If you use something like corn gluten meal as a pre-emergent treatment for weeds, you might knock some out (the time for that has passed). And if the grass is still tender, you can kill it with a 10% vinegar and orange oil mix (there is a commercial product called Avenger) you can kill it. The combination of vinegar and orange oil may be enough to kill the mature grass, but if not, digging it out is the most effective approach, so if you're going to try vinegar, do it as soon as you start seeing the sprouts and the distinctive clump forming.
Weed control.
(Image comes from http://courses.missouristate.edu/pbtrew ... sgrass.htm)