Symptoms
Irregular chewing damage on leaves from marginal feeding or skeletonization. Frass visible on leaves and ground. Severe infestations cause complete defoliation. Young larvae feed in groups, mature larvae feed alone.
Prevention
Inspect plants regularly, especially leaf undersides for egg masses. Encourage natural enemies (parasitic wasps, predatory birds). Remove egg clusters by hand. Maintain diverse plantings to support natural enemies.
Treatment
Organic
Apply Bacillus thuringiensis (Bt var. kurstaki) targeting young larvae. Spray neem oil or spinosad. Hand-pick large caterpillars. Release Trichogramma egg parasitoids.
Chemical (last resort)
Apply chlorpyrifos or cypermethrin when populations exceed economic threshold. Target early instars. Avoid broad-spectrum sprays during flowering to protect pollinators.
Affects 1 crop
Sources
MARDI Pest Management Guide; DOA Extension Bulletin