Oak tree dying one limb at a time from top down
The top limb from an otherwise healthy 20 ft. oak has died and the leaves turned brown. I cut the limb off in early spring. Now I see it has another dead branch near the top. What would you think is causing this and is there something I can do to save this tree? I have a sprinkler system so it gets a regular watering.
Crown die back is a symptom of stress. But there's not enough information to identify the cause of that stress, so all I can offer is some general direction.
That looks like a small, young Red Oak, from your photo. Red Oaks are very prone to Oak Wilt, and limbs should never be cut during the time the disease is traveling -- spring and fall. So please be very careful not to prune during that time. The good news is the bare branch is not from Oak Wilt, which can kill the entire tree in a matter of weeks.
Now, onto more likely causes of stress in Oak trees - you say you have a sprinkler system, but is the water reaching the deep roots of that oak? The amount of water that can keep a lawn alive may not reach deep enough for trees. Texas had extreme drought in 2011-2012 that stressed trees severely, but it takes years for that stress to show up on trees. Also that stress may have just weakened the tree and allowed some other pest to move in.
Here is an article on the effect of that drought on Oaks and the further problems to watch for: http://texasforestservice.tamu.edu/main/article.aspx?id=16442
In addition to drought stress problems, there are a variety of illnesses that can stress your tree. So here is another article on the diseases and problems of Oaks, and their control:
I hope you can use that information to better narrow down what is ailing your tree. If you have more information or additional symptoms, that would be helpful in finding a specific cause.