As a head gardener, i use roundup all the time. It's safe and effective on pretty much everything.
Ive used it 50/50 roundup concentrate/water to kill 12" diameter willow stumps and also used it to kill bullrushes in ornamental ponds. It zaps pretty much all perennial weeds although ive had a 10 year battle with marestail but the roundup is slowly winning. I use it on brambles, nettles, bindweed, thistles and im even using it on a huge berberis that has been cut down to ground level and starting to re-grow....it's sorting that out a treat.