Quackgrass is one of the worst lawn weeds. Any chemical product that will kill quackgrass will also kill the grass in your lawn. That means you either have to put up with the quackgrass or kill the entire area and start over. Here's another thought for you to keep in mind: A quackgrass infestation in your yard is mainly an aesthetic problem. Completely renovating a whole acre of lawn would be quite an undertaking. To kill all of the quackgrass in your lawn, you'll have to spray the area at least twice with an herbicide before reseeding or sodding. That's a lot of expense and backbreaking effort. Even though quackgrass is not beautiful, I find that I can live with a bit of it. My lawn, at least when it's freshly mowed, still looks pretty nice, quackgrass and all.