|What are these small grey bugs in my canola?
If these bugs are 3-4 mm in length, have a pronounced snout and are an ashy, charcoal grey color then they are probably cabbage seedpod weevils.
What kind of damage can the cabbage seedpod weevil do to my crop?
There are two kinds of damage that can occur on canola. The first comes as potential yield loss when the adult weevils feed on the flower buds of the crop. This causes the flower to die. Yield loss due to this feeding is more evident in dry years when the canola crop can’t compensate for the loss. The second type of damage is from the larva feeding inside the pods. Each larvae can feed on up to 5 seeds during it’s development. This only relates to 15-20% of the potential yield of the crop, but the feeding makes the pod more prone to early shattering, which also causes yield loss. An indirect form of damage can occur when fungus enters the pod through the larvae exit hole and infects the pod.
What are the thresholds for cabbage seedpod weevil?
The general rule of thumb for thresholds is 3-4 weevils per sweep in a field. The sweeps should be done at ten different locations in the field and do ten 180 degree sweeps at each location. The weevils might be in higher numbers along the edges of the field so make sure you pick some locations within the interior of the field to have an accurate representation of the distribution of the weevils. These sweeps should be done from bud through flowering.
How many generations of cabbage seedpod weevil are there per year?
There is just one generation per year, and it takes about eight weeks to develop from egg to adult.
How can I control cabbage seedpod weevil?
Trap cropping has been suggested as a control method. This can be done in a couple of ways. Planting early flowering polish canola around the edge of an Argentine canola field will keep the weevil in the earlier flowering crop. This can also be done by planting a strip of canola early around the edge of the field and planting the rest of the field a few days later. Chemical control of cabbage seedpod weevil is limited to Matador 120 EC. Preharvest interval is 7 days before being swathed or harvested. Therefore it is critical to apply at the right stage of the crop, which is the late bud to early flowering. This will prevent egg laying in the newly formed pods.
Cabbage Seedpod Weevil
Canola Council of Canada
Prepared by Lisa Adam, Ag-Info Centre, Alberta Agriculture and Rural Development.