What Worm Is Eating My Evergreen?

Identification

• A wide number of evergreen varieties are susceptible to damage from bagworms (Thyridopteryx ephemeraeformis). The worm or caterpillar is the larval stage of a native Pennsylvania moth. The host range of the pest include more than 100 types of plants, according to the Pennsylvania Cooperative Extension. Evergreen hosts of bagworms include arborvitae, spruce, pine, juniper and cedar.

Description

• Female adult bagworm is worm-like and does not have wings, eyes, functional legs or mouth parts. Females spend their entire life in the bags constructed during the larval stage. Adult males are black moths with transparent wings. Pest presence is established by the small, 1- to 2-inch-long bags that the worms weave with their silk and pieces of foliage. These bags contain the eggs that start to hatch in May and the small larvae crawl out and weave and feed inside their own bags. Mature larvae are dirty gray.

Damage

• Bagworm larvae feed on the upper epidermis of leaves and needles of infested plants, creating brown spots and holes in the foliage. Though bagworms are also likely to infest deciduous plants, the damage is worse on evergreens. Larger larvae can eat entire leaves, leaving only the veins on broadleaf trees and the whole needles of evergreens. Bagworm presence is usually undetected until the tree has been damaged extensively and the larvae are mature.

Management

• You can control population of bagworms by picking out the bags manually from the trees and destroying them during fall, winter and very early spring before the eggs hatch. This is possible only when the tree has few bags. Serious infestations are best controlled with recommended insecticides that include acephate, carbaryl and azadiractin. Insecticides are most effective when used on young larvae that are less than ½ inch long. This is usually between early and mid-June. Time your pesticide application carefully as larger larvae are hard to control.