Bayer CropScience - Pestspotter - Cabbage seed weevil

Pest: Cabbage seed weevil

Identification
The adults are grey and up to 3 mm long with a typical weevil long curved proboscis. The larvae are white, legless, up to 5 mm and with a brown head and are typically `C` shaped.

Symptoms
The adult weevil usually lays a single egg in a seed pod. After hatching the larvae feed on the developing seeds. The damage done by the developing larvae is relatively minor but the secondary damage caused by pod midges which lay their eggs via the puncture holes is more economically damaging.

Life cycle
Seed weevils invade OSR crops as temperatures increase during May. After about 3 weeks of feeding the females begin to lay eggs in the pods and this continues until the seeds are formed. When fully fed the larvae leave the pods to pupate in the soil with the adults emerging later in the summer. The cabbage seed weevil has one generation per year.

Importance
Cabbage seed weevils are widespread throughout the UK although they are generally considered to less abundant than in previous years. Adult feeding on the young flowers and pods has little impact on yield, so treatment is not necessary during migration into crops. Larvae feeding in the pods can cause severe losses with up to 60% of pods affected, additional yield losses may result from Brassica pod midge which can exploit feeding damage and egg laying scars to deposit their eggs.

Threshold

ADAS thresholds are 0.5 weevils / plant in northern Britain and 1 weevil / plant elsewhere.