Herbicides are chemicals used in the control and killing of weeds in the home landscape or garden. Before selecting an herbicide, it is important to know the type of weed requiring control. Grassy weeds have slender stems and leaves. Broad-leaved weeds are wider. Contact your local university extension office for a weed identification key for your area.
Postemergence herbicides are used on weeds that are already established, germinated and visible. The herbicide is applied directly to the weed and is used on grassy and broad-leaved weeds. Postemergence herbicides are either contact or systemic. Contact herbicides kill only the portion of the weed touched by the herbicide. Good coverage of the weed is necessary to kill the plant. Systemic postemergence herbicides travel through the body of the weed, disrupting functions such as photosynthesis and the creation of pigment in the plant. Postemergence herbicide works best in conjunction with a pre-emergence herbicide.
Pre-emergence herbicides are used before a weed has germinated. The herbicide is applied to the soil in early spring when the soil is thawed and the seed is ready to germinate. The herbicide attacks the seed, disrupting the germination process. Pre-emergence herbicides work well on summer annual weeds. A second application of a pre-emergence herbicide nine weeks after the initial application aids in season-long control. Pre-emergence herbicides are used when there is a history of summer annual weeds in the gardening area.
Selective and Nonselective
Selective herbicides are used on specific weed varieties. They are formulated to kill that weed only. Some plants are still susceptible to the poisons in the herbicide. Check your desired plant variety and whether it is susceptible to the selective herbicide being used. Nonselective herbicides kill any plant it comes in contact with. Use nonselective herbicides to clear an entire area of vegetation. Nonselective herbicides are useful for weed control in open ground where a ground cover such as turf grass is required.