A herbicide is used to kill unwanted plants. Plants are living Organisms belonging to the kingdom Plantae. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often based on plant hormones. WEED (1390 AM) is a Radio station broadcasting a Spanish format Hormones (from Greek ὁρμή - "impetus" are chemicals released by cells that affect cells in other parts of the body Herbicides used to clear waste ground are nonselective and kill all plant material with which they come into contact. Plants are living Organisms belonging to the kingdom Plantae. Some plants produce natural herbicides, such as the genus Juglans (walnuts). Walnuts (genus Juglans) are Plants in the family Juglandaceae. They are applied in total vegetation control (TVC) programs for maintenance of highways and railroads. Vegetation is a general term for the plant life of a region it refers to the Ground cover provided by plants Smaller quantities are used in forestry, pasture systems, and management of areas set aside as wildlife habitat. A habitat (which is Latin for "it inhabits" is an Ecological or environmental area that is inhabited by a particular Species.
Herbicides are widely used in agriculture and in landscape turf management. Agriculture refers to the production of goods through the growing of plants and fungi and the raising of domesticated Animals The study of agriculture In the U. S. , they account for about 70% of all agricultural pesticide use. 
Prior to the widespread use of chemical herbicides, cultural controls, such as altering soil pH, salinity, or fertility levels, were used to control weeds. In Agriculture cultural control is the practice of modifying the growing environment to reduce the prevalence of unwanted pests Examples include changing soil Mechanical control (including tillage) was also (and still is) used to control weeds.
The first widely used herbicide was 2,4-dichlorophenoxyacetic acid, often abbreviated 2,4-D. 24-Dichlorophenoxyacetic acid (24-D is a common systemic Herbicide used in the control of broadleaf weeds It was first commercialized by the Sherwin-Williams Paint company and saw use in the late 1940s. It is easy and inexpensive to manufacture, and kills many broadleaf plants while leaving grasses largely unaffected (although high doses of 2,4-D at crucial growth periods can harm grass crops such as maize or cereals). The low cost of 2,4-D has led to continued usage today and it remains one of the most commonly used herbicides in the world. Like other acid herbicides, current formulations utilize either an amine salt (usually trimethylamine) or one of many esters of the parent compound. Trimethylamine is an Organic compound with the formula N(CH33 Esters are a class of Chemical compounds and Functional groups Esters consist of an inorganic or organic Acid in which at least These are easier to handle than the acid.
2,4-D exhibits relatively good selectivity, meaning, in this case, that it controls a wide number of broadleaf weeds while causing little to no injury to grass crops at normal use rates. A herbicide is termed selective if it affects only certain types of plants, and nonselective if it inhibits a very broad range of plant types. Other herbicides have been more recently developed that achieve higher levels of selectivity than 2,4-D.
The 1950s saw the introduction of the triazine family of herbicides, which includes atrazine, which have current distinction of being the herbicide family of greatest concern regarding groundwater contamination. Atrazine, 2-chloro-4-(ethylamine-6-(isopropylamine-s-triazine an Organic compound consisting of an s- Triazine -ring is a widely used Herbicide. Atrazine does not break down readily (within a few weeks) after being applied to soils of above neutral pH. Under alkaline soil conditions atrazine may be carried into the soil profile as far as the water table by soil water following rainfall causing the aforementioned contamination. Atrazine is said to have carryover, a generally undesirable property for herbicides.
Glyphosate, frequently sold under the brand name Roundup, was introduced in 1974 for non-selective weed control. Glyphosate (N-(phosphonomethyl glycine is a non-selective Systemic Herbicide, absorbed through the leaves injected into the bole or applied to the stump of Roundup is the brand name of a systemic broad-spectrum Herbicide produced by the U It is now a major herbicide in selective weed control in growing crop plants due to the development of crop plants that are resistant to it. The pairing of the herbicide with the resistant seed contributed to the consolidation of the seed and chemistry industry in the late 1990s.
Many modern chemical herbicides for agriculture are specifically formulated to decompose within a short period after application. This is desirable as it allows crops which may be affected by the herbicide to be grown on the land in future seasons. However, herbicides with low residual activity (i. e. , that decompose quickly) often do not provide season-long weed control.
Certain herbicides affect metabolic pathways and systems unique to plants and not found in animals making many modern herbicides among the safest crop protection products having essentially no effect on mammals, birds, amphibians or reptiles. Some herbicides can cause a variety of health effects ranging from skin rashes to death. The pathway of attack can arise from intentional or unintentional direct consumption of the herbicide , improper application resulting in the herbicide coming into direct contact with people or wildlife, inhalation of aerial sprays, or food consumption prior to the labeled pre-harvest interval. Under extreme conditions herbicides can also be transported via surface runoff to contaminate distant water sources. Surface runoff is a term used to describe when soil is infiltrated to full capacity and excess Water, from Rain, Snowmelt, or other sources flows Most herbicides decompose rapidly in soils via soil microbial decomposition, hydrolysis or photolysis and some herbicides are more persistent with longer soil half-lives. Half-Life (computer-game page here It's already listed in the disambiguation page Other alleged health effects can include chest pain, headaches, nausea and fatigue. All organic and non-organic herbicides must be extensively tested prior to approval for commercial sale and labeling by the Environmental Protection Agency. However, because of the large number of herbicides in use, there is significant concern regarding health effects. Some of the herbicides in use are known to be mutagenic, carcinogenic or teratogenic. In Biology, a mutagen ( Latin, literally origin of change) is a physical or chemical agent that changes the genetic information (usually DNA) The term carcinogen refers to any substance Radionuclide or radiation that is an agent directly involved in the promotion of Cancer or in the fatation of its propagation Teratology stems from the Greek ( Genitive) meaning monster, or marvel and, meaning word, speech.
However, some herbicides may also have a therapeutic use. Current research aims to use herbicides as an anti-malaria drug that targets the plant-like apicoplast plastid in the malaria-causing parasite Plasmodium falciparum. Malaria is a vector -borne Infectious disease caused by Protozoan Parasites It is widespread in tropical and subtropical regions including Plastids are major Organelles found in plants and algae Plastids often contain pigments used in photosynthesis and the types of pigments present can change Parasitism is a type of symbiotic relationship between Organisms of different Species. Plasmodium falciparum is a Protozoan Parasite, one of the species of Plasmodium that cause Malaria in humans
Classification of herbicides
Herbicides can be grouped by activity, use, chemical family, mode of action, or type of vegetation controlled.
- Contact herbicides destroy only the plant tissue in contact with the chemical. Generally, these are the fastest acting herbicides. They are less effective on perennial plants, which are able to regrow from rhizhomes, roots or tubers.
- Systemic herbicides are translocated through the plant, either from foliar application down to the roots, or from soil application up to the leaves. They are capable of controlling perennial plants and may be slower acting but ultimately more effective than contact herbicides.
- Soil-applied herbicides are applied to the soil and are taken up by the roots of the target plant.
- Pre-plant incorporated herbicides are soil applied prior to planting and mechanically incorporated into the soil.
- Preemergent herbicides are applied to the soil before the crop emerges and prevent germination or early growth of weed seeds. Preemergent herbicides prevent the Germination of seeds by inhibiting a key Enzyme.
- Post-emergent herbicides are applied after the crop has emerged.
Their classification by mechanism of action (MOA) indicates the first enzyme, protein, or biochemical step affected in the plant following application. In Pharmacology, the term mechanism of action (MOA refers to the specific biochemical interaction through which a drug substance produces its pharmacological effect The main mechanisms of action are:
- ACCase inhibitors are compounds that kill grasses. Acetyl coenzyme A carboxylase (ACCase) is part of the first step of lipid synthesis. Thus, ACCase inhibitors affect cell membrane production in the meristems of the grass plant. The ACCases of grasses are sensitive to these herbicides, whereas the ACCases of dicot plants are not. Dicotyledons, or "dicots", is a name for a group of Flowering plants whose Seed typically has two embryonic leaves or Cotyledons There
- ALS inhibitors: the acetolactate synthase (ALS) enzyme (also known as acetohydroxyacid synthase, or AHAS) is the first step in the synthesis of the branched-chain amino acids (valine, leucine, and isoleucine). The acetolactate synthase (ALS enzyme (also known as acetohydroxy acid synthase or AHAS is the first step in the synthesis of the Branched-chain amino acids ( Valine Valine (abbreviated as Val or V) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH(CH32 Leucine (abbreviated as Leu or L) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH2CH(CH32 Isoleucine (abbreviated as Ile or I) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH(CH3CH2CH3 These herbicides slowly starve affected plants of these amino acids which eventually leads to inhibition of DNA synthesis. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this They affect grasses and dicots alike. The ALS inhibitor family includes sulfonylureas (SUs), imidazolinones (IMIs), triazolopyrimidines (TPs), pyrimidinyl oxybenzoates (POBs), and sulfonylamino carbonyl triazolinones (SCTs). ALS is a biological pathway that exists only in plants and not in animals thus making the ALS-inhibitors among the safest herbicides.
- EPSPS inhibitors: The enolpyruvylshikimate 3-phosphate synthase enzyme EPSPS is used in the synthesis of the amino acids tryptophan, phenylalanine and tyrosine. Tryptophan (abbreviated as Trp or W) is one of the 20 standard amino acids, as well as an Essential amino acid in the Human diet Phe redirects here For the BitTorrent feature see PHE. For the constellation see Phoenix (constellation. Tyrosine (abbreviated as Tyr or Y) or 4-hydroxyphenylalanine, is one of the 20 Amino acids that are used by cells to synthesize They affect grasses and dicots alike. Glyphosate (Roundup) is a systemic EPSPS inhibitor but inactivated by soil contact. Glyphosate (N-(phosphonomethyl glycine is a non-selective Systemic Herbicide, absorbed through the leaves injected into the bole or applied to the stump of
- Synthetic auxin inaugurated the era of organic herbicides. They were discovered in the 1940s after a long study of the plant growth regulator auxin. Auxins are a class of Plant growth substance (often called Phytohormone or Plant hormone) Synthetic auxins mimic this plant hormone. They have several points of action on the cell membrane, and are effective in the control of dicot plants. 2,4-D is a synthetic auxin herbicide.
- Photosystem II inhibitors reduce electron flow from water to NADPH2+ at the photochemical step in photosynthesis. They bind to the Qb site on the D1 protein, and prevent quinone from binding to this site. Therefore, this group of compounds cause electrons to accumulate on chlorophyll molecules. Chlorophyll is a green Pigment found in most Plants Algae and Cyanobacteria. As a consequence, oxidation reactions in excess of those normally tolerated by the cell occur, and the plant dies. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state The triazine herbicides (including atrazine) and urea derivatives (diuron) are photosystem II inhibitors. 
Almost all herbicides in use today are considered "organic" herbicides in that they contain carbon as a primary molecular component. A notable exception would be the arsenical class of herbicides. Sometimes they are referred to as synthetic organic herbicides. Recently the term "organic" has come to imply products used in organic farming. Organic farming is a form of agriculture that relies on Crop rotation, Green manure, Compost, Biological pest control, and mechanical Cultivation Under this definition an organic herbicide is one that can be used in a farming enterprise that has been classified as organic. Organic herbicides are expensive and may not be affordable for commercial production. They are much less effective than synthetic herbicides and are generally used along with cultural and mechanical weed control practices.
Organic herbicides include:
- Spices are now effectively used in patented herbicides. A spice is a dried Seed, Fruit, Root, Bark or vegetative substance used in Nutritionally insignificant quantities as a Food additive
- Vinegar is effective for 5-20% solutions of acetic acid with higher concentrations most effective but mainly destroys surface growth and so respraying to treat regrowth is needed. Vinegar is an acidic liquid processed from the Fermentation of Ethanol in a process that yields its key ingredient Acetic acid (also called ethanoic acid Resistant plants generally succumb when weakened by respraying.
- Steam has been applied commercially but is now considered uneconomic and inadequate. Uses A Steam engine uses the expansion of steam in order to drive a Piston or Turbine to perform Mechanical work.  It kills surface growth but not underground growth and so respraying to treat regrowth of perennials is needed.
- Flame is considered more effective than steam but suffers from the same difficulties. A flame is often defined as the visible (light-emitting part of a Fire. 
Most herbicides are applied as water-based sprays using ground equipment. Ground equipment varies in design, but large areas can be sprayed using self-propelled sprayers equipped with a long boom, of 60 to 80 feet (20 to 25 m) with flat fan nozzles spaced about every 20 in (500 mm). Towed, handheld, and even horse-drawn sprayers are also used.
Synthetic organic herbicides can generally be applied aerially using helicopters or airplanes, and can be applied through irrigation systems (chemigation).
- Control is the destruction of unwanted weeds, or the damage of them to the point where they are no longer competitive with the crop.
- Suppression is incomplete control still providing some economic benefit, such as reduced competition with the crop.
- Crop Safety, for selective herbicides, is the relative absence of damage or stress to the crop. Most selective herbicides cause some visible stress to crop plants.
Major herbicides in use today
- 2,4-D, a broadleaf herbicide in the phenoxy group used in turf and in no-till field crop production. 24-Dichlorophenoxyacetic acid (24-D is a common systemic Herbicide used in the control of broadleaf weeds Now mainly used in a blend with other herbicides that allow lower rates of herbicides to be used, it is the most widely used herbicide in the world, third most commonly used in the United States. It is an example of synthetic auxin (plant hormone). Auxins are a class of Plant growth substance (often called Phytohormone or Plant hormone)
- atrazine, a triazine herbicide used in corn and sorghum for control of broadleaf weeds and grasses. Atrazine, 2-chloro-4-(ethylamine-6-(isopropylamine-s-triazine an Organic compound consisting of an s- Triazine -ring is a widely used Herbicide. Still used because of its low cost and because it works extrodinarily well on a broad spectrum of weeds common in the U. S. corn belt, Atrazine is commonly used with other herbicides to reduce the over-all rate of atrazine and to lower the for potential groundwater contamination, it is a photosystem II inhibitor.
- clopyralid is a broadleaf herbicide in the pyridine group, used mainly in turf, rangeland, and for control of noxious thistles. Clopyralid (36-dichloro-2-pyridinecarboxylic acid is a selective Herbicide used for control of broadleaf weeds especially Thistles and Clovers For Notorious for its ability to persist in compost. It is another example of synthetic auxin.
- dicamba, a persistent broadleaf herbicide active in the soil, used on turf and field corn. Dicamba (36- dic hloro-2- m ethoxy' b' enzoic a cid is an Herbicide used to control annual and perennial broadleaf weeds in grain It is another example of synthetic auxin.
- Glufosinate ammonium, a broad-spectrum contact herbicide and is used to control weeds after the crop emerges or for total vegetation control on land not used for cultivation. DL-Phosphinotricin is a Herbicide commonly used in plant Molecular biology and plant tissue culture 
- Glyphosate, a systemic nonselective (it kills any type of plant) herbicide used in no-till burndown and for weed control in crops that are genetically modified to resist its effects. Glyphosate (N-(phosphonomethyl glycine is a non-selective Systemic Herbicide, absorbed through the leaves injected into the bole or applied to the stump of It is an example of an EPSPs inhibitor.
- Imazapyr, is a non-selective herbicide used for the control of a broad range of weeds including terrestrial annual and perennial grasses and broadleaved herbs, woody species, and riparian and emergent aquatic species.
- Imazapic, is a selective herbicide for both the pre- and post-emergent control of some annual and perennial grasses and some broadleaf weeds. Imazapic kills plants by inhibiting the production of branched chain amino acids (valine, leucine, and isoleucine), which are necessary for protein synthesis and cell growth. Valine (abbreviated as Val or V) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH(CH32 Leucine (abbreviated as Leu or L) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH2CH(CH32 Isoleucine (abbreviated as Ile or I) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH(CH3CH2CH3
- Linuron, is a non-selective herbicide used in the control of grasses and broadleafed weeds. It works by inhibiting photosynthesis.
- Metolachlor, a pre-emergent herbicide widely used for control of annual grasses in corn and sorghum; it has largely replaced atrazine for these uses. Metolachlor is a Herbicide from the chloroacetanilide family developed by Ciba-Geigy. Atrazine, 2-chloro-4-(ethylamine-6-(isopropylamine-s-triazine an Organic compound consisting of an s- Triazine -ring is a widely used Herbicide.
- Paraquat, a nonselective contact herbicide used for no-till burndown and in aerial destruction of marijuana and coca plantings. Paraquat is the trade name for NN'-Dimethyl-44'-bipyridinium dichloride, a Viologen. More acutely toxic to people than any other herbicide in widespread commercial use.
- picloram, a pyridine herbicide mainly used to control unwanted trees in pastures and edges of fields. Picloram is a systemic herbicide used for general woody plant control sold under the trade names Tordon and Grazon. It is another synthetic auxin.
- Triclopyr, a systemic, foliar herbicide in the pyridine group. Triclopyr is a systemic foliar Herbicide in the Pyridine group It is used to control broadleaf weeds while leaving grasses and conifers unaffected.
Herbicides of historical interest
- 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) was a widely used broadleaf herbicide until being phased out starting in the late 1970s. 245-Trichlorophenoxyacetic acid (245-T a synthetic Auxin, is a chlorophenoxy acetic acid herbicide used to defoliate broad-leafed plants While 2,4,5-T itself is of only moderate toxicity, the manufacturing process for 2,4,5-T contaminates this chemical with trace amounts of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Polychlorinated dibenzodioxins ( PCDD s or simply dioxins, are a group of Halogenated Organic compounds which are significant because they act TCDD is extremely toxic to humans. With proper temperature control during production of 2,4,5-T, TCDD levels can be held to about . 005 ppm. Before the TCDD risk was well understood, early production facilities lacked proper temperature controls. Individual batches tested later were found to have as much as 60 ppm of TCDD.
- 2,4,5-T was withdrawn from use in the USA in 1983, at a time of heightened public sensitivity about chemical hazards in the environment. Public concern about dioxins was high, and production and use of other (non-herbicide) chemicals potentially containing TCDD contamination was also withdrawn. Polychlorinated dibenzodioxins ( PCDD s or simply dioxins, are a group of Halogenated Organic compounds which are significant because they act These included pentachlorophenol (a wood preservative) and PCBs (mainly used as stabilizing agents in transformer oil). Pentachlorophenol (PCP is a synthetic substance that was first produced in the 1930s Some feel that the 2,4,5-T withdrawal was not based on sound science. 2,4,5-T has since largely been replaced by dicamba and triclopyr. Dicamba (36- dic hloro-2- m ethoxy' b' enzoic a cid is an Herbicide used to control annual and perennial broadleaf weeds in grain Triclopyr is a systemic foliar Herbicide in the Pyridine group
- Agent Orange was a herbicide blend used by the U. Agent Orange is the code name for a powerful Herbicide and Defoliant used by the U S. military in Vietnam between January 1965 and April 1970 as a defoliant. It was a 50/50 mixture of the n-butyl esters of 2,4,5-T and 2,4-D. Because of TCDD contamination in the 2,4,5-T component, it has been blamed for serious illnesses in many veterans and Vietnamese people who were exposed to it. However, research on populations exposed to its dioxin contaminant have been inconsistent and inconclusive. Agent Orange often had much higher levels of TCDD than 2,4,5-T used in the US. The name Agent Orange is derived from the orange color-coded stripe used by the Army on barrels containing the product. It is worth noting that there were other blends of synthetic auxins at the time of the Vietnam War whose containers were recognized by their colors, such as Agent Purple and Agent Pink. The Vietnam War, also known as the Second Indochina War, or the Vietnam Conflict, occurred in Vietnam, Laos and Cambodia Agent Purple is the code name for a powerful Herbicide and Defoliant used by the U Agent Pink is the code name for a powerful Herbicide and Defoliant used by the U
- ^ Kellogg RL, Nehring R, Grube A, Goss DW, and Plotkin S (February 2000), Environmental indicators of pesticide leaching and runoff from farm fields. Agriculture refers to the production of goods through the growing of plants and fungi and the raising of domesticated Animals The study of agriculture A bioherbicide (or biopesticide is a Herbicide that is based on a living organism such as Fungi, bacteria or Protozoa, which eats or renders The term carcinogen refers to any substance Radionuclide or radiation that is an agent directly involved in the promotion of Cancer or in the fatation of its propagation Agriculture refers to the production of goods through the growing of plants and fungi and the raising of domesticated Animals The study of agriculture The Federal Insecticide Fungicide and Rodenticide Act (or FIFRA) Et seq. The United States of America —commonly referred to as the There are numerous health hazards that can affect people in their natural environment In Biology, a mutagen ( Latin, literally origin of change) is a physical or chemical agent that changes the genetic information (usually DNA) Organic farming is a form of agriculture that relies on Crop rotation, Green manure, Compost, Biological pest control, and mechanical Cultivation Organic horticulture is the science and art of growing fruits vegetables flowers or ornamental plants by following the essential principles of organic agriculture in soil For related pages see Aerial application, Sprayer, Spraying and Spray nozzle. Pesticides vary in their effect on Bees. Contact Insecticides those which kill by touching the organism affect the Worker bee that The Rainbow Herbicides are a group of chemicals used by the United States military in Southeast Asia during the Vietnam War. Soil contamination is caused by the presence of man-made chemicals or other alteration in the natural soil environment Surface runoff is a term used to describe when soil is infiltrated to full capacity and excess Water, from Rain, Snowmelt, or other sources flows Teratology stems from the Greek ( Genitive) meaning monster, or marvel and, meaning word, speech. WEED (1390 AM) is a Radio station broadcasting a Spanish format Weed control is the botanical component of Pest control, stopping weeds from reaching a mature stage of growth when they could be harmful to Domesticated Plants United States Department of Agriculture Natural Resources Conservation Service. Retrieved on 2007-10-03. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 42 BC - First Battle of Philippi: Triumvirs Mark Antony and Octavian fight an indecisive battle with Caesar's
- ^ Stryer, Lubert (1995). Biochemistry, 4th Edition. W. H. Freeman and Company, pp. 670. ISBN 0-7167-2009-4.
- ^ Spray Weeds With Vinegar?
- ^ Weed Management in Landscapes
- ^ Organic Weed Management in Vineyards
- ^ Kolberg, Robert L. , and Lori J. Wiles. 2002. Effect of steam application on cropland weeds. Weed Technology. Vol. 16, No. 1. p. 43–49
- ^ Flame weeding for vegetable crops
- ^ Fact sheet
Manufacturers and distributors
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