Cabbage worms on cabbage, broccoli and kale
The caterpillars rest along the midrib on the underside of the leaf, and as they grow they move into the centre of the plant and the forming head. Bt has to be eaten, so spray both leaf surfaces while the caterpillars are small and before they reach the head. The Thuricide label says to repeat weekly as needed and to reapply after heavy rain. UC IPM rates Bt as low in toxicity to the Cotesia wasps and other natural enemies.
At a glance
- Damage
- Large ragged holes in brassica leaves, caterpillars and green frass in the heads
- Type
- Chewing
- Settings
- Field, Garden
- Threshold
- No garden threshold; commercial growers treat at 10–50% of plants infested, lowest once heads form (UMass, Wisconsin)
- Ally
- Bacillus thuringiensis kurstaki
- Rate
- Label rate — Thuricide 1–3 tsp per gallon for imported cabbageworm on broccoli, Brussels sprouts, cabbage, cauliflower, collards and kale; DiPel DF 0.5–2 lb per acre
How to confirm it
A velvety green caterpillar, up to about 1–1¼ inches (25–30 mm), with a thin yellow stripe down the middle of the back, lying still along a leaf vein. It crawls slowly and does not arch its back. Wet green frass collects at the leaf bases and in the head, and white butterflies with black wing tips fly over the plants by day.
Identification, lifecycle, degree days and every control option are on the full Cabbage worms profile. Not sure it is this pest? Answer four questions about the damage.