How to Manage Pests

UC Pest Management Guidelines


Saltmarsh Caterpillar

Scientific Name: Estigmene acrea

(Reviewed 6/08, updated 5/10)

In this Guideline:


Adult moths are white with orange abdomens and black spots on their wings. Unlike females, the hind wings of male moths are orange. Larvae, or caterpillars, are black with many tufts of long orange, black, and white hairs, and tend to curl up in a ball when disturbed. Very young caterpillars feed in a large, gregarious mass for the first two to three instars before dispersing. Mature caterpillars are almost 2 inches long.

Overwintering mature caterpillars pupate in spring. Emerging moths lay their round, shiny eggs in several rows forming a neat cluster on the undersides of leaves. There are several generations each year.


When saltmarsh caterpillars first hatch, they remain clustered and feed on the undersides of the leaves where the eggs were laid. They skeletonize the foliage of plants adjacent to the egg mass. As caterpillars grow and disperse, they eat small holes (0.25-0.4 inch [6-10 mm] diameter) in the leaves. This type of damage is generally of little or no concern, but the caterpillars can also make superficial bites in the fruit, causing losses.


Biological control generally keeps populations of saltmarsh caterpillar low. If late summer populations develop, a spot treatment may adequately control these caterpillars.

Biological Control
Young larvae have a high mortality rate, perhaps from a naturally occurring virus, which helps to limit populations. There are also a number of natural enemies, including parasitic wasps and flies that help to control this pest.

Cultural Control
Caterpillars migrating from adjacent fields or uncultivated areas can be stopped by physical barriers such as a plowed ditch, a ditch of water, or a slippery, vertical aluminum foil fence several inches tall.

Organically Acceptable Methods
Cultural and biological controls and sprays of Bacillus thuringiensis sprays and the Entrust formulation of spinosad are acceptable for use on organically certified strawberries.

Treatment Decisions
Sprays are best applied while the young caterpillars are still in the gregarious, skeletonizing phase. They are most susceptible to Bacillus thuringiensis at this time. Because populations are localized, spot treatments are recommended.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (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 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 label of product being used.
  (Entrust)# 1.25–1.5 oz 4 1
  (Success) 6 fl oz    
  COMMENTS: Most effective against younger larvae. Rotate to an insecticide with a different mode of action after two successive applications. Maintaining proper pH of the spray tank water is critical for maximum efficacy.
  (various products) Label rates 4 0
  COMMENTS: Use when loopers are in the 1st or 2nd instar. Apply to plants when they are dry.
  (Intrepid 2F) 6–12 fl oz 4 3
D. DIAZINON* 50WP 2 lb 3 days 5
  COMMENTS: Do not use unless saltmarsh caterpillars pose a serious threat to the crop; diazinon is harmful to mite predators and outbreaks of twospotted spider mites may occur following its use. Do not allow this material to run off into surface waters.
+ 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.
# Acceptable for use on organically grown produce.
* Permit required from county agricultural commissioner for purchase or use.
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: Strawberry
UC ANR Publication 3468

Insects and Mites

  • F. G. Zalom, Entomology, UC Davis
  • M. P. Bolda, UC Cooperative Extension, Santa Cruz County
  • S. K. Dara, UC Cooperative Extension, Santa Barbara County
  • S. Joseph, UC Cooperative Extension, Monterey County
Acknowledgment for contributions to the Insects and Mites:
  • P. A. Phillips, UC IPM Program and UC Cooperative Extension, Ventura County
  • N. C. Toscano, Entomology, UC Riverside

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