Herbicide

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Herbicide , also known as weedkiller , is a chemical used to control undesirable plants. Selective herbicides control certain weed species, while leaving the desired plant relatively unharmed, while non-selective herbicides (sometimes called total weedkiller in commercial products) can be used to clean up waste land, industrial sites and construction, railroads and rail embankments because they kill all plant material with which they touch. Regardless of selective/non-selective, other important differences include persistence (also known as remaining action : how long the product stays in place and remains active), means absorption (whether it is absorbed by leaves on the ground only, through roots, or by other means), and action mechanism (how it works). Historically, products such as common salt and other metal salts are used as herbicides, but these are gradually disliked and in some countries this number is prohibited because of their persistence in soil, and poisoning and groundwater contamination problems. Herbicides have also been used in war and conflict.

Modern herbicides often mimic natural plant hormone imitations that interfere with the growth of target plants. The term organic herbicides has become a herbicide meant for organic farming. Some plants also produce their own natural herbicides, such as the genus (walnuts), or paradise trees; acts such as natural herbicides, and other related chemical interactions, called allelopathy. Because of herbicide resistance - a major concern in agriculture - a number of products incorporate herbicides in various ways of action. Integrated pest management can use herbicides along with other pest control methods.

In the US in 2007, about 83% of all herbicidal use, determined by the weight applied, was in agriculture. In 2007, world pesticide expenditures totaled about $ 39.4 billion; The herbicide is about 40% of the sale and is the largest part, followed by insecticides, fungicides, and other types. Smaller numbers are used in forestry, pasture systems, and management of areas set aside as wildlife habitats.

Video Herbicide

History

Before the widespread use of chemical herbicides, cultural controls, such as changing soil pH, salinity, or fertility rates, are used to control weeds. Mechanical controls (including soil preparation) are also (and still are) used to control weeds.

First herbicide

Although chemical herbicide research began in the early 20th century, the first major breakthrough was the result of research conducted in England and the United States during the Second World War into the potential use of herbicide in war. The first modern herbicide, 2,4-D, was first discovered and synthesized by W. G. Templeman at Imperial Chemical Industries. In 1940, he pointed out that "Properly used growth materials will kill certain broadleaf weeds in cereals without damaging plants." In 1941, his team managed to synthesize chemistry. In the same year, Pokorny in the US achieved this as well.

Independently, the team under Juda Hirsch Quastel, who worked at the Rothamsted Experimental Station made the same discovery. Quastel was assigned by the Council of Agricultural Research (ARC) to find methods to improve crop yields. By analyzing the soil as a dynamic system, rather than an inert substance, it is capable of applying a technique such as perfusion. Quastel is able to measure the effects of various plant hormones, inhibitors and other chemicals on the activity of microorganisms in the soil and assess their direct impact on plant growth. While full-time units remain confidential, certain discoveries are developed for commercial use after the war, including the 2.4-D compounds.

When 2.4-D was released commercially in 1946, it sparked a world revolution in agricultural produce and became the first successful selective herbicide. This allows for highly improved weed control in wheat, corn (maize), rice, and similar cereal grass plants, for killing dicoty (broad-leaved plants), but not most monocots (grass). The low cost of 2,4-D has led to continued use today, and remains one of the most commonly used herbicides in the world. As with other acidic herbicides, the present formulation uses an amine salt (often trimethylamine) or one of the many esters of the parent compound. It's easier to handle than acid.

Further discovery

The triazine herbicide family, which included atrazine, was introduced in the 1950s; they have the current difference as the most apprehensive herbicide family related to groundwater contamination. Atrazine is not readily biodegradable (within weeks) after application to soil above neutral pH. Under alkaline soil conditions, atrazine can be brought into the soil profile as far as the water table by ground water after rain causes the contamination. Atrazine is thus said to have a "residue", a property generally undesirable for herbicides.

Glyphosate (Roundup) was introduced in 1974 for selective weed control. Following the development of glyphosate resistant plant crops, it is now used extensively for selective weed control in planting crops. The herbicide pair with resistant seeds contributed to the consolidation of the seed and chemical industries in the late 1990s.

Many modern chemical herbicides used in agriculture and gardening are specifically formulated to decompose within a short time after application. This is desirable, because it allows plants and plants to be planted afterwards, which otherwise can be affected by herbicides. However, herbicides with low residual activity (ie, rapidly decomposing) often do not provide weed control throughout the season and do not ensure that weed roots are killed under construction and paving (and can not appear destructively in the coming years), therefore there is still a role for weedkillers with high persistence levels in the soil.

Maps Herbicide

Terminology

Herbicides are often grouped according to the location of their action, because as a general rule, herbicides in the same class of action will produce similar symptoms in susceptible plants. Classification based on herbicide action sites is relatively better as herbicide resistance management can be handled better and more effectively. Classification by action mechanism (MOA) shows the first enzyme, protein, or biochemical step affected in the following application of the plant.

List of mechanisms found in modern herbicides

• ACCase inhibitors: Acetyl coenzyme A carboxylase (ACCase) is part of the first step of lipid synthesis. Thus, ACCase inhibitors affect the production of cell membranes in meristems from grass plants. The ACCases of the grass are sensitive to these herbicides, while the dicoty plant ACCESS is not.
ALS inhibitors: enzyme acetolactate synthase (ALS) (also known as acetohydroxyacid synthase, or AHAS) is the first step in the synthesis of branch-chain amino acids (valine, leucine, and isoleucine). These herbicides slowly starve the affected plants of this amino acid, which eventually leads to inhibition of DNA synthesis. They affect the grass and dikotil alike. The ALS inhibiting family includes various sulfonylureas (SUs) (such as Flazasulfuron and Metsulfuron-methyl), imidazolinones (IMIs), triazolopyrimidines (TPs), pyrimidinyl oxybenzoates (POBs), and sulfonylamino carbonyl triazolinones (SCTs). The ALS biological pathway exists only in plants and not animals, thus making ALS inhibitors among the safest herbicides.
• EPSPS inhibitors: Enolpyruvylshikimate enzyme 3-phosphate synthase (EPSPS) is used in the synthesis of tryptophan amino acids, phenylalanine and tyrosine. They affect the grass and dikotil alike. Glyphosate (Roundup) is a systemic EPSPS inhibitor that is attenuated by ground contact.
• Synthetic auxins inaugurate the era of organic herbicides. They were discovered in 1940 after a long study of auxin plant growth regulators. Synthetic Auxins mimic these plant hormones. They have several points of action on the cell membrane, and are effective in controlling dicotyles. 2,4-D is a synthetic auxin herbicide.
• The Photosystem II inhibitor reduces the flow of electrons from water to NADP at a photochemical step in photosynthesis. They bind the Qb site on the D1 protein, and prevent quinone binding to this site. Therefore, this group of compounds causes the electrons to accumulate on the chlorophyll molecule. As a result, oxidation reactions exceeding that normally tolerated by the cell occur, and the plant dies. Triazine herbicides (including atrazine) and urea derivatives (diurons) are photosystem II inhibitors.
• The Photosystem I inhibitor steals electrons from the normal path through FeS to Fdx to NADP leading to the direct release of electrons in oxygen. As a result, reactive oxygen species are produced and oxidation reactions are more than those normally tolerated by cells to occur, leading to crop deaths. Bipyridinium herbicides (such as diquat and paraquat) inhibit FeS until the Fdx step of the chain, while diphenyl ether herbicides (such as nitrofen, nitrofluorphene, and acifluorfene) inhibit Fdx to NADP steps.
• HPPD inhibitors inhibit 4-Hydroxyphenylpyruvate dioxigenase, which is involved in the breakdown of tyrosine. Tyrosine splitting products are used by plants to make carotenoids, which protect chlorophyll in plants from being destroyed by sunlight. If this happens, the plant becomes white due to the loss of chlorophyll, and the plant dies. Mesotrione and sulcotrione are herbicides in this class; drug, nitisinone, is found in the course of developing this herbicidal class.

Groups of herbicides (labeling)

One of the most important methods to prevent, delay, or manage resistance is to reduce dependence on a single herbicide action mode. To do this, farmers need to know how herbicides they want to use, but the relatively complex biochemical properties of plants make this difficult to determine. Efforts are made to simplify the understanding of the herbicide action mode by developing a classification system that classifies herbicides in a way that works. Finally the Herbicide Resistance Action Committee (HRAC) and the Weed of America Science Institute (WSSA) developed a classification system. WSSA and HRAC systems differ in group appointments. Groups in WSSA and HRAC systems are each determined by numbers and letters. The purpose of adding the "Group" classification and how it works on herbicide product labels is to provide a simple and practical approach to passing information to users. This information will facilitate the development of consistent and effective educational materials. This should increase user awareness about herbicide action actions and provide more accurate recommendations for resistance management. Another goal is to make it easier for users to keep a record of what herbicide action actions are used in a particular field year after year.

Family chemistry

Detailed investigations of the chemical structure of the active ingredients of listed herbicides indicate that some parts (parts are parts of a molecule that can include all functional groups or parts of functional groups as substructures; functional groups have the same chemical properties each time they occur in different compounds) have the same mechanism of action. According to Forouzesh et al . 2015, this section has been assigned to chemical names and active ingredients which are then classified in appropriate chemical families. Knowing about herbicide chemical groupings can serve as a short-term strategy for managing resistance to action sites.

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Usage and app

Most herbicides are used as water-based sprays using soil equipment. Soil equipment varies in design, but large areas can be sprayed using self-propelled sprayers equipped with a long boom, from 60 to 120 feet (18 to 37 m) with sprinkling nozzles spaced 20-30 inches (510-760 mm) apart. Towed, handheld, and even horse drawn distillers are also used. In large areas, herbicides can sometimes also be applied by air using helicopters or aircraft, or through irrigation systems (known as chemigation).

A further method of herbicide application developed around 2010, involves clearing the soil from an active weed seed bank rather than just killing weeds. It can successfully treat the annual crop but not the perennials. Researchers at the Agricultural Research Service found that applying herbicides to fields at the end of the weed growth season greatly reduced their seed production, and therefore less weeds would return the following season. Since most weeds are seasonal, their seeds will only survive on the ground for one or two years, so this method will be able to destroy such weeds after several years of herbicide use.

Weeds can also be used, where the axis dampened with herbicides is hung from the boom and dragged or rolled over a higher weed plant. This allows the treatment of weeds of higher grasslands by direct contact without affecting short but related plants in desert prairies underneath. This method has the benefit of avoiding spray sprays. In Wales, a scheme that offers free wiper-free rentals is launched in 2015 in an effort to reduce the level of MCPA in the water field.

Abusing and misapplication

Volatilization herbicides or spray sprays can cause herbicides to affect the surrounding land or plants, especially in windy conditions. Sometimes, the wrong field or plant can be sprayed by mistake.

Use politically, militarily and conflict

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Health and environmental effects

Herbicides have widely varying toxicities in addition to acute toxicity arising from the rapid consumption of significant quantities, and chronic toxicity arising from long-term environmental and workplace exposures. Many of the common herbicide suspicions revolve around the confusion between a valid statement of acute toxicity as opposed to the same statement of a lack of chronic toxicity at the recommended level of use. For example, while glyphosate formulations with high dye adren- vators are highly toxic, their use is found to be uncorrelated with health problems such as cancer in a large Department of Health study of 90,000 family members of farmers for more than one year. period of 23 years. That is, studies show a lack of chronic toxicity, but can not question the acute toxicity of herbicides.

Some herbicides cause various health effects from skin rash to death. An attack path may arise from intentional or intentional intentional consumption, improper application that results in herbicide in direct contact with a person or wildlife, inhale air spray, or food consumption before the labeled preharvest interval. In some circumstances, certain herbicides may be transported through surface washing or runoff to contaminate groundwater or distant surface water sources. Generally, conditions that promote herbicide transport include intense storm events (especially shortly after application) and land with limited capacity to absorb or retain herbicides. The properties of herbicides that increase the likelihood of transport include persistence (resistance to degradation) and high water solubility.

Phenoxy herbicides are often contaminated with dioxins such as TCDD; studies have shown that such contamination results in a small increase in cancer risk after exposure to the workplace to these herbicides. Triazine exposure has been implicated in a possible association of increased risk of breast cancer, although the causal relationship is still unclear.

Herbicide producers sometimes make false or misleading claims about the safety of their products. Chemical manufacturer Monsanto Company agreed to change its ads after pressure from New York Attorney General Dennis Vacco; Vacco complains of misleading claims that glyphosate-based herbicides, including Roundup, are safer than table salt and "practically non-toxic" to mammals, birds and fish (although evidence of this is said to be hard to find). Roundup is toxic and has caused untreated after digestion in amounts ranging from 85 to 200 ml, although it has been digested in large amounts of 500 ml with only mild or moderate symptoms. Manufacturers of Tordon 101 (Dow AgroSciences, owned by Dow Chemical Company) have claimed Tordon 101 has no effect on animals and insects, despite evidence of a strong carcinogenic activity of the active ingredient Picloram in studies in mice.

The risk of Parkinson's disease has been shown to increase with occupational exposure to herbicides and pesticides. Paraquat herbicides are thought to be one such factor.

All commercial, organic, and inorganic herbicides should be tested extensively before they are approved for sale and labeled by the Environmental Protection Agency. However, because of the large number of herbicides used, concerns about health effects are significant. In addition to the health effects caused by the herbicide itself, commercial herbicide blends often contain other chemicals, including the active ingredients, which have a negative impact on human health.

Ecological effects

The use of commercial herbicides generally has a negative impact on bird populations, although the impact is highly variable and often requires field studies to predict accurately. Laboratory studies often overestimate the negative impact on birds due to toxicity, predicting serious problems not observed in the field. Most of the observed effects are not caused by toxicity, but habitat changes and reduced number of bird species dependent on food or shelter. The use of herbicides in silviculture, used to support certain types of growth after clear-cutting, can lead to significant reductions in bird populations. Even when herbicides that have low toxicity to birds are used, they reduce the abundance of many types of vegetation in which birds depend. The use of herbicides in agriculture in the UK has been attributed to the decline of seed-bearing bird species that depend on weeds killed by herbicides. High use of herbicides in neotropic farming areas has been one of the factors involved in restricting the use of agricultural land for migratory migratory birds.

Frog populations can be adversely affected by the use of herbicides as well. While some studies have shown that atrazine may be teratogenic, causing demasculinization in male frogs, the US Environmental Protection Agency (EPA) and the independent Scientific Advisory Panel (SAP) examined all available studies on this topic and concluded that "atrazine does not adversely affect the development of gonad amphibians based on laboratory reviews and field studies. "

Scientific uncertainty about the full effects of herbicides

The health and environmental effects of many herbicides are unknown, and even the scientific community often disagrees with risks. For example, a 1995 panel of 13 scientists reviewing the study of 2,4-D carcinogenicity has divided opinion about the possibility of 2,4-D causing cancer in humans. In 1992, the study of phenoxy herbicide was too little to accurately assess the risk of many cancers of this herbicide, despite strong evidence that herbicidal exposure was associated with an increased risk of soft tissue sarcoma and non-Hodgkin's lymphoma. In addition, there are some opinions that herbicides may play a role in the sex reversal of certain organisms undergoing temperature-dependent sex determination, which can theoretically alter the sex ratio.

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Resistance

Weed resistance to herbicides has been a major concern in crop production worldwide. Resistance to herbicides is often associated with a lack of herbicide rotation programs and ongoing herbicide applications with the same action location. Thus, a correct understanding of herbicide action sites is essential for strategic planning of herbicide-based weed control.

Plants have developed resistance to atrazine and ALS-inhibitors, and more recently, to glyphosate herbicides. Marestail is one of the weeds that has developed glyphosate resistance. Glyphosate-resistant weeds are present in most soy, cotton and corn farms in some US states. Weeds that can withstand some other herbicides are spreading. Only a few new herbicides are approaching commercialization, and no one has a molecular action mode that has no obstacles. Since most herbicides can not kill all weeds, farmers rotate plants and herbicides to stop resistant weeds. During the early years, glyphosate is not subject to resistance and allows farmers to reduce the use of rotation.

A family of weeds that includes waterhemp (Amaranthus rudis) is the greatest concern. A 2008-9 survey of 144 water populations in the world in 41 Missouri counties revealed glyphosate resistance in 69%. Weeds from about 500 sites across Iowa in 2011 and 2012 reveal glyphosate resistance in about 64% of hemp water samples. The use of other killers to target "weed" weeds has become common, and probably enough to stop the spread of resistance From 2005 to 2010 researchers found 13 different weed species that have developed resistance to glyphosate. But since then only two have been found. Resistant weeds of different herbicides with very different biological action modes are on the rise. In Missouri, 43% of samples were resistant to two different herbicides; 6% reject three; and 0.5% reject four. In Iowa 89% of waterhemp samples held two or more herbicides, 25% resisted three, and 10% with five.

For southern cotton, the cost of herbicides has increased from between $ 50 and $ 75 per hectare a few years ago to about $ 370 per hectare by 2013. The resistance contributes to a massive shift from growing cotton; Over the last few years, cotton-growing areas have fallen by 70% in Arkansas and by 60% in Tennessee. For soybeans in Illinois, the cost increases from about $ 25 to $ 160 per hectare.

Dow, Bayer CropScience, Syngenta and Monsanto all developed herbicide-resistant seed varieties other than glyphosate, which would make it easier for farmers to use alternative weed killers. Although weeds have evolved some resistance to the herbicide, Powles says new combo seeds and herbicides should work well if used with proper rotation.

Biochemical resistance

Resistance to herbicides can be based on one of the following biochemical mechanisms:

• Site-targeted Resistance: This is due to the reduced (or even missing) herbicidal ability to bind to the target protein. The effect is usually associated with enzymes with important functions in the metabolic pathway, or components of the electron transport system. Site-targeted resistance may also be due to overexpression of target enzymes (via gene amplification or alteration in gene promoters).
• Non-site-targeted endurance: This is due to a mechanism that reduces the number of active herbicide compounds that reach the target site. One important mechanism is the enhanced metabolic detoxification of herbicides in weeds, leading to an insufficient amount of active substances reaching the target site. Reduced absorption and translocation, or sequestration of herbicides, may also result in insufficient herbicide transport to the target site.
• Cross resistance: In this case, a single resistance mechanism causes resistance to some herbicides. The term target-site cross-resistance is used when the herbicide binds to the same target site, whereas non-target-site cross-resistance is caused by a non-target-site mechanism (eg, enhanced metabolic detoxification) requiring resistance. across herbicides with different action sites.
• Many obstacles: In this situation, two or more resistance mechanisms are present in individual plants, or in plant populations.

Resistance Management

Worldwide experience is that farmers tend to do little to prevent developing herbicide resistance, and only take action when it is a problem in their own farm or neighbors. Careful observation is important so that any reduction of herbicidal properties can be detected. This may indicate a growing resistance. It is imperative that resistance is detected in the early stages as if it becomes an acute, whole-farm problem, the more limited options and the greater costs are almost inevitable. Table 1 lists the factors that allow the risk of resistance to be assessed. An important prerequisite for confirmation of resistance is a good diagnostic test. Ideally this should be fast, accurate, inexpensive and easily accessible. Many diagnostic tests have been developed, including greenhouse pot test, petri dish test and fluorescence chlorophyll. A key component of such tests is that the suspect population's response to herbicides can be compared to those known to be susceptible and resistant to standards under controlled conditions. Most cases of herbicide resistance are a consequence of repeated use of herbicides, often associated with plant monocultures and reduced cultivation practices. Therefore, it is necessary to modify these practices to prevent or delay the onset of resistance or to control the existing resistant populations. The main purpose is to reduce selection pressure. A unified grass management approach (IWM) is required, where as many tactics as possible are used to combat weeds. In this way, less dependence is placed on the herbicide and the selection pressure should be reduced.

Optimizing herbicide inputs to economic threshold levels should avoid unnecessary herbicides and reduce selection pressure. Herbicides should be used for their greatest potential by ensuring that time, dose, method of application, soil and climatic conditions are optimal for good activity. In the UK, partially weeded grasses such as Alopecurus myosuroides (blackgrass) and Avena spp. (Wild oats) can often be controlled adequately when herbicides are applied at 2-3 leaf stages, while subsequent applications in 2-3 tiller stages can fail badly. Spraying sprays, or applying herbicides only to infested areas, is another way to reduce overall herbicide use.

Table 1. The agronomic factors that influence the risk of developing herbicide resistance

Approach to treat resistant weed

Alternative Herbicides

When resistance is first suspected or confirmed, alternative efficacy tends to be the first consideration. The use of alternative herbicides that remain effective in a resistant population can be a successful strategy, at least in the short term. The effectiveness of alternative herbicides will largely depend on the degree of cross resistance. If there is resistance to one herbicide group, then herbicide use from another group can provide a simple and effective solution, at least in the short term. For example, many triazine-resistant weeds are readily controlled by the use of alternative herbicides such as cultivated or glyphosate. If resistance extends to more than one herbicide group, then the choice is more limited. It should not be assumed that the resistance will automatically extend to all herbicides with the same mode of action, although it is wise to assume this until proven otherwise. In many weeds, the level of cross-resistance among the five ALS inhibiting groups varies considerably. Much will depend on the existing resistance mechanism, and it should not be assumed that this will always be the same in different populations of the same species. These differences are caused, at least in part, in the presence of different mutations confers the resistance of the target location. As a result, selection for different mutations can result in different cross-resistance patterns. Increased metabolism can affect herbicides that are closely related to different degrees. For example, populations of Alopecurus myosuroides (blackgrass) with improved metabolic mechanisms show resistance to pendimethalin but not to trifluralin, although both are dinitroanilines. This is due to differences in the susceptibility of these two herbicides to oxidative metabolism. As a result, care is needed when trying to predict the efficacy of alternative herbicides.

Mixes and order

The use of two or more herbicides that have different mode of action can reduce the selection for resistant genotypes. Ideally, each component in the mix must:

• Active on target sites
• Have a high level of efficacy
• Detoxified by different biochemical pathways
• Have the same persistence in the ground (if this is a residual herbicide)
• Provide negative cross resistance
• Synergize activity from other components

There is no mixture that tends to have all of these attributes, but the first two listed are the most important. There is a risk that the mix will choose for resistance to both components in the long run. One practical advantage of the sequence of two herbicides compared with the mixture is that a better assessment of the efficacy of each herbicide component is possible, provided that sufficient time elapses between each application. The disadvantage with the sequence is that two separate applications must be created and possibly applications that will be less effective in the weeds that survive the first application. If this is resistant, then a second herbicide in the sequence may increase selection for resistant individuals by killing damaged vulnerable plants but not killed by the first application, but allowing larger, less affected, and survival-resistant plants. This has been cited as one of the reasons why ALS-resistant Stellaria media has evolved in recent Scotland (2000), although the regular use of sequences combines mecoprop, herbicide with different mode of action.

Herbicide rotation

Herbicide rotation from different chemical groups in consecutive years should reduce selection for resistance. This is a key element in most resistance prevention programs. The value of this approach depends on the degree of cross resistance, and whether dual resistance occurs because of several different resistance mechanisms. The practical problem is the lack of awareness of farmers from different herbicide groups. In Australia a scheme has been introduced where identifying letters is inserted on product labels as a means of enabling farmers to differentiate products with different modes of action.

Agricultural practices and resistance: case studies

Herbicide resistance is an important issue in Australian agriculture, after many Australian sheep farmers began exclusively to grow wheat in their pastures in the 1970s. The introduced ryegrass varieties, while good for grazing sheep, compete intensely with wheat. Ryegrasses produce so many seeds that, if left unchecked, they can actually strangle a field. Herbicides provide excellent control, while reducing soil disturbance due to less need for plowing. In less than a decade, ryegrass and other weeds began to develop resistance. In response, Australian farmers changed the method. In 1983, ryegrass patches had become immune to Hoegrass, a family of herbicides that inhibited an enzyme called acetyl coenzyme A carboxylase.

More recently, the term "organic" has implied a product used in organic farming. Under this definition, organic herbicides are one that can be used in agricultural enterprises that have been classified as organic. Depending on the application, they may be less effective than synthetic herbicides and are generally used in conjunction with cultural and mechanical weed control practices.

Homemade organic herbicides include:

• Corn gluten meal (CGM) is a natural pre-emergence weed control used in turfgrass, which reduces the germination of many broadleaf weeds and grasses.
• Effective vinegar for 5-20% acetic acid solution, with the highest concentration most effective, but severely damages surface growth, so respraying to treat regrowth is required. Endurance plants generally give up when attenuated by respraying.
• Steam has been applied commercially, but is now considered uneconomical and inadequate. It controls surface growth but not underground growth and so respraying to treat plant growth regrowth is necessary.
• Flame is considered more effective than steam, but suffers from similar difficulties.
• D-limonene (orange oil) is a natural decomposing agent that peels the skin or cuticles from weeds, causing dehydration and ultimately death.
• Saltwater or salt applied to the appropriate strength to rootzone will kill most plants.
• Monocerin produced by certain fungi will kill certain weeds like Johnson's grass.

Historical and other interests

• 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) is a widely used broadleaf herbicide until it is gradually removed from the late 1970s. While 2,4,5-T itself was only moderate toxicity, the manufacturing process for 2,4,5-T fouled this chemical with trace amounts 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). TCDD is highly toxic to humans. With proper temperature control during the production of 2,4,5-T, TCDD levels can be retained up to about 0.005 ppm. Before TCDD risks are well understood, initial production facilities do not have proper temperature control. The individual batches tested were later found to have as much as 60 ppm TCDD. 2,4,5-T was withdrawn from use in the United States in 1983, at a time when increased public sensitivity about chemical hazards in the environment. Public concerns about dioxin are high, and the production and use of other (non-herbicidal) chemicals that potentially contain TCDD contamination are also withdrawn. These include pentachlorophenol (wood preservative) and PCB (mainly used as stabilization agent in transformer oil). Some people feel that the withdrawal of 2,4,5-T is not based on sound science. 2,4,5-T has been replaced by caged and triclopyr.
• Agent Orange is a mixture of herbicides used by the British military during Malaya Emergency and the US military during the Vietnam War between January 1965 and April 1970 as defoliant. It is a 50/50 mixture of n -butyl esters of 2,4,5-T and 2,4-D. Due to TCDD contamination in the 2.4,5-T component, it has been blamed for serious illness in many affected people.
• Diesel, and other heavy oil derivatives, are known to be used informally, but are usually prohibited for this purpose.

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See also

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References

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Further reading

• Brief History of On-track Weed Control in N.S.W. SRA during Steam Era Longworth, Jim Australian Railway Historical Society Bulletin, April, 1996 pp99-116

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External links

General Information

• National Pesticide Information Center, Information on pesticide related topics
• National Agricultural Statistics Service

Regulatory policy

• US EPA
• British Pesticides Safety Directorate
• European Commission pesticide information
• Canadian Pest Management Agency

Source of the article : Wikipedia