Abstract
Canola and industrial rapeseed (Brassica napus L.) and mustard (Sinapis alba and Brassica juncea) are economically important crops in North America, and canola can be used to produce edible oil, rapeseed can be used for biodiesel and mustard can be used as spice. Both spring and winter cultivars are attacked by different pests starting from seed emergence to maturity. Among the various pests, flea beetles (Coleoptera: Chrysomelidae: Galerucinae: Alticini), and Cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae) are the most devastating pest affecting canola, industrial rapeseed, and mustard in the Pacific Northwest. The brassicas are vulnerable to flea beetles during their seedling stage as the flea beetles chew leaves and tender stems causing up to 35% yield loss if unmanaged. Cabbage seedpod weevil colonizes canola, rapeseed, and mustard during the flowering and podding stage and feed on the buds, flowers and developing pods which can cause up to 30% yield loss. Vulnerability to flea beetles vary among canola, industrial rapeseed, and mustard cultivars, whereas there is limited knowledge on the availability of cabbage seedpod weevil resistant or tolerant cultivars to be used in the management of cabbage seedpod weevil. Therefore, there is the need for research to be conducted on the roles of cultivar, seed treatment, and foliar spray in managing crucifer flea beetles in oilseed brassicas and to evaluate winter and spring canola cultivars to cabbage seedpod weevil damage and yield.The first objective of this study was to evaluate variability in susceptibility to flea beetle damage among commonly grown brassica cultivars in the Pacific Northwest, assess seed treatment effectiveness, and quantify the impact of flea beetle injury on yield across canola, industrial rapeseed, and mustard cultivars. Our study was done using a split plot design with four replications in the summer of 2024 and 2025 at the University of Idaho research farm, Moscow, ID. Six cultivars were tested and three were canola, two were mustard, one was industrial rapeseed tested with (IndustriousT) and without (IndustriousN) seed treatment.
All other entries were treated with insecticidal and fungicidal seed treatment. There were two treatments which were foliar insecticide treatment with Grizzly Too (lambda cyhalothrin) and no foliar insecticide treatment. Data on the percentage of leaf area damage was visually assessed on 20 seedlings sampled per plot weekly for four weeks starting from the cotyledon stage to the four-leaf stage. Results from the study showed differences in cultivar susceptibility to flea beetle damage. The effectiveness of neonicotinoid seed treatment was confirmed in our study. Foliar insecticide applications reduced damage and increased yield, but its effect depended on insecticide application time and cultivar. This result suggests the need for integrated pest management approach to control flea beetles.
The second objective was to assess cultivar susceptibility to cabbage seedpod weevils and assess the effects of cabbage seedpod weevil exit holes damage on yield in different winter and spring cultivars. Using replicated plot studies at three locations over two years, we assessed five commonly grown winter and spring cultivars respond to flea beetle damage, and the effect of the damage on yield. Primary racemes from randomly selected five plants in the four plots for all selected cultivars were collected. For processing, a pod on each raceme was carefully examined for the cabbage seedpod weevil exit holes, after which all racemes for a cultivar were threshed, and seeds were weighed to determine the seed yield of the cultivar. Results from the study showed that cabbage seedpod weevil damage level was driven primarily by location. We also observed cultivar susceptibility to cabbage seedpod weevil damage, but it was not consistent across years. Additionally, the variation in the susceptibility was not environmentally stable. Monitoring cabbage seedpod weevils using sweep net, using weather informed forecasting tools and combining other integrated pest management tools could be a better approach to manage cabbage seedpod weevils.