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Answer from Zach Schumm, Utah Plant Pest Diagnostic Lab, Arthropod Diagnostician (received 7/1/20) -

The "fuzzy" critters are a type of woolly aphid (not sure of the species, but they all behave similarly), which can cause the leaves to curl. The fuzziness that these insects have are due to waxy secretions that they use to protect themselves, among other things.

The good news is that large (i.e., not saplings) healthy trees don't typically suffer at the hands of these aphids. If you're seeing the whole tree beginning to look like this, then you may want to think about some sort of management, but right now I don't think it's necessary if it's only on certain parts of the tree.

The other reason I am hesitant to control these insects with some sort of insecticide / chemical is because the other image you submitted with little "balls" on the end of web-like stalks are lacewing larva eggs. These larvae are voracious predators of soft bodied insects, and they absolutely love to eat aphids. If you spray to control the aphids, you can also kill the lacewings that are beneficial and offering natural control of the aphids that will (probably) prevent them from damaging more areas of the tree. These eggs are actually super interesting. They are laid on the stalks so that predatory insects (such as ants) have a hard time reaching them and eating them. So, you'll want to keep the lacewing eggs around.

You can just remove the aphid-infested leaves with pruners if you wish (I know the curled areas are unsightly). Unless most of the tree is heavily infested, I don't think there is a ton to worry about right now, especially with knowing that predatory insects are in the area!

Here are some links to some information pages and fact sheets on these insects:

• Woolly aphids (ash example)
• Woolly apple aphid (a specific species that can be a pest on ash)
• Fact sheet on lacewings/antlions

Let me know if you have any further questions! 

Best