How to Manage Pests
UC Pest Management Guidelines
Scientific name: Spodoptera exigua
(Reviewed 12/09, updated 5/10)
In this Guideline:
DESCRIPTION OF THE PEST
Adult beet armyworms are small, mottled-gray or dusky-winged moths. Females lay eggs in clusters on leaves; the clusters are covered with fluffy, dirty white scales. Eggs hatch in a few days and tiny caterpillars begin feeding while still clustered together on the plant. In 2 to 3 weeks beet armyworm larvae are full grown and about 1 inch long. The body is smooth with few hairs and predominantly green with mottled dark lines along the back. Just above the spiracle, lengthwise along the body, is a dark green to black line edged on each side with white. There is usually a small dark spot above the spiracle on the second pair of true legs.
In addition to peppers, beet armyworm feeds on sugarbeet, alfalfa, beans, tomatoes, and a variety of weeds such as lambsquarters, redroot pigweed, and nettleleaf goosefoot. During winter and spring, the population is concentrated on weeds, but in late spring moths begin laying eggs in the pepper field when the plants are young. Newly hatched larvae feed together near the egg cluster and gradually disperse as they grow; they skeletonize leaves and may spin a loose webbing over the feeding site. Older larvae chew irregular holes in leaves and feed on young fruit.
Beet armyworm is a serious pest of peppers. It feeds on both leaves and fruit. As the fruit forms, beet armyworm bores into the calyx end. Both defoliation and fruit loss result from the feeding. Unlike many caterpillar pests, the feeding is quite messy, with webbing and excrement present.
Regular monitoring of the leaves and fruit is important in detecting an infestation of beet armyworms. Treatments may be necessary if fruit damage is occurring.
Many natural enemies attack beet armyworms. Among the most common parasites are the wasps Hyposoter exiguae and Chelonus insularis, and the tachinid fly Lespesia archippivora. Viral diseases may also be important; however, none of these organisms provide reliable control of armyworms when they feed on the fruit.
Organically Acceptable Methods
Biological control and sprays of Bacillus thuringiensis or the Entrust formulation of spinosad are acceptable for use on an organically certified crop.
Monitoring and Treatment Decisions
Sampling guidelines for beet armyworm in peppers have not been developed. Pheromone traps are useful for determining when major flights occur but not for predicting damage. Look for the cream-colored egg mass or, later, for the feeding on the seedlings and leaves to determine if beet armyworms are present. Also, sample fruit when it first appears. A 5-minute timed search is useful in determining the need for treatment. On average, if one or more larvae or egg masses are found in 5 minutes, treatments may be justified. Ground applications provide maximum effectiveness of the pesticide. Treat if beet armyworms are on the fruit.
UC IPM Pest Management Guidelines:
Insects and Mites
E. T. Natwick, UC Cooperative Extension, Imperial County