Property, Gardens & Trees

Fall Cankerworm

They emerge as adults in October. Adult females are wingless, grayish brown, and about 12 mm long, while the grayish brown, adult male moths have wings with a span of about 30 mm. The adult females climb host trees and shrubs, and mate; each female then lays about 100 eggs on the upper twigs and branches.

Health Effects

These caterpillars can cause significant damage to trees, often causing complete defoliation of a tree. However, a mature, strong tree can survive one to two seasons of complete defoliation. That said, more than three years of defoliation from cankerworm feeding can potentially kill branches.

What homeowners can do to control Cankerworms

Tree banding is an effective method of controlling cankerworms. Adult female cankerworm moths are wingless and need to crawl up the trunks of trees to lay their eggs. Tree bands trap the adult moths as they are crawling up the tree, which usually begins mid-September.  Banding a tree takes just three steps:

  1. Wrap a 10-15 cm (4-6 inch) wide strip of fibreglass insulation around the trunk approximately 1.5 m (5 ft) off the ground.
  2. Cover the insulation with cling wrap. Be sure to wrap it tightly so that the insulation is pushed into the crevices of the bark and to leave a bit of plastic above and below the insulation. This may take two or three layers of cling wrap.
  3. Spread a layer of petroleum jelly or a similar sticky substance on the plastic in a band about 10 cm (4 inches) wide.

Inspect the band regularly and remove any large debris such as leaves. Reapply the sticky material as required. Be sure to remove all tree bands by mid-December. Leaving tree bands on over the summer can cause mold and rot to develop, causing more harm to the tree than the cankerworms.

Fall Cankerwork up close

Fall Cankerworm on Tree