Linda, welcome to the Stew! Please, clarify your post. Is your crepe myrtle doing fine, or are the leaves brown now? I often need things explained to me!
Give us a little more information about it. How long ago did you plant it, where (not address just USDA zone or state) how often do you water it, have you fertilized it? Crepe Myrtles will live on what Mother Nature gives them after they have been in the ground for a year. Don't need fertilizer either. They do need full sun and hot weather...are they getting that where you are?