Controlling Catalpa Worms (Sphinx Moth Caterpillars) with Bt or Sevin

Managing Catalpa Defoliation for a Cleaner Yard

A 100-year-old, 70-foot catalpa suffers annual caterpillar infestations. The owner wants the worms gone—they don't fish and hate the "scraggly" summer appearance.

Pest ID

Catalpa worms = caterpillars of the catalpa sphinx moth (Ceratomia catalpae). They defoliate heavily but rarely kill mature trees.

Control Options

• Bt (Bacillus thuringiensis): Products like Dipel, Green Light Worm Killer. Caterpillars must ingest treated leaves. Safe for beneficials. Apply late July, repeat every 2 weeks through August.
• Carbaryl (Sevin): Contact insecticide. Spray foliage AND trunk (catches descending pupating larvae). Broader spectrum—impacts beneficials.

Application Challenge

70-foot canopy requires high-pressure sprayer or professional arborist. Hose-end sprayers reach ~25 ft. Consider trunk injection (systemic) by a certified applicator for full coverage.

Ecological Note

Catalpa worms are native; birds and wasps prey on them. Total eradication disrupts local food webs. Tolerance may be wiser than chemical war.