The trouble with the "live and let live" approach with smutgrass is that, although the cattle might eat it prior to emergence of seedheads and/or soon after shredding, it will nevertheless go to seed and eventually take over the pasture. Over time you'll have more and more of those thick clumps of it, making more & more seed to spread to other pastures. The last time we had it was on a place that got turned into rowcrop land so I'm not positive of the best herbicide to use. I think txag mentioned Roundup and I guess that would be what I'd try first for spot spraying. If Roundup doesn't work and you are afraid of Velpar because of nearby trees, etc. I'd probably do a little test by spot spraying with an extra heavy dose of Remedy + water + surfacant to see if that kills it and if it doesn't I'd use a heavier concentration of Remedy & diesel. The Remedy/diesel mix has killed out virtually every kind of grass I've had growing around huisach bushes & trees when it's the later species that I was aiming to kill -- but that's an expensive route for killing grass. Like most undesirable stuff, it is drought tolerant.