As I was looking at my cherry tree today, I saw this odd growth on the leaves. There are dark brown/black bumps on the leaves, and they are slimy. On the badly decayed leaves, there is a stringy cobweb-like growth.

What is this and what should I do about it? Is there a spray or other treatment I can apply to the tree to get rid of it?
Thanks

Looks like aphids. I'd spray them with a basic insecticide but someone else might have a better solution.

My vote is aphids also. Try insecticidal soap.

Thanks for the replies, I took a closer look and realize that they are aphids. I'll probably spray with insecticides as you recommend.

The bad news is that most of the aphids are hiding out in those bundles of leaves. The good news is that summer heat kills them. The bad news is that they will be back next year. The good news is that there is a systemic insecticide that you can pour on the ground before the tree leafs out. The bad news is that your aphids are on your cherry tree and you can't use a systemic without killing you too.

Spray with insecticidal soap - make sure you drench every surface. You may want to find some concentrated insecticidal soap because those little spray bottles are not going to go far enough.