Bagworm Infestation on Pine Trees: Identification and Control

The "cocoons" made from dead needles with worms emerging are bagworms (Thyridopteryx ephemeraeformis). These caterpillars construct spindle-shaped bags from silk and plant debris, carrying them as they feed. They attack many evergreens, including pine, arborvitae, juniper, and spruce.

Life Cycle & Damage

• Eggs overwinter in the female's bag.
• Larvae hatch in late spring (May–June), disperse, and begin building tiny bags.
• They feed through summer, enlarging bags to 1.5–2 inches.
• Heavy infestations defoliate and can kill branches or entire trees.

Control Options

Mechanical (Best for Small Trees/Light Infestations)

• Hand-pick and destroy bags fall through spring before eggs hatch.
• Drop bags in soapy water or crush them.

Biological: Bacillus thuringiensis (Bt)

Apply Bt (e.g., Dipel, Thuricide) when larvae are small (June–early July). Bt is specific to caterpillars and safe for beneficials. Thorough coverage is essential.

Chemical Insecticides (For Larger Larvae/Heavy Infestations)

• Spinosad (Captain Jack's Deadbug Brew)
• Permethrin (Bonide Eight, Hi-Yield)
• Cyfluthrin (Bayer Advanced)
• Carbaryl (Sevin)
• Apply when bags are small; late summer applications are less effective.

Key Timing

Monitor in late May–early June for tiny new bags. Treat then for best results. Large trees may require professional equipment for full coverage.

Prompt action this season and bag removal this winter will break the cycle and protect your pines.