Mountain ash are very prone to borers that kill the tree in this fashion. Barring some chemical interference like lawn fertilizers or weed killers, I would suspect that the tree may have a borer. Check around the base of the tree for holes in the 1/4 inch range in size. This will tell you what has happened.

The other problem with this tree is a rather large vertical crack starting from the ground and going right up. It's a frost crack - has been there for at least 2 years that I've noticed. From what I read, frost cracks on ash trees don't necessarily kill a tree but do give bugs an opportunity to crawl in there. After Rick's suggestion that it might be another borer, which I hadn't considered, I read about the Redheaded Ash Borer and the Banded Ash Clearwing Borer, native pests that attack ash trees. I'm quite certain there's something buggish in that tree, based on the woodpecker activity which is almost constant. I'm also thinking this tree is a goner - perhaps not from EAB but something else, slowly but surely. I'll still check it closely - I got some plants from southern Ontario a couple of years - is it possible for EAB to have travelled that way? Those plants are now planted right near that ash tree but that's got to be a stretch, no? Having to remove the tree will affect some plants that now benefit from the midday shade it provides (but they can be easily moved). Having to remove it will mean less ash seeds. Having to remove it give me the opportunity to plant something new there, and that's okay with me.

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.

toronado, let me be clear. After 12 years, no more FULL DOSE treatment will be required. And your State Agricultural department should advise citizens when that time has come locally. Since in some area's it might be 10, and others 14 years. After that point, sporadic low dose treatments will continue to be required, to make sure local populations of EAB are truly wiped out. But also know, presently this is only theory about how long low dose applications will still be required. Now if one planted new ash tree or no longer treated theirs after that 12 year stage, scientifically there will no longer be enough of an EAB population to critically damage unprotected trees. And healthy Ash can easily repair any damage caused by low populations of borers. But if EAB does have just enough untreated or no longer treated trees locally, it could take a decade or more for EAB populations to possibly reach "Infestation" levels again. By utilizing limited food supply, compared to beginning of event when borers have almost endless supply of unprotected trees to "Exponentially" build numbers with. To "Responsibly" prevent this, all local ash tree owners would need to low dose their Ash once, every four or five years for at least one decade. Since any remaining EAB locally would have no choice but to feed on remaining treated trees, which has proven to kill them off. With a list of all remaining Ash tree locations, a local municipality could assure local EAB populations are kept in check by coordinating this process. Even inexpensively contracting to have all remaining public and private trees retreated during same year, twice a decade. Remember, EAB is causing "Functional extinction" of its only remaining live food source. Plus we have better EAB detection traps now, which could keep an eye on local populations. Even if someone was to bring EAB back to your town. So far borers kill off all wild sapling Ash trees before they reach species seeding age. Which is 10 for Green, and age 20 for White Ash. And those few wild Ash found surviving EAB attack, cannot be utilized by borers to survive on. Also any "Lingering" ash that do survive borer attack while every tree around them dies off. Inevitably succumb to borers as well. And by collecting enough wild locally evolved seeds before forests completely succumbs to EAB, there is good possibility that someday in future. Conservationists can use seeds to bring back 4 or more wild Ash species. Or even possibility that nurseries can once again begin selling Ash trees that are not crossbred for resistance against borers. For example, we can again plant Elms because they have been cultivated for resistance against Dutch Elm Disease. But fact is, cultivars will never grow up to look like unique locally evolved organisms enjoyed before DED arrived to America. And scientists cannot utilize cultivars to repopulate wild forests. Plus for native Elm, they will need to be continually retreated for rest of their lives. Since DED fungus will always exist locally, by utilizing continuous supply of new trees, which are only threatened after age 25-45. For Elm, their is always hope that mother nature will evolve a cure someday against DED naturally. But Roman Empire began loosing Elms to DED way back in year 300, and European wild Elms have yet to evolve a resistance. We now know that EAB arrived to America way back in early 1990's, and it took them time to build to tree killing populations. The first person that began successfully treating trees against EAB, was Wayne White back in 2001. One year before Asian borers were even officially identified. Since he could see that a type of "Phloem/ bark borer were cause of tree damage, he realized we already had successful Systemic product for Bronze Birch borers. As a Michigan Arborist who had been continually retreating trees for 12 years, he was one of first able to determine that Full dose treatment was no longer needed. And that it was now possible for tree owners to treat the trees themselves by applying sporadic low dose applications. Also, the whole idea of importing and locally releasing Asian bugs known to feed on EAB. Was to keep borer populations in check or to eradicate what remained, only after peak event. Plus we now know there are several native bugs that kill EAB, like Smoky banded wasp. Along with Woodpeckers. So all I can say presently toronado, is stay tuned. Once borers wipe out every Ash tree in America from Canada down to Panama, it will be more difficult to reintroduce EAB locally by transporting infested firewood. (Fresno is Ash in Spanish)