This week I have seen a few samples of Japanese Maples in the hotline office with severe bagworm feeding damage. Bagworms feed on many trees including maple, boxelder, sycamore, willow, black locust, elm, linden, poplar, oak, apple, wild cherry, sassafras, and persimmon; but the preferred hosts are conifers.
Beginning in late May through mid-June, larvae of this native moth feed causing defoliation on their host plants. Damage is most noticeable on ornamental plantings rather than in forests and woodlands.
The bags they create are camouflaged with pieces of plant material, and may be mistaken for natural parts of the tree. Females do not look like moths (no wings, legs, antennae, eyes, or mouthparts) and remain in silken bags throughout their entire lives. When larvae are fully grown, their protective bag is 1.0 to 1.5 inch long.
In late summer, male moths (black, with nearly clear wings approximately 1 inch across), emerge from their bags after pupation. One generation occurs per year.
Where practical, bagworms can be removed with scissors or a sharp knife. Chemical control is effective, particularly in June and early July when the bags are small. Recommended insecticides include Dipel and Sevin.