Managing Cabbage Root Fly Cabbage root fly larvae eat the roots of brassica (cabbage family) plants including cabbage, cauliflower, Brussels sprouts, kale and turnip although some suffer less than others. With kale, for example, I find Italian kale is a problem while Russian or curly kale usually emerges unscathed. Root fly can be an issue at any time of the season but it is more of a problem in spring and early summer when cabbage family plants are young. Older plants usually survive an attack