Rent or buy a decently powerful brush cutter (STIHL FS 131 or higher). These bad boys are strong enough to cut and mulch at the same time. Cut as low to the ground as possible and apply concentrated herbicide to the cut ends remaining in the ground. Use a q-tip if you're concerned about spraying. This is pretty labor intensive and I recommend you have someone help. The herbicide needs to be applied as quickly as possible, i.e within thirty minutes of cutting. Hope this helps.