I know this solution is a little off topic, but for persistent plant control I have found epdm roof liner or pond liner over a freshly mowed or hacked down area to be highly effective. Make sure to get as close to the ground as possible and stake down the edges with zinc coated metal stakes. One year should kill the vast majority of problem plants, two is better if you are patient.
The epdm rubber blocks out sunlight and water, and it bakes in the sun. Try to keep it from being punctured anywhere other than where your stakes are.
It takes time but the material is designed to be outside and UV stable, requires no pesticides, and is easily reusable.
Word of warning...the stuff is heavy.
