How to Manage Pests

UC Pest Management Guidelines


Forest Tent Caterpillar

Scientific names: Malacosoma disstria

(Reviewed 3/09, updated 3/09)

In this Guideline:


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 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. Populations usually decline naturally due to disease.

Common name Amount per acre** REI+ PHI+
(Example trade name) (conc.) (dilute)
(hours) (days)

Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
  (various products) Label rates 4 0
  COMMENTS: Best when applied to small larvae.
** For dilute applications, rate is per 100 gal water to be applied in 300–500 gal water/acre, depending on the 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 these two intervals is the minimum time that must elapse before harvest may occur.
# 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 are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Almond
UC ANR Publication 3431

Insects and Mites

F. G. Zalom, Entomology, UC Davis
D. R. Haviland, UC IPM Program, UC Cooperative Extension, Kern County
E.J. Symmes, UC Cooperative Extension, Butte Coounty
K.Tollerup, UC IPM Program, Kearney Agricultural Center, Parlier

Acknowledgment for contributions to Insects and Mites:
C. Pickel, UC IPM Program, UC Cooperative Extension, Sutter and Yuba counties
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
R. A. Van Steenwyk, Insect Biology, UC Berkeley
R. E. Rice, Kearney Agricultural Center, Parlier
L. C. Hendricks, UC Cooperative Extension, Merced County
R. L. Coviello, UC Cooperative Extension, Fresno County
M. W. Freeman, UC Cooperative Extension, Fresno County

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