Answer: If you haven't caught the critters in the act of munching on your cabbage leaves, they've probably left the area, so treatment isn't necessary. Normally it's cabbage worms that damage cabbage leaves, but slugs can do damage, as well. Since they feed at night, they're hard to detect - except for the holes they leave and their slimy trails. Check your plants for slug trails. If you find some, set some beer traps out to capture them. Otherwise, I'd say the critters have gone to other hunting grounds and no treatment is necessary.
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