Tim Morton wrote:

Sounds like cabbage loopers to me... they tore up my broccoli this year.
They were my "sacrificial" plants, and the rest of the garden did fine.
Organic Gardening has this write up
on possible solutions
http://www.organicgardening.com/feat...-9-266,00.html
...........................

Just as likely it could be imported cabbage worms. It doesn't
matter, the treatment is the same. BT works wonders. I have much
better results with a form that you mix with water and spray on. (I
use Dipel.)
In the mean time, pick off all that you can find because they can
destroy the entire plant if left alone.
http://ceenet.msue.msu.edu/ipm/CAT03...bbageworms.htm

Steve