Landscape and Nursery - Bagworm Season

Bagworm season is upon us. It is important to control bagworms when they are small. Insecticide treatments should be made this month. The following is information on bagworm.

The bagworm, Thyridopteryx ephemeraeformis, is a key pest of many evergreen species, as well as some deciduous trees and shrubs. The best time for management is when the larvae are small during mid-June. Wide dispersal occurs mainly through movement of infested plants, or by wind blown larvae in June, since adult females can’t fly. Bagworms overwinter as eggs inside the female bag (several hundred eggs in each). Eggs hatch from late May through early June. Young larvae crawl out of the bag, feed and construct silken shelters over their bodies. Over their 8-10 week feeding period, bagworms enlarge their bags with pieces of foliage. Mature larvae (in August) loop strands of silk around a twig that firmly attaches the bag. During September and early October males leave their cases and fly to bags containing females where mating occurs. Bagworm feeding on needles and leaves is especially destructive to evergreen plants since evergreens cannot reproduce new foliage. Bagworm infestations generally go unnoticed until bags are large and damage is complete. Early detection requires careful examination of plants for small bagworms attached to the leaves or needles of host plants.

Control with chemicals is best achieved when applications are made when the insect is small. Products available for control are sprays of B.t.'kurstaki' (i.e. Dipel), insect growth regulators (IGR's) such as Confirm (tebufenozide), or reduced-risk products like Conserve (spinosad). Applications should be made before the end of June and coverage is important for the best results. Compounds such as Tempo or Permethrin Pro or other labeled pyrethroids as well as acephate (Orthene) control older larvae.

Information from Gregory Hoover, Ornamental Extension Entomologist and Brian Kunkel, Ornamental IPM specialist, UD.