Biology of cabbage stem weevil in vegetable brassicas and oilseed rape
Cabbage stem weevil affects oilseed rape and vegetable brassicas. Although it rarely causes economic damage in oilseed rape, cosmetic damage can be a problem for high-value brassica crops.
Risk factors in brassicas
- Spring crops in southern counties
- Minor pest in winter crops
Scientific name: Ceutorhynchus pallidactylus
Adults are 3 mm long with a long snout, reddish legs and antennae. They are dark grey with a fine layer of yellow-white scales and a white spot in the middle of the back.
Larvae are creamy white with a brown head and no legs and grow to 4–5 mm long. At maturity, they bore an exit hole in the lower stem and drop to the soil to pupate.
Cabbage stem weevil life cycle and crop damage
Sep–Mar: Adults overwinter in sheltered locations.
Apr–May: Adults migrate into the crop, laying eggs in clusters under the leaf surface. Blisters near the main vein on lower leaves in early summer indicate where eggs have been laid.
May–Jul: Eggs hatch and larvae tunnel into the stem to feed. At maturity, they drop to the soil to pupate, leaving visible exit holes in the stem.
Aug: Adults emerge and feed for a short time.
Non-chemical and chemical control
Early drilling can minimise the risk of damage, as established plants show a greater tolerance to the feeding.
Natural enemies include spiders, ground beetles, rove beetles, predatory flies, and parasitoids of egg, larval and adult stages.
Check crops in late spring/early summer for migrating adults. It is possible to trap adults in yellow water traps to indicate when females are laying eggs.