Plants that are out of place in a lawn are considered weeds. The problem with weeds is that they constantly breed and spread. Weed control requires equal amounts of cultural control and proper lawn care--and herbicides if the problem is not contained. Herbicides may be required in pre-emergent form, which kills weeds before the seed germinates, or post-emergent form, which kills them once they are established.
Mow your lawn regularly, removing 1/3 of the grass blade at a time to improve grass density and prevent weed growth. Fertilize regularly using a complete fertilizer and aerate your lawn using a core aerator to improve drainage, remove thatch and improve grass density.
Pull weeds as they appear by hand, suggests the University of Wisconsin, to save time and money. If there are isolated incidents of weeds, this may be the best method of control while the lawn establishes itself.
Apply a pre-emergent herbicide throughout the lawn using a fertilizer spreader recommends the University of Missouri Extension. Follow the instructions on the label and apply half the rate of herbicide in one direction, and the other half crossing it, making sure to overlap during passes. Apply pre-emergent herbicides two weeks ahead of weed germination in mid-April. Gently spray the herbicide with water to activate the granules.
Spray established weeds with a post-emergent herbicide. Apply the herbicide on a day without wind and when rain is not expected for at least 48 hours to prevent runoff.