I moved into my house about three years ago. I moved in July that year and my lawn was covered in quack grass. The only two things I found that worked was digging up the
roots of the quack grass. I found the best way to do this is in the early fall just before the quack grass starts to die off. I dig up as many of the roots as I possibly can and than seed like crazy. The other way is to cover it with plastic until it dies off ,loosen the soil and then seed.