Back in July, I was at the University of Kentucky's annual turf field day. During the cool season turfgrass tour, we were shown a plot of weeds\grasses that contained nimblewill. Next to that plot was a treated plot of grass that had no nimblewill. Dr. A.J. Powell, who was conducting the tour, indicated that they (UK) were testing "Mesotrione" (Syngenta, I think) as a selective herbicide for turf use. It killed the nimblewill.
The bad part to all of this is that mesotrione has not been labled for turf, and he didn't know when it might be labled. Probably after many millions of dollars have been paid to someone.
I do believe that mesotrione is labeled for agricultural use (corn).