Bagworms Diagnostic Guide

Thyridopteryx ephemeraeformis

Native to the United States, the bagworm, Thyridopteryx ephemeraeformis, is a defoliating caterpillar in the order Lepidotera that commonly feeds on the foliage of many coniferous and deciduous trees east of the Rocky Mountains. The bagworm’s self- spun bag, which can be found hanging from the host plant by mid-summer is unsightly. Excessive feeding can strip away large quantities of leaves, causing branch dieback, and dead patches on the host plant.

Trees at Risk

Bagworms affect: arborvitae, fir, hemlock, juniper, pine and spruce, baldcypress, black locust, honeylocust, sweetgum and sycamore, boxelder, cotoneaster, maple, elm, buckeye, willow, crabapple, linden, poplar, and many more trees.

Crab Apple





Bald Cypress

Signs of Damage

  • Yellow spots on the foliage, usually in the upper portions of the tree, in late summer.
  • Dead, open patches are common on coniferous hosts.
  • 1-1/2 inch to 2 inch cone shaped bags hanging from tree branches by late summer.
  • Often heavy defoliation by late summer.
Bagworm Signs

Bagworm Signs

Physical Appearance

  • The larvae are splotched brown to black, but are seldom seen as they remain in the self-spun bag.
  • Adult males have clear wings and bodies covered in fur.
  • Adult females are worm-like, lacking eyes, wings, functional legs, and mouthparts.
Bagworm Pupa

Treatment Strategy

Bagworms are difficult to control because they often go undetected until it is too late in the season to treat effectively. It is important to treat the larvae before they mature because young larvae are more sensitive to treatments. This means treatment is necessary in early spring to mid-summer. Picking bags off by hand can help to reduce populations, but is not always feasible. Look for bags during the winter to identify plants for treatment the following year.

  • Soil Application using Lepitect

    Dosage: 0.2 oz/in DBH on trees less than 15 in DBH. 0.4 oz/in DBH on trees greater than 15 in DBH
    Timing: Apply two weeks prior to anticipated outbreak in mid to late May/early June
    Re-Treatment: A second application 30 days later will provide additional control if larvae are still feeding.
    Lepitect Systemic Tree & Ornamental Insecticide
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  • Foliar Spray using Conserve

    Dosage: 6 fl oz/100 gal
    Timing: As larvae are crawling out of the bags to feed in midsummer. Begin sprays at 600 GGD.
    Re-Treatment: Repeat applications at 7-14 day intervals through 900 GGD.
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Treatment Expectations

Multiple trial results have shown Lepitect™ to be effective in controlling bagworms on deciduous trees and evergreens. Controlling bagworms on larger trees does not occur as quickly (2-3 weeks). Lepitect™ soil applications last for 30 days after treatment. If timed properly, a foliar spray of Conserve™ will control larvae. However, these sprays are ineffective if they are not properly timed or if they are not applied properly to fully penetrate the canopy.

A Diagnostic Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy Use of the images does not imply endorsement of treatments by

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