I have green worms on my broccoli.
BT AKA Bacillus Thurigensis works quite well. It's the spores of a disease that kills cabbage moth larvae (the green worms in question). The stuff I got is a powder you mix with water and spray on the plants. The worms stop feeding almost immediately after ingesting it, and die a few days later. Harmless to people, unless great-great-great grandpa was a cabbage moth. There are varieties that work well on potato beetles as well. You need to re-apply after a rain if there are still worms present. See also "bug juice," though the family may not want to use that blender for marguerites afterward...
Gary Woods AKA K2AHC- PGP key on request, or at
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Zone 5/6 in upstate New York, 1200' elevation. NY WO G