OUTSIDE: Beware Bagworms

Published 11:49 am Monday, August 12, 2019

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By Steve Roark

Tri-State Outside

Bagworms are a common landscape pest this time of year, especially on evergreens, especially arborvitae. A large enough population can seriously damage and eventually kill a tree.

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There are several bagworm species, but the most common one is the evergreen bagworm (Thyridopteryx ephemeraeformis). The adults are moths with clear wings (unusual for a moth) and large feather-like antennae. They’re most recognized during their larval stage by the portable bags they build out of bits of leaves and twigs held together by very tough webbing. They look like round spear heads and are usually brown in color.

They start out small at the beginning of summer but grow to be over 1-2 inches long as the worm expands its home. They crawl around on trees eating the foliage with only their head and legs sticking out of the bag. When at rest they retreat completely inside the bag. Large populations of the little pests can do serious damage by stripping off large portions of the tree foliage. Evergreens are most often attacked, but I have seen them work on maples as well. Late in the summer the larvae pupate inside the bags and become adults. The females normally don’t leave their home until eggs are laid in the bag.

The insects can be controlled by a number of insecticides, including Sevin, Orthene, and Malathion. Normally two applications a week apart are needed for good control and be sure to follow label directions. If you want to go the organic route you can try Dipel insecticide or pick off the bags and drop them in kerosene or put them in a bag and give it a good stomping. Be sure and pick off as many bags as you can find, and this is where the eggs are for next year’s population. Don’t let them remain overwinter.

For insect or disease problems on trees and shrubs contact your local state Forestry office or County Extension Agent.