Damage caused by the brassica pod midge on oilseed rape

Brassica pod midge lays its eggs in damaged pods and in the holes left by cabbage seed weevil. Larvae feeding within the pods can cause distortions and pod shatter, resulting in seed loss.

• The adult midge is a weak flyer, so crops on headlands are more exposed. Consequently, the largest yield losses often occur in small narrow fields
• Reduced risk in fields that are at least 0.5 km away from areas with hosts in the previous 1–2 years

Scientific name: Dasineura brassicae

Adults are small and dark orange.

Eggs are minute.

Mature larvae are white, 2 mm long, with no legs or distinct head.

Jul–Feb: Larvae overwinter in the soil.

Mar–Apr: Adults emerge.

May–Jul: Adults mate. Females fly to oilseed rape to locate cabbage seed weevil holes and damaged areas. Here, minute eggs are laid in clusters inside the pod. Adults are poor fliers, so damage appears worse on headlands and may lead to an initial overestimation of yield impacts.

Jun–Jul: Large numbers of larvae hatch and feed on the inner walls of the developing pods. Infested pods become yellow, deformed and split prematurely, leading to loss of seed. Larvae drop to the soil to form cocoons, sometimes leading to a second generation.

Non-chemical control

Blocking oilseed rape fields and rotating the crop around the farm helps reduce the effect of immigrant pests.

Several wasp parasitoids, including Omphale clypealis and Platygaster subuliformis, may attack pod midge, killing up to 75% of larvae. Other natural enemies include spiders, ground beetles, rove beetles and predatory flies.

Monitoring

Monitor and control cabbage seed weevil – this is the most effective way of avoiding damage from the brassica pod midge.

Thresholds

Control of brassica pod midge is dependent on the control of cabbage seed weevil. Thresholds for cabbage seed weevil are one weevil per two plants in the north of the UK and one weevil per plant elsewhere.

Insecticide resistance

None known.