Tillage methods of getting rid of fescue involve 1) burning or mowing, 2) then discing deep or plowing, followed up by 3) cover cropping with extremely high rates of oats. Not that this is your scenario with fescue, etc. but I only bring this up to say that a heavy crop of oats will get ahead of most spring weeds & grasses, as they are very prolific and get a good start ahead of them. Then perhaps you can switch over come Aug/Sept for your fall plot.
Buckweat later is also another option, but I might think about discing/planting or spraying/planting after the initial flush of weeds as others have alluded to.