The cabbage worm is not really a worm at all. This pest of the Cabbage Family (brassicas) is actually a caterpillar! It is the larva stage of the cabbage white butterfly. These pests can be seen flying around your garden in late spring and through the summer.
The butterflies feed on nectar and lay yellow, oval-shaped eggs on the underside of brassicas. Caterpillars soon grow to about an inch, eating leaves of the Cabbage Family. These caterpillars can even eat into the center of a cabbage head! Although damage is usually minimal, just holes in leaves which are still edible, large infestations can decimate plants that rely on leaves for photosynthesis.
Monitor your brassicas for cabbage worm damage. You may notice the white butterflies in your yard or holes in plant leaves. Look underneath leaves for eggs and caterpillars. These can be squished or handpicked and destroyed. Dropping the pests into soapy water will do the job.
Row covers or nylon stockings on cabbage heads can be used to prevent an infestation. These implements should be in place in the spring, before the first cabbage white butterfly is spotted.