Sometimes the edges of the spots may appear irregular or feathery. To manage aspen leaf spot, rake fallen leaves in the autumn to prevent the spread of the fungus in the spring. Aspen leaf spot is usually not severe enough to warrant the use of fungicide, but if the symptoms occur year after year, apply a product such as Daconil 2787 in the spring when leaves are emerging from the bud. It's too late to apply fungicide once the symptoms are evident. Read and follow label directions carefully.
Aspens are very sensitive to many pesticides.
If applied incorrectly, pesticides can cause the leaves to turn black. Permission is hereby given to duplicate this Plant talk Colorado TM script as is if credit is given to the sources.