Howdy folks,
In regards to this message:
I asked this same question last winter, and was told to wait until July or
August because that is when the things that cause wilt are not active.

I just trimmed mine a week ago. I don't know what is right because of
totally conflicting information on here.

Bob
As Victoria, pointed out checking with Texas A&M is always a good
idea.
Here is a page regarding pruning and Oak Wilt at:

http://dallas.tamu.edu/oakwilt/

It states in greater detail what has been said already, but it is well
worth reading. The activity of the bug that is one of the vectors for
infestation is year round, but is at it's greatest level of activity
in spring and early summer, which sounds like most bugs I'm on a first
name basis with.
I always tell people, no matter what you hear from anyone, no matter
how authoritative they sound, always double check info, I have found
the usenet groups very helpful not just in terms of the questions and
ideas raised but by pointing me to other sources of info like the TAMU
sites etc.

Take care,
Steve Coyle
www.austingardencenter.com