Armyworms

Beet armyworms may be abundant on asparagus ferns in low desert valleys of Imperial and Riverside counties any time from May to October. In other locations they are relatively minor pests. The adult is a small, mottled gray or dusky-winged moth. Females deposit pale greenish or pinkish, striated eggs on the asparagus ferns in small or large masses covered with white cottony material. The eggs hatch in a few days, and the tiny caterpillars begin feeding on the cladophylls (branchlets) in the plant canopy. Larger larvae feed on the epidermis of the branches of the ferns. The caterpillars become full grown in about 2 to 3 weeks and are about 1.25 inches long. They may be olive green to almost black in color with a yellow stripe on each side of the body. Beet armyworms may become abundant and cause severe injury to asparagus ferns in summer and fall.

Western yellowstriped armyworm may be abundant on asparagus ferns in low desert valleys of Imperial and Riverside counties anytime from June through October but in other areas is a relatively minor pest. The adult is a small, mottled gray or dusky-winged moth. Females deposit eggs, laid in clusters and covered with a gray, cottony material, on the asparagus. The eggs hatch in a few days, and the tiny caterpillars begin feeding on the cladophylls (branchlets) in the plant canopy. Larger larvae feed on the epidermis of the fern's branches. The caterpillar is usually black with two prominent stripes and many narrow bright ones on each side. At maturity it is about 1.5 to 2 inches long.

Larvae feed mostly at night on the epidermis of asparagus fern branches, often girdling the branch and causing the ferns to die.

Good weed management can help prevent the buildup of armyworms. Treatments may be necessary when armyworms are in the field and damage is occurring.

Sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are acceptable for use on an organically certified crop.

Armyworm eggs and larvae are easier to find on weeds near asparagus fields than in the fields when the ferns are large. Chenopodium spp. (e.g., lambsquarters, goosefoot) are particularly attractive to beet armyworm during fern stage. Monitor fields twice weekly because populations can build quickly. Adult beet armyworm activity can be monitored by using pheromone traps placed along the edges of fields. This technique is good for detecting populations of migrating moths.

Treat when larvae are visibly present in the ferns. Treatments are most effective when larvae are small; large larvae are more difficult to kill, especially with Bacillus thuringiensis products. Treat at dusk or at night; larvae are more active at dusk until twilight, and insecticides such as Bacillus thuringiensis products are susceptible to photodegradation.