Lowes or Home Depot sells a "total vegatation kill" that works great. Just be careful not to over spray.
I may be wrong but I think round up is inert once it hits the soil
Glyphosate is only effective on the foliage, it gets bound up in contact with soil.
I spot-spray in my garden all the time. On weeds in close with plants I want to keep, I put a rock on the weed, bending it away from the plant, and spray the weed alone. I move the rock the next day and water the weed.
Pramitol is another matter; it will travel through the soil. (Looking up 'Scythe' now)