I saw a post from a year ago about aspen bugs, with a picture of the same issue my aspen's have… clumps of leaves being stuck together with some white powdery looking stuff in the middle. There was not an identifying response that I saw so I'm wondering if there might be a answer now. Can you tell me what they might be and how to treat them?
I believe this is Wooly Aphid (compare photo below).
They can be removed by a strong stream of water. I have included two websites for further information.
Aphids on Shade Trees and Ornamentals no. 5.511