Is this a familiar scene for anyone? Bagworms (actually caterpillars) are a true problem in the Nashville area, and because they are attracted to plants such as arborvitae, cedars, junipers, spruces & other conifers, their ‘bags’ can be easily mistaken for pine cones or other plant structures and ignored until the damage is irreparable. The caterpillar constructs its bag from plant material as it feeds on the leaves of the plant, enlarging the bag as it goes. Bagworms can defoliate an evergreen in a very short time span, killing it completely.
We have recently found many cases of bagworms destroying beautiful arborvitae, junipers, spruces & cedars. The photo above shows damage done to a lovely Glauca Pendula Cedar. By the time the bagworms were noticed and picked off, defoliation to the center of the tree had already occurred and the tree browned quickly.
Bagworms spend the winter as eggs inside the females’ bags, and hatch in late April through mid May. Young larvae are tireless in their search for food, continually feeding on the tree’s leaves and constructing the camouflaging shelter over their body. By August, the bagworms attach permanently to a twig or branch and go into the resting stage before becoming adult. The males then leave the bags to search for immobile females, which can lay several hundred eggs in the bag, leave the bag & die. The eggs remain in the bag over winter, until hatching in spring.
The best time to treat bagworms by pesticide is when they are very young, usually in early June. As the bags grow and harden they can become highly impervious to pesticide spray- even to the point of being rainproof. At the later stages, they must be picked off by hand & destroyed, as they are literally strangling the branches on which they reside & feed. Of course, this must be done before the eggs hatch- in fall, winter or early spring. Otherwise, a chemical application will be necessary for control.