Cabbage Looper

Adult moths have brown mottled forewings marked in the center with a distinctive silvery figure-8. Larvae are smooth-skinned, green caterpillars usually with a narrow, white stripe along each side, several narrow lines, and a few long bristles down the back. They may grow up to 1.5 inches long and can be distinguished from most other common caterpillars by their distinctive looping movement in which they arch the middle portion of their body to bring the prolegs forward to meet the front legs. Older larvae spin silken cocoons and pupate, usually attached to leaves. Eggs are ridged and dome-shaped and laid singly on the undersurface of leaves. Cabbage looper may have numerous generations and continue to develop all year long in California cilantro and parsley. The highest numbers usually occur in the fall.

Cabbage loopers may occur at any time during the growing season. Infestations early in the season on seedling plants may result in damage to cotyledons, new leaves, and terminal buds. Looper eggs are deposited singly, usually on the underside of younger leaves. Young larvae feed primarily on the underside of leaves, skeletonizing them. Contaminated leaves with insect remains and frass reduce crop marketability.

Cabbage loopers have many natural enemies that frequently keep looper numbers below economic levels, if they are not killed by insecticide treatments for other pests. Monitor regularly to determine the number of loopers and natural enemies.

Important parasites include the egg parasite Trichogramma pretiosum, three wasps that attack the caterpillars Hyposoter exiguae, Copidosoma truncatellum, Microplitis brassicae, and the parasitic tachinid fly Voria ruralis. Naturally occurring nuclear polyhedrosis virus disease can also play a role under certain circumstances; the bodies of diseased caterpillars turn into shapeless sacks of dark liquid and can often be spotted hanging from leaves.

When looper numbers are near the treatment threshold during monitoring, but there are many parasitized or diseased individuals, delay application of pesticide for a few days to determine if natural enemies will bring numbers down on their own. If an application is necessary, use Bacillus thuringiensis to minimize injury to natural enemies.

Cultural control can reduce cabbage looper numbers. Disc fields immediately following harvest to remove the food source for any remaining larvae. Discing also damages or kills pupae. Destroy weeds along field borders.

Biological control and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are organically acceptable management tools.

Monitor adult flights throughout the season with pheromone traps (delta, wing, or bucket type) to determine when to begin looking for loopers and if a pesticide application is warranted.

1. Set out first traps when seedlings emerge. Replace trap bottoms monthly or when they become covered with debris.
2. When increasing numbers of moths are found in the traps, indicating a flight peak, it is time to start monitoring crop foliage for eggs and small larvae.
3. Check 25 plants selected randomly throughout the field.
4. Look for eggs and small larvae on the underside of leaves.
5. If leaves have holes, search the general area for the caterpillar.

Treat seedlings or small plants if numbers of medium-sized to large caterpillars are high enough to affect growth. Where possible, use a selective insecticide to avoid harming natural enemies. Bacillus thuringiensis and most other selective insecticides are very effective against cabbage loopers, especially when applied to early-instar caterpillars (i.e., very young). Cabbage loopers are also controlled with the more toxic materials recommended for use against other lepidopterous (caterpillar) pests. If economically damaging numbers of other caterpillars such as armyworms are present, the use of a carbamate or pyrethroid may be warranted.