They are found feeding on feeder roots or boring into the taproot. After feeding 3 to 5 weeks, larvae pupate in roots or surrounding soil. Adults may emerge from pupae within 2 to 3 weeks, or the pest may overwinter as pupae when conditions are unfavorable for development. There are at least two to three generations in cool, moist climates along the coast.
Tunnels provide entryways for pathogens that cause blackleg and bacterial soft rot.
Cauliflower and Brussels sprouts may be more susceptible than hybrid cultivars of broccoli, and crops planted in winter and spring suffer more damage than summer planted crops. Where maggots are a perennial problem, grow seedlings for transplants in fumigated soil in the greenhouse or under frames of clear plastic or organdy. Avoid hardening transplants near infested fields. Direct-seeded crops may avoid some injury when a set of drag chains is attached behind the planter to eliminate the moisture gradiant in the seedrow. Adult flies are believed to be able to locate the seed row for egglaying by honing in on the higher moisture levels created when the soil is overturned for planting.