It’s Raining Worms!
Severe
infestations of these pests can make it seem like worms are dropping
from above! My first recollection of these insects was during a picnic
in Lock Port when we had to sit far away from the elm trees to avoid
these landing in our potato salad.
These pesky larvae are the
rapidly growing off spring of two different insects. Spring Canker Worm,
Paleacrita vernata and Alsophila pometaria , the Fall Canker Worm.
Between the two they can defoliate your trees faster than a late frost.
These indiscriminate feeders will dine on, apple, ash, beech, birch, box elder, elm, hickory, lindens, other maples and oaks.
The
adult males of these insects are nondescript grey moths; the females
are similar but are wingless and crawl up host trees to lay eggs. The
larvae are 20 to 30 mm long, (1 inch) and can be green to reddish brown
or black with several stripes along their bodies. Larvae inch along in a
looping manner and are sometimes called inch worms because of this.
There tube shaped bodies have small bumps or pro legs on the front lower side tat aid in identification.
The Fall Canker Worm has three sets of these pro legs and the Spring
Canker Worm two.
Damage occurs when the voraciously feeding larvae
devour leaves, skeletonizing the leaves leaving only the veins and mid
rib of the leaves. Several years of heavy infestation can lead to
mortality in affected trees.
Adults emerge in the fall in the case
of Fall Canker Worms and spring for the Spring Canker Worm. The Fall
Canker Worm mates, lay eggs and dies shortly afterwards leaving their
eggs to overwinter on the tree. Spring Canker Worms overwinter as pupae
in the soil and emerge in spring as adults.
The wingless Spring
Canker Worm females crawl up the tree and lay their eggs in early
spring. Eggs from both types of insects hatch around the time of
American elm bud break. They work their way out to the new foliage and
begin feeding.
The wingless female is the key to success when it
comes to using controls like sticky bands around the bark of trees.
Paper bands backed with insulation covered with sticky tangle foot stops
the females as they migrate up the tree to lay eggs. These should be
removed from time to time to prevent damage to the bark. When using them
take care that the females have not formed a bridge allowing others to
avoid being stuck in the sticky trap. Bacteria based sprays that work
well on Canker Worms are available and can be effective if applied while
the larvae are actively feeding. Chemical controls are also available
check label directions for timing and application recommendations.
If
you have questions Certified Arborists are industry recognized experts
in plant insect and diseases control. Contact your I.S.A. Certified
Arborist to see if you have this damaging plant pest.