You saw NO dieback last year?

No, the tree was dormant by then, I would hope.

Healthy, dormant trees can take an amazing amount of winter cold and be okay.

That is not to say that trees never die from extreme cold. It is not unheard of that a tree can get damaged by a very hard winter.

If that were my tree, I would take a sample branch of the healthy portion, and a sample of the portion that did not put out buds, and take them both to the extension office and ask what's wrong.

Looks to me like y'all have both anthracnose and wilt in your area (I don't know exactly where in the state you are) and they exhibit differently on the different oaks, but the red oaks are highly vulnerable.

Did you do any pruning in the spring last year?

Rat_Patrol, one thing that bothers me as I look at your images, is that I see a number of branches in the canopy that appear to have some die-back.

This shows when I look at the overall tree, and see a high number of limbs that do not have any small branches and that appear to have died back and broken off at some point.  

The death of those limbs did not happen this spring.  They were likely already dead going into the winter.

In a large tree, you have to be looking at it, and looking FOR issues to see it, because if you just look and see green, you might not notice a problem.

If the tree was already under stress going into the winter, it might have taken a harder hit from that cold weather.

What you have to figure out is what was killing those branches.

It could be canker as the other poster suggested. but I don't see any indications on the main trunk, and for the tree to be deteriorating that quickly, I'd think you'd see some evidence on the bark.

There are other things killing oaks in your area, and yes, some of them can spread to your other oaks.

This is why I would suggest getting a determination on what it is.

If youend up having to remove the tree, you might even need to coat the stump, depending on what's killing the tree, to keep the stump from being a host for a fungal disease.  

You might NOT, depending on what it is.

Gotta find out what's killing that tree.

ETA:  Mature oaks have a strong branching structure, with a few large limbs terminating in thickly grouped, smaller, leaf-producing branches.    So as the tree grows older, it's normal to have some limb drop.  So that alone would not send me running if you didn't have the lack of spring buds.    

But the tree should put out evenly, and it's not.


ETA:  Did y'all have a late-spring freeze, after the green was already showing in the buds?

Even at the tight bud stage, a very hard freeze in spring can do that--cause die-back.  Your indication that it's the windward side of the tree that is worst , is my reason for asking.

I think when you have a wonderful tree like this one, it pays to not assume, but to figure out what's happened.  Too many people just automatically cut it because that's their knee-jerk response.  You may or may not need to remove the tree, but I always believe in saving a mature tree like that if I can manage it.

That was my first thought, but he didn't have any visible symptoms that caught his attention last year, and from everything I'm reading, it seems like it happens in stages--and he should have seen the wilt on at least part of the tree before losing so much of it.

Have you seen the progression of wilt on trees up there? (I mean, have you observed a tree with the disease in progress?)

Ii noticed this too....about the trimming...just from a quick check of oak deaths in Minnesota.  It seems that spring pruning is especially bad for transfer of a couple of the more contagious fungal infections.

My suggestion to go to the county agent with samples is strictly for benefit of his other trees.

If this one is going to fade away, I don't think he can save it. It would be nice if it would linger, though.  

Apparently there are some decent treatments available if the disease is caught early, and people do well taking proactive measures when they are forced to remove a tree, as long as they know what killed it.

But it should be noted that iron deficiency can be managed using soil amendments (acidification) and injections without damaging the tree in that way.

Pin Oaks in particular are known for getting chlorotic, at least around here.  An arborist's way would be to correct the availability of the mineral via uptake rather than  put the tree at risk by damaging its protective layers, xylem, and phloem (water/mineral flow layers which lie in the outer layers of wood just beneath the bark.)

Sad truth.

Buckshot, is that your career?