Managing cabbage seedpod weevils (Coleoptera: Curculionidae) in canola (Brassicaceae) – areLygus(Hemiptera: Miridae) affected?

Abstract

Cabbage seedpod weevil (Ceutorhynchus obstrictus Marsham; Coleoptera: Curculionidae) and Lygus Hahn (Hemiptera: Miridae) species are part of the late season insect pest complex of canola (Brassica Linnaeus; Brassicacea) in the southern prairies of Canada. From 2010 to 2013, large strips in 73 commercial fields were studied in southern Alberta to validate action thresholds for cabbage seedpod weevil and assess the impact of insecticide spraying at the early flower stage for cabbage seedpod weevils on abundance of Lygus at the pod stage. Only fields planted in April accumulated the damaging populations of cabbage seedpod weevils, such that the application of an insecticide resulted in significant yield protection. The economic injury level for the cabbage seedpod weevil was calculated at 20 cabbage seedpod weevils per 10 sweeps, but an action threshold of 25–40 is recommended because sampling mainly occurs along the edge where cabbage seedpod weevils are initially concentrated. At the pod stage, Lygus were lower in strips sprayed with insecticides at the early flower stage than in those not sprayed, but the differences were not statistically significant. Furthermore, Lygus were generally below economically damaging levels in early seeded fields. Therefore, there is no benefit of spraying early seeded fields to attempt to prevent Lygus outbreaks when cabbage seedpod weevils are below thresholds because Lygus may pose a risk only in fields planted later in the season.

Current and potential pest threats for canola in the Canadian Prairies

“…21 Sweep netting adult populations during early flowering of canola allows farmers to determine whether economic thresholds of 25 to 40 weevils per 10 sweeps are reached. 22 Lygus bug species distribution and abundance have been documented through ecoregions across the Canadian Prairies. 51 Well-defined economic thresholds exist for Lygus with crop growth and lygus stage considerations 22,25 but these are currently being re-evaluated.…”

“…22 Lygus bug species distribution and abundance have been documented through ecoregions across the Canadian Prairies. 51 Well-defined economic thresholds exist for Lygus with crop growth and lygus stage considerations 22,25 but these are currently being re-evaluated. Field scouting of populations and predictive modeling will be of value to canola farmers to manage these pests.…”

“…Yield loss is caused through seed consumption within developing canola pods where the larvae develop and feed 21 . Sweep netting adult populations during early flowering of canola allows farmers to determine whether economic thresholds of 25 to 40 weevils per 10 sweeps are reached 22 . Lygus bug species distribution and abundance have been documented through ecoregions across the Canadian Prairies 51 .…”