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Bagworms on Pine: Bt Fails on Mature Bags, Switch to Contact Sprays

Why Your Spray Didn't Work

Bt only kills young caterpillars that eat it. Once bagworms are in their 1.5–2.5 in. bags, they're protected. Contact/stomach insecticides (Orthene, bifenthrin, carbaryl, spinosad) must coat foliage so larvae ingest it when they emerge to feed.

Action Now

Hand-pick reachable bags.
Spray Orthene or bifenthrin thoroughly on foliage.
Next year: spray Bt in late June when bags are small.

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