Management of rape winter stem weevil on oilseed rape

Rape winter stem weevil is an occasional pest, where damage is caused by larvae feeding within the stem, which can cause stunting and lateral shoots to be produced in spring. Larvae can be distinguished from cabbage stem flea beetle by the brown head and lack of legs. 

• Risk increases risk near wooded areas 

Scientific name: Ceutorhynchus picitarsis 

Adult beetles are 2.5–4.0 mm long, metallic black, with elongated snouts, elbowed antennae and reddish–brown leg tips. 

Larvae hatch white, plump and legless, with an orange-brown head. They can reach 5 mm in length. 

Mar–Apr: Adults invade autumn–sown oilseed rape crops and feed on leaves. 

May–Aug: Eggs are laid in punctures and crevices in the leaf stalk and plant crown. Egg laying continues throughout winter in mild conditions. Hatching larvae bore into the stem and down to the crown of the plant to feed. 

Sep–Oct: Mature larvae descend to the soil to pupate. 

Oct–Mar: Adults emerge from the soil and disperse to woods and hedges, where they enter a resting phase. 

The effect of larval feeding can vary widely, depending on the number of eggs laid on the plant. The larvae can destroy the terminal shoot. This either kills the plant or results in the development of secondary shoots. Surviving plants may be stunted with a rosette-like appearance. Attacked crops tend to be irregular and patchy, with uneven flowering and ripening. 

Non-chemical control 

Natural enemies include spiders, ground beetles, rove beetles and several parasitoid species.

Monitoring 

Monitoring can be challenging because adults and larvae are difficult to find. Inspect the crop for young larvae from late October, especially in fields with a history of attack by this pest. 

Thresholds 

None established. 

Insecticide resistance 

None known in the UK.