Ahh...

First of all, it would help a lot to know where you live and type of soil. I may figure it out just like that. Sometimes, I see wrong red oak for the type of soil. It is common but I know how to look for the right one now. All I have to do during the winter is look at the terminal buds. They should be at least 1/4". Usually the ones with 1/8" buds do very poorly in alkaline soil.

Another question is - Did you use weed and feed fertilizer? It's a big no-no for the lawn with trees and shrubs.

Lastly, Did you make sure not to plant it too deep? The root flares should be barely exposed. The hole should have been shallow and wide like 5-7 feet of loose soil for roots to spread out rapidly and be covered with mulch for at least several years.

Thanks for the response. We live in the Fort Worth area and have sandy loam soil. We try to stay organic, so our grass is not feed with weed killer.
We did not plant the tree ourselves. It was newly planted when we bought the house.
My first fear is oak wilt, which I know means I have to bring the tree down. Before we do something that harsh, I'd like to be sure there couldn't be another cause for the wilting leaves.

Sounds like it may be planted too deep (happens a lot by builders or the people hired by builder). Can you see where the root flares are? Consider yourself lucky for having such wonderful soil! Sadly, you may have to start over with a new tree. Can you take pictures and post them on here (use photobucket website to load pictures on here). It could be plainly wrong red oak. http://www.cityofirving.org/inspections/red-oak.html

I agree with Lou. If that tree comes out of the ground like a telephone pole, it likly is planted too deeply. Start removing soil to expose the root flare. If it involves removing 5"or 6" of soil you may need to start over. Very rare for very young trees to be bothered with oak wilt.