A pre-emergent application now controls summer annual weeds.  The weeds you are seeing now germinated in October/November.  If you have an abundance of winter annual weeds, then plan to use a pr-eemergent in Sept. and skip overseeding.  And now would be a good time to control those winter annual weeds with a post-emergent broadleaf weed killer before they get too big and flower and produce seeds.

Spring applications of pre-emergent are timed for control of crabgrass.  In the Richmond area, the time to put down the pre-emergent is when the forsythia bushes (yellow flowering shrubs) are at 50% full bloom.