Bagworms are caterpillars that feed on the foliage of plants such as conifers, junipers, oaks and arborvitae. Spray the bagworms while they are still actively eating, for the best control. Use an insecticide such as permethrin, spinosad or trichorfon, according to the University of Illinois. After the pupate stage, spraying has no affect in killing them.
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Joyce Starr is a freelance writer from Florida and owns a landscaping company and garden center. She has published articles about camping in Florida, lawncare, gardening and writes for a local gardening newsletter. She shares her love and knowledge of the outdoors and nature through her writing.