The Cabbage Seedpod weevil (CSW) was first detected in Montana during the 1999 growing season in very low levels in Fergus County.
The CSW has been a severe pest of canola in the northwestern US and southern Alberta reducing seed yeilds by 15 - 30%. In 1996 CSW
was found primarily in the Lethbridge area but by 1998 had moved into southern-most Alberta.
Cabbage seedpod weevils are small (2.5-3 mm), ash gray or black in color with a strongly curved snout. Adults overwinter under litter
and in light soils. They become active in spring, flying at temperatures above 60 F. Overwintered adults feed on early crucifer crops or
weeds in spring before laying eggs.
Eggs are laid singly on pods that are about 1 inch long. Eggs hatch within 5 to 30 days, depending on temperature. Larvae spend 3-4
weeks in the pod, each larvae consuming 5-7 canola seeds. In addition to larvae damaging seeds they also increases the risk of pod shatter
at harvest. When feeding is completed, the larva chews a round exit hole at the base of the pod and drops to the ground to pupate. New
adults emerge within 2-4 weeks and feed on green stem and pod material but do little damage. New adults find suitable overwintering sites
in soil or in dry clumps of vegetation in preparation for overwintering.
Population and flight activity of adult weevils peak at full bloom and continues into the early pod-set period. Monitor field using a sweep
net concentrating sampling on early bud through pod-set. One threshold is 5 -10 weevils per sweep, although results from University of
Idaho have found that populations as low as 3 - 6 adults per sweep when temperatures are warm, can cause economic loss. Treatment is
recommended near the end of bloom (10-20% bloom remain) when 2-3 weevils per plant are present.
Insecticide treatments registered for CSW include Capture 2EC and parathion. Do not spray when pollinators are present and notify
beekeepers before spraying.. (Greg Johnson)