Hmmmm, there I was, weeding around my various brassicas, when I spied a cabbage white flutterbye laying her eggs on the underside of one of my young kale plants. I have to be vigilant otherwise everything will be decimated in no time.
EJ, we have the same problem with our squash plants. I haven't found any preventive measure to keep them off. We just harvest the squash and then let the butterfly caterpillars do their thing.
Caught red-handed....or red-abdomened, as the case may be. I have to cover my brassica's with enviromesh each year or they'd decimate my crops.
I try to take care of everything organically but there are times it just doesn't work...they can sure multiply and destroy things. Hungry little things...