Several times in my life for various whatever reason, mostly on those tree of heavens which is basically a weed tree, I tried to kill them after cutting them down. Nothing ever worked. Then this guy told me once that if you drill holes in the trunk and pour motor oil over it it kills the tree. It works wonders, I took down four real skinny tall trees a couple years ago because I wanted to plant evergreens instead. The area needed for light for them to successfully grow, I used the motor oil on them also and only one which had a rather high, maybe a foot up from the grown trunk ended up sprouting at the base, the others died. I think if I trim that other closer to the ground it will probably kill that one to.