Evaluation of foliar and seed treatments for control of the cabbage seedpod weevil (Coleoptera:Curculionidae) in canola

Caged assays and field tests were used to evaluate the effectiveness of organophosphorus, pyrethroid, neonicotinoid, and biologically derived insecticides for reducing populations of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), a new pest of canola in Canada. Complete mortality of caged weevils occurred 48 h after treatment with disulfoton, deltamethrin, carbofuran, oxydemeton-methyl, and chlorpyrifos. Under field conditions, using plots or large strips in commercial fields from 1998 to 2001, only deltamethrin and cyhalothrin-lambda (both pyrethroids) consistently reduced weevil densities, even at high population levels. Chlorpyrifos also significantly reduced weevil numbers and damage in some years, but results were variable and efficacy was too low to manage weevils under outbreak densities. Other insecticides such as spinosad provided moderate weevil control and may have a role in weevil management depending on their effect on beneficial insects relative to more efficacious insecticides. Treatment of canola seed with imidacloprid, lindane, or acetamiprid did not reduce weevil damage. Further research is needed to establish economic thresholds for C. obstrictus in canola, to assess the effect of insecticides on nontarget natural enemies of canola insect pests, and to assess the potential for integration of chemical agents with biological and cultural control strategies.