Vegetable weevil larvae
Courtney Piesse (Agronomique Services) reports finding vegetable weevil larvae causing extensive feeding damage to a six leaf canola crop near Bannister. Courtney estimated there was about 20-30 weevil larvae per plant. The feeding damage is confined to about 20% of the paddock along a strip near where the crop borders bushland. The crop received a post sowing pre-emergence application of bifenthrin/chlorpyrifos. A border control spray of alphacypermethrin will be applied to the damaged area.
Vegetable weevil larvae are also present in a pasture near Woogenellup. They are not causing any production loss.
Vegetable weevil eggs are laid in autumn and develop into larvae in winter. Capeweed is one of their favoured host plants, but they are also found on canola. They usually move from dying capeweed plants onto canola crops. These larvae live for one to two months feeding on leaves of plants before pupating in the soil. Adults emerge from the pupae and feed until summer when they hibernate under pieces of wood, rock, fallen stubble, etc. until the following autumn when they become active again. They have one generation per year.
Vegetable weevil larvae can be hard to find but are usually seen on the underside of leaves.
Vegetable weevil larvae can be confused with the caterpillars of moth species. They are a yellow to green colour with a flattened slug like legless body and they have a smallish brown head. They can cause significant damage when in high numbers.
Adult weevils are about 10mm long with two short white stripes at an angle on each side of its abdomen. The adult weevils hide under surface debris during the day. Damage from vegetable weevil is usually worst next to paddock edges and bush areas, or parts of the paddock that had capeweed in the previous year.
Pesticide options for the control of vegetable weevil can be found in DPIRD’s 2021 Autumn Winter Insecticide Guide.
For more information on weevils visit DPIRD's:
- Diagnosing weevils in canola page
- 2021 PestFax Issue 3 article Identifying and managing weevils in canola
- Identifying soil beetle pests page.
Insect larvae can be tricky to correctly diagnose sometimes due to their similarities in appearance. Fortunately growers and consultants can use the free PestFax Reporter app to request a diagnosis. Users just need to take clear close up photos of the larva and any plant damage and include any other helpful background information when submitting a report.
Article authors: Alan Lord (DPIRD South Perth) and Svetlana Micic (DPIRD Albany).