Effect of late season insect infestation on yield, yield components and oil quality of Brassica napus, B-rapa, B-juncea and Sinapis alba in the Pacific Northwest region of the United States

The effect of late season insect infestation on seed yield, yield component s, oil content and oil quality of two canola species (Brassica napus L. and B. rapa L.) and two mustard species (B. juncea L. and Sinapis alba L.) was examined over 2 years. In each year, ten genotypes from each species were evaluated with late season insects controlled with either methyl parathion or endosulfan insecticides, and without insecticides. Major late season ins ect damage in 1992 was caused by cabbage seedpod weevil (Ceutorhynchus assi milis Paykull), while diamondback moth (Plutella xylostella L.) and aphids (primarily cabbage aphids, Brevicoryne brassicae L.) were major insect pest s in 1993. Insecticide application was very effective in controlling diamon dback moth larvae and adult cabbage seedpod weevils, but only partially eff ective in controlling aphids. Higher numbers of diamondback moth larvae wer e observed on mustard species compared to canola species. S. alba was compl etely resistant to cabbage seedpod weevil and there was no damage due to th is pest observed. Aphid colonization was observed on plants from all specie s, but infestation on S. alba and B. rapa occurred too late to have a major effect on seed yield. Seed oil content of canola species was significantly reduced by insect damage although oil quality (indicated by fatty acid pro file) was not affected by insect attack. Uncontrolled insect infestation re duced seed yield of canola species by 37 and 32% in B. napus and B. rapa, r espectively. Least yield reduction occurred in S. alba, where average yield reduction from plants in untreated control plots was < 10% of insecticide treated plants. S. alba, therefore, has good potential as an alternative cr op suitable for northern Idaho because it can be grown with reduced late se ason insecticide application.