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Fall Cankerworm

Stephen Bambara, Extension Entomologist

CAUTION: This information was developed for North Carolina and may not apply to other areas.


Fall Cankerworm, Alsophila pometaria (Harris), Geometridae, LEPIDOPTERA

General Information

The fall cankerworm is a native insect ranging across the Eastern half of North America from Texas to Nova Scotia. This inch-worm caterpillar will periodically outbreak in large numbers every several years. Outbreaks are more common in the northern regions. In North Carolina, outbreaks have been rare, except parts of Charlotte (Mecklenburg County). South central areas of the city repeatedly suffer high numbers for unexplained reasons. (Spring cankerworms, Paleacrata vernata, are quite similar, but the adults emerge closer to spring, eggs are hidden in bark cracks, and the larvae have different coloration and just two pair of hind prolegs.)

Biology

The fall cankerworm has four life stages, egg, caterpillar, pupa, adult. The adult male is a small brown moth and the adult female grey, with reduced wings, and unable to fly. At the first cold temperatures in the late fall (late November), the adult moths leave their cocoons in the soil. Female moths crawl up the trunks of trees or any vertical object, looking for the highest point or branches on which to lay eggs.

FALL cankerworm tiny caterpillars emerge in the early spring when leaves just begin to open (around late February) and feed immediately. As a tree's young leaves and buds are destroyed, plants may respond with new buds and leaves. Cankerworms generally don't kill trees, but this defoliation can drain a tree of some of its energy and may make it weaker. Feeding may continue well into April and cankerworm larvae can blow or drop to an adjacent branch or tree by silk strands. The "inch worms" measure up to one inch in length and may be light green or dark green. When the caterpillars have completed feeding, they will string down to the ground on a silken thread and burrow into the soil to make a new cocoon.

Identification

Cankerworms are one of the few caterpillars feeding very early in the season. Unlike the hairy tent caterpillars, it is smooth-bodied and does not build tents in the crotches of trees or elsewhere. When it crawls, it does so using the "measuring" movement characteristic of this group of inch-worms.

female wingless moth with eggs on twig

Adult female moth with eggs.

fall cankerworm

Inch-worm caterpillar.

banded tree trunks

Tree banding.

Control

Chemical- Under the approval of the NC Department of Agriculture & Consumer Services, the City of Charlotte has sprayed infested areas by air with plane or helicopter. The pesticide of choice has been B.t. (Bacillus thuringiensis) a naturally occuring bacteria that as been used by organic farmers and gardeners for decades. It has no known adverse affects on humans, wildlife, pets, fish or honey bees.

Foliar sprays containing B.t. are done in the spring while the small caterpillars are feeding. They stop eating soon after ingestion and die a few days later. Homeowners can use this same product on small trees, but large trees would require professional spray equipment and some amount of cost. Liquid Sevin (carbaryl) for example, could be sprayed on foliage, but would require applications every five days for several times. It would also harm the beneficial insects and may produce a worse situation in upcoming seasons. Insecticidal soap is extremely safe and has no residual. That means that it will kill only the soft-bodied insects that directly contact the spray. About three sprays per week would be required. Large tree spraying is both expensive and troublesome. Other foliar insecticides might include those containing spinosad, bifenthrin, permethrin, or chlorantraniliprole.

Click to enlargeband drawing

Tree Banding- Tree banding in November and December can be an effective way to block wingless females from crawling to the tops of trees to lay eggs. Traps should be in place about mid-November through all January. A sticky agent such as Tanglefoot™ is applied to a band around the tree, rather than the tree itself to protect the bark. Some stores in the Charlotte area sell tree banding supplies and pretreated bands.

Step 1: Install a strip of batting or insulation around the tree a few feet above ground level and below all limbs.

Step 2: Position a band of tar paper or roofing felt 6-12 inches wide, around the trunk circumference covering the batting. Short staples may be used for this. Do not use nails. Electrical tape might be used for small smooth-barked trees.

Step 3: Apply the Tanglefoot or sticky material in a band several inches wide onto the tar paper. Wear disposable gloves for easy clean up. Bands must remain sticky and clear of excessive debris, and may need to be "refreshed" periodically.

See also:
Penn State Fact Sheet
PDF
The city of Charlotte, NC information site.
An Assessment of Tree Banding Techniques to Capture Cankerworm by LaFrance & Westwood.

Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.
Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact your county North Carolina Cooperative Extension Service agent.

Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.
© 2001 NC Cooperative Extension Service


ENT/ort-153
Prepared by Stephen Bambara, Extension Specialist based on "The Fall Cankerworm", 1997. North Carolina Cooperative Extension Service. Anon. Photo credits, John H. Ghent, USFS; Tim Tigner, VAFS; Keith Douce, UGA.


Web page last reviewed January, 2011 by the webperson.