| Cankerworms, also known as inchworms, are of two
types—the fall cankerworm or the spring
cankerworm depending upon when the females lay
their eggs. They attack apple and cherry fruit trees,
as well as many other ornamental and shade trees.
Symptoms and Diagnosis
Leaves have skeletonizing insect feeding damage.
Complete defoliation and crop loss may occur; or
after repeated damage, less and less fruit is
produced until little, if any, fruit matures. Damage is
first evident in the early spring or summer after trees
have fully leafed out. This is about the time that
larvae of both species emerge and begin to feed.
Life Cycle
Cankerworms are small worms, only getting up to
an inch long. Adult males are small, gray moths with
a wingspan reaching only 1 inch long. The females
of both species are wingless.
FALL CANKERWORM: The adult fall cankerworm,
Alsophila pometaria, emerges from the ground in
late November or early December. The wingless
adults climb up the trunk of the host tree and lay
eggs on twigs and branches. The eggs hatch and
larvae begin feeding about the same time leaves
begin to emerge. Larvae feed for about a month
before they fall to the ground to pupate. The worms
have brown backs with white stripes running
lengthwise down their backs. The fall cankerworm
has three sets of prolegs. This distinguishes it from
the spring cankerworm that has only two sets
of prolegs.
SPRING CANKERWORM: The adult spring
cankerworm, Paleacrita vernata, emerges in late
February or early March. The wingless adults climb
up the trunk of the tree and lay eggs in cracks in the
bark and underneath the bark and bud scales.
Yellow-striped green worms hatch at the same time
as fall cankerworm larvae and follow the same
general feeding pattern. They too drop to the ground
where the larvae overwinter in a protective cell.
Spring cankerworm larvae have only two pairs
of prolegs.
Integrated Pest Management Strategies
1. Sticky barriers may be banded around tree
trunks. Apply a band of a sticky material, such as
Tanglefoot, around the trunks of trees in October.
The sticky material will trap the wingless females
of the fall cankerworm moths as they crawl up
the tree trunk to lay eggs in late November or
early December. Renew the traps in February to
trap the emerging female adults of the spring
cankerworm that climb the trunk to lay eggs in
late February or early March.
2. Prevent larvae from emerging. In the spring apply
a horticultural oil spray on the tree before the
larvae hatch, about the time trees just begin to
leaf out in the spring.
3. Spray Bt (Bacillus thuringiensis) or Sevin after
leaves are fully expanded and flowering is
finished. Repeat this application two more times, at
14-day intervals. Sevin is very toxic to bees, hence
spraying should be delayed until after flowering to
limit damage to these beneficial insects. | 
