Question: My cedar trees are loaded with bagworms. How can I control them? Will they kill the trees?
Answer: Bagworms are larval insects that devour the small needles of junipers, bald cypress, Italian and Arizona cypress and arborvitae, among many other evergreens. Once stripped, these plants are lethargic about leafing back out again. They show up in late spring (usually mid- to late May or very early June). Watch for first evidence of the tiny bags being carried on the backs of the pests. You may also notice that the plants begin to get thin. Spray them with B.t. or a general-purpose insecticide at once. If you leave them until they have tied their bags around the twigs you will have a much more difficult time controlling them. On a related note, it's not uncommon for small twigs to die from the constriction of the old bagworm fibers 2 or 3 years after the bags are attached.