Use herbicides as a last resort—when nothing else works on a particular weed or when your lawn is completely overrun. And follow directions carefully. Used incorrectly, herbicides can injure or kill turf and other desirable plants.
If you use an herbicide, choose one that's labeled as safe for the type of turf you're growing and effective against the weeds you've got. The label states when and in which conditions to use the product. Some herbicides work only within a certain temperature range; others work only when applied at a specific time of year.
Herbicides fall into three major categories: preeemergence herbicides, postemergence herbicides and weed-and-feed products.