Managing cabbage seedpod weevils (coleoptera: Curculionidae) in canola (brassicaceae)-are lygus (hemiptera: Miridae) affected


Cárcamo, H.A., Meers, S.B., Herle, C.E. (2019). Managing cabbage seedpod weevils (coleoptera: Curculionidae) in canola (brassicaceae)-are lygus (hemiptera: Miridae) affected, 151(1), 85-93.

Plain language summary

Cabbage seedpod weevils and lygus bugs are two common insect pests that attack canola. Economic damage occurs when the plants are at the pod stage when the insects eat the seeds. Currently only insecticides are available as the main management strategy and farmers spray the crop at early flower to reduce weevil numbers before they lay eggs inside the pods. It was not known if lygus bugs are managed through this single spray. Our study showed that the two insect pests do not reach high numbers in the same field. Early seeded fields have more weevils but fewer lygus and the opposite happens in fields planted late. So, spraying for weevils at the flower stage will also reduce lygus numbers at the pod stage, but the abundance of lygus bugs in fields sprayed for weevils are generally very low. In other words those fields where weevils are high, tend to have low lygus numbers and do not warrant control at the pod stage even if no insecticide is sprayed at the flower stage. In conclusion, canola fields should be monitored for lygus abundance at the end of flowering and a control decision should be made at that time. For weevils, canola fields need to be monitored as soon as the plants start to flower.


© 2018 Her Majesty the Queen in Right of CanadaÂ. 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.

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