If you have a weedy, creeping grass in your bluegrass lawn, you have no good options. It really doesn't matter whether the weedy grass is zoysiagrass, Bermudagrass, creeping bentgrass, or some similar rogue grass. The only way to truly get rid of the zoysiagrass (or whatever it is) is to kill the entire infested patch with glyphosate (Roundup), then reseed or resod the affected area. Treat only the undesirable grass; glyphosate kills bluegrass too. But it leaves no residue in the soil, so you can replant quickly after the weedy grass dies.