DNR Northern Region - RHINELANDER - Landowners and forest managers across northern Wisconsin are noticing a browning of aspen and alder leaves this summer. The trees are not dying, say Department of Natural Resource ... More... RHINELANDER - Landowners and forest managers across northern Wisconsin are noticing a browning of aspen and alder leaves this summer. The trees are not dying, say Department of Natural Resource foresters, they are under attack by two insects. “On the aspen we have a caterpillar called the aspen blotchminer,” said Brian Schwingle, DNR Forestry Entomologist, “and our alder are being attacked by the alder flea beetle.” He added that regardless of the unsightly browning of the leaves caused by the insects, the trees will survive. The blotchminer infestation is from the St. Croix River on the Minnesota border to Oneida County, primarily north of U.S. Highway 8 including Lincoln County. This tiny caterpillar’s damage was noticeable in northern Wisconsin last year, Schwingle said. The first sign of infestation is small pale green blotches on aspen leaves. The forester explained that as the caterpillar feeding continues between the upper and lower leaf surfaces, the blotches enlarge, merge and fade to brown. The ultimate appearance of aspen trees suffering heavy damage involves a two-toned crown, that is, green on top and brown below. “Because the feeding is heaviest along stand edges and in the bottom half to two-thirds of the crown,” Schwingle said, “the trees rarely suffer any significant damage, and controlling the insect is not necessary.” Pockets of severe defoliation of tag alder are scattered from Washburn County to Langlade County. The flea beetle eats the insides of the leaves between the upper and lower surfaces. The insects black larvae and the cobalt blue adults feed on alder leaves causing them to turn brown and curl up. This infestation will only last 2 – 3 years.