By Darrell Blackwelder
Leyland cypress and arborvitae have the potential to become seriously damaged or killed outright by bagworms. Cooperative Extension has received calls earlier this week complaining about the insect, which is now feeding at a rapid rate.
Homeowners with Leyland cypress, arborvitae and other conifers need to check their shrubs carefully to determine if bagworms are indeed present and actively feeding.
Bagworms first appeared about nine years ago on Leyland cypress and other evergreen shrubs. Over-planting of Leyland cypress and arborvitae make these shrubs easy prey for insects to spread with little or no control. Moth larvae hatch in the early summer and spin down on silken threads. The immature larvae are blown about by the early spring breezes, landing on adjacent trees and shrubs. The larva forms a protective cocoon or bag made of spent twigs or leaves. The bag is firmly attached by a sturdy silk band, which the bagworms usually wrap around a twig.
Scores of larvae that feed during June and July have the potential of defoliating the shrub. Apparently, when the newly hatched larvae reach a plant that is different from its parent’s host plant, these insects often have difficulty in adapting to it and may die or may produce only a few offspring.
Unfortunately, after several years of struggling to keep from going extinct, the bagworm population develops the right combination of genes for a new plant and the new plant is covered with bagworms.
These insects can completely defoliate a shrub in a matter of days, easily killing the plant.
Many people have informed me that they have returned from a week’s vacation and their shrubs are completely defoliated. Bagworms are particularly fond of Leyland cypress and arborvitae.
Insecticidal sprays applied in the early larval stage easily kill the insect. Shrubs with a few larvae can be controlled by handpicking. As the insects mature, they increase in size and become resistant to insecticides. As the summer progresses, the larvae are more difficult to control. As the larvae mature, they pupate and are impossible to kill. The sheer size of these shrubs can be difficult or in some cases impractical to spray with pesticides.
Go to http://www.ces.ncsu.edu/ depts/ent/notes/O&T/trees/ort081e/BAGWORM.pdf for more detailed information on life cycles and a complete list of recommended pesticides for control.
Darrell Blackwelder is county extension director for Rowan County North Carolina Cooperative Extension. Call 704-216-8970.