Pest Control, Bt
Bt is the spores of the bacteria Bacillus thurungiensis. It is used to protect plants against caterpillar damage. It works by infecting the caterpillars that ingest it and killing them.
Bt should be sprayed on plants in the evening, as sunshine will deactivate it. Spray when you notice the white butterflies re-appearing or on noticing caterpillar damage. Use on brassicas, tomatoes (against tomato fruit worm and looper caterpillar), lettuces (diamondback moth caterpillars)