Cabbage Looper

Cabbage looper larvae (caterpillars) grow up to 1-2/5 inch long and are green with lengthwise, narrow, yellowish or white stripes along the sides and top. They commonly move in a "looping" manner as they arch their abdomen upwards to pull their rear legs forward as they walk. True loopers (Geometridae) have one pair of mid-abdominal prolegs (leglike appendages), on segment 6. Cabbage loopers (Noctuidae subfamily Plusiinae) have two pairs of prolegs on the mid abdomen, on segments 5 and 6. Most other species of Noctuidae (e.g., armyworms and cutworms) and also Tortricidae (leafrollers) have four pairs of prolegs, on segments 3, 4, 5, and 6.

Adults (moths) are a mottled mix of black, brownish, gray, tan, and white. Near the center of each forewing is a silvery or whitish marking resembling a figure eight or looped string. At rest adults are about 1 inch long, and the wingspan is about 1-1/2 inch. The dome-shaped, spherical egg is pale green to whitish and laid singly or less commonly in a loose group of several under leaves. The brown to dark reddish pupa is about 1-1/2 inches long and occurs within loosely woven silk of the last instar. Pupae occur on plants near chewed foliage, on the ground in plant debris, or in topsoil, especially during the winter.

Young cabbage looper larvae feed primarily on the underside of lower leaves, skeletonizing them similar to the damage of young beet armyworms, which can also be present. Older cabbage loopers chew entirely through leaves and sometimes flowers.

Biological and cultural controls and insecticide application are used to manage cabbage looper.

Cabbage looper has many natural enemies that frequently keep its abundance below economic levels in the field unless they are killed by the use of broad-spectrum, persistent insecticides. Parasitic wasps include the tiny egg parasitic Trichogramma spp. and larger wasps that attack the caterpillars, including Copidosoma truncatellum, Hyposoter exiguae, and Microplitis brassicae. Tachinid flies such as Voria ruralis also commonly kill the loopers; these include species that lay eggs inside older loopers causing dark egg-laying wounds and species that lay their oval, whitish eggs on caterpillars. The dark, oblong pupae of tachinids commonly occur near cabbage looper chewing damage and a looper pupa with a parasite emergence hole. In some areas, the Trichoplusia ni nuclear polyhedrosis virus is an important biological control agent and occurs naturally.

Except for various predators and egg parasites, most of these natural enemies do not kill the loopers until they are older larvae or pupae, so larvae continue feeding and damaging crops sometimes through to the last instar even though parasitized or infected. Natural enemies do greatly reduce subsequent generations of the pest and its damage, including individuals migrating between crops and into growing areas.

Trichogramma spp. are commercially available for release to kill cabbage looper eggs, preventing larval emergence and feeding. To time the release the Trichogramma parasites, use blacklight traps that at night attract adults of various insects or species-specific, pheromone-baited, sticky traps to monitor adult activity to determine when adult moths are active and laying eggs.

For biological control to be effective rely on caterpillar-specific Bacillus thuringiensis (Bt), somewhat selective products such as certain insect growth regulators and spinosad, and contact insecticides such as oils. Employ nonchemical controls and other natural-enemy conservation methods as discussed in Biological Control, Protecting Natural Enemies and Pollinators, and Natural Enemy Releases for Biological Control of Crop Pests.

Keep production areas free of weeds (e.g., mustards) and other noncrop hosts of armyworms, cutworms, cabbage loopers, and other moth pests. Exclude the night-flying adults by screening greenhouse vents with mesh of sufficient surface area to allow adequate ventilation. Completely screening shade houses and other partially open growing areas is especially important when crops or nearby areas are lighted at night; artificial nighttime lighting attracts some moths. Individual seedling flats may also be covered by screens to exclude adults and larvae. Row covers and exclusion netting keep moths from field production as long as the mesh prevents entry of adults. Hold row covers above plant surfaces with hoops or other supports to eliminate oviposition through the mesh. Supervise work practices to ensure covers and screens are properly maintained.

Changing the color of security lamps from other than yellow or white, installing motion detectors to trigger security lights instead of continuous lighting at night, and hooding growing and security lamps to project light downward can also reduce the moth attraction.

Biological and cultural controls are organically acceptable management methods. Entomopathogenic nematodes (e.g., Heterorhabditis and Steinernema spp.), and the microbial insecticides Bacillus thuringiensis ssp. aizawai, Bt ssp. kurstaki, and certain spinosad formulations (Entrust Naturalyte, Entrust SC) are acceptable for organic production.

Visually inspect plants periodically to detect larvae and their chewing damage, excrement, and webbing. Especially if Bt sprays are planned, use pheromone traps to determine adult flight, which precedes periods of mating and egg laying. When adults are trapped, larvae likely are or will soon be present and Bt application is warranted because it is most effective against young larvae. Make at least a second application 7 to 10 days later because Bt is not persistent and not all eggs are laid or hatch at the same time. Additional applications may be needed as long as moths continue to be active. For guidelines on when to treat, see Establishing Action Thresholds.

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