Agriculture: Almond Pest Management Guidelines

Forest Tent Caterpillar

  • Malacosoma disstria
  • Description of the Pest

    The forest tent caterpillar overwinters in the egg stage, and eggs give rise to destructive caterpillars in spring and early summer. The caterpillars are grayish with yellow stripes along the side, separated by a broad blue stripe. There is a row of white, keyhole-shaped spots on the back. There is one generation each year.


    Defoliation caused by tent caterpillars may be serious on individual trees and along orchard edges, but is usually randomly scattered throughout the orchard. Young orchards are usually the most severely affected. From April to June, caterpillars feed on leaves; young caterpillars skeletonize the leaves, whereas older caterpillars consume the leaf, leaving only the midvein.


    On small trees, infested twigs may be cut out and destroyed. Spray programs for other insects generally reduce forest tent caterpillar numbers. If insecticide treatments are required, localized treatments on individual trees and branches are generally all that is necessary. Spray when small caterpillars are first observed. Cateripllar numbers usually decline naturally due to disease.

    Common name Amount per acre REI‡ PHI‡
    (Example trade name) (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: Best when applied to small larvae.
    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 these two intervals is the minimum time that must elapse before harvest may occur.
    # Acceptable for use on organically grown produce.
    1 Rotate pesticides 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; pesticides with a 1B group number should be alternated with pesticides that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).
    Text Updated: 08/17
    Treatment Table Updated: 08/17