Cabbage root fly

Delia radicum

1. Identification

• Common name: Cabbage root fly
• Scientific name: Delia radicum L.
• Order: Diptera
• Family: Anthomyiidae

2. Pest description

• Adults resembling small house flies, 5–7 mm, with a greyish body.
• White, cylindrical, legless larvae that feed on the roots and collar of the plants.
• Brown pupae, formed in the soil.
• White, elongated eggs, laid at the base of the plants or in the adjacent soil.

3. Main hosts

• Cabbage, broccoli, cauliflower, turnip, radish and other Brassicaceae.
• It can attack young plants in nurseries and production fields.

4. Symptoms and damage

• Sudden wilting of young plants.
• Yellowing and curling of the leaves.
• Extensive damage to the roots and collar, with galleries and necrosis.
• Plants easily pulled up due to root destruction.
• Reduced growth and total losses in seedlings.
• Greater susceptibility to secondary infections.

5. Biological cycle

• Two to three generations per year, depending on temperature.
• Adults emerge in spring.
• Egg-laying at the base of the plants or in the soil.
• Larvae feed for 2–3 weeks.
• Pupation in the soil, where they can overwinter.
• Emergence favoured by moist soils and mild temperatures.

6. Monitoring

• Yellow chromotropic traps for the detection of adults.
• Observation of wilting symptoms and damage to the collar.
• Sampling of young plants for the detection of larvae.
• Intensive monitoring in spring and early summer.
• Recording of favourable conditions (high humidity and moderate temperatures).

7. Management measures

• Cultural: crop rotation with non-host species; use of insect-proof nets; destruction of crop residues; sowing in less favourable periods; improvement of soil drainage.
• Biological: conservation of natural enemies; application of entomopathogens to the soil; use of specific parasitoids when available.
• Integrated protection: continuous monitoring; targeted treatments when thresholds are reached; use of traps for population reduction; irrigation management to avoid excess moisture; judicious application of authorised insecticides.

Bibliographic references

• EPPO Global Database – Delia radicum.
• CABI Invasive Species Compendium – Delia radicum.
• Finch, S. (1989). Ecology and control of cabbage root fly.
• Vernon, R. S. (1999). Monitoring and management of Delia spp..