The below average temperatures the last few days has delayed crabgrass germination and thus premergence annual grass herbicides should still be effective if applied this week in the northern half to 2/3rds of the state. Most of the preemergence herbicides do have some post-emergence properties that will burn back small crabgrass (one or two leaf stage), but this is not always reliable. If you see or suspect crabgrass is already germinating in hotspots next to sidewalks, consider using dithiopyr (Dimension) because it has both pre and post activity. Or you could tank-mix pendimethalin or prodiamine with any of the post-emergence products like MSMA (variety of brandnames), fenoxaprop (Acclaim), or quinclorac (Drive).