Many canola fields have a combination of insects feeding on the crop, including lygus bugs and cabbage seedpod weevils, or bertha armyworm and zebra caterpillars. Economic spray thresholds are calculated based on individual species. We don’t have scientific evidence to combine thresholds, but where an “additive” effect of multiple species can make sense is when more than one species are feeding on key yield-producing areas — flowers, buds or pods — at the same time.
For example, lygus and cabbage seedpod weevil will both feed on pods. If they are in the same field and if they are both at 50% or more of their economic spray thresholds, spraying may provide an economic benefit. Bertha armyworm and zebra caterpillar are also pod feeders, but they will also feed on other parts of the plant.