Herbicides kill plant life, either targeting specific types of plants or killing anything that's alive and green. Gardeners apply herbicides to control weeds in their lawns and gardens, and according to the National Pesticide and Information Center (NPIC), hundreds of herbicide products are available. NPIC reminds homeowners to follow product instructions precisely, remember that more is not better and consult a local extension office for advice and recommendations on what products to use.
Benefin, which is also sold under the trade names Balan and Balfin, treats weed problems in lawns and some agricultural fields. Benefin is a preemergent herbicide, which means that it must be applied to soil before weeds emerge. It works by destroying weeds as they germinate and exerts no effect on mature weeds. The Cornell University Pesticide Management Education Program recommends incorporating it deeper than two inches into cultivated soil. Benefin adheres well to the soil, meaning that there is little risk of leaching into groundwater, and it will provide yearlong weed control.
Several popular herbicides available at many garden supply stores combine mixtures of 2,4-D, dicamba, mecoprop (MCPP) and monosodium acid methanearsonate (MSMA), including Bayer, Ortho and Spectracide weedkillers. Because these are postemergent products, they are applied directly to weeds after they appear. University of California Integrated Pest Management Online cautions that while these products kill most broadleaf weeds, they can also kill ornamental plants if they come in contact with roots that have grown into the yard.
Bentazon controls yellow nutsedge and some broadleaf weeds, although it also has restrictions about the type of grass on which it can be used. In addition to use on lawns, bentazon has some agricultural applications. According to Cornell University's Extension Toxicology Network, bentazon works on contact, disrupting the ability of weeds to convert sunlight into chemical energy. Visible injury occurs in as little as four to eight hours. Labels bear a cautionary notice because bentazon is mildly toxic to people and other animals.
One of the best known herbicides is glyphosphate, sold under the trade name Roundup. Roundup is a nonselective herbicide, so it will kill any plant it is applied to, including lawn and garden plants. Roundup is mildly toxic and an eye irritant, according to Cornell University's Extension Toxicology Network. Roundup does not pose a high environmental risk because of leaching, although it attaches so tightly to soil products that it may enter surface waters because of erosion.