One reviewer noted that Preen isn't a crabgrass killer but a preventer ... two early-spring applications when Preen should be most effective. Scotts Turf Builder Halts crabgrass preventer has ...

This herbicide is safe for cool-season turf grasses that have just been seeded and is most effective ... herbicide to treat crabgrass compared to broadleaf weeds, and total control may require ...