One of the more common pests of canna is corn earworm. The adult is a night-flying moth that lays yellow eggs on the undersides of the canna leaves. The eggs hatch out into green, brown, or yellow-striped caterpillars that feed for several weeks. Since they begin their lives on the under side of leaves, Sevin dust is not as effective as liquid Sevin which can be sprayed onto the leaf underside. The worms must eat some of the Sevin to kill them. If the dust is only on the upper leaf surface where they're not feeding it won't be effective.