I don't have any expert advice for you, but I just wanted to say I feel really bad for you. I can just imagine her spraying the Roundup like she was putting out a fire. Roundup and weeds are all she knows. I love my trees. I've lived with them for many years and have an emotional attachment to them. As far as dealing with her - find out what the laws are first. Then read her the riot act, calmly but assertively, and tell her what the law requires. (Maybe give her a photocopy or a phone number to call if she has questions.) Give her a deadline to make the corrections, and tell her you will take further action with an impartial third party if she does not do so. If she makes any remarks other than "I'll take care of it immediately!" then just tell her clearly that she does not understand how serious a matter this is, and that her actions are a clear-cut violation of your property rights. The longer she ignores it, and the condition of your property continues to deteriorates, the more difficult it will be for her to resolve financially. If she gives you a hard time, tell her that her attitude is unacceptable, and forces you to put the matter into the hands of a third party immediately. And follow through, of course. This approach has worked for me, and I have never had to take legal recourse, because my no-nonsense attitude gets their attention. It is also civil discourse, and there have never been left over bad feelings. Good that she is moving, but you need to think and quickly if you want her to correct the damage that has been done, that you can at this point document, before she is gone and can ignore you. Good luck. Stick up for your trees!

There is not always a visible reason. Perhaps the dead tree had some wound to its root system no one ever saw. Then when the winter was cold it had xx% less energy available to overcome. I insist trees of various species do have an average life span. Someone shows you a Sequoia that is 300 years old and no one is impressed. Someone finds a 300 year old Cercis canadensis L. (Eastern Redbud) and they just might make the newspaper.

Big rootball(s) may actually be dry below the surface despite weather. Poke around in them to see, you may be surprised to find dust inside. Much field stock is grown on clay-like soils that may repel water once allowed to dry out. Trees may not be kept adequately watered after being dug and transported, stored before final purchase, and become quite dry during this period. Here I often seen wilted specimen-sized trees sitting out of the ground, waiting to be planted on commercial and public(!) projects. If it turns out the maple has been lost do not replace with another Norway maple is this is a pest species in North America.

Hi gardengal48, thanks for the reply. The wet bark is because I'd just sprayed it with the hose while watering our herb garden a few minutes before I took the photos. When the trees were planted in May 2013 they were brought burlapped ... and that was removed when they put it in the hole. They amended the soil with Mycorrhizal fungi which you can kind of see in this photo: I think it was probably this stuff. Keep in mind that was all 4 years ago. The tree seemed to establish easily and well, and grew beautifully. By last September (2016) it looked great: And it continued that way through October 2016 when it dropped all its leaves: But this Spring was a different story. The other maple that was planted at the same time leafed out nicely, and this one did not. Something definitely must've happened over the winter. Sorry I don't have a better photo of the trunk at the moment ... Thanks again for any thoughts you might have about cause, and potentially saving the tree.