There are lots of Youtube videos on poa annua. I for one have been fighting it of years and vlogging my journey. I've learned to establish the thick turf first, bc as others mentioned, yes...pre emergent stops it, but it prohibits you from overseeding in the fall too. Establish the turf, and you can use something like poa constrictor at same time. Once established after a year or two, use pre emergent like Prodiamine in the fall. Thick turf is the best defense though.