A few years ago a neighbour advised a chemical spray for nettles where we were sorting out to park the car. I'm sure it was roundup too. Very powerful.
It killed the nettles within the week but we also found dead bumble bees and a few days running dead birds in the allotment.

Its one thing killing pests but another losing bug catchers and pollinators in our small plot.
The pesky pheasants nesting in the farm field behind us didn,t succumb tho!! Still chasing them off my crops!
When it came to sorting the large patch around fruit trees we decided to dig them out. They were also a deep layer of roots over the ground but clearance was surprisingly easy and quick and very little has grown back since. The chooks now help with what tries to grow here now