Your purple ash has Ash Flower Gall Mite, more of a cosmetic problem than a pest that you would need to treat.  The mites distort the male flower on ash trees, producing a highly disfigured gall.  In the fall they will dry and turn brown.  There is no evidence that the injury significantly damages the health of the tree.

It's hard to treat a large tree, but in the spring you could apply Sevin, as indicated in this fact sheet:

https://hort.extension.wisc.edu/articles/ash-flower-gall/#:~:text=An%20application%20of%20carbaryl%20(Sevin,reduce%20the%20number%20of%20galls.