Editing Herbicide (section)

===First herbicides===
[[File:2-(2,4-dichlorophenoxy)acetic acid 200.svg|thumb|[[2,4-D]], the first selective chemical herbicide, was discovered during the [[Second World War]].]]
The major breakthroughs occurred during the [[Second World War]] as the result of research conducted independently in the United Kingdom and the United States into the potential [[herbicidal warfare|use of herbicides in war]].<ref>{{cite book|url=https://books.google.com/books?id=hVK4vrpma2YC|title=Herbicides and Plant Physiology|author1=Andrew H. Cobb |author2=John P. H. Reade |year=2011|publisher=John Wiley & Sons|chapter=7.1|isbn=9781444322491}}</ref> The compound [[2,4-D]] was first synthesized by [[W. G. Templeman]] at [[Imperial Chemical Industries]]. In 1940, his work with [[Indole-3-acetic acid|indoleacetic acid]] and [[1-Naphthaleneacetic acid|naphthaleneacetic acid]] indicated that "growth substances applied appropriately would kill certain broad-leaved weeds in cereals without harming the crops,"<ref>{{Cite journal |last=Troyer |first=James R. |date=March 2001 |title=In the beginning: the multiple discovery of the first hormone herbicides |url=https://www.cambridge.org/core/product/identifier/S0043174500009954/type/journal_article |journal=Weed Science |language=en |volume=49 |issue=2 |pages=290–297 |doi=10.1614/0043-1745(2001)049[0290:ITBTMD]2.0.CO;2 |s2cid=85637273 |issn=0043-1745}}</ref><ref>{{cite journal |doi=10.1126/science.100.2590.154 |title=The Herbicidal Action of 2,4 Dichlorophenoxyacetic and 2,4,5 Trichlorophenoxyacetic Acid on Bindweed |date=1944 |last1=Hamner |first1=Charles L. |last2=Tukey |first2=H. B. |journal=Science |volume=100 |issue=2590 |pages=154–155 |pmid=17778584 |bibcode=1944Sci...100..154H }}</ref> though these substances were too expensive and too short-lived in soil due to degradation by [[Microorganism|microorganisms]] to be of practical agricultural use; by 1941, his team succeeded in synthesizing a wide range of chemicals to achieve the same effect at lower cost and better efficacy, including 2,4-D.<ref>{{Cite journal |last=Templeman |first=W. G. |date=1945 |title=Harnessing the hormones |journal=Ctry. Life |issue=98 |pages=923}}</ref> In the same year, R. Pokorny in the US achieved this as well.<ref>{{cite book|url=https://books.google.com/books?id=Xpx25mRzF_YC|title=A History of Weed Science in the United States|author=Robert L Zimdahl|year=2007|publisher=Elsevier|isbn=9780123815026}}</ref> Independently, a team under [[Juda Hirsch Quastel]], working at the [[Rothamsted Research|Rothamsted Experimental Station]] made the same discovery. Quastel was tasked by the [[Agricultural and Food Research Council|Agricultural Research Council]] (ARC) to discover methods for improving crop yield. By analyzing soil as a dynamic system, rather than an inert substance, he was able to apply techniques such as [[perfusion]]. Quastel was able to quantify the influence of various [[plant hormone]]s, inhibitors, and other chemicals on the activity of microorganisms in the soil and assess their direct impact on [[plant growth]]. While the full work of the unit remained secret, certain discoveries were developed for commercial use after the war, including the 2,4-D compound.<ref>{{cite book|doi=10.1021/ba-1950-0001.ch045|chapter=2,4-Dichlorophenoxyacetic Acid (2,4-D) as a Selective Herbicide|title=Agricultural Control Chemicals|series=Advances in Chemistry|year=1950|last1=Quastel|first1=J. H.|isbn=978-0-8412-2442-1|volume=1|pages=244–249|publisher=American Chemical Society }}</ref>

When 2,4-D was commercially released in 1946, it became the first successful selective herbicide, triggering a worldwide revolution in agricultural output. It allowed for greatly enhanced weed control in [[wheat]], [[maize]] (corn), [[rice]], and similar [[cereal]] grass crops, because it kills [[dicots]] (broadleaf plants), but not most [[monocots]] (grasses). 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.<ref>{{cite web |date=2015 |title=2,4-D Benefits |url=http://www.24d.org/benefits/default.aspx |url-status=dead |archive-url=https://web.archive.org/web/20151102024718/http://www.24d.org/benefits/default.aspx |archive-date=2015-11-02 |access-date=2015-11-06 |publisher=The Industry Task Force II on 2,4-D Research Data}}</ref> Like other acid herbicides, current formulations use either an amine salt (often [[trimethylamine]]) or one of many [[ester]]s of the parent compound.