I had a small shrub growing on top of a wall. I think it was elderberry. I cut this down a couple of years ago, but it then regrew. Unfortunately it has quite cleverly distorted the drain pipe, which has added to the problem, but giving it a steady supply of water! I have now cut it down and pulled out a rootstock about the size of a fist. However there are still a few roots that go down into the wall cavity and I doubt I will be able to remove these.
So, what is the best way to treat the roots, so they don't resprout. I understand that ammonium sulphamate, which was sold as root out has now been banned.
Appreciate some tips. Thanks Tim