Not sure but it might have broken on that poor looking graft union.

I seriously doubt that is a graft union failure. Look at the solid, healthy wood that is exposed. No rotting and no bark inclusions. It also doesn't look like there was an air pocket there. Just clean, severed wood. No peeling and the break goes completely through. I would think a tree falling over from a weak joint would show tearing, peeling or splintering and likely would not have broken all the way through.

I believe I see serrations in there, like a cutting instrument was used. Was there any sawdust or chips laying around indicating that some tool was used to saw, chop or hack the trunk apart? Check down under the grass.

Any beavers in your area?

I admit that someone or something cutting that tree down would have chosen a few inches higher where the trunk is much narrower. But the more I look at those serrations the more I suspect a tool was used. In fact it reminds me of occasions where I have used a bow saw to cut down a small tree and the blade keeps pinching and I have to come in from different angles to struggle through the cut with noone to help me and the tree leaning this way and that way.

Yeah, this was no accident. I think someone did it with a hand saw, maybe attacking from one side and then another. That would account for the multiple cut angles. Look for sawdust or wood bits. And of course let us know what you find.

Thank you all for your interest and comments, this is a real puzzle to me. We found no sign of sawdust or wood bits. The tree appeared to be very healthy, had at least 5 nice little apples already starting to get red. No beavers close by that I'm aware of (although last year our neighbor had a persistent one about 1/2 mile down our road that kept damming up a brook & causing flooding damage).

I've had no experience with graft failure. Can a healthy tree just pop off of it's graft? We did have very bad wind and rain around the time that it happened. No sign of animal disturbance in the mulch around the base. Think I need to read up a little on graft failure...

I had the very same thing happen with my 2 year old Honey Crisp apple tree. It was lying down with just a tiny bit of bark attached and I believe the graft failed. This was the first year I had any apples so I was very disappointed but Gurney's gave me a credit to use to replace it. I had never heard of a graft failing but there was a small hollow area as yours appears to have. It very well could have been a failure.

I am in no way affiliated with Gurney's but they do come through if there is a problem.

Another vote for graft failure. It can be caused by something like a virus infection. The tree snaps off at the union.

I think someone did it with a hand saw, maybe attacking from one side and then another.

The reason being why it wasn't done by animal or human saw,..look close around the outside of bark,..all looks torn and broken, no entry marks of any teeth, a good gust of wind can bring it down.

bummer...it almost certainly is a graft failure..had the same thing happen to my Tropic sweet apple tree.

True, I don't see any very smooth areas where a saw would have moved along. And a saw would have left some some debris.

Yet I have never seen wood snap as cleanly as that, right across the grain no less. No splintering or peeling. Possibly some tearing.

+1 for catastrophic graft failure. Have seen it more than a few times.

Turns out that I had purchased this tree from Gurneys 2 years ago. Sent them an email along with the pictures, will let you know how it turns out.

My local nursery has a one year guarantee, so luckily I was able to get mine replaced, but I'd be surprised if they did anything after 2 years..guess it can't hurt to ask.

Staking young trees a couple of years is always a good thing, most grafts are vulnerable the first few years. My latest purchase I put in about 2 weeks ago [Superior plum ] has a ugly union, staking it, hopefully it will grow OK..I didn't complain,..seems I'm always a victim for ugly trees.

This one I purchased from another nursery last year, just dug up, barely hung in last year and has died,..ugly graft, was infected with some black thing.