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Problem: Cankerworms - Alsophila pometaria Also known as measuring worms, inch worms, or loopers.
Hosts: Has a wide host range but prefers elm, hackberry, and honeylocust.
Description: Two species of cankerworms occur. Both attack early in the spring just as the leaves are beginning to appear, or they sometimes attack the buds before the leaves open. The spring cankerworm is the more common species in Kansas. Adult females of both species are wingless moths. The fall cankerworm adult emerges in October and November, whereas the spring cankerworm adult does not emerge until late February and March. The females of both species crawl up the trunk of the tree to deposit eggs. Eggs of both species hatch in April or early May and the young devour the developing leaves. Dispersal is accomplished when the small caterpillars are blown from one tree to another. Large numbers of larvae may annoy passersby because the often hang from a strand of silk. Upon maturity, larvae descend to the ground on a silk thread. They then burrow into the ground, spin a cocoon and pupate.
The spring cankerworm larvae vary in color from reddish to yellowish-brown or yellowish green and may even be blackish. Usually there is a yellowish stripe on the side of the body though this may be missing. Fall webworm larvae color ranges from light green to very dark brownish-green with a wide, dull, dark longitudinal stripe down the center of the back. Fall webworm has three pairs of prolegs while the spring cankerworm has only two.
Both species have one generation per year. Defoliation is often not readily apparent, although trees may appear dead because they are late in leafing out. Caterpillars begin as hole feeders, then progress to free feeding as they get bigger.
Recommendation: Applying bands of sticky material to the trunks of individual trees to catch the wingless females as they crawl upwards to lay their eggs is an old technique that is worth of more frequent use. This technique has failed in the past because people did not understand that there are two species of cankerworms and they crawl up the trees in different seasons. The fall cankerworms crawls up the tree in October and November and the spring cankerworm in late February and March. In addition, they failed to realize that sticky bands exposed to changing temperatures, blowing dust, etc., lose their stickyness and will not catch the females.
Sticky bands should be made from materials that are non-toxic to the tree. Sticky material is sold under the trade names, “Tanglefoot,” “Stickem,” or “Tack Trap.” Apply a band about 4-6 inches wide evenly around the trunk, preferably 6-7 feet high, but lower if the tree branches are below this height. Do not scrape the rough bark to make a smooth surface. This may expose living tissue that can be injured. The sticky material may also be applied to a strip of paper, cloth or burlap that is tacked to the trunk, so it may be removed after the cankerworm season. Make sure all crevices in the bark under the paper or cloth are plugged to prevent females from crawling under.
Insecticide applications including those containing Bacillus thuringiensis are
quite effective if applied when the larvae are small. Other effective insecticides include
malathion, carbaryl (Sevin), acephate (Orthene) and cyfluthrin
(Tempo). Rapping on branches will disturb cankerworms and cause them to reveal their
presence by dropping down on silken threads.
References:
1. Insects and Mites Associated With Shade Trees and Woody Ornamentals, pg 12, K-State Research and Extension Pub S-85
2. Life Histories of Common Insects, Mites and Nematodes Infesting Ornamental Plants in Missouri, Missouri Department of Agriculture, pg F-22 through F-25
Last Update: 03/28/2003
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