Besides carrots, it also attacks other plants including parsnips, celery, celeriac, and parsley. The carrot rust fly maggot damages plants by eating the small fibrous roots and by tunneling in larger roots. A rust-colored material develops in the tunnels, giving the insect its name. Affected plants may become yellow, stunted, and die. Usually the plant tops continue to look healthy.
Maggots often continue to feed in stored carrots.
Disease organisms may enter the feeding tunnels and cause them to rot. It lays eggs in May and June on the soil surface around the plants. The eggs hatch in a few days and the maggots, the only plant-injurious stage, feed on and in the roots. The puparia stay in the soil near the roots until August when the adult flies emerge. The new flies lay more eggs which change to maggots.