By Linda Williams, DNR Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov or 920-360-0665
It seems to be a good year for insects, and several leaf beetles and leaf rollers have caused localized defoliation already this summer.
One of these defoliators is the imported willow leaf beetle larvae, which may feed in groups. The dark, shiny adult beetles can also feed on the leaves, but the larvae seem to do more concentrated damage.
Similar beetle larvae were observed feeding as a group on aspen leaves, which could be the same leaf beetle since imported willow leaf beetles can feed on both willow and aspen. Or it could be one of the other leaf beetles that feed on aspen, like the American aspen leaf beetle. Both species have dark-colored larvae that feed in groups.
Leafrollers and leaf tiers also seem to be common this year. While oak leafrollers and oak leaf tiers are causing significant defoliation in several areas of the state, other leaf rollers have also been observed. These caterpillars use silk to tie leaves in a way that creates a tube or a folded shelter that the caterpillars can then safely feed within. Many rolled leaves can make a tree look very thin, but generally, the damage has been less than 20% rolled leaves so far this year.
The maple leafroller is causing light defoliation in maples in north-central Wisconsin. Several caterpillars, including two leaf-tying species, are defoliating black locust in Oneida and Marinette counties. Additionally, large aspen tortrix and woolly aphids have been rolling aspen tree leaves.
No management action is needed at this time.