Applying herbicides is only one of several methods to control or reduce weed populations in the garden, yard or farm. The popularity of herbicides over other methods is due in part to the relative ease and infrequency of application, the satisfaction of watching weeds die, and speed of the results. While synthetic herbicides achieve results faster, they tend to be more toxic to humans, animals and the area they are used on than organic herbicides.
Organic herbicides include horticultural vinegar, corn gluten and herb oils such as cinnamon oil. Horticultural vinegar and herb oil solutions are applied to adult plant leaves during sunny days to destroy leaves. Since the roots are generally not affected, several applications may be necessary before the weeds die. Corn gluten is applied as a pre-emergent, destroying seedlings as they attempt to establish roots. Corn gluten and cinnamon oil are on the Organic Materials Review Institute (OMRI) approved list of herbicides for use in organic farming.
There are a variety of synthetic herbicides that destroy weeds post-emergence or act as a pre-emergent. Systemic synthetic herbicides are applied only once on above-soil parts of the plant, and poison the entire plant by traveling along the water and nutrient transport systems of the treated plants. Care must be taken with systemic herbicides, as they are rarely plant-specific, and will harm any desirable plants they come into contact with.
Herbicides can help control invasive species of plants. Some have been designed to be plant specific, either in what they kill or in application techniques. This can help prevent unintended plant mortality. As always, however, it is up to the person applying the herbicide to be aware of the species of plant he or she is killing, as well as possible side effects on beneficial insect and wildlife populations.
The majority of herbicides available on the market are not plant-specific. Products such as stump-killers must be applied by drilling a hole in the weed tree and inserting the herbicide. This can be time-consuming and impractical for wide expanses of weed trees. The fact that most types of herbicides are available to the general public means that consumers who don't distinguish between beneficial plants or plants that serve a vital ecological purpose often apply herbicides inappropriately.
Mechanically or manually removing weeds, using cover crops between planting, rotating crops and ornamentals and mulching are methods that some organic producers use to control weed populations. Farmers and gardeners that practice sustainable growing techniques encourage predatory plants, animals and microbes to control weeds, and always diversify their crops to take advantage of the competitive mechanisms of multiple species to help reduce weed problems.