Bagworms on Arborvitae: Identify, Remove, and Spray Early

Cone-shaped bags with moving worms on browning arborvitae are bagworms. They strip foliage and can kill the tree if unchecked.

Lifecycle

• Eggs overwinter in last year’s bags.
• Hatch mid-late May → tiny larvae build “ice cream cone” bags.
• Feed all summer, enlarge bags. Pupate early fall.

Control

1. Hand-pick bags fall–early spring (before hatch).
2. Spray when larvae small (<1/2 inch): Sevin, Dursban, diazinon, malathion, or Bacillus thuringiensis (BT).
3. BT only works on young larvae. Large bags need conventional insecticide.

Check Neighbors

Spray adjacent arborvitae if infested. Preventive spray justified on previously heavily infested plants.