Are you sure it's a Texas ash and not an Arizona ash? I've seen that in a lot of Arizona ash trees in my neighborhood. My Texas ash has a dead limb every here and there, but never a whole section like that. If you can reach it, cut a piece off and see if it has verticillium wilt. Mine may have that. I need to cut an older limb to find out.

Marti8a, thanks. I had specifically asked for a Texas Ash when I had planted this tree. Perhaps they screwed up and gave me a wrong variety? How can one tell whether I have a Texas or Arizona ash? I will do the check you recommend.

Here's a website that tells some differences. I always look at the leaves. The Arizona ash trees around here have longer leaves. If you would like, I'll go pick some leaves from each tree and put them side by side for a photo.

Here's an A&M website Q&A that says something above Arizona ash losing leaves, and an A&M page on how to identify a Texas ash. The Dirt Doctor website also says that a Texas ash planted in an area with too much moisture is more susceptible to borers, so they aren't immune either.