June 09, 2009

Bagworms, Theridopteryx ephermaeformis, often called "evergreen bagworms," are native to the United States and are found throughout eastern and central Nebraska. Bagworms feed on a wide variety of trees and shrubs, but prefer evergreens, especially juniper.

Bagworms overwinter as eggs within bags fastened to twigs. Eggs hatch in late May and early June. Immediately after hatching, some of the caterpillars release a streamer of silk and are blown by the wind, establishing new infestations on nearby trees. Others begin to spin tiny, one-eighth inch protective cases or "bags" around themselves. These bags are constructed of silk and fragments of needles or leaves. As bagworms grow, leaf fragments are added to bags, which often grow to 2 inches in length by the end of the summer. Larvae feed until late August or early September. Male bagworm moths emerge in September and mate with the wingless females through the bag opening. Female moths deposit their eggs within their own bags, drop to the soil and die. Each female can produce 500 to 1,000 eggs. There is only one generation per year.

Bagworms feed on most coniferous plants and on many deciduous trees and shrubs. Common evergreen hosts include juniper, arborvitae, spruce and pine. The earliest sign of bagworm injury in evergreens is brown or stressed needles at the tips of branches. This is caused by the tiny first-stage bagworm caterpillars etching needle surfaces as they feed. Heavy infestations of older bagworms are capable of completely defoliating a tree or shrub. These plants can be severely stressed or even killed if control measures are not taken. Less severe injury will slow growth and stunt plants. Bagworms are especially damaging to conifers because destroyed foliage is not regenerated.

Bagworm infestations on smaller trees and shrubs can be controlled by removing bags during the winter and early spring before egg hatch begins in late May. Destroy bags by crushing or immersing them in soapy water. If bags containing larvae are discarded on the ground, the larvae may return to host plants.

Insecticides are most effective when applied during the early stages of bagworm development. For prevention of early season damage, apply sprays from mid- to late-June when bags are less than 1/2 inch long. Insecticidal applications applied later in the summer when bagworms are larger will likely result in much less effective control. By late August, chemical control is no longer feasible, as most bagworms will have ceased feeding and pupated within their bags.

Insecticidal sprays, whether involving a single tree in the landscape or a shelterbelt, require thorough coverage to penetrate the canopy and contact the feeding bagworms. It is generally preferable to use ground equipment capable of delivering higher spray volumes and pressures. Aerial applications may fail to provide thorough enough coverage resulting in less than satisfactory bagworm control.

Reduced-risk options: Insecticides containing Bacillus thuringiensis (Bt), spinosad, or neem oil (azadirachtin) and insecticidal soaps are quite effective against young bagworm larvae, but may require repeated applications. These products generally have minimal impact on beneficial insects. Additional insecticide options for bagworm control on ornamental plants include: acephate, bifenthrin, chlorantraniliprole, carbaryl, cyfluthrin, dimethoate, esfenvalerate, fluvalinate, lambda-cyhalothrin, malathion, permethrin and tebufenozide.

6/9/09-DM

Contacts:

Fred Baxendale - Ph.D.
Entomology
Professor
(402) 472-8699

James Kalisch
Entomology
Extension Technologist
(402) 472-8691

James Kalisch
Entomology
Extension Technologist
(402) 472-8691

Dan Moser
IANR News & Photography Coordinator
(402) 472-3007

Department:
Extension