Mpb58 wrote:
my neighbor installed an inground pool close to my back property. I have lost
a flowering plum, and an evergreen so far, and now a lilac bush. could the
fumes from their chlorine be doing this?

Reading your post a 2nd time, whats the possibility that the roots
of your trees were cut when the pool hole was dig and thats caused
them to die? Now if they were Chinese Elms like my *&^%$#@
neighbors have, the stinking things would still thrive. Nothing
kills those trees.