Utilize floating row covers to prevent adult butterflies from laying eggs on the plants. This method is most effective if applied when plants are young. Regularly inspect the plants for eggs, larvae, or worms, and remove them manually. Crush the eggs and dispose of the worms away from the garden. Interplanting with aromatic herbs like thyme, sage, or rosemary may deter the adult butterflies from laying eggs. A bacteria that specifically targets caterpillars, Bt can be applied as a spray to the affected plants. It's considered an acceptable option in organic gardening as it is non-toxic to humans and other animals. Planting a sacrificial crop that the cabbage worms prefer may divert them from your main crop. Mustard is often used for this purpose. If it fits within your permaculture system, free-ranging chickens or ducks can help by foraging for cabbage worms. After harvest, turning the soil can expose pupae, leading to their desiccation or making them accessible to predators.