Since I mentioned it in other comments, RoundUp (Glyphosate) probably would work, if you have it available where you live -- you spray it on actively growing plants, and it kills including the roots, leaving no dangerous residue. The bigger and healthier the plants, the better it works.
We've used it on something called tackweed: watering the area to make it grow, spraying all the plants with roundup, ripping out the dead stuff and throwing it away, then repeating over and over, until all the seeds were germinated and killed. A local farmer uses it when time to rotate his hay crops from alfalfa -- spraying it right before cutting (because it leaves no residue in the plant), which allows him to cut and then the cut plants die. (I'm guessing that is a standard practice.)
Do not spray on a windy day -- it will damage or kill any greenery it touches. Read and heed the warnings on the labels, etc.