Questions have been coming in regarding the Cabbage Seedpod Weevil in canola (Figure 1). If you haven’t already checked your fields, now is the time to see if you have this tiny weevil waiting to potentially impact yields. Despite its small size, this pest can reduce yields by as much as 50% if left unchecked. To determine if cabbage seedpod weevil needs to be treated, fields should be scouted twice a week starting when plants are 10-20% in bloom and continuing through the flowering period. For B. napus canola varieties, this equates to 10 to 16 flowers on the main stem. For B. rapa varieties, this will equate to 6 to 12 flowers on the main stem. Using a heavy canvas sweep net, take 10 sweeps starting at the edge of fields and work inwards as you go. Don’t be surprised if you only find this pest concentrated on field borders. However, during outbreak infestations, it may be found throughout the entire field.
An insecticide application is warranted when 30 to 40 adult weevils are collected from 10 sweeps. The Canola Council of Canada has recently lowered the above-mentioned threshold to 20 weevils in 10 sweeps. For more information about this pest, i.e., what it looks like and its biology and impact on canola production, check out the WSU Extension Fact Sheet.
For questions or comments, contact Dale Whaley via email at dwhaley@wsu.edu or phone at 509-745-8531.