hard to give any advice w/o a pic...

and i am leery of relying on a self-admitted NEWBIES diagnosis ....

i would presume gall.. and ignore until the leaves fall off.. and then the problem goes away ... there is NOTHING to do when dealing with gall ....

BTW... i would NEVER spray a stressed tree.. for any reason... why double its stress???

pic please.. or compare at link ..

i wish you all the luck in the world.. keep it properly watered.... and review the copy/paste link below .. and lets discuss.. what you did.. if anything.. that is contrary to proper planting ... perhaps we will replant it in fall ....

ken

ps; i would not have bought a tree with such... unless it was some sublime variegated.. only one in the country plant .... newbie lesson #1 ... buy clean stock ... dont you think ... and if your nursery cant provide such.. find a better nursery .... and that was lesson #2 ... lol ..

planting guide: https://sites.google.com/site/tnarboretum/Home/planting-a-tree-or-shrub

Here is a link that might be useful: link

Generally speaking, oak leaf galls and spots are nothing at all to worry about. The effect on the tree's health is generally negligible.

Galls are a nearly inevitable part of being an oak tree. In the US, there are more than 2,000 species of gall-forming insects, and about 60% of them specialize on trees in the oak family. Twig galls can sometimes be problematic, but leaf galls are just an aesthetic issue unless it's a really extreme case.

My Pin oak has several of them already, I thought at first they were acorns, as they are brown, but they are always on my 2 pin oaks, so same ole, same ole. I haven't tried the Sessile oak, and don't know much about them, I have 3 Q. Robur, all 3 are different from each other in growth form and speed. All 3 are from one tree in England. I got acorns on ebay from England. One is upright fast growth, but not columnar, one fat and short, the other kinda short, but the branches go outward and curve upward, kinda spookily. I love all of them, though.

I looked at my Q. Robur today and one of them has what the OP described. The other 2 don't. I'm sure it's just superficial. The one affected is in a low area, the others are uphill.