Cabbage Loopers

Trichoplusia ni

Cabbage Loopers is treated as a species-level vegetable caterpillar pest affecting brassicas, lettuce, celery, beans, tomatoes, and many greenhouse vegetables. Larvae chew irregular holes, contaminate heads with frass, and can feed within cabbage or lettuce folds where sprays and predators have limited reach.

Identification

Larvae are green with a white lateral stripe and only two pairs of abdominal prolegs, producing the characteristic looping gait. Adults are mottled gray-brown moths with a silver figure-eight mark on each forewing. The relevant host or site is brassicas, lettuce, celery, beans, tomatoes, and many greenhouse vegetables. Examine lower leaf surfaces and inner wrapper leaves; use beat or leaf counts and note larval size. Small larvae and fresh windowpaning are the most actionable findings.

Symptoms / Signs

Larvae chew irregular holes, contaminate heads with frass, and can feed within cabbage or lettuce folds where sprays and predators have limited reach. Fresh feeding carries live larvae or new frass; old scars persist.

Life Cycle / Process

Eggs are laid singly on foliage. Larvae pass through several instars, then form a loose silken cocoon on the plant. Multiple generations occur in warm weather. Larvae cause the damage, except grasshoppers, whose nymphs and adults chew. Control works best before larvae enlarge, bore, or seal themselves in silk.

Prevention

Inspect incoming plants and propagation material for eggs, small larvae, webbing, mines, or frass. Maintain crop records that link host stage with first egg or larval detection. Priority inspection target: brassicas. Focus species or category: Cabbage Loopers.

Management / Control

Use exclusion netting on small plantings, remove infested leaves, conserve parasitoids, and apply Bt or another selective labeled product while larvae are small. Resistance management is important in repeatedly treated vegetables. Base action on active feeding, larval size, crop stage, and tolerance. Killing moths or butterflies after eggs are laid does not reverse existing injury. Recheck the same unit for fewer larvae and less new feeding.

Procedure Steps

1. Inspect the true feeding site and collect the smallest active larvae. 2. Record eggs, larval size, frass, feeding, and natural enemies consistently. 3. Apply Bt, virus, or a selective labeled insecticide while larvae are small and exposed. 4. Close the Cabbage Loopers incident only after new injury stops.

Safety Notes

Protect food, seed, packaging, workers, and Myco-Patrons during inspection and treatment. Use tamper-resistant placements where baits or traps are necessary, and keep pesticides off food-contact surfaces. Structural or termite work may require a licensed Florida pest-control operator.