Pre-emergent herbicides are applied to prevent the germination of grassy weeds like crabgrass,goosegrass,and annual bluegrass. They need to be applied prior to the germination of grassy weeds in order to control them. They do not actually stop the seeds from germinating, they prevent weed grasses by killing the root that the newly germinating seed tries to establish. They must receive moisture from rain or snow to activate the “barrier” they create. The longer a pre-emergent sits on soil without being washed in, the more the active ingredient degrades. We begin applying pre-emergent in early February. We also mix fertilizer and broadleaf weed control with this application. This fertilizer app greens up the turf when soil temps warm.