I have several sugar maples along my driveway that I planted maybe 7 years ago. They have done pretty well, but this year one of them seems to be dying out, one branch at a time. I first noticed one branch had browned maybe 3 weeks ago but thought it had just been damaged. Then two more turned brown so I looked at it more closely and noticed the trunk had some cracks in it that I didn't see on the other trees, although there was no oozing or anything of that nature. Since I took the photo maybe a week ago, the top has also died out, but maybe a third of the branches still look normal. I am concerned that whatever is going on may eventually spread and the whole tree will die.

I have also noticed a few similar looking dead branches in some of the other mature trees on the other side of the driveway. I have never seen anything like it in the 10 or so years I have lived here. I'm in SW Missouri, and it's been a relatively "normal" summer, not exceptionally hot or cool. Very wet spring, but since June it's been about normal, maybe slightly below normal precip.

Any ideas what might be causing this?