I am trying to find out if perennial rye can be seeded in cold soil the spring...say about 3 weeks before normal greenup...say green up (and earliest sprouting of new seeds) is about April 8 around here, (so we would have to seed about March 15). And then, would the new grass be tall enough to withstand Dimension crabgrass control before crabgrass appeared...(which is about June 8 around here). That gives you 8 weeks. The timing for success would be critical.
Your only other choice would be to apply Tupersan (siduron) on new grass in spring and follow up with Dimension. The short time of Dimension post-emergent effects might work...and if not, clean it up with quinclorac.