Fuzzy seed like
Thanks for your question. What you have appears to be a type of oak fuzzy galls. These are caused by small insects, typically gall wasps. It is the leafs response to the larvae from the tiny gall wasp feeding on the leaves. The particular species will have to be determined by close examination of the gall.
In general, the galls are not harmful to the trees and there is really no insecticide that is effective since the wasps are tiny and not easily seen, plus the larvae are well-protected from pesticides within the galls. Additionally, insecticides applied are very likely to be harmful to beneficial insects. As the leaves are developing the tree forms a covering over the eggs to protect the leaf tissue, so the leaf galls do not interfere with the ability of the tree to photosynthesize.
There is also a link attached discussion of foliar spray of potassium and fertilizers in general. This is not a treatment for the galls but possibly providing nutrients to the tree through their leaves during a serious gall infestation. Depending on the size of your tree this may not be practical.
I have listed links which may better explain galls for you. Also you may want to cant your County OSU Extension with several of the fuzzy galls for their examination if possible as their hours may be effected by the present pandemic situation.
Thank you again for allowing us to help you with your gardening questions. Here are some other helpful websites:
Lorain County OSU Extension Office
42110 Russia Road
Elyria, OH 44035