the amino acids tryptophan, phenylalanine and tyrosine. they affect grasses and dicots alike. glyphosate (roundup) is a systemic epsps inhibitor inactivated by soil contact. auxin-like herbicides: the discovery of synthetic auxins 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 in some way. they have several points of action on the cell membrane, and are effective in the control of dicot plants. 2,4-d, 2,4,5-t, and aminopyralid are examples of synthetic auxin herbicides. photosystem ii inhibitors reduce electron flow from water to nadp+ 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 causes 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. photosystem i inhibitors steal electrons from ferredoxins, specifically the normal pathway through fes to fdx to nadp+, leading to direct discharge of electrons on oxygen. as a result, reactive oxygen species are produced and oxidation reactions in excess of those normally tolerated by the cell occur, leading to plant death. bipyridinium herbicides (such as diquat and paraquat) inhibit the fes to fdx step of that chain, while diphenyl ether herbicides (such as nitrofen, nitrofluorfen, and acifluorfen) inhibit the fdx to nadp+ step. hppd inhibitors inhibit 4-hydroxyphenylpyruvate dioxygenase, which are involved in tyrosine breakdown. tyrosine breakdown products are used by plants to make carotenoids, which protect chlorophyll in plants from being destroyed by sunlight. if this happens, the plants turn white due to complete loss of chlorophyll, and the plants die. mesotrione and sulcotrione are herbicides in this class; a drug, nitisinone, was discovered in the course of developing this class of herbicides. herbicide group (labeling) one of the most important methods for preventing, delaying, or managing resistance is to reduce the reliance on a single herbicide mode of action. to do this, farmers must know the mode of action for the herbicides they intend to use, but the relatively complex nature of plant biochemistry makes this difficult to determine. attempts were made to simplify the understanding of herbicide mode of action by developing a classification system that grouped herbicides by mode of action. eventually the herbicide resistance action committee (hrac) and the weed science society of america (wssa) developed a classification system. the wssa and hrac systems differ in the group designation. groups in the wssa and the hrac systems are designated by numbers and letters, respectively. the goal for adding the “group” classification and mode of action to the herbicide product label is to provide a simple and practical approach to deliver the information to users. this information will make it easier to develop educational material that is consistent and effective. it should increase user's awareness of herbicide mode of action and provide more accurate recommendations for resistance management. another goal is to make it easier for users to keep records on which herbicide mode of actions are being used on a particular field from year to year. chemical family detailed investigations on the chemical structure of active ingredients of the registered herbicides showed that some moieties (moiety is a part of a molecule that may include either whole functional groups or parts of functional groups as substructures; a functional group has similar chemical properties whenever it occurs in different compounds) have the same mechanisms of action. according to forouzesh et al. 2015, these moieties have been assigned to the names of chemical families and active ingredients are then classified within the chemical families accordingly. knowing about herbicide chemical family grouping could serve as a short-term strategy for managing resistance to site of action. use and application herbicides being sprayed from the spray arms of a tractor in north dakota. 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 long booms, of 60 to 120 feet (18 to 37 m) with spray nozzles spaced every 20–30 inches (510–760 mm) apart. towed, handheld, and even horse-drawn sprayers are also used. on large areas, herbicides may also at times be applied aerially using helicopters or airplanes, or through irrigation systems (known as chemigation). a further method of herbicide application developed around 2010, involves ridding the soil of its active weed seed bank rather than just killing the weed. this can successfully treat annual plants but not perennials. researchers at the agricultural research service found that the application of herbicides to fields late in the weeds' growing season greatly reduces their seed production, and therefore fewer weeds will return the following season. because most weeds are annuals, their seeds will only survive in soil for a year or two, so this method will be able to destroy such weeds after a few years of herbicide application. weed-wiping may also be used, where a wick wetted with herbicide is suspended from a boom and dragged or rolled across the tops of the taller weed plants. this allows treatment of taller grassland weeds by direct contact without affecting related but desirable shorter plants in the grassland sward beneath. the method has the benefit of avoiding spray drift. in wales, a scheme offering free weed-wiper hire was launched in 2015 in an effort to reduce the levels of mcpa in water courses. there is little difference in forestry in the early growth stages, when the height similarities between growing trees and growing annual crops yields a similar problem with weed competition. unlike with annuals however, application is mostly unnecessary thereafter and is thus mostly used to decrease the delay between productive economic cycles of lumber crops. misuse and misapplication part of a series onpollutionair pollution from a factory air acid rain air quality index atmospheric dispersion modeling chlorofluorocarbon exhaust gas haze indoor air internal combustion engine global dimming global distillation ozone depletion particulates persistent organic pollutant smog aerosol soot volatile organic compound biological biological hazard genetic introduced species (invasive species) digital information electromagnetic light ecological overillumination radio spectrum natural ozone radium and radon in the environment volcanic ash wildfire noise transportation land water air rail sustainable transport urban sonar 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clutter overhead power lines traffic signs vandalism war chemical warfare herbicidal warfare (agent orange) nuclear holocaust (nuclear fallout - nuclear famine - nuclear winter) scorched earth unexploded ordnance war and environmental law water agricultural wastewater diseases eutrophication firewater freshwater groundwater hypoxia industrial wastewater marine debris monitoring nonpoint source see misc section nutrient ocean acidification oil spill pharmaceuticals freshwater salinization septic tanks sewage septic tanks pit latrine shipping stagnation sulfur water surface runoff turbidity urban runoff water quality misc point source area source legacy pollution lists diseases law by country most polluted cities least polluted cities by pm2.5 treaties categories by country environment portal ecology portal herbicide volatilisation or spray drift may result in herbicide affecting neighboring fields or plants, particularly in windy conditions. sometimes, the wrong field or plants may be sprayed due to error. use politically, militarily, and in conflict handicapped children in vietnam, most of them victims of agent orange, 2004 although herbicidal warfare uses chemical substances, its main purpose is to disrupt agricultural food production and/or to destroy plants which provide cover or concealment to the enemy. during the malayan emergency (1948–1960), the british military deployed herbicides and defoliants in the malaysian countryside (including crop fields) in order to deprive malayan national liberation army (mnla) insurgents of cover, potential sources of food and to flush them out of the jungle. deployment of herbicides and defoliants served the dual purpose of thinning jungle trails to prevent ambushes and destroying crop fields in regions where the mnla was active to deprive them of potential sources of food. herbicides and defoliants were also sprayed from royal air force (raf) aircraft. the use of herbicides as a chemical weapon by the u.s. military during the vietnam war has left tangible, long-term impacts upon the vietnamese people and u.s soldiers that handled the chemicals. more than 20% of south vietnam's forests, and 3.2% of its cultivated land were sprayed at least once between during the war. the government of vietnam says that up to four million people in vietnam were exposed to the defoliant, and as many as three million people have suffered illness because of agent orange, while the red cross of vietnam estimates that up to one million people were disabled or have health problems as a result of exposure to agent orange. the united states government has described these figures as unreliable. health and environmental effects