I have been told and have reason to believe that a small hole drilled near the base of a tree and the hole filled with neat Roundup can kill a tree - or at least make it so sick the owner may consider it's removal. This is best done just before it comes into leaf.
Disclaimer - I myself and none of my family have, of course, never taken part in any such action.
I wish someone knew who owns the tall birches and conifers the other side of the brook from my garden. In summer they cut out a lot of sunlight and now their leaves are starting to clutter up my garden.
My neighbour's silver birch tree has grown so tall that it cuts out a lot of sunlight from my garden. I was getting myself into action mode (she is a fearsome lady of 40 something - me a wimp? - never) when yesterday I heard the dulcet tones of a chain-saw and to my delight looked out in time to see the tree being reduced in size until it reached the height of my wall - oh there is a God up there