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Herbicides are chemical compounds used to kill plants, control plants or inhibit a plant's normal growth. The way this is achieved varies, depending on the chemical composition of the herbicide and the desired outcome. Herbicides kill or damage a plant either by direct contact or by a systemic action that absorbs the herbicide and then transports it to parts of the plant that an herbicide cannot be directly applied to, like the roots.
Herbicides are classified into one of two general categories: selective or non-selective. Selective herbicides kill or control plants that have a particular unwanted characteristic, like the broad leaves of dandelions, but surrounding vegetation is unaffected. Non-selective herbicides, as the name suggests, do not discriminate.
There are several subcategories within the two main types of herbicides. Subcategories classify a herbicide by a distinguishing feature or quality of an individual herbicide. Such features might be the use, method of application or chemical composition. -
Selective herbicides are formulated to only attack a specific attribute of a plant and will not kill or affect surrounding vegetation that do not have the particular characteristic. Selective herbicides are commonly used to control weeds in grass lawns and turf.
Selective herbicides are applied after the weed has established into a plant. Application can take several different forms, from spraying or granules to adding it to the soil. Selective herbicides do not prevent the germination of weed seeds, so repeat applications are oftentimes needed. Other factors to be aware of to ensure success in applying selective herbicides include climate conditions, the amount applied and the pollination cycle of the weed. Always carefully read and follow the directions on the label of the herbicide you use. -
Total vegetation control or plant kill best describes non-selective herbicides. Within the non-selective herbicide category are pre-emergent and post-emergent herbicides. Pre-emergent herbicides are applied during the dormant period of seeds to stop the seed germination. A popular pre-emergent product is Preen, which comes in a granule formula that is worked into the soil and inhibits germination. Timing is crucial with any pre-emergent to guarantee successful elimination of unwanted weed seeds.
Non-selective post-emergent herbicides can be applied in the same manner as selective herbicides, although more care needs to be taken to avoid applying the herbicide to plant areas not intended to be killed. There are many types and categories of post emergent non-selective herbicides to choose from, and one key factor to note is that there are non-selective herbicides, like the popular brand Roundup, that destroys unwanted plants but does not affect the ability of the soil to continue to grow vegetation. There are also non-selective herbicides that will not only kill the existing vegetation but destroy the ability of the soil to grow any organic matter in the foreseeable future. This type of non-selective herbicide is most commonly used for roadways and areas where bare ground is desired. -
Long before chemicals were used to formulate herbicides, gardeners and farmers used commonly found organic substances to control weeds. Organic herbicides work best on young, tender weeds, are not as potent as commercial herbicides and will typically not give the same results but are much more environmentally friendly.
For small areas, spot control or vegetation that grows between bricks, stones and pavers in walkways, boiling water works quite well. Simply boil the water and use a tea kettle to pour the water on the weed or plants. The hot water will kill the foliage and the root system quickly.
Vinegar, or acetic acid, in a 5 percent concentration that most home use vinegar comes in, can be an effective herbicide sprayed on young weeds. A study using vinegar as a herbicide performed by the Sustainable Agricultural Systems Laboratory, part of the USDA, found that vinegar can kill several important weed species at various growth stages. Selected annual weeds were 80 to 100 percent killed when the vinegar applied was at 10 percent, 15 percent or 20 percent acetic acid concentration. Acetic acid does not appear to be as affective on perennial weeds, and because multiple applications are sometimes needed, this method of weed control may alter the pH value of the underlying soil, making it more acidic.
There are also home recipes and other commercial organic herbicides now available to the environmentally conscious gardener that are improving in their effectiveness as more gardeners and companies experiment with the use and applications. -
Because of the wide variety of herbicides and the chemical combinations used to formulate them, always read the label and any accompanying literature for the herbicide you plan to use. This information will not only tell you how and under what conditions to use the product but also any health hazards and treatments, should an accident occur with the herbicide.
That may not be enough to prevent future health repercussion from exposure to a herbicide today. As an example, the well-known and used herbicide Roundup has long been promoted as non-toxic to animals and humans, but recent research in France has discovered that when the active ingredient in Roundup, glyphosate, was tested on four different human cell groups, each of the cell groups' cells died within 24 hours. Because the formula and ingredient content of Roundup is a "trade secret," the research on health issues is just now revealing potential risks.
As beneficial and convenient as herbicides might be, there can be long-term damage to one's health and the environment. Great care in applying and handling of chemical herbicides should always be taken.
