Question
We live in North Texas and have several white oaks in our yard.  One of the trees is dropping leaves.  It did this last Spring also.  In the fall I fertilized it. This Spring it budded out and looked great with abundant leaves.  However, after a month now the leaves are dropping again.
You can easily pull the leaves off the branches. The leaves are green, but upon close examination, the stems where the leaf was connected to the branch are a brownish/black.  Some still have a tiny bit of green.
If I pull leaves off the other trees, they are hard to remove and the stem area that connected the leaf to the branch is green.
I don't think this is Oak Wilt, because the leaves are green and we have not observed any beetles on the tree.
What do you think is causing this and can we do anything to save the tree??  Please help.  Thanks  

Answer
From the description I can not tell what the problem would be. I would suggest that you call the local office of the Texas Forest Service and ask one of their Foresters to take a look. Texas Forest service has an excellent Pest Management  section and they should be able to ID the problem after looking at it. Here is the contact web page for the Pest Management staff. Ron Billings, Don Grosman or Joe Pace should be able to help you. All are friends and you can tell them I sent you.

http://txforestservice.tamu.edu/main/article.aspx?id=1170

Here is the contact page for the county Foresters. http://txforestservice.tamu.edu/main/article.aspx?ctrl=14