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by Lee Townsend, Extension Entomologist

University of Kentucky Department of Entomology

Paleacrita vernata (Spring cankerworm)

Alsophila pometaria (Fall cankerworm)

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diagrams showing numbers and arrangement of prolegsCankerworm is the general name given to a group of inchworm caterpillars that feed on deciduous trees and move with a distinctive crawl. A reduced number of fleshy legs on the abdomen gives these caterpillars a unique looping gait. Most cankerworms have five pairs of fleshy abdominal legs compared to six on the typical caterpillar. The spring cankerworm has two pairs of prolegs and a single stripe alone the side while the fall cankerworm has three paris of legs and three stripes. The color of both species is variable.

Cankerworms are present every year, usually the damage goes unnoticed and healthy trees are not harmed by light feeding. However, damaging outbreaks occasionally occur and can continue for two to three seasons. Feeding begins in early spring as leaves start to expand and continues for three to four weeks. These caterpillars eat elm, apple, oak, and many fruit and shade trees, consuming entire leaves and leaving only the large veins. The greatest feeding occurs about the time the leaves become fully developed. Trees may be completely stripped of leaves during outbreak years and may be stressed or weakened as they use reserves to refoliate. Full grown cankerworks either crawl or drop to the ground on silken threads and pupate in the soil. There is one generation each year.

Generally, is is not practical to control cankerworms in forests and woodlots but homeowners may choose to protect landscape trees from defloiation. If an outbreak can be anticipated, tanglefoot applied to tree trunks in a band two to four feet aboveground will prevent female moths from crawling up and laying eggs in the trees. This technique may be preferred to insecticide sprays, especially when dealing with very large trees. Insecticides labeled for caterpillar control on shade trees should be applied before most larvae are more than one inch long.

Fall cankerworm larva

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CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.


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