Question: What will kill bagworms on my junipers, and when do I need to use it?
Almost any general-purpose insecticide will control bagworms if you apply it before they seal themselves in their fibrous bags. If you watch in late spring you may be able to see the very early stages of their feeding. All of a sudden, you’ll notice that the plants’ branches aren’t as full as normal. On closer inspection you’ll see the very small worms working their way over the branches, carrying their bags on their backs. That’s the time to treat. Once they have quit feeding you must hand-pick the bags to get rid of the over-wintering insects. They can denude plants entirely, in which cases they rarely come back.