In aspen, a single heavy defoliation can reduce growth by 50-60 percent in that year. Two years of heavy defoliation reduces growth by up to 90 percent. However, within a year after an outbreak, growth generally recovers to normal levels. Certain risk factors can increase the likelihood of trees dying. Tree age, tree species, site quality and weather can all interact to increase or decrease tree mortality.
Older trees are more likely to die than younger ones.
Oaks and paper birch appear to be more at risk than aspen or sugar maple. Trees growing under less than ideal conditions are more prone to die. As an example, surveys in Minnesota found more dead aspen trees on wet sites following an FTC outbreak. Drought conditions would also make tree mortality more likely. Applied Control Small landscape trees and shrubs can be protected by hand removal of egg masses or caterpillars.