An organic way to get rid of the lil blighters
Flour as Pest Control
# Dust the cabbage leaves with white flour. The best time to do this is right after it rains or in the morning while there is still dew. The cabbage worms eat the flour, become bloated and die.
Protection
# If the cabbage crop is planted in its own bed, cover all the cabbage with a row cover as a physical barrier.
Use Natural Enemies
# The cabbage worm's natural enemies are tachinid flies, wasps and spiders. Encourage beneficial insects into your yard by not using pesticides and planting native vegetation.