Bagworm Control on Blue Spruce: Timing and Treatment Options

Managing Bagworms on a Large Blue Spruce in Maryland

Bagworms (Thyridopteryx ephemeraeformis) are caterpillars that build spindle-shaped bags from silk and foliage. On a tall spruce, reaching all bags is challenging.

Immediate Actions (Late Summer)

• Hand-pick reachable bags: Drop in soapy water. Best for light infestations.
• Foliar spray if coverage possible: Use Bt (Bacillus thuringiensis) or spinosad – effective on young larvae, safer for beneficials. Sevin (carbaryl), Orthene (acephate), or pyrethroids also work but harm pollinators.

Best Long-Term Solution: Soil-Applied Systemic

Bayer Advanced 12-Month Tree & Shrub Insect Control (imidacloprid) applied to soil in early spring (when buds swell) provides season-long protection. Roots translocate it to foliage; feeding larvae die.

• Apply now? No. Fall application is ineffective – trees are shutting down, minimal uptake.
• Mark calendar for March–April 2025 treatment.

Why Systemic Beats Spraying Tall Trees

• No spray drift, no ladder work.
• Protects new growth all season.
• One application per year.

Combine spring systemic with fall hand-picking for complete management.