Hello, Thank you for contacting Ask Extension. In order to be able to give you a better assessment of the tree, I need a few more pictures from you. Could you send me a picture of the entire tree, with trunk and root flare at different positions around the tree? Also, a picture of one of the infected leaves? That would help me to better access what is going on.

Thank you for contacting Ask Extension. Thank you for sending the additional pictures because it helped in determining what is going on with your Oak tree. There are multiple problems occurring with your tree.

First off, it would be beneficial if you removed 3-4 feet of sod out away from the tree, all around, and mulch with 3-4 inches of mulch. Do not pile the mulch up around the tree, but leave about 2-3 inches from the trunk open. The grass may be taking up water before it can get to the trees’ roots. This is causing leaf scorch, which is why some of the leaves are turning prematurely brown. You need to make sure that the tree is getting at a minimum of 1 inch of water/week if it does not rain. It is a young tree and does not have the root system that an older tree might have.

Second, the irregular brown spots on the leaves are some sort of fungal issue. To determine exactly what fungus is attacking it, you can send a leaf sample to the MSU Plant Diagnostic Lab. Plant & Pest Diagnostics (msu.edu) I would also do a soil test to determine the pH of the soil in the area, because of the chlorotic appearance of the leaves, which are yellow due to a lack of chlorophyll.

Third, there is a lot of lichen on the bark which could indicate a very slow growing tree. Lichen is the white and greenish growth on the trunk of the tree. An arborist on site could check to see how much growth the branches have each year. If it is under what it should be that maybe the result of all the other factors impacting the tree. www.treesaregood.com is where you can find a local arborist.

I am including several publications for your reference:

https://extension.wvu.edu/lawn-gardening-pests/plant-disease/landscape-tree-disease/leaf-scorch

https://extension.umd.edu/resource/lichen-algae-and-moss-trees/https://www.canr.msu.edu/news/mulch_just_do_it

Also, here is a link if you would want to do a soil test and check your pH. Home | MSU Soil Test

You are more than welcome! Good luck on your tree!