Loopers

Loopers arch their backs as they crawl along in a "looping" manner. Cabbage loopers usually have a narrow, white stripe along each side and several narrow lines down the back. Eggs are dome-shaped, and laid on the undersurfaces of older leaves. Adult moths have brown, mottled forewings marked in the center with a small silver figure 8.

Young larvae feed primarily on the undersides of lower leaves, skeletonizing them. High numbers of loopers can damage seedlings severely enough to kill them or slow growth enough to inhibit uniform maturing of the crop. Older larvae may burrow into the head from the top.

Loopers have many natural enemies that often keep their numbers below economic thresholds. Maximize the use of these natural enemies by limiting treatments, especially between thinning and heading. In some areas, an important biological control agent is nuclear polyhedrosis virus that occurs naturally in the field. Bodies of loopers killed by the virus are dark, soft, and shapeless with their body contents often spilling onto the leaves.

Another important natural enemy in southern California, the parasitoid wasp, Trichogramma pretiosum, which attacks looper eggs and eggs of other caterpillars such as corn earworm and tobacco budworm . Eggs parasitized by Trichogramma turn black as the immature parasitoid matures inside the egg and are easy to distinguish from non-parasitized eggs that remain white except for a black spot that appears just before hatching. Parasites that attack looper caterpillars include the tachinid fly, Voria ruralis, and three wasps, Hyposoter exiguae, Copidosoma truncatellum, and Microplitis brassicae.

Use biological control and sprays of Bacillus thuringiensis, and the Entrust formulation of spinosad in organically certified crops. Note that spinosad is detrimental to beneficial syrphid flies.

Look for signs of looper feeding: plants with holes in outer leaves, feces, and caterpillars feeding on edge of hole.

• Check fields twice a week once seedlings emerge. Loopers, cabbageworms, armyworms, corn earworms, tobacco budworms, cutworms, and other caterpillars that feed on leaves and heads of lettuce can be assessed together, but species identification is important in choosing an insecticide.
• Check at least 25 plants for caterpillars in each quadrant of a 40- to 80-acre field twice a week. Fields smaller than 40 acres may require fewer samples. In fields where the crop is heading, stop at five different locations in each quadrant and sample five plants at each location.
• Apply insecticide on seedlings or small plants if numbers of medium-size to large loopers are large enough to stunt growth. Spray well-established plants only if you find an average of more than one-half larvae per plant. For cabbage looper control, the best time to apply insecticide is in the afternoon.