Cankerworms Abundant in Saskatoon Again this Year

Cankerworms and leafrollers are an annual issue for Saskatoon’s urban forest. The trees may experience heavy defoliation but, unless there are underlying issues, The trees will put out new leaves and recover. 

Cankerworms, also known as loopers and inchworms, are found primarily on elm, but will also feed on other tree species. The fall and spring cankerworm species often feed together during June and July. The caterpillars can be found hanging from silken threads underneath infested trees and can be a nuisance. 

Leafrollers often feed while concealed within leaves that are rolled or tied together with silk webbing. Leafrollers can be found on a wide variety of trees. The leaves will often remain rolled throughout the summer but leafrolling does not affect a tree’s health. 

Tree banding can be used to deter cankerworms; however, it is not effective against leafrollers or other insects in the urban forest. The best time to place bands on trees is from September to May to help prevent the wingless adult female cankerworm moths from climbing host trees to lay their eggs. It is important to remove the bands at the beginning of June because the bands can collect moisture and cause the trunk to rot.  

The City does not control cankerworms, or leafrollers as they typically do not impact the health of the trees they attack. Homeowners interested in controlling them on their own trees should contact a horticulture professional for advice. For additional information on insects and tree diseases, please visit saskatoon.ca/treepests.