Imported Cabbageworm

• Large, ragged holes chewed through leaves — not just the edges
• Pale green caterpillars, about an inch long, on leaf surfaces and undersides
• Green pellet-shaped frass (droppings) on leaves and soil below
• White butterflies fluttering around brassicas in daytime
• Skeletonized inner leaves on cabbage heads
• Small round eggs laid singly on the underside of leaves

The adult white butterfly overwinters as a chrysalis and emerges in early spring. It lays eggs singly on brassica leaves from spring through fall, completing two to four generations per season depending on climate. Caterpillars feed for two to three weeks before pupating. Populations tend to peak in late spring and again in late summer.

1. 01Cover plants with floating row cover at planting — the most reliable prevention
2. 02Inspect leaf undersides weekly and hand-pick caterpillars and crush eggs
3. 03Apply Bacillus thuringiensis var. kurstaki (Bt) spray — a naturally occurring bacterium lethal to caterpillars but harmless to other insects. Reapply after rain
4. 04Parasitic wasps (Cotesia glomerata) are effective natural controls — avoid killing them with broad sprays
5. 05Spinosad is an option for heavier infestations when Bt is not controlling them

If you're seeing heavy damage despite Bt applications and row cover isn't practical for your setup, an extension advisor can confirm the species and suggest whether diamondback moth or cabbage looper might also be involved — the management differs somewhat.

• Cabbage Caterpillars— University of Maryland Extension
• Imported Cabbageworm — New England Vegetable Guide— UMass Extension