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(Delia radicum (=Hylemya brassicae))
Cabbage maggots tunnel into roots and stems, causing plants to wilt. Look for white larvae and brown pupae below soil line.
Adults are gray flies, 1/4 inch (6 mm) long, with long legs. Larvae are white tapering maggots burrowing in roots.
Throughout North America.
Cabbage family plants.
Injury usually shows first as sickly or stunted plants that suddenly wilt in the midday heat. This is caused by maggots boring into the roots. Plants may die, often because entry wounds from maggots allow diseases to infect roots; surviving plants yield poorly..
Pupae overwinter in the soil. The adult flies emerge from late March (in warmer regions) onward. Females lay eggs in the soil beside the plant roots. After they hatch, the larvae tunnel in roots for 3-4 weeks, then pupate in soil for 2-3 weeks. Two to four generations per year.
Plant radishes earlier and cabbages later than usual to avoid main generations. Cover seedlings with floating row covers; make sure the edges are buried in soil. Set out transplants through slits in tar-paper squares to prevent females from laying eggs. Burn or destroy roots of cabbage family plants when you harvest the tops.
Apply insect parasitic nematodes to soil around roots. If pest populations are moderate, repel females by mounding wood ashes, diatomaceous earth, hot pepper, or ginger powder around base of stems.