Agriculture: Strawberry Pest Management Guidelines

Saltmarsh Caterpillar

Description of the Pest

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.

Damage

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.

Management

Biological control generally keeps saltmarsh caterpillar numbers 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 caterpillar numbers. There are also several 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

Use cultural and biological controls and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad 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 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.
 
A. SPINOSAD
(Entrust)# 1.25–2 oz 4 1
(Success) 4–6 fl oz 4 1
MODE-OF-ACTION GROUP NUMBER1: 5
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. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
B. BACILLUS THURINGIENSIS ssp. KURSTAKI#
(various products) Label rates 4 0
MODE-OF-ACTION GROUP NUMBER1: 11A
COMMENTS: Use when loopers are in the 1st or 2nd instar. Apply to plants when they are dry.
 
C. METHOXYFENOZIDE
(Intrepid 2F) 6–12 fl oz 4 3
MODE-OF-ACTION GROUP NUMBER1: 18
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.
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: 07/18
Treatment Table Updated: 07/18