Cabbage root fly
Delia radicum
Role in the garden
A grey fly whose white larvae devour the roots and collar of young cabbages and other brassicas: the plants wilt in full sun and pull out of the ground without effort.
Activity period
Three to four generations, from April to October; the first, in April-May, is the most dangerous for young plants
How to attract / manage it
Collars at the base of the plants, insect net, vigorous planting, ground beetles and rove beetles.
Practical guide
Where to find them
All brassicas, especially young cabbage plants transplanted in spring, as well as turnips, radishes and swedes whose roots are tunnelled.
Prevention
Fit a collar (cardboard, felt) of 10-15 cm around the collar of each plant as soon as it is transplanted to prevent egg-laying, cover with an insect net, transplant stocky, well-rooted plants, encourage ground beetles and rove beetles (predators of the eggs and larvae), practise a long rotation.
Early signs
Young cabbages wilting in the hot hours then recovering in the evening, leaves turning bluish, a plant that pulls out without resistance; gnawed roots occupied by small white larvae.
Action / control
Pull up and destroy affected plants (the larvae continue their cycle in them), earth up still-vigorous plants to induce new roots, and protect the next planting with collars and net. There is no curative treatment in the garden.
Sources
- INRAE, Ephytia : Hypp et Biocontrol, Delia radicum (mouche du chou)
- RHS : Cabbage root fly (rhs.org.uk)
- Jardiner Autrement (SNHF) : fiche Mouche des légumes
Favourite plants / resources
Related plant entries
Radish
A brassica with an ultra-short cycle (3-4 weeks in spring), the best row-marker for slow sowings (carrot, parsnip). Lets you occupy a space while waiting for the main crop. To be avoided before cabbage (same family, common clubroot).
Cabbage
A brassica with a long rotation: 4 to 5 years between two brassicas, 8 to 10 years after a clubroot attack (Réussir Fruits & Légumes, 2022), whose spores (Plasmodiophora brassicae) can contaminate the soil for up to 20 years (RHS). Very greedy (nitrogen, calcium, water). To be planted after a legume to benefit from the nitrogen.
Turnip
A fast-growing root brassica (5 to 8 weeks): ideal as an intercrop between two longer crops, or in succession after peas to use the fixed nitrogen.
Swede (rutabaga)
A keeping vegetable par excellence: stores in a cellar or clamp all winter. Well adapted to the cool, damp climates of the north.