What is your future plan for the plot? A lot of good strong sprays will be in the soil for a while preventing seeds from germinating. Is that what you want?
Roundup will actually do well for your weeds, you justneed to spray when the weeds are actively growing. Your timing was off the first time.... Roundup has zero effect on the soil, so weeds will be sporuting and growing the next day again.....
Milestone is another good one that will kill off all the boradleaves in a pasture setting and lingers a while, mixed with Roundup it will kill everything.
Paraquat is the big soil sterilizer, but it is dangerous to handle, follow the instructions carefully.
--->Paul