By Brett Rumpel, Crop Pest Regulatory and Survey Technician, Regina
The cabbage seedpod weevil is a European pest of canola, brown mustard, and cole crops, but will also feed on several cruciferous weeds. Canola and brown mustard are considered 'true' hosts because the weevil can complete larval development on these plants. cabbage seedpod weevil is invasive and was first reported in Saskatchewan in 2000.
Larvae feed on developing seeds, whereas the adults feed on pods in late-canola crops. Adults also feed on developing flower buds and young flowers, causing bud-blasting. Fungal infections associated with holes made by females to introduce eggs, and shattering can also affect the infested pod, further reducing yields. Infested pods are often distorted.
Adult cabbage seedpod weevil has a narrow, curved proboscis (snout), is ash grey, and three to four mm in length (Fig. 1), and will play dead when disturbed.
Cabbage seedpod weevil has one generation per year. Adults overwinter along the field margins, under leaf litter and emerge in April to mate and feed. Females lay eggs in developing pods. They lay on average, one egg per pod. Larvae feed for about six weeks then, drop to the ground to pupate.
Seeding later in the season can be beneficial to reduce the risk of infestation. The strategy reduces the synchrony of adult emergence and egg laying and vulnerable stages of the crop. Planting a trap crop of either an early-flowering canola variety or seeding the field margins earlier is also an efficient cultural control. It concentrates the population on the field margins and allows population control over a reduced area.
Members of the wasp family Pteromalidae are an enemy of cabbage seedpod weevils. Although these have been effective in the US, introduced parasitoids have so far had a limited impact on populations in Canada.
Insecticides registered for the control of cabbage seedpod weevil can be found in the Guide to Crop Protection. The time to scout for the insect is to begin sampling at the bud stage and continue through flowering. Chemical control is recommended when an average of 25 to 40 weevils is collected in ten sweeps. This range is associated with fluctuation in crop price. High value crops mean lowered tolerance of weevils. Sample multiple locations to get a better assessment of the whole population.
The ministry is currently surveying cabbage seedpod weevils to evaluate the spread and prevalence of populations throughout the province.