I have this in my garden and it is a right pain. I manage to keep on top of it in my garden by weeding on a weekly basis from the moment new plants emerge in the spring, and right through the summer. I use glyphosphate too but this only works for a few weeks so repeated applications are necessary. Unfortunately, my garden backs onto wild, unmanaged area and the weed originates from there so each season the seeds are blown into my garden. I have accepted that it will never go, but with vigilance and persistence I can keep on top of it. Dig it up or use weedkillers before it flowers, but also dig up every visible bit of the white roots as it will re grow from the smallest piece.