I live in Houston and have a small Arizona Ash tree (about 12 ft tall and the trunk diameter is about 3" and just noticed it has some very small, dark brown ants coming out of some of the imperfections in the bark.

I notice them at the very base of the tree near the ground and even coming out of the holes about 6' up. I feel like my tree hasn't been growing much since I planted it about 3 years ago.

Could the ants be stunting the growth, and if so how do I get rid of them with no apparent ant bed to poison?

If they are killing it, they are doing you a favor.

just kidding, is the Arizona ash the "good ash"

I don't have anything useful to add, I just though I would share my distaste for the ash trees at my parents house.

Howard Garret (aka The Dirt Doctor) in his book has this to say about the Arizona Ash: DO NOT PLANT. Lots of problems with infestation and is short lived.

He loves the Texas Ash, said it should be used more. In fact, on his advise, we planted one in our backyard in an attempt to use 75% native Texas trees. He said it is native to parts of east Texas. I love it.