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.
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 chemical treatments. Treatments in May/Early June (600-900 GDD) with Lepitect, Mectinite, or Lepitect infusible will be very effective against young larvae. Picking bags off by hand can help to reduce populations, but is usually not feasible for commercial companies. Look for bags during the winter to identify plants for treatment the following year.
Other Treatment Practices
- Promote health and vigor with proper irrigation, mulching, proper pruning and prescription based fertilization practices.
- The bags may be picked off the plant by hand and destroyed. Late fall is the easiest time to do this.
- Bacillus thuringiensis (Bt.) treatments may be effective on young larvae when applied during early summer after egg hatch.
- Timing is best after larvae have enlarged, but before pupation begins in later summer.
Multiple trial results have shown Lepitect to be effective vs. bagworm on deciduous and evergreens. Control on larger trees will not occur as quickly (2-3 weeks). Lepitect soil applications last for 30 days after treatment. For leaf feeding insects, Mectinite may provide suppression only (50% control) in the second season after application. Annual treatments may provide higher levels of control than every other year. Target early instar stages.
Signs of Damage
- Stripping of the foliage, usually in the upper portions of the tree, in late summer
- Branch dieback, and dead, open patches are common on coniferous hosts
- 1-1/2 inch to 2 ½ inch , cone shaped bags hanging from tree branches by late summer in which the larvae are enclosed
- The larvae are mottled 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
Trees At Risk
- Arborvitae (Thuja)
- Fir (Abies)
- Hemlock (Tsuga)
- Juniper (Juniperus)
- Pine (Pinus)
- Spruce (Picea)
- Baldcypress (Taxodium)
- Black locust (Robinia pseudoacacia)
- Honeylocust (Gleditsia triacanthos)
- Sweetgum (Liquidambar styraciflua)
- Sycamore (Platanus occidentalis)
- Boxelder (Acer negundo)
- Cotoneaster (Cotoneaster)
- Maple (Acer)
- Elm (Ulmus)
- Buckeye (Aesculus)
- Willow (Salix)
- Crabapple (Malus)
- Linden (Tilia)
- Poplar (Populus)
- Eggs hatch in late spring (yellowwood and yucca bloom). Young larvae emerge, construct a silk-like bag about 1/8 inch long around its body, and begin feeding on plant tissue.
- The larvae continue to feed into mid-summer until pupation begins. As the larvae feed and grow, the bag enlarges. Pupation lasts two to three weeks.
- By late summer the male adults emerge from the bag and mate.
- The females remain in the bag. After mating the female encases the egg mass, and remains in place until spring.
- One generation per year.
Ohio State University
Virginia Cooperative Extension
Johnson, W.T., Lyon, H.H. 1991. Insects That Feed On Trees and Shrubs.
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.