My aspens have a sticky, clear residue on the leaves, what’s wrong?

Answer 1

Daga,

It is most likely that you have "honeydew" which is excess sugar secreted by sap eating insects such as aphids, whiteflies, scales, etc. Have you noticed any of the leaves turning black or dark (dirty looking), as well? Perhaps it's too cold in your area at this time of year, but many times a sooty mold (as just described) develops on the honeydew. Control the insects causing the honeydew for a longer-term solution to your problem, and meanwhile, rain and/or water sprayed from a garden hose will wash most or all the honeydew from your Aspen leaves.

Answer 2

You may have tent catepellars, or just a bacteria. have an arborist help you out.