More crazy stuff on my trees this time

Ok so I don't know much about these thing but i've uploaded some photos of these weird pimples on the leaves of my trees and i was wondering if anyone knows what they are and how to get rid of them cuase they're slowly killing my trees.


thank you in advance,
the plant rookie

 

The tree is a Hackberry Celtis occidentalis. The lumps are galls, caused by insects or gall-mites; generally they don't cause significant damage. Best option is to sweep up all the leaves as soon as they fall in autumn, and dispose of them well away from the tree - that should break the life-cycle of the insect/gall-mite, make them unable to start a new generation next year. You probably won't be able to stop them completely, but you should be able to reduce the numbers enough to make the problem insignificant.

 

thank you very much for your help! do you by chance know what i can do to get rid of japanese beetle?