An herbicide is used to kill unwanted plants. 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. Herbicides used to clear waste ground are nonselective and kill all plant material with which they come into contact. Some plants produce natural herbicides, such as the genus Juglans (walnuts). They are applied in total vegetation control (TVC) programs for maintenance of highways and railroads. Smaller quantities are used in forestry, pasture systems, and management of areas set aside as wildlife habitat. For other uses, see Plant (disambiguation). ... Look up crop in Wiktionary, the free dictionary. ... Yellow starthistle, a thistle native to southern Europe and the Middle East that is an invasive weed in parts of North America. ... Hormone is also the NATO reporting name for the Soviet/Russian Kamov Ka-25 military helicopter. ... For other uses, see Plant (disambiguation). ... For other uses, see Walnut (disambiguation). ... Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants, and is, by far, the most abundant biotic element of the biosphere. ... Look up habitat in Wiktionary, the free dictionary. ...

Herbicides are widely used in agriculture and in landscape turf management. In the U.S., they account for about 70% of all agricultural pesticide use.^[1]

History

This section does not cite any references or sources. (July 2007) Please improve this section by adding citations to reliable sources. Unverifiable material may be challenged and removed.

Prior to the widespread use of chemical herbicides, cultural controls, such as altering soil pH, salinity, or fertility levels, were used to control weeds. Mechanical control (including tillage) was also (and still is) used to control weeds. Image File history File links Question_book-3. ... In agriculture cultural control is the practice of modifying the growing environment to reduce the prevalence of unwanted pests. ...

The first widely used herbicide was 2,4-dichlorophenoxyacetic acid, often abbreviated 2,4-D. 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. These are easier to handle than the acid. 2,4-Dichlorophenoxyacetic acid (2,4-D) is a common systemic herbicide used in the control of broadleaf weeds. ... Trimethylamine, also known as NMe3, N(CH3)3, and TMA, is a colorless, hygroscopic, and flammable simple amine with a typical fishy odor in low concentrations and an ammonia-like odor in higher concentrations. ... For other uses, see Ester (disambiguation). ...

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 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. Atrazine, 2-chloro-4-(ethylamine)-6-(isopropylamine)-s-triazine, is an s-triazine-ring herbicide that is used globally to stop pre- and post-emergence broadleaf and grassy weeds in major crops. ...

Glyphosate, frequently sold under the brand name Roundup, was introduced in 1974 for non-selective weed control. 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. It has been suggested that Roundup be merged into this article or section. ... Roundup is the brand name of a systemic, broad-spectrum herbicide produced by the U.S. life sciences giant Monsanto. ...

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.

Health effects

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 mamals, 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. 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-lives. 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. Runoff flowing into a stormwater drain Surface runoff is water, from rain, snowmelt, or other sources, that flows over the land surface, and is a major component of the water cycle[1][2]. Runoff that occurs on surfaces before reaching a channel is also called overland flow. ... Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ... In biology, a mutagen (Latin, literally origin of change) is an agent that changes the genetic information (usually DNA) of an organism and thus increases the number of mutations above the natural background level. ... In pathology, a carcinogen is any substance or agent that promotes cancer. ... Teratogenesis is a medical term from the Greek, literally meaning monster making. ...

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. Red blood cell infected with Malaria (Italian: bad air; formerly called ague or marsh fever in English) is an infectious disease which causes about 500 million infections and 2 million deaths annually, mainly in the tropics and sub-Saharan Africa. ... The Apicoplast is a relict, non-photosynthetic plastid found in the malaria parasite, Plasmodium falciparum. ... Plant cells with visible chloroplasts. ... A parasite is an organism that spends a significant portion of its life in or on the living tissue of a host organism and which causes harm to the host without immediately killing it. ... Binomial name Welch, 1897 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.

By activity:

• 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.

By use:

• 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.

• 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. The main mechanisms of action are: Preemergent herbicides prevent the germination of seeds by inhibiting a key enzyme. ... Wikipedia does not yet have an article with this exact name. ...

• 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.

• 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). These herbicides slowly starve affected plants of these amino acids which eventually leads to inhibition of DNA synthesis. 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. They affect grasses and dicots alike. Glyphosate (Roundup) is a systemic EPSPS inhibitor but inactivated by soil contact.

• Synthetic auxin inaugurated the era of organic herbicides. They were discovered in the 1940s after a long study of the plant growth regulator auxin. 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. As a consequence, oxidation reactions in excess of those normally tolerated by the cell occur, and the plant dies. The triazine herbicides (including atrazine) and urea derivatives (diuron) are photosystem II inhibitors.^[2]

Orders see text Dicotyledons or dicots are flowering plants whose seed contains two embryonic leaves or cotyledons. ... 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). ... Valine is an amino acid that cannot be synthesized by humans, so it is considered an essential amino acid for human life. ... Leucine is one of the 20 most common amino acids and coded for by DNA. It is isomeric with isoleucine. ... Isoleucine is an α-amino acid with the chemical formula HO2CCH(NH2)CH(CH3)CH2CH3. ... This article is about the class of chemicals. ... Tryptophan (abbreviated as Trp or W)[1] is one of the 20 standard amino acids, which are the building blocks of proteins, and an essential amino acid in the human diet. ... Phenyl alanine is an α-amino acid with the formula HO2CCH(NH2)CH2C6H5. ... Tyrosine (from the Greek tyros, meaning cheese, as it was first discovered in 1846 by German chemist Justus von Liebig in the protein casein from cheese[1][2]), 4-hydroxyphenylalanine, or 2-amino-3(4-hydroxyphenyl)-propanoic acid, is one of the 20 amino acids that are used by cells... It has been suggested that Roundup be merged into this article or section. ... IAA appears to be the most active Auxin in plant growth. ... Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. ... The most fundamental reactions in chemistry are the redox processes. ...

Organic Herbicides

Almost all herbicides in use today are considered "organic" herbicides in that they contain carbon as a primary molecular component. An 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. 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 farming is a psuedoscientific form of agriculture which avoids or largely excludes the use of synthetic fertilizers and pesticides, plant growth regulators, and livestock feed additives. ...

Organic herbicides include:

• Spices are now effectively used in patented herbicides.

• Vinegar^[3] 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. Resistant plants generally succumb when weakened by respraying.

• Steam has been applied commercially but is now considered uneconomic and inadequate.^[4][5][6] 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.^[7]

For other uses, see Spice (disambiguation). ... Vinegar is sometimes infused with spices or herbs—as here, with oregano. ... For other uses, see Steam (disambiguation). ... Flame generated by the burning of a candle. ...

Application

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).

Terminology

• 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. 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).
• atrazine, a triazine herbicide used in corn and sorghum for control of broadleaf weeds and grasses. 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. 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. 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.^[8]
• 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. 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.
• Linuron, is a non-selective herbicide used in the control of grasses and broadleafed weeds. It works by inhibiting photosynthesis.
• metoalachlor, a pre-emergent herbicide widely used for control of annual grasses in corn and sorghum; it has largely replaced atrazine for these uses.
• Paraquat, a nonselective contact herbicide used for no-till burndown and in aerial destruction of marijuana and coca plantings. 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. It is another synthetic auxin.
• Triclopyr

2,4-D (or 2,4-dichlorophenoxyacetic acid) is a common systemic herbicide used in the control of broadleaf weeds. ... Atrazine, 2-chloro-4-(ethylamine)-6-(isopropylamine)-s-triazine, is an s-triazine-ring herbicide that is used globally to stop pre- and post-emergence broadleaf and grassy weeds in major crops. ... Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) is a selective herbicide used for control of broadleaf weeds, especially thistles and clovers. ... Dicamba is an herbicide used to control annual and perennial broadleaf weeds in grain crops and grasslands, and it is used to control brush and bracken in pastures. ... DL-Phosphinotricin is an herbicide commonly used in plant molecular biology and plant tissue culture. ... It has been suggested that Roundup be merged into this article or section. ... Valine is an amino acid that cannot be synthesized by humans, so it is considered an essential amino acid for human life. ... Leucine is one of the 20 most common amino acids and coded for by DNA. It is isomeric with isoleucine. ... Isoleucine is an α-amino acid with the chemical formula HO2CCH(NH2)CH(CH3)CH2CH3. ... Atrazine, 2-chloro-4-(ethylamine)-6-(isopropylamine)-s-triazine, is an s-triazine-ring herbicide that is used globally to stop pre- and post-emergence broadleaf and grassy weeds in major crops. ... Paraquat is the trade name for N,N-Dimethyl-4,4-bipyridinium dichloride, a viologen. ... Picloram (C6H3Cl3N2O2) is colorless compound used as a herbicide. ... Triclopyr is a systemic, foliar herbicide in the pyridine group. ...

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. 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). 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. These included pentachlorophenol (a wood preservative) and PCBs (mainly used as stabilizing agents in transformer oil). 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.

• Agent Orange was a herbicide blend 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.

2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) is an herbicide used to defoliate broad leafed plants. ... (Redirected from 2,3,7,8-tetrachlorodibenzo-p-dioxin) Dioxins form a family of toxic chlorinated organic compounds that bioaccumulate in humans and wildlife due to their fat solubility. ... Polychlorinated dibenzodioxins are a group of halogenated organic compounds which are significant because they act as environmental pollutants. ... Pentachlorophenol (C6HCl5O) is a synthetic fungicide which is an organochloride. ... PCB may refer to: Brazilian Communist Party (in Portuguese, Partido Comunista Brasileiro) Communist Party of Bolivia (in Spanish, Partido Comunista de Bolivia) Pakistan Cricket Board PCB Piezotronics PCBoard, a bulletin board system software Police Complaints Board, which oversaw the system for handling complaints made against police forces in England and... Dicamba is an herbicide used to control annual and perennial broadleaf weeds in grain crops and grasslands, and it is used to control brush and bracken in pastures. ... Triclopyr is a systemic, foliar herbicide in the pyridine group. ... For other uses, see Agent Orange (disambiguation). ... Combatants Republic of Vietnam United States Republic of Korea Thailand Australia New Zealand The Philippines National Front for the Liberation of South Vietnam Democratic Republic of Vietnam People’s Republic of China Democratic Peoples Republic of Korea Strength US 1,000,000 South Korea 300,000 Australia 48,000... Agent Purple is a cousin of the Agent Orange and Agent Pink herbicides. ... Why are there links to a page that doesnt exist? ...

See also

• Agriculture
• Bioherbicide
• Carcinogen
• Farming
• Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) of the United States (covers herbicides despite title)
• List of environmental health hazards
• Mutagen
• Organic farming
• Organic gardening
• Pesticide application
• Pesticide toxicity to bees
• Rainbow Herbicides
• Soil contamination
• Surface runoff
• Teratogen
• Weed Science
• Weed control

A bioherbicide is a herbicide that is based on a living organism, such as fungi, bacteria or protozoa. ... Look up carcinogen in Wiktionary, the free dictionary. ... Farming, ploughing rice paddy, in Indonesia Agriculture is the process of producing food, feed, fiber and other desired products by cultivation of certain plants and the raising of domesticated animals (livestock). ... is only done after a period of data collection to determine the effectiveness for its intended use, appropriate dosage, and hazards of the particular material. ... 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) of an organism and thus increases the number of mutations above the natural background level. ... Organic farming is a psuedoscientific form of agriculture which avoids or largely excludes the use of synthetic fertilizers and pesticides, plant growth regulators, and livestock feed additives. ... It has been suggested that this article or section be merged with Organic horticulture. ... Pesticides vary in their effect on bees. ... The term Rainbow herbicides refers to several defoliants used by the U.S. military during the Vietnam War: Agent Orange Agent Purple Agent Pink Agent Green Agent Blue Agent White ... Excavation of leaking underground storage tank causing soil contamination Soil pollution comprises the pollution of soils with materials, mostly chemicals, that are out of place or are present at concentrations higher than normal which may have adverse effects on humans or other organisms. ... Runoff flowing into a stormwater drain Surface runoff is water, from rain, snowmelt, or other sources, that flows over the land surface, and is a major component of the water cycle[1][2]. Runoff that occurs on surfaces before reaching a channel is also called overland flow. ... Teratogenesis is a medical term from the Greek, literally meaning monster making. ... This article does not cite its references or sources. ... Weed control, a botanical component of pest control, stops weeds from reaching a mature stage of growth when they could be harmful to domesticated plants, sometimes livestocks, by using manual techniques including soil cultivation, mulching and herbicides. ...

References

1. ^ Kellogg RL, Nehring R, Grube A, Goss DW, and Plotkin S (February 2000), Environmental indicators of pesticide leaching and runoff from farm fields. United States Department of Agriculture Natural Resources Conservation Service. Retrieved on 2007-10-03.
2. ^ Stryer, Lubert (1995). Biochemistry, 4th Edition. W.H. Freeman and Company, pp. 670. ISBN 0-7167-2009-4. 
3. ^ Spray Weeds With Vinegar?
4. ^ Weed Management in Landscapes
5. ^ Organic Weed Management in Vineyards
6. ^ Kolberg, Robert L., and Lori J. Wiles. 2002. Effect of steam application on cropland weeds. Weed Technology. Vol. 16, No. 1. p. 43–49
7. ^ Flame weeding for vegetable crops
8. ^ Fact sheet

Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 276th day of the year (277th in leap years) in the Gregorian calendar. ...

External links

General Information

• National Pesticide Information Center (NPIC) Information about pesticide-related topics.

Manufacturers and distributors

• Bayer Cropscience
• Dowagro
• DuPont http://www2.dupont.com/Agriculture/en_US/
• Syngenta
• BASF
• Monsanto

Regulatory policy

• US EPA
• UK Pesticides Safety Directorate
• European Commission pesticide information

Usage statistics

• USDA

Natural herbicides

• Herbicidal activity of Veronica filiformis

2,4,5-T

• www.gr.nl[['Link title'Bold text]]