Pre-Emergent Crab Grass Application for 2019
You still have time to apply a crabgrass preemergent. In general, Crabgrass seeds germinate when soil temperatures average 55-60 degrees F. for seven days to ten days. There are different microclimates in your yard and soil temperatures may be different in areas such as south-facing areas, near sidewalks, etc. If you do not have a soil thermometer (and most people don't!), during and shortly after, forsythia bloom is a rough guide for application timing. Here is more information on crabgrass, preemergents, and tips for application
University research has shown that proper mowing (3-4 inches), fertilizing, and repairing bare spots will also help to prevent crabgrass.