Cabbages, cauliflowers, kale, broccoli and other brassicas can be demolished in Summer by cabbage white butterfly caterpillars. You can opt to grow them only in the cooler months to avoid this problem. Or you can use a Dipel spray which is suitable for Certified Organic produce. This spray is effective if you are diligent in applying it but you must reapply after every rain shower. Alternatively you can cover your cabbages with a very fine mesh to stop the butterflies laying their eggs on your crops. Mine worked extremely well last year – supported by hoops of plastic water pipe and with polyester fleece ends. It provided wind and bird protection and shade which suited the greens.