Bagworms can cause serious, even fatal, damage to a variety of trees and shrubs.
A bagworm infestation often will not be readily noticeable until after substantial damage has been done and the insects have retreated into their bags. According to Dr. Lee Townsend, extension entomologist with the University Of Kentucky College Of Agriculture, it is time to check for bagworms.
Small bagworm larvae have been feeding and growing for about a week, and the bags that they carry are getting larger. They are still small. The damage is easy to overlook, but this is the time to check for them in the landscape, especially where they were a problem last year.
Bagworms prefer juniper, arborvitae, spruce, pine and cedar, but also attack deciduous trees. They can be controlled, but success requires early detection and some persistence to make sure the first treatment was successful. If only a few small trees or shrubs are infested, handpicking and destroying attached bags may provide satisfactory control. This must be done effective during fall, winter or early spring before the eggs hatch.
When many small bagworms are present and feeding, an insecticide may be needed to prevent serious damage. It is best to treat while the larvae are still small (less than a half-inch long), usually in early June. Small larvae are more vulnerable to insecticides, and feeding damage is relatively minor. Carefully inspect susceptible landscape plants. Young bagworms are hard to see at first; look closely for the small, upright bags which have the appearance of tiny ice cream cones made of bits of plant material.
Control options include products containing Bt, carbaryl, neem, pyrethriods, and spinosad sprays.
For additional information about insect management, please call the Clark County Office of the University of Kentucky Cooperative Extension Service at 744-4682.