Insect Pests of Winter Canola with Emphasis on Cabbage Seedpod Weevil Damage Assessment.
Rufina Ward, Ernst Cebert, Ken Ward, and Suresh Kumar. Dept of Plant and Soil Sciences, Alabama A&M Univ, PO Box 1208, Normal, AL 35762
The cabbage seedpod weevil, Ceutorhynchus obstrictus (Coleoptera: Curculionidae), is the most dominant and destructive insect pest on winter canola (Brassica napus) in north Alabama. However, secondary pest species also warrant monitoring; these include diamondback moth (Plutella xylostella), tarnish plant bugs (Lygus lineolaris), clover stem borer (Languria mozardi), false chinch bug (Nysius sp.), thrips (Frankliniella sp.) and turnip aphid (Lipaphis erysimi), flea beetles (Phyllotreta sp.) and root maggot (Delia sp.). Aphids have been reported to severely damage canola in other areas in the southeast; however, they have not presented any major problem in our evaluation plots. Cultivars evaluated in this study were Jetton, Celsius, Explorer and Banjo; they were selected for their superior agronomic qualities. Each cultivar was planted following standard planting practices in 100x50 m2 plots with four replications arranged in randomized complete block design. Seasonal changes in population levels of cabbage seedpod weevil (CSPW), diamondback moth (DBM), tarnish plant bugs (TPB) and clover stem borer (CSB) were determined. Insects were sampled weekly by making 30 sweeps across each canola plot at flowering period. Collected insects were frozen overnight prior to counting and identification. Results showed significant variation in CSPW and TPB counts over time, but no significant variation was detected between test cultivars. Significantly higher DBM infestation occurred on Celsius than on other cultivars; infestation was lowest on Banjo. DBM population followed a steady decline throughout reproductive stage of the plant. CSB infestation was insignificant on all cultivars. Assessment of damage caused by cabbage seedpod weevil was done on each test cultivar by examining all pods on the primary raceme of each of three plants randomly selected per replication. Pods were examined for exit holes and other signs of larval feeding or presence. Correlation between cabbage seed pod weevil damage and seed yield for each test cultivar was determined.