Horticulture/2,4-Dichlorophenoxyacetic acid

Dichlorophenoxyacetic acid (2,4-D, or C8H6Cl2O3) is a common systemic herbicide used in the control of broadleaf weeds. It is the third-most widely used herbicide in North America and the most widely used herbicide in the world. It was developed during World War II by a British team at Rothamsted Experimental Station, under the leadership of Judah Hirsch Quastel, aiming to increase crop yields for a nation at war. When it was commercially released in 1946, it became the first successful selective herbicide and allowed for greatly enhanced weed control in wheat, maize (corn), rice, and similar cereal grass crop, because it only kills dicots, leaving behind monocots.

2,4-D is sold in various formulations under a wide variety of brand names. It continues to be used for its low cost, despite the availability of more selective, more effective, and less toxic products.

2,4-D is a member of the phenoxy family of herbicides, which include:


 * 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)
 * 2-methyl-4-chlorophenoxyacetic acid (MCPA)
 * 2-(2-methyl-4-chlorophenoxy)propionic acids (mecoprop, MCPP)
 * 2-(2,4-dichlorophenoxy)propionic acid (dichloroprop, 2,4-DP)
 * (2,4-dichlorophenoxy)butyric acid (2,4-DB)

2,4-D is manufactured from chloroacetic acid and 2,4-dichlorophenol, which is itself produced by chlorination of phenol. The production process creates several contaminants including isomers, monochlorophenol, and other polychlorophenols and their acids.

The powerful defoliant and herbicide Agent Orange, used extensively throughout the Vietnam War, contained 2,4-D. However, the controversies associated with the use of Agent Orange were associated with a contaminant (dioxin) in the 2,4,5-T component.

Uses
2,4-D is most commonly used for:


 * Weed control in lawns and other turf
 * No-till burndown
 * Control of weeds and brush along fences and highway and railroad rights of way
 * Conifer release (control of broadleaf trees in conifer plantings)
 * Grass hayfields and pastures
 * Cereal grains
 * Corn and sorghum (occasionally)

Over 1500 herbicide products contain 2,4-D as an active ingredient

Action
2,4-D is a synthetic auxin, which is a class of plant growth regulators.

Precautions
The LD50 in rats has been reported as 375 and 666 mg/kg in two different studies. Single oral doses of 5 and 30 mg/kg body weight did not cause any acute toxic effects in human volunteers.

The amine salt formulations can cause irreversible eye damage.