Armyworms

In addition to eggplants, armyworms feed on sugarbeet, alfalfa, beans, eggplants, 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 host crops when the plants are young. Eggs tend to be laid on fully expanded young leaves. Newly hatched larvae feed together near the egg cluster and gradually disperse as they grow.

Beet Armyworm

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.

Western Yellowstriped Armyworm

Larvae of the western yellowstriped armyworm are almost black, with two prominent and many fine, bright yellow stripes on the side. At maturity it is approximately 1.5 to 2 inches long. Eggs are laid in clusters on the upper side of leaves and covered with a gray, cottony material. Eggs hatch in a few days and larvae reach full size in 2 to 3 weeks. Larvae pupate on or just under the soil surface. Adults are brown moths that primarily fly at night but may be encountered flying up as you walk through the field. There are at least five generations per year in the low desert and four generations in the Central Valley. This pest may be abundant at any time from June to early September.

Feeding by armyworms on the leaves, flowers, and fruit of eggplants can cause serious problems. As the fruit forms, armyworms may feed on calyx and can scar small fruit. Both defoliation and fruit loss result from the feeding.

Regular monitoring of the leaves and fruit is important in detecting an infestation of armyworms.

Many natural enemies attack armyworms and prevent a large number of the population from reaching maturity. 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.

Biological control and sprays of Bacillus thuringiensis or the Entrust formulation of spinosad are acceptable for use on an organically certified crop.

Sampling guidelines for armyworms in eggplants have not been developed. Look for the cream-colored egg mass or, later, for feeding on pigweed, nettleleaf goosefoot, and lambsquarters plants in and around the field. If armyworms are present on these weeds, also examine the eggplants. Treat if foliar damage is occurring.