Bagworms are caterpillars that make distinctive “spindle-shaped” bags on a variety of ornamental trees and shrubs throughout Georgia. They have been known to attack both deciduous and evergreen trees, but are most often found on cedar, cypress, arborvitae, juniper, spruce and pine. I was on a site visit this past week and saw this pest devouring a Leyland cypress.
They also can be seen on deciduous plants, including rose, maple, elm and sycamore.
Bagworms injure host plants by stripping off large amounts of foliage. Severe infestations can cause tree death. Bagworms often go unnoticed because their bags can easily be mistaken for natural cones.
Bagworms are the larval stage of a moth. Only the males of the species develop into moths capable of flight. The larvae are dark brown with yellow heads and yellow and black spots over the body. Adult females stay in caterpillar form. They are wingless and lack eyes and antennae.
Bagworms survive the winter as eggs inside old bags. The eggs hatch in mid- to late May. The new larvae construct bags by using silk and small bits of plant material. The new bags resemble tiny upside-down ice cream cones. As the larvae grow, they continue to add more plant material and enlarge the bag. They use the bags as shelter when disturbed.
Bags reach their ultimate size of 1 ½ to 2 inches in early fall. The larvae permanently attach their bags to twigs and transform into the pupa stage. Pupation lasts from seven to 10 days, after which the adults emerge. The flying males go out in search of immobile females. After mating, the females lay 500-1,000 eggs and then die.
Because the larval stages of the bagworm are fairly immobile, it is common to see one plant covered with bagworms, while an identical plant nearby is bagworm-free.
The easiest method of bagworm control is hand picking. If only a few small trees or shrubs are infested, picking off the bags and disposing of them is often satisfactory. The best time to do this is in winter or early spring. This will prevent new eggs from hatching out and re-infesting the same plants.
Insecticides are best used when small crawling larvae are observed in spring, usually late May through June. Young bagworm larvae are especially sensitive to the bacterium Bacillus thuringiensis, also known as B.t. It is sold under many common brand names, including “Dipel,” “Thuricide” and “Caterpillar Killer.” The bacterium causes a disease which kills the caterpillars while not affecting humans. Conventional chemicals, such as malathion and bifenthrin, also can be used for control of young bagworms.
If you suspect you may have bagworm issues in your landscape, scouting is the key to prevention and control. Keep a close eye on susceptible plants, especially evergreens. They cannot recover from defoliation like some deciduous species, so early identification is crucial.
For additional questions, contact Effingham County Extension Agent Sam Ingram at 754-8040 or email firstname.lastname@example.org.