Impact
Variegated cutworm, Peridroma saucia, is the a common cutworm species in the San Luis Valley.

Cabbage loopers, Trichoplusia ni., also are a common pest of vegetables, including lettuce and potato, and flowers.

Armyworms, Pseudaletia unipuncta, can occasionally cause severe damage to crops throughout the San Luis Valley. This insect prefers grasses, notably small grains, but will feed on some broadleaf crops such as potatoes after grain matures.

Description and Symptoms

Cutworms

Cutworms feed at night. During the day they can be found under clods of soil or in cracks in the ground near injured plants.

Cutworms have a smooth appearance, three pairs of legs and five pairs of prolegs.

Damage early in the season includes stems cut off at or below ground level. Later, chewed foliage is the most common symptom. Tubers that are exposed on the surface or in cracks in the soil can be chewed by some cutworms.

Cutworms overwinter as immature larvae or eggs in the soil.

Loopers

Loopers have green bodies that taper to the head with a white line on each side and two white lines down the back with three pairs of prolegs.

Irregular cut holes in the leaves is typical looper damage.

Armyworms

Mature larvae are about 1 1/2 inches in length, smooth-bodied, and dark grey to greenish-black in color. They are characterized by five stripes, three on the back and two on the sides, running the length of the body. The stripes on the sides are pale orange with a white outline. The head capsule is remarkable for its honeycomb of black markings.

Dense grass is preferred for egg laying. Armyworm problems in potatoes originate from these sites.

Larvae feed at night and on cloudy days, and hide under crop debris during sunny periods.

Armyworm damage to leaves usually is restricted to field edges bordering. small grains.

Integrated Management

Control weeds to prevent fall egg laying by cutworms.

Control cutworms, armyworms and loopers only when scouting indicates a potentially damaging infestation.

Pesticide applications to control armyworms usually can be restricted to field edges.

Treat infested areas in a specific field using appropriate insecticides when control is necessary.

This material is based on work supported by the San Luis Valley Water Quality Demonstration Project Best Management Practices Advisory Committee, Colorado State University Cooperative Extension, Farm Service Agency, Natural Resources Conservation Service, and the U.S. Department of Agriculture under authorization as 1991 U.S. Department of Agriculture Water Quality Demonstration Project.