Could be iron chlorosis. How large is the tree, and do all the leaves look like this?

The first things I think of when I hear of brown leaves on an oak tree in the summer are drought or Oak Wilt.

Chlorosis would be easy to test for. It is usually caused by alkaline soil. Get one of those soil PH tests.

It’s a pretty big tree. Most of the leaves have brown on them. Some more than others. I will get a ph test! If it is alkaline what do I need to do? So you don’t think it’s a disease or something killing the tree? That’s what I was worried about.

Pictures of the trunk and the entire tree would be helpful along with any other info you can provide. Has there been any construction or digging near the tree recently? We're seeing lots of weather-related tree problems this year in the midwest and the east. What has your weather been like this year?

I will post a pic tomorrow as it’s dark now. It’s been super hot for the past several weeks and we’ve had no rain. Our yard looks brown everywhere but this is the only tree doing this so it had me concerned.

As I said, someone proposed chlorosis. That one is easy to test for.

My first thoughts were drought or oak wilt (a disease/fungus).

Has there been new construction? What trees are doing well? (Maybe they are all super drought tolerant species?)

No new construction. We have several maples, a sweet gum, and some weeping cherry trees. There is another large tree near the oak but I’m not sure what kind it is. It’s doing ok too.

Very doubtful that it's iron chlorosis. The leaves would be much lighter yellow in color.

Here are some additional pics.

With grass and weeds that close to the tree, make sure the trunk and root flare are not being damaged by lawn mowers or trimmers. If that is not happening, my best guess would be that lack of water is to blame. I am not familiar with the effects of oak wilt, however.

I've come across a number of red oaks around here that look just like that. It's difficult to diagnose because the symptoms can be caused by a number of factors including drought, excess water/poor drainage, soil compaction, root damage, high salt levels in the soil, or bacterial leaf scorch. See oak leaf scorch . With the additional photos I'd agree that it's not likely to be iron chlorosis, though soil pH could be a contributing factor. It does not appear to be oak wilt.

So what should my next steps be? I’m having a tree removed in our front yard next week and I’m going to ask their opinion too. I’m not sure if they will know as they’re just a tree removal company.

Ideally, get an opinion from a certified arborist specializing in plant health care. In the meantime, since it's been dry at your location, be sure to irrigate the root zone.