That is a fungus working on the dead wood inside the tree, isn't really infectious to other trees unless they also have dead wood inside and are the same or similar species. And someone needs to learn to prune correctly - leaving those nubs is a no-no. Branches should be cut to the "branch collar." hortster

Thanks for the info. Yes I was referring to VW, I've heard it referred as Maple Wilt and that's much shorter to type out. :) I have read about it and I still don't seem to get great info on the spread in distance in any landscape suburban area. We live in close proximity, in a more city setting. I am more concerned because we have a lovely neighborhood but our neighbors to our left and the neighbor next to them (with the trees in question) don't seem to be very concerned with proper lawn care. They don't mulch properly or prune what they should, like dead branches and they are late in tidying up fallen leaves in autumn. My trees line that side of the property to them and we are quite attached to them, they create very a beautiful wall. I just was trying to gage if there is anything I could do to prevent mine, if I'm reading into some dead branches and curling leaves too much. You google those symptoms and you get VW. I had called a nursery and they told me its tar spot because we've had more rain then normal. It that doesn't seem to fit dead leaves accordingly to any googling. I understand VW can live in the soil for many years, but these trees both, since both have the symptoms, one just one tiny branch the other more extensive but not bad, are probably 50-70 years old. So I guess I was just trying to get a little peace of mind but seem to be making it worse as I am just not sure on what it is. Both trees look as they normally do any other year minus these brown curled dead branches.

I understand the problem. To my knowledge, in most communities, if any part of any vegetation, trees etc. aren't actually OVER your property line, then you have no right to cut, trim etc. Hard to tell from the photo but it seems it's not actually over your property, From what you say about the neighbor, my opinion is that you could approach him in a nice way and explain your concerns. If he's halfway decent and respects your worries, he may do something about it as soon as possible. If, on the other hand, he's a jerk and gives you grief, what have you really lost? Nothing ventured, nothing gained as they say. I have a similar problem with a neighbor who doesn't care about anyone else and doesn't respect my property. He is more blatant about it though, and has actually had a large drain pipe spilling over the wall into my property, had been throwing yard waste and other debris into my garden, and most recently placed cinder blocks, boards, a trash can and a ceiling fan on my sidewalk! I have had to confront him on all these things, and although I was polite, I was also very direct in telling him what I thought. Those issues have been corrected except for the refuse on the sidewalk, since I only told him about it yesterday. That's because I didn't see it there until the snow melted. We'll never be friendly, but I figure if he's going to be a jerk, then I have no reason not to let him know how I feel when he does these things. i.e. nothing to lose. It's not like you'd make an enemy or something if he's already acting like one! So I say let him know of your concerns, in a definite but friendly manner. If he removes the broken limbs, great, and if not, he probably wasn't going to anyway. Good luck!

Many trees gdow from suckers. It looks like the sucker is clear of the rotting trunk so I think you will be fine. Cottonwood grows from cuttings also btw. As far as the lean, if it is leaning towards the sun it may really want to grow that way. Either way with a potentially huge tree like Cottonwood I would try to prune it reasonably straight.