Larvae on cauliflower stem

Larvae on cauliflower stem

© Rasbak

Type: Pests

Cabbage root fly (Delia radicum)

This innocuous-looking fly lays its eggs on the soil surface near brassica roots. When they hatch, the 6-8mm long maggots begin eating the roots. The maggots go through a brown pupal stage before emerging as adults, mating, and infecting new plants. There are typically three generations every year, with the pupae of the third generation overwintering in the soil, emerging in the spring to begin on a new crop.


  • Leaves may have a bluish tinge
  • Damage to the roots means that plants tend to wilt in dry weather and can be pulled up easily
  • Growth will be reduced and seedlings and young plants may die
  • Brassicas grown for their roots may be totally unusable
  • The white maggots are often clearly visible when the roots are examined

Prevention & control

  • Practise good crop rotation to ensure that adults emerging from last year's pupae do not meet a brassica crop
  • Prevent the flies getting near the crop with insect mesh or fleece
  • Cabbage collars, proprietory or homemade (from cardboard, carpet underlay or roofing felt), will prevent the fly accessing the soil and any eggs it does lay will dry out on the surface.
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