Baxter County Master Gardener Program • University of Arkansas System • Division of Agriculture • © 2013 BCMG
Bagworms on arborvitae and juniper are active this time of year, and doing some serious damage. They also attack pine, spruce, cypress, black locust, willow, sycamore, apple, maple, elm, poplar, oak, and birch. They attack the buds of conifers causing tip dieback and open dead areas.
Extensive defoliation may occur followed by the death of the plant. They have one generation a year and over-winter as eggs in the female bag. There can be as many as 300-1000 eggs in a single bag. Hatching occurs in May-June depending on weather. When the larvae hatch they leave the bag, spinning down from it by a strand of silk that often acts like a parachute to carry them to new hosts. There they immediately spin themselves a bag, which becomes covered with plant debris from the host as they crawl around feeding. This camouflages them so well that they often go unnoticed until considerable damage has been done. In fact many homeowners fail to notice them until they have matured and permanently glued themselves to a stem. At that point they have quit feeding and the damage has been done for the year.
The first line of defense is hand picking and destroying the bags. Be sure to remove the silk that binds the bag to the stem as it may cause girdling later. A biological control that works well is BT (Bacillus thuringiensis). This product only kills caterpillars. It will not harm beneficial insects.
More Chemical Control Options:
Department of Plant Pathology - Plant Health Clinic News
Baxter County Extension Office