UC IPM Online UC ANR home page UC IPM home page


SKIP navigation


How to Manage Pests

UC Pest Management Guidelines

Larva of forest tent caterpillar.


Tent Caterpillars

Scientific names: Western tent caterpillar: Malacosoma californicum
Forest tent caterpillar: Malacosoma disstria

(Reviewed 5/06, updated 4/09)

In this Guideline:


Tent caterpillars overwinter in the egg stage; eggs give rise to caterpillars in spring and early summer. The western tent caterpillar is hairy and dull yellow brown with a row of blue spots adjacent to orange spots on top of the body. The forest tent caterpillar is dusky gray, sparsely hairy, with fine yellow-brown stripes on the shoulder and side separated by a broad blue lateral stripe. Its most distinguishing feature is a series of white diamond or keyhole-shaped spots running along its back. Both caterpillars have one generation each year.


Damage caused by tent caterpillars may be serious on individual trees. From April to June western tent caterpillars build large silken tents over leaves on which they feed. Forest tent caterpillars build mats of webbing rather than tents. They forage in all directions from these mats but return to the colony when not feeding. Tent caterpillars do not eat leaf veins.


Populations of tent caterpillars tend to be concentrated in individual trees scattered throughout the orchard. Treatment is only occasionally required and can be limited to small areas of the orchard.

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

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

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy, impact on natural enemies and honey bees, and impact of the timing on beneficials. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
  (various products) Label rates 4 0
  COMMENTS: Most effective on small caterpillars. Does not destroy natural enemies.
B. DIAZINON* 50 WP 3 lb 1 lb 24 21
  4EC 3 pt 1 pt 24 21
  COMMENTS: Avoid drift and runoff into surface waters. Where plums are grown near waterways, do not use diazinon.
** 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 (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.
Not recommended or not on label.
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 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: Plum
UC ANR Publication 3462
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
K. R. Day, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to Insects and Mites:
R. E. Rice, Kearney Agricultural Center, Parlier

Top of page

Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2017 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance.

Agriculture and Natural Resources, University of California

Accessibility   Contact webmaster.