organically grown produce.
    Text Updated: 09/15
    Treatment Table Updated: 09/15