Small bagworms are feeding now. It takes careful inspection to detect small larvae wrapped in silk bags with pieces of leaf attached (Figure 1). Check small trees and shrubs that have a history of problems to see if the insects are active.
Bagworm caterpillars feed for about 6 weeks, enlarging the bag as they grow and withdrawing into it when disturbed. Older larvae strip evergreens of their needles and devour whole leaves of susceptible deciduous species, leaving only the larger veins. When abundant, the caterpillars can defoliate plants. Heavy infestations over several consecutive years, especially when coupled with other stresses, can lead to plant death.
When many small bagworms are present and feeding, an insecticide may be needed to prevent serious damage. The best time to apply an insecticide is while larvae are still small (less than 1/2 inch long), usually in early June. Small larvae are more vulnerable to insecticides, and feeding damage is relatively minor. Choices for bagworm control include products containing neem, Bt, Spinosad, pyrethroids (bifenthrin, cyfluthrin, cyhalothrin, or permethrin), or carbaryl (Sevin).
By Lee Townsend, Extension Entomologist