Cankerworms Abundant in Saskatoon 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 recover and produce new foliage.
Cankerworms, also known as loopers and inchworms, are found primarily on the leaves of elm, ash, and maple trees. The fall and spring cankerworm species often feed together during June and July. They can be found hanging from silken threads underneath infested trees and can be a nuisance.
Leafrollers feed while concealed within leaves that are rolled or tied together with silk webbing. Ash trees are their preference, but they also attack other tree species. The larvae will feed in mid- to late-June, but the leaves will remain rolled throughout the summer.
Tree banding can be used to deter cankerworms; however, it is not effective against leafrollers. 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. Unlike the adult female cankerworm, the female leafrollers have wings and will fly from tree to tree to lay their eggs.
The City does not control cankerworms, forest tent caterpillars, 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 information on Dutch elm disease, wildlife, tree defoliators, and urban pests such as mosquitoes, please visit www.saskatoon.ca/pests.