Is something devouring your evergreens? Look closely, the culprit may be camouflaged and right in front of you! Bagworms are caterpillars that make distinctive spindle-shaped bags on a variety of trees and shrubs throughout Kentucky. They attack both deciduous trees and evergreens, but are especially damaging to juniper, arborvitae, spruce, pine and cedar.
Large populations of bagworms can strip plants of their foliage and eventually cause them to die. This insect is most easily recognized by the case or bag that the caterpillar forms and suspends from the plant on which it is feeding. The bag is made of silk and bits of host foliage. These materials are interwoven to disguise and add strength to the case. Because the bag blends in, infestations often go unnoticed until it is too late.
If there are only a few bagworms on your trees or shrubs, picking the bags off by hand and disposing of them may afford satisfactory control. This approach is most effective during fall, winter or early spring before the eggs hatch in May.
When there is a high number bagworms infesting a tree or shrub, an insecticide may be needed to prevent serious damage. The best time to apply an insecticide is while the larvae are still small (less than 1/2-inch long). In Kentucky, this is usually in June. Small larvae are more vulnerable to insecticides because they have not fully made their bag yet. During this time they look like an upside down ice cream cone. Once the caterpillar is wrapped entirely in its bag, insecticides will not be effective.
For more information on bagworms, check out https://entomology.ca.uky.edu/ef440.
Submitted by Amanda Sears, Agent for Horticulture, Madison County Cooperative Extension Service