Agriculture: Plum Pest Management Guidelines

Western Tussock Moth

  • Orgyia vetusta
  • Description of the Pest

    The full-grown western tussock moth larva is 1.5 to 2 inches in length, generally gray in color with numerous colored spots, four prominent white tufts of hair on its body, and two black tufts on its head and one on its posterior end. The adult female moth is wingless and light silver gray. Males are winged and also gray in color. Larvae appear in spring and become adults in May, June, and July. These adults produce caterpillars that feed for 40 to 60 days before they pupate. There are two generations of tussock moth in southern California, but only one in northern California.


    The caterpillars feed on foliage and young fruit, devouring large portions of leaves or entire leaves, and making irregular holes in the fruit.


    Natural enemies usually keep tussock moth under control.

    Organically Acceptable Methods

    Bacillus thuringiensis sprays and pruning out infestations are organically acceptable management methods.

    Monitoring and Treatment Decisions

    On small trees, cut out and destroy infested twigs. Spray programs for other insects generally reduce populations. If insecticide treatments are required, localized treatments on individual trees and branches are generally all that is necessary. Treat when small caterpillars are first observed. The addition of a wetting agent to increase penetration of the webbing by the insecticide enhances control.

    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: Most effective on small caterpillars. Does not destroy natural enemies.
    ** For dilute applications, 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.
    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.
    # Acceptable for use on organically grown produce.
    Not recommended or not on label.
    1 Rotate insecticides 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; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B. Mode-of-action group numbers for insecticides and miticides (un=unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee).
    Text Updated: 04/09
    Treatment Table Updated: 04/09