Carrots, radishes, cole crops, onions and other root crops
The maggots feed for 3-4 weeks on roots. Heavily infested plants turn yellow and their roots have numerous tunnels made by the maggot while feeding on the roots and in case of onions on the bulbs.
The root maggots attack onions, carrots, cabbages, and other root crops. The adult root maggot looks like a small housefly. They lay eggs in cracks in the soil or plant stems at soil level. The legless maggots are white to yellowish white in color. The root maggots tend to have about three generations in Illinois particularly the onion maggot.
Commercial - rotate onions with other crops to control onion maggots. Commercial and home gardeners - there are natural enemies of root maggot larvae such as ground beetles and other predators such as tiny wasps. Red varieties of cabbages are resistant to cabbage root maggots, disk/rototill crop residues underneath the soil immediately after harvest to reduce overwintering sites, use soil-applied insecticides recommended in your state.