Description:
Adult moths are drab gray, delicate with green markings.
Males have a wingspread of about 1 inch while the females are wingless.
Cankerworms, like other members of this family, often are called "inchworms"
because of the way they crawl. They arch their back into a loop, anchor the hind
legs and extend the front to move ahead. The spring cankerworm has two pairs of prolegs
on the abdomen, while the fall cankerworm has three pairs of abdominal prolegs.
Larvae grow to 1 inch, are variable in color and marked predominantly with green,
brown and pale yellow longitudinal stripes.
There are many other species of inchworms many of these are cryptically colored.
Inchworms may sometimes be confused with loopers which are in the family Noctuidae.
Most adult Geometridae have winged females. Wings may be rounded or highly irregular
is shape, and dull to brightly colored. Moths in this family often hold their wings
together over the back like a butterfly at rest.
Life Cycle:
Females can only migrate by walking because they are wingless.
Females crawl up the tree trunks and onto branches to lay eggs in
clusters of about 100 in bark crevices or on the limbs.
The eggs of spring cankerworms hatch in a few weeks while the eggs of
the fall cankerworm remain from November until March or April.
Both species hatch from eggs in the spring when trees are just
reaching budbreak and new foliage is expanding. Larvae feed on leaves
for about 3 to 4 weeks before they drop to the ground on silken
thread and pupate in the soil. Caterpillars may be blown in the wind
to new locations when suspended on silken threads. Cankerworms
remain in the soil as pupae until the adults emerge in the spring or
fall depending on the species.
Pest Status:
Can be major defoliators of broad leaf trees with widespread outbreaks
occurring in some years; defoliated trees typically survive and leaf out again;
caterpillars can be a nuisance when abundant.
Control:
Control is suggested for valuable trees such as new transplants,
specimen trees in a home landscape or fruit and nut bearing trees.
If a tree has low vigor or has had a previous history of defoliation or
other problems such as drought or disease, it is more likely to be damaged
by cankerworm defoliation and should be treated.
However, cankerworm control is not always justified.
Large, healthy trees can withstand total defoliation without significant damage.
Trees that are defoliated early in the year will leaf out again and show no signs
of the damage. Inspect trees in the spring. Both larvae and damage should be present
before control is justified.
Since female moths must crawl from the ground up into the tree,
placing a band of sticky material, such as tanglefoot, around the base of the tree 3 or 4
feet from the soil can trap most cankerworms.
However, this method is not reliable for total control since emergence and egg laying
may be prolonged. Also, tree bands would be needed in both fall and spring to control
cankerworms effectively, and small larvae can migrate easily from tree to tree by dropping
on a silken thread and blowing in the wind.
The surest cankerworm control measure is an insecticide timed to kill early larvae.
Spraying is not recommended once caterpillars are near their full size. At that time both the
caterpillar damage and nuisance are nearly over and sprays are not beneficial.
