Adult cabbage root flies resemble house flies. The larvae are white, legless and headless maggots that feed on the roots and can kill seedling and recently transplanted brassicas.
Vegetables affected by cabbage root fly will show the following:
Cabbages and other brassicas make poor growth and may wilt and die, especially recent transplants in early summer
Root crops, such as swede, turnip and radish are ruined when white maggots, up to 9mm long, tunnel into the edible part of the roots
Occasionally the maggots will tunnel into individual buttons on Brussels sprout plants