A: You are being visited by cabbage loopers. You may have seen the small white moths flying around the cabbages, and we’ve had an exceptionally long season of them this year.
Plants with minor damage are salvageable; but badly damaged plants will look a lot better sooner if you simply replace them. Spray existing and any new replacements with one of two different sprays – either B.T. (bacillus thuringiensis) or spinosad. Both are organic insecticides with very low toxicity to mammals (us, pets, etc.) and are very effective. Spray weekly until you get full control.