It's possible you have cabbage worms, which can be treated with Bt (Bacillus thuringiensis), a naturally occurring bacterial disease that only affects caterpillars.
It's probably a very small green worm..I use Sevin Dust.
I am looking for something natural to kill the bugs that is not harmful to people or pets.This question is a follow up ...for bugs eating cabbage plants.
Bt is not harmful to people or pets. It is approved for organic production.
the best & safest way to go about this is buy yourself some lady beetles & some Praying Mantis Egg sacks. buy some lacewings too. these are all predator eating bugs That will have zero interest in your garden plants, but will feel like they are at a smorgasbord with all the pests you may have.
I do not like or trust chemicals, so I refuse to use them.