NC State Extension Publications

General Information

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Female fall cankerworms, Alsophila pometaria, are brownish to silvery, broad, wingless insects. Males are gray moths with indistinct darker spots that form two lines across each wing. Eggs are tiny and barrel-shaped with a dark line around the top rim and a tiny, dark spot in the top. Fall cankerworm caterpillars are loopers, that is, they have a gap between the first six legs and the last four legs (prolegs) so that they "inch" along as they crawl. These caterpillars may be pale green with even paler stripes or may have very dark lines down the back and along the sides.

Female fall cankerworm moth on bark.

Female fall cankerworm moth on bark.

Female fall cankerworm moths on sticky trap.

Female fall cankerworm moths on sticky trap.

Fall cankerworm moth with her eggs.

Fall cankerworm moth with her eggs.

Male fall cankerworn on sticky trap.

Male fall cankerworn on sticky trap.

Fall cankerworms feeding on oak leaves.

Fall cankerworms feeding on oak leaves.

Fall cankerworm green phase.

Fall cankerworm green phase.

Biology

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Fall cankerworms can be locally abundant and a real nuisance in the landscape. These insects are called FALL cankerworms because the females emerge from November through January from the soil and crawl to twigs of hardwood trees to lay eggs in a tight cluster of about 100 on the twigs. Female fall cankerworms are wingless and silvery gray. The eggs overwinter and hatch in spring about the time the buds break. Newly hatched, tiny caterpillars skeletonize the leaves as they feed. Older caterpillars devour all but the midrib. The caterpillars are loopers or inchworms. They mature in five or six weeks and then spin down to the ground where they pupate in the soil in a cocoon of tough silk. This pest remains in the cocoon until the next fall or winter when they emerge after a hard freeze.

Host Plants

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Fall cankerworms sometimes become abundant enough to cause severe defoliation of ash, basswood, beech, black cherry, red maple, sugar maple, red oak, and white oak, but also infest apple, birch, boxelder, dogwood, elm, hickory, and other hardwoods. These latter species are especially vulnerable when growing under or near the more favored hosts. Because of our long growing season, a spring defoliation is not as damaging to shade trees as it is further north where trees have less time to compensate for the loss of leaves. However, repeated defoliation can weaken trees and make them more susceptible to other stresses, such as age, drought, other insects, and disease. People also object to the frass raining down from heavily infested trees and they object to the worms spinning down on their silk strands.

Management

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Trees can be banded with sticky material to prevent females from climbing up to lay eggs. Tree bands usually entail wrapping a narrow band of cotton batting or fiberglass insulation around a tree trunk then wrapping this material in plastic or tape. Apply sticky material like Tanglefoot to the plastic to catch female moths as they climb. The batting helps fill bark grooves to prevent moths from getting under the band. These traps should be installed after leaf fall and just after the first hard freeze. They should be checked periodically because the bands may become covered with moths or debris. Later moths will crawl over the bodies of their unfortunate comrades and will continue up the tree to lay their eggs. Thus with heavy populations, the moths may need to be scraped off from time to time and additional sticky product added to the plastic strips. In some cases entire cities or neighborhoods may band all susceptible trees in an attempt to reduce tree defoliation. The large scale benefits of this have not been established but the bands are certainly useful for monitoring to identify heavily infested areas.

Once caterpillars begin feeding, spring insecticides, such as those containing Beauveria bassiana, can be used to reduce their abundance and defoliation. Caterpillars only feed for six weeks so unless they are treated soon after hatching the benefits, in terms of reducing defoliation, will be minimal.

Residential Recommendation

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Trees can be banded with sticky material to prevent females from climbing up to lay eggs. Tree bands usually entail wrapping a narrow band of cotton batting or fiberglass insulation around a tree trunk then wrapping this material in plastic or tape. Apply sticky material like Tanglefoot to the plastic to catch female moths as they climb. The batting helps fill bark grooves to prevent moths from getting under the band. These traps should be installed after leaf fall and just after the first hard freeze. They should be checked periodically because the bands may become covered with moths or debris. Later moths will crawl over the bodies of their unfortunate comrades and will continue up the tree to lay their eggs. Thus with heavy populations, the moths may need to be scraped off from time to time and additional sticky product added to the plastic strips. A parasite of the eggs, Telenomus alsophilae, is a major factor in the decline of fall cankerworm populations. However, the build up of the parasites usually follows the build up of the fall cankerworms, so a good deal of defoliation may occur before the fall cankerworm population collapses. At least 14 pesticides are labeled for caterpillar control in the landscape. This species is not particularly resistant to pesticides.

References

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For assistance with a specific problem, contact your local Cooperative Extension center.

Authors

Professor and Extension Specialist
Entomology and Plant Pathology
Professor Emeritus
Entomology and Plant Pathology
Extension Specialist (Home Ornamentals/Turf)
Entomology and Plant Pathology

Publication date: March 27, 2013
Revised: Sept. 18, 2019

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