Rainbow herbicide

The Rainbow Herbicides are a group of "tactical use" chemicals used by the United States military in Southeast Asia during the Vietnam War. Success with Project AGILE field tests with herbicides in South Vietnam in 1961 and inspiration by the British use of herbicides and defoliants during the Malayan Emergency in the 1950s led to the formal herbicidal program Trail Dust (see Operation Ranch Hand). Herbicidal warfare is the use of substances primarily designed to destroy the plant-based ecosystem of an agricultural food production and/or destroying foliage which provides the enemy cover.

The United States discovered 2,4-D (2,4-dichlorophenoxyacetic acid) during World War II. It was recognized as toxic and combined with large amounts of water or oil to function as a weed-killer. Army experiments with the chemical eventually led to the discovery that 2,4-D combined with 2,4,5-T (2,4,5-trichlorophenoxyacetic acid) yielded a more potent herbicide. It was found that 2,4,5-T was contaminated with 2,3,7,8-Tetrachlorodibenzodioxin (TCDD), commonly called "dioxin". Young found that samples of 2,4,5-T in Agents Pink and Green had double the TCDD concentration of Agents Purple or Orange.

The Agents used in southeast Asia, their active ingredients and years used were as follow:

In Vietnam, the early large-scale defoliation missions (1962-1964) used 8,208 gallons of Agent Green, 122,792 gallons of Pink, and 145,000 of Purple. These were dwarfed by the 11,712,860 gallons of Orange (both versions) used from 1965 to 1970. Agent White started to replace Orange in 1966; 5,239,853 gallons of White were used. The only agent used on a large scale in an anti-crop role was Blue, with 2,166,656 gallons used. The bombardment occurred most heavily in the area of the Ho Chi Minh Trail.

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