I used chaparral last year. Applied at 2.5 oz/acre mixed with fertilizer.
Put it out May 4th when the weeds were past a foot tall on a pasture that had been abused for years before I bought the place, hayed and overgrazed with no fertilizer or herbicide at all.
Results were slow it took 10 days to phase the weeds and several weeks to knock them down.
But it was very effective and I have no where near as many weeds this year with just the one application of chaparral.
I plan to use it again this year.