Last week I stopped at a rest area on I-29 north of Hamburg IA, and noticed a dramatic display of the pinecone-like bagworm “bags” covering an ornamental evergreen. These 1 to 1 ½ inch long bags of dead needles or leaves are remnants of last year’s cases made by the larva of this interesting moth. Bagworms feed most notably on arborvitae and junipers but also can infest other conifers and some broadleaved trees and shrubs.
- Cut the bags from the tree (scissors work well) before the larvae hatch (by early May). But to have success, you need to be thorough, getting them all. Carry the removed bags away for disposal, or,
- Apply an insecticide to treat newly emerged larvae in early June.
Remember that larvae must be present and actively feeding to be controlled by the insecticide. Effective products for homeowner use include Bt products like Dipel® (if available), carbaryl (Sevin® and others), malathion, permethrin (Ortho Max®, Eight®, Spectracide Bug Stop®, et al.), Conserve® and others. Two weeks after treatment, look for live bagworms to see if a second treatment is needed. These insecticides may kill beneficial insects so use them with care and follow the label instructions.
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