Sound advice from our Earl May Experts on controlling bagworms:
Hand-picking is the best way to control light infestations on small plants during the dormant season. Destroy bags by burning or by crushing. If bags containing larvae are discarded on the ground, the larvae may return to the host plants.
Plan to apply insecticides to control next year’s small larvae in June. Bacillus thuringiensis, BT or Thuricide is a natural control that is effective. Other insecticides currently labeled for bagworm control include Systemic Insect Control, Malathion and Eight. Affected plants must be thoroughly covered with the insecticide so that it is ingested by the insects as they feed.
Feeding by mature caterpillars slows in August before pupation into the adults, so chemical control in late summer and fall may not be effective.