Bagworms on Leyland Spruce: Identification and Control

3-ft Leyland spruces have 20–30 pine-cone-like cocoons with brown caterpillars inside. What are they? Will they kill trees?

Pest: Bagworms (Thyridopteryx ephemeraeformis)

• Spindle-shaped silk bags camouflaged with plant debris (1.5–2.5")
• Larvae: brown/tan with black mottling; females remain larviform in bag
• Hosts: arborvitae, red cedar, pine, spruce, cypress, juniper, many deciduous trees
• Females don't fly → rapid local population buildup
• Heavy defoliation → branch dieback, plant death

Control

Mechanical: Hand-pick bags in late fall (cut silk band to prevent girdling).
Chemical: Stomach insecticides on young larvae (thorough foliage coverage). Options: acephate (Orthene), bifenthrin (Talstar), carbaryl (Sevin), chlorpyrifos (Dursban), diazinon, dimethoate (Cygon), malathion, nicotine sulfate, pyrethrum, rotenone.