If I were you I would avoid using any kind of toxic chemical because it will ultimately leak into the groundwater of you and your neighbors.
If you get sheets of thick black plastic and lay it down over the earth, securing it down with metal pins or bricks, you can kill all the plant life below. This may take longer than a chemical, but you wont be poisoning the earth and the soil.
You can also use boiling water but it sounds like you have quite a bit of ground to cover so I would recommend laying down the plastic.
