Delia brassicae
Pest description and crop damage White maggots that feed on roots and underground stems and weaken, lodge, and kill plants. Adult is a small gray fly that lays white, oblong eggs at plant bases.
Management-chemical control
azadirachtin (Neemix 4.5 IGR) at 7 to 16 fl oz/A (0.021 to 0.049 lb ai/A). PHI 0 days. REI 4 hr. Begin applications at first sign of infestation. Multiple applications and thorough coverage are necessary for effective control. Apply every 7 to 10 days as needed. This botanical pesticide acts slowly. Spray early, well before harvest, and check for effect. Some formulations are OMRI-listed for organic use.
See also:
Broccoli, Brussels sprout, cabbage, cauliflower-Cabbage maggot