Early leaf disease causes aspen trees in Northeast Wisconsin to look thin, with small, off-color leaves. / Photo Credit: Linda Williams, Wisconsin DNR

By Linda Williams, Forest Health Specialist, Woodruff;
Linda.Williams@wisconsin.gov or 920-360-0665

Did you notice the many aspen trees in the Northwoods starting to drop their leaves in early September? These leaves were yellow with brown blotches or were brown and curled, and there were a lot of them falling.

Earlier in the growing season, you may have noticed that some trees had very thin crowns. These thin-crowned trees are the same ones that have been dropping leaves prematurely.

What is the culprit? Leaf disease.

Early in the season, many aspen trees had very thin crowns and, from a distance, appeared to be defoliated. Upon closer examination, however, there was very little insect damage on the leaves. Instead, examinations showed they had been infected by fungal disease. Those trees had leaves that were small and off-color, and many leaves were mottled in color and slightly wrinkled. They remained that way throughout the growing season.

Early in the growing season, leaves of a diseased aspen tree look small, mottled and slightly wrinkled. / Photo Credit: Linda Williams, Wisconsin DNR

Samples sent to the Wisconsin Department of Natural Resources Forest Health Laboratory early in the growing season found Marssonina leaf blight. Additional samples may yield additional fungal leaf disease pathogens.

Minnesota reported similar issues this year in their August issue of the Forest Insect and Disease Newsletter.

Aspen leaves that were infected early in the season dropped prematurely in September, with blotches showing on the leaves. / Photo Credit: Linda Williams, Wisconsin DNR

No control is necessary in forested areas. Fungicides are available for yard trees if desired. If the weather next spring is a little bit drier, the leaf diseases should not be as bad as what was seen this year.