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Cabbage and onion maggots

Quick facts

  • Two important root maggot species found in Minnesota are onion maggots (Delia antiqua) and cabbage maggots (D. radicum).
  • Root maggots can occur in any year but are more common during cool, wet springs.
  • Infested plants can appear discolored, wilted or stunted.
  • Damage can be severe enough to kill affected vegetables.
  • Physical barriers, like row covers, are the best way to manage them.

How to identify root maggots

Adults

  • 1/4 inch long
  • Dark gray with dark-colored stripes 
  • They resemble small house flies

Larvae

  • Legless maggots 
  • 1/4 inch long 
  • Yellowish-white 
  • Shaped like cylinders, tapering towards the head
    Dark gray adult onion maggot fly
    Onion maggot adult
    Three cabbage maggot larvae feeding in the main root of a young cauliflower plant.
    Multiple cabbage maggot larvae feeding on the roots of cauliflower.

    Plants attacked by root maggots

    Green onion with a tunnel near its roots.
    Onion maggot damage

    Onion maggots attack

    • Onion
    • Garlic
    • Carrot
    • Radish

    Cabbage maggots attack

    • Cabbage
    • Broccoli
    • Cauliflower
    • Brussels sprouts
    • Radishes
    • Turnips

    Biology

    • Root maggots spend the winter as pupae in the soil.
    • In spring, the maggots transform into adult flies.
    • Adult females lay about 50-200 small, white eggs at the base of plant stems and in nearby cracks in the soil.
    • The eggs hatch within a week into small, legless, whitish maggots.
    • Maggots move into the soil and feed on the roots, root hairs and germinating seeds of crucifers or onions.
    • After feeding for three to four weeks, maggots convert into pupae in plant roots or the surrounding soil.
    • There are several generations per year.

    Damage caused by root maggots

    A large cabbage field with areas of wilted and discolored plants.
    Cabbage fed on by cabbage maggots becomes stunted and discolored and eventually wither and die.
    • Root maggots have several generations in a year, but most of their damage is limited to early spring plantings.
    • Seedlings and transplants suffer more damage from root maggots during a wet, cold spring.
    • The maggots feed on roots and bulbs, creating tunnels.
    • Plants first begin to wilt and can become stunted and yellowed.
    • Heavily damaged plants can ultimately die.

    Managing root maggots in home gardens

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    Managing root maggot on farms

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    Authors: Marissa Schuh, IPM Extension educator, Jeffrey Hahn, and Suzanne Wold-Burkness, College of Food, Agriculture and Natural Resource Sciences

    Reviewed by Bill Hutchinson

    Reviewed in 2022

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