An herbicide is generally applied before or after the crop emerges, depending on the weed species to be controlled. Trifluralin can also be used as a preemergence herbicide in carrots. Sprinkler irrigation is required for incorporation and activation of the material if it is applied after planting. This method of use will increase the activity on shallowly emerging weeds, such as common purslane, but will limit soil longevity and effectiveness on weeds germinating from deeper in the soil. This herbicide will control annual broadleaf weeds better then trifluralin, particularly nightshade, mustards, and sowthistle.
Effectiveness is reduced when grasses are under moisture stress.
Later growth stages of annual grasses are more difficult to control. This herbicide will not control annual bluegrass. Linuron can also be used as a postemergent herbicide in carrots. It is applied over the top of the crop when the carrots are 3 inches tall. It controls emerged weeds and also has soil residual activity against later emerging weeds.