Braconid wasps for cabbage worms
Cotesia glomerata attacks young cabbageworms, and its larvae emerge from the full-grown caterpillar to spin a cluster of 20–30 cocoons (UF/IFAS). In Massachusetts it has largely been replaced by Cotesia rubecula, introduced in 1988, which averaged 75% parasitism in surveys in 2007 and 2009 (UMass). Destroying caterpillars with cocoons beside them kills the next generation of wasps.
Before you act
Small parasitic wasps (the common Cotesia species are only 2–3 mm long) whose larvae develop inside a caterpillar or an aphid and kill it. The white, rice-grain cocoons standing up on the back of a hornworm are theirs, and a hornworm carrying them should be left on the plant. How to recognise it, what it is confused with and how to keep it around are on the full Braconid wasps profile.
Other controls for cabbage worms
- Bacillus thuringiensis kurstakiMicrobial insecticide · 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
- Trichogramma spp.Egg parasitoid wasp · One card of about 100,000 T. brassicae per acre per week, for about 4 weeks or through the crop (UMass); 1–2 /ft² in gardens
- Tachinid fliesWild parasitoid · wild, attract it
- Paper waspsWild predator (stings) · Wild — tolerate nests away from doors and paths