I've had multiple post oaks die over the last several years. Every one of them looked healthy and then small pieces of bark started falling off followed by more and more bark until large areas of bark were missing. These are large mature trees some that are 30-35 ft tall.

The area was a very dense area of almost entirely post oaks and shrub/briars. Most of the ground in the area was covered with many years of dead leaves. 7-8 yrs ago we cleared out some of the trees and cleared a house lot. The house was built 3 yrs ago. I noticed the trees starting to die before construction started.

What is going on?

Post oaks do not like their roots smashed, such as clearing a lot or natural shrubbery removed from around them.

Three years is the magic number you need to clear, as they will typically die within three years from the shock if they are going to. Doesn't mean they won't die after three years, just less of a chance.

Most likely that is what it is, however there some type of bore beetle that can be infected from a disease from one tree and bore into another and spread the disease. You could pay a tree guy to come out, but he will most likely confirm they died from the shock of root smash and natural vegetation being removed.

The drought has had a lot to with these trees dying. I live North of Fort Worth and have lost about 8 trees in the last 3 years along with other people in my neighborhood. I have had several lose the bark like you are talking about and I do believe that it is some type of boring insect. I have kept these watered good and so far still alive. Have 40 plus trees on little over an acre so have just cut them up for the fireplace. Probably needed thinning anyway.

I've had around 75-100 , 15-18 inch dia. Post oaks die the past two years due to the drought.

Wife and I bought a house last May in Bryan, had to immediately drop 4 mature post oaks, then had to drop another 3 later in the fall. Tree guy said it was the previous droughts over the past few summers that tore em up, followed by the wet summer of 2014. As stated before, he said post oaks have a pretty sensitive root structure, and the shock of the drought, followed by the shock of basically being flooded did em' in.

I don't mean to dispute the word of others here, but it's likely other factors than just drought contributed to these losses. They were already in a weakened/diseased state. Much like how people die every year from colds and flu, but their immune system had been previously compromised.

A lot of mesquite trees died during the drought of the ' 50's that my dad swore was actually the result of a bad freeze one winter. But there's no doubt the drought contributed by making them weaker and more susceptible.

Same here, had a arborist come out and look.
He said Oak Wilt. All trees apparently have it, but healthy trees are able to fight it off.
Trees weakened by drought cannot fight it off. Nothing you can really do but do a rain dance.
The past two years of better rainfall should reverse the trend as the trees regain health and strength.
I'm still losing trees but at a vastly reduced rate.

Post oaks are Extremely sensitive to changes in the soil around them. If you remove or add topsoil over the roots, you will likely kill them. The drought hasn't helped much, either. We lost quite a few to oak tree decline years ago, also.

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Post oaks are Extremely sensitive to changes in the soil around them. If you remove or add topsoil over the roots, you will likely kill them. The drought hasn't helped much, either. We lost quite a few to oak tree decline years ago, also.

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Well crap, I was probably going to add some top soil to promote grass growth.

2-3" shouldn't hurt a thing.

Strangely enough the trees around my lateral lines are flourishing.

OP - also, drainage and irrigation can wreak havoc on post-oaks. Depending on your soil, the sub-soil water table, how much you water, and if the water drains away from the trees, you can quickly kill a PO from over watering, covering the root system with sod (followed by over-watering), or dropping sidewalks or other landscaping drainage barriers that create dams and cause water to back-up around the root system.

I've spent the money to gain an education on post oaks from a very good arborist. I learned a lot about their root systems, irrigation, soil drainage in order to keep mine healthy.

Good luck!

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OP - also, drainage and irrigation can wreak havoc on post-oaks. Depending on your soil, the sub-soil water table, how much you water, and if the water drains away from the trees, you can quickly kill a PO from over watering, covering the root system with sod (followed by over-watering), or dropping sidewalks or other landscaping drainage barriers that create dams and cause water to back-up around the root system.

I've spent the money to gain an education on post oaks from a very good arborist. I learned a lot about their root systems, irrigation, soil drainage in order to keep mine healthy.

Good luck!

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Luckily overwatering due to drainage is not an issue. I haven't put any sod out, choosing instead to leave the ground alone for the most part. Seeded rye and bermuda around my house to have a bit of a lawn. The trees closest to the house seem to be holding up great, probably due to watering the lawn. Just have to wait and see. There are easily 150 PO on my 5 acre lot. Hopefully I don't lose to many more.

I had heard to expect ~30% of the trees to die when I installed irrigation and sod 6 years ago.
That's when the drought hit.
I didn't lose 1 tree where I installed irrigation, only trees in unirrigated parts of the property.
The irrigation kept my trees alive around the house.
With more normal rain I don't think I watered around the house but 1-2 times all last year.

We have had Post Oak canker SE of Seguin.

Here is good info.

http://harris.agrilife.org/files/2011/05/oakdisease.pdf

It's a post oak. You likely sneezed or looked at it wrong.

Seriously, once you built your house, you killed them.

Don't get me wrong, Post Oaks need water, and in a draught providing appropriate irrigation provides them needed nutrients. I'm referring to folks that move in to a home, drop down St. Augustine sod around every single post-oak, and go to watering it every other day 45 minutes a station. If drainage is an issue (not sandy soil) or you've got subsoil water table issues that develop because of your new foundation, etc. the result is often overwatered trees and lots of dead PO's. Neighbors down the street were clueless about this and killed 5 mature trees in 3-4 months.

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Don't get me wrong, Post Oaks need water, and in a draught providing appropriate irrigation provides them needed nutrients. I'm referring to folks that move in to a home, drop down St. Augustine sod around every single post-oak, and go to watering it every other day 45 minutes a station. If drainage is an issue (not sandy soil) or you've got subsoil water table issues that develop because of your new foundation, etc. the result is often overwatered trees and lots of dead PO's. Neighbors down the street were clueless about this and killed 5 mature trees in 3-4 months.

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True. It was the drought that actually saved my trees around the house in the irrigation zones as odd as that sounds.

To OP. It is probably hypoxylon cancre. This I believe resides in these naturally. And stress makes it rear its head. The drought caused this on a bunch of my post oaks. Some pin oaks and even on some elms. Strips of bark at first. Then you see it all on the tree. Sometimes the spots will ooze. Sucks when most of the trees it hurts are old mature ones. I am starting to grow burr oaks as they can resist this problem much better than others. I guess I will find out.

I think the reason I've gotten in to tree identification and biology is that for 12 years my wife and I lived in our first house that had a single, planted live oak in the front yard. 1 tiny, poorly maintained, pathetic little tree. Like most young and broke couples, we bought a tiny track (not sure on spelling there, is it track or tract?) home and I certainly didn't have money or time to nurture a planted tree. We moved a few years ago and when we were looking for lots to build, I told the developer to take me to the lots with the thickest stands of mature trees. I'd lived 12 years without trees, I needed to make up for it.

I guess that started my fascination. Bought a couple of "trees of texas" type tree ID books and began going around the property trying to ID the trees. Had an arborist come out, check my ID's, talk about common diseases, maintaining post-oak health, etc. Best 75 bucks I've spent in a long time. I've got a great variety on just a 1.3 acre lot. I live in B/CS so we've got plenty of post oaks, but some beautiful mockernut hickory, winged elm, a gum bumelia, a huge stand of flaming prairie sumac (one is 25 feet tall which is pretty rare), and even an eve's necklace. The arborist told me it was the first eve's necklace he'd ever seen around B/CS. Of course, we are loaded with yaupon. Some arborists think that it's beneficial to leave a good stand of yaupon around your larger post-oaks and of course leave the soil natural and undisturbed, as the oak and yaupon may have a symbiotic relationship.

I've got a 4 year old son now and it's great walking around with him and ID'ing the trees. I'm also a huge history fan and I often like to sit out back with an adult beverage at sunset and look at the canopy of post oak's and hickory, listen to the crickets and owls, and think what my property (and the whole area) looked like two or three hundred years ago when it was the southern end of the comancheria and all the mature post oaks and hickory that tower around me were just saplings. Helps keep things in perspective.

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Post oaks do not like their roots smashed, such as clearing a lot or natural shrubbery removed from around them.

Three years is the magic number you need to clear, as they will typically die within three years from the shock if they are going to. Doesn't mean they won't die after three years, just less of a chance.

Most likely that is what it is, however there some type of bore beetle that can be infected from a disease from one tree and bore into another and spread the disease. You could pay a tree guy to come out, but he will most likely confirm they died from the shock of root smash and natural vegetation being removed.

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I don't understand most of this.

I bet you there's aluminum in the roots making them die.

Post oaks cannot tolerate root disturbance or severe drought, and for me, the drought has killed about 50%.
The live oaks have done much better, but it seems the age of the tree has a lot in survival rate. No young trees died, with several mature trees dying all around

Hypoxylon Canker

http://txforestservice.tamu.edu/main/article.aspx?id=1262

Well it's been a year since most of these posts and we've had a very wet Spring and early Summer. Now, the heat is on. I lost one post oak last summer and I had one cut down yesterday. These two oaks we next to each other with canopies touching. The canopy of a third post oak as recently turned light and then yellow and now some leaves are brown. The 3rd tree is not near the other two, but is exhibiting the same symptoms. I had a tree guy look at it and he suggested treating it with a fungicide and nutrients which we did. Still looks yellow, if not more so. Our house was built in 2012, so we are just beyond the critical first 3 years, but we do have St. Augustine grass and a sprinkler system that we are running 2x/week. BTW, the "tree guy" cooperated what my neighbor's tree guy said about their dead post oak, Post Oaks are drought tolerant trees. Since we've had drought conditions for the past few years followed by a deluge this Spring, many of the post oaks are dying. Was the money I spent to treat the 3rd tree for naught? I have 10 other post oaks that are healthy and one sick cedar elm that is touching the sick post oak.Thanks in advance for your advice!

The area west B-CS (Snook and beyond) has a very noticeable number of dead post oaks..all leafed out this spring, but now 100% brown and assumed dead. It's common to see a few die, but this year is certainly an increase over normal.

Neil Sperry also mentioned the Hypoxylon Canker, but it's just a guess.

Still losing 2-5 trees a year. Leaf out in spring and then die. Sucks