Biology and control of cankerworms in North Dakota

E-999; Cankerworms are important defoliators of shade and ornamental trees in North Dakota. Several tree species are affected by cankerworm infestations but elm, hackberry and apple are most vulnerable. To a lesser extent, defoliation may also occur on basswood, oak, boxelder, maple and ash. While defoliation in a single season may not damage a large, mature, vigorous tree, defoliation over several consecutive seasons weakens trees and makes them more susceptible to drought, herbicide drift and other insect pests. If defoliation by canker? worms or other insects occurs several years in a row, these combined stresses may kill the tree directly or increase its susceptibility to disease