Chemical weed controls are more commonly called herbicides. They can be in liquid or granular forms. Using granular (i.e. weed & feed type fertilizers) the lawn should be wet (early morning dew is ideal) so the granules stick to the leaves.
Selective: A selective herbicide controls certain plant species without seriously affecting the growth of other plant species. The majority of herbicides used are selective herbicides.
Nonselective: Nonselective herbicides control green plants regardless of species. These are generally used to kill all plants, such as in the renovation or establishment of a new turf area, for spot treatment, or as a trimming material along sidewalks, etc. Glyphosate (Roundup), Glufosinate (Finale), and Diquat (Reward) are examples of nonselective herbicides. are examples of nonselective herbicides.
Contact: Contact herbicides affect only the portion of green plant tissue that is contacted by the herbicide spray. These herbicides are not translocated or moved in the vascular system of plants. Therefore, these will not kill underground plant parts, such as rhizomes or tubers. Contact herbicides often require repeat applications to kill regrowth from these underground plant parts. Examples of contact herbicides include the organic arsenicals (MSMA, DSMA), bentazon (Basagran), glufosinate (Finale), and diquat (Reward).
Systemic: Systemic herbicides are translocated in the plant's vascular system. The vascular system transports the nutrients and water necessary for normal growth and development. Systemic herbicides generally are slower acting and kill plants, over a period of days. Examples of systemic herbicides include glyphosate (Roundup), 2,4—Dichlorophenoxyacetic acid (2,4-D), dicamba (Banvel), imazaquin (Image), and sethoxydim (Vantage).
Herbicides are useful, effective tools in the control of weeds in turf areas. Product labels should always be read and followed when using a herbicide, or any other pesticide. Herbicides are not a miracle cure, as they provide only short-term relief from weeds. The best approach is an integrated regime of proper mowing, fertilization, irrigation, and use of other cultural practices to maintain a vigorous turf.