It is usually referred to by its ISO common name 2,4-D.[4] It is a systemic herbicide that kills most broadleaf weeds by causing uncontrolled growth, but most grasses such as cereals, lawn turf, and grassland are relatively unaffected.

2,4-D is one of the oldest and most widely available herbicides and defoliants in the world, having been commercially available since 1945, and is now produced by many chemical companies since the patent on it has long since expired.

It can be found in numerous commercial lawn herbicide mixtures, and is widely used as a weedkiller on cereal crops, pastures, and orchards.

[6] The first scientific publication describing the 2,4-D structure and plant growth regulating activity was by Percy W. Zimmerman and Albert E. Hitchcock at the Boyce Thompson Institute,[7] who were not the original inventors.

[8] William Templeman found that when indole-3-acetic acid (IAA), a naturally-occurring auxin, was used at high concentrations, it could stop plant growth.

The production processes may create several contaminants including di-, tri-, and tetrachlorodibenzo-p-dioxin isomers and N-nitrosamines, as well as monochlorophenol.

Uncontrolled, unsustainable growth ensues, causing stem curl-over, leaf withering, and eventual plant death.

Along roadways, railways, and power lines, it is used to control weeds and brush which might interfere with safe operation and damage equipment.

Along waterways, it is used to control aquatic weeds that might interfere with boating, fishing, and swimming or clog irrigation and hydroelectric equipment.

Swimming is restricted for 24 hours after application of certain 2,4-D products applied to control aquatic weeds to avoid eye irritation.

[44] In June 2015 the World Health Organization's International Agency for Research on Cancer confirmed its 1987 classification of 2,4-D as a possible carcinogen.

[50] A July 2013 Four Corners investigation found elevated levels of dioxins in a generic version of 2,4-D, one of Australia's most widely used herbicides.

[40]: 54  2,4-D is broken down by microbes in soil, in processes that involve hydroxylation, cleavage of the acid side-chain, decarboxylation, and ring opening.

[18] 2,4-D has a low binding affinity in mineral soils and sediment, and in those conditions is considered intermediately to highly mobile, and therefore likely to leach if not degraded.

As a result of the extensive metadata on environmental behavior, physiology, and genetics, 2,4-D was the first herbicide for which the bacteria actively responsible for in situ degradation were demonstrated.

[65] In October 2014, the US EPA registered Enlist Duo, an herbicide containing the less volatile 2,4-D choline salt, glyphosate, and an antidrift agent, for use in six states: Illinois, Indiana, Iowa, Ohio, South Dakota, and Wisconsin.

[20] In November 2015, the EPA attempted to withdraw its own approval of Enlist Duo, as a result of legal actions against both the agency and Dow by two U.S. groups.

On January 25, 2016, the US Ninth Circuit Court of Appeals denied EPA's motion to vacate its Enlist Duo registration.

[66][67] On 21 August 2013, the Australian Pesticides and Veterinary Medicines Authority (APVMA) banned selected 2,4-D high volatile ester (HVE) products due to their environmental hazards.

[69] In 2010, Dow published that it had created genetically modified soybeans made resistant to 2,4-D by insertion of a bacterial aryloxyalkanoate dioxygenase gene, aad1.

[70][71][72]: 1  Dow intended it to be used as an alternative or complement to Roundup Ready crops due to the increasing prevalence of glyphosate-resistant weeds.

[21] In September 2014, the USDA also approved Dow's maize and soybeans, and in October, the EPA registered the "Enlist Duo" herbicide containing 2,4-D and glyphosate.