I'm not sure if it is feasible where you are but we opt to go a less toxic route which sounds feasible for you if you are only doing 1/4 acre plots.

Two things you can do, solar burning (if the plot gets a few hours of sun per day), basically do black plastic sheets over the area. Best to just set it up at the beginning of the summer and pull it when you are ready to plant. Second method is a controlled burn which works just as well. Burns work the best especially if you can get the grass kind of tall first. Then you can mow it and let the clipping dry and use them for fuel. This kills the grass at the roots as well as cooking the seeds.

Burning works best in my opinion since you dont have to worry about pre-emergent since you kill the seeds also with the burn.