Cabbage seedpod weevils (Ceutorhynchus obstrictus) are small, grey beetles from the family Curculionidae, which are 3 to 4 mm long with a long curved snout or rostrum (Fig. 1). Their larva are small, white grubs that can reach 5 to 6 mm long. Adults emerge in the spring from overwintering sites such as ditches and shelter belts and feed on early flowering host plants including volunteer canola and wild mustard. Cabbage seedpod weevils move to canola fields when the crop starts to bud and flower, where they feed on pollen and buds from the canola plants.
Egg-laying occurs when canola pods begin to develop. Female cabbage
seedpod weevils typically deposit a single egg into a seedpod, but can lay two
or more per pod during outbreaks. Upon
hatching, larvae begin to feed on the seeds for a period of about 50 days. Once
they mature, larvae chew an opening in the wall of the seedpod and exit, pupating
in the soil below. After about ten days as pupae, adults emerge and feed on the
maturing canola seedpods before moving to overwintering sites.
Severe damage to canola crops can occur as a result of both
the larva and adults feeding on seedpods. Larval feeding on seeds can cause misshapen
pods and leave small exit holes when the larva emerge to pupate. The economic
threshold at which pesticide application is recommended is 2.5 to 4 weevils per
sweep.
Figure 1. Cabbage
seedpod weevil adult. Photo credit: linsepatron CC-BY 2.0.
While not currently present in the Peace River region, cabbage
seedpod weevils are a major pest in southern Alberta. Models predict that they
will gradually disperse into all canola production areas, including the Peace River
region. The Beaverlodge Integrated Pest Management program monitors for
presence of cabbage seedpod weevils in the Peace River Region by performing our
annual
canola survey. Sweep-net collections are performed at canola fields
throughout the region when 10-20% of plants are flowering.
To help us complete our canola survey this year, we need permission
to enter canola fields across the Peace River region. You can help us monitor for
pests like the cabbage seedpod weevil here!
Author: Gareth Larsen