The best defense is a good offense. A healthy lawn will win out in the competition against weeds for light, moisture and soil nutrients.
Two factors are important in determining what method to use in managing weeds. The type of weed is the first. They are classified as either broadleaf, grass or sedge. The life cycle of the weed is the second factor. Annuals have a one year life cycle, biennials have a two year life cycle and perennials have more than two years in their life cycle. Annual weeds usually get a pre-emergent treatment from a lawn care professional where the herbicide acts on the sprouting seed and keeps it from forming roots thus killing the weed before it emerges. Perennial broadleaf weeds are better treated with a post-emergent herbicide. Once weeds have emerged they are much harder to control as the herbicide will also damage turf grass.