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.
