Controlling Bagworms

Bagworms are native to Missouri and found extensively throughout Missouri. This insect, the bagworm, produces a protective silken bag around its body, and many homeowners confuse this bag for a part of the tree or a pinecone. During the insect’s life on the tree, it rapidly consumes needles and leaves, defoliating entire plants before your very eyes. Plants that are attacked become weakened or unsightly, and smaller evergreens may not recover from a heavy bagworm infestation. It is not uncommon for complete defoliation to occur with heavy infestations. Bagworms primarily attack needle-leafed evergreens such as juniper, spruce, and arborvitae, but also attack deciduous trees such as honey locust and bald cypress. In late May to mid-June, bagworm larvae (caterpillars) emerge from previous years’ bags and immediately start producing their own protective bag around their body. A larva produces its bag using bark, leaves and twigs woven together with silk for strength and camouflage. The larva’s head and legs are freeallowing it to move about the plant and feed on the foliage. The larva will spend its entire life in the bag and complete its development by mid-September. If a tree is completely defoliated, the larvae will crawl off the tree with their bags and search for a new plant to feed on.

The best control for bagworm is to remove and destroy the bags as soon as they appear. Any bags left on the tree will provide a source of insects for subsequent years. Some species of birds are able to open the bags and feed on the larvae. Bagworms can be controlled chemically, but the treatment must occur in the spring as soon as the eggs hatch and the larvae begin emerging from the over-wintering bag. Chemical control becomes much less effective once the larvae get larger and more protected in their bag. The ideal time for a chemical treatment is late May or early June.

For more information on web producing insects, refer to MU Extension Guide G7250 ( http://muextension.missouri.edu/xplor/agguides/pests/g07250.htm).

Mary Kroening Dept. of Horticulture 573-882-9633

Bruce A. Barrett, Extension Entomologist