Around here to plant fescue and have only fescue growing, I apply a nonselective herbicide to kill everything, give it a couple of weeks to do its job then plow and till the soil and seed. If you are further north, you may have a different process and different kinds of grass that compete with fescue. We have bermuda grass here as our primary lawn grass and it is extremely invasive. If you don't mind other grasses but want the weeds out you might want to just overseed. I overseed each fall to try to keep the fescue as thick as possible and that tends to keep the bermuda grass out. To overseed I rent an aerator, put the seed down then go over the yard with aerator so the dirt plugs will cover the seed when they melt down through the grass. It seems to work fairly well. I applied a weed killer this spring called TriMec 992 and I don't have a weed in my yard, yet. Seems to be really effective. This is one of my major interest areas so sorry if I got wordy.
