Crabgrass is an annual grass that produces a lot of seed. The seed sits in the soil waiting until the soil temperature warms up to make it sprout. Once it sprouts, it grows very rapidly in open sunny areas branching and making much more seed for the next year. You can stop this annual grass from sprouting by applying a pre-emergent crabgrass preventer before it sprouts.
Lawn care companies are out applying preventative before it sprouts (granular or liquid). How do you know if it is too late to apply?
The best rule of thumb is to see if the Lilacs have started to bloom yet. Crabgrass starts to grow around the time that Lilacs start to #flower. So if the Lilacs have not started to bloom in your area yet, there is still time to get your grass treated to prevent the weedgrass from growing this year.
If you did not have any crabgrass last year, you can probably skip the application this year.