Anti-plant Chemical Warfare: From Charles and Francis Darwin to Richard Nixon

Matthew Meselson
Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA

In their 1880 book „The Power of Movement in Plants“, Charles Darwin and his son Francis describe experiments in which oat and other seedlings exposed to light bend toward the light but do not do so if the tip of the seedling is shielded. Observing that the bending occurs a short distance from the tip, they concluded that „…some influence is transmitted from the upper to the lower part, causing the latter to bend.“ In the 1930s at the California Institute of Technology, indole-3-acetic acid was shown to be such an „influence“.
During WWII in the US and the UK, synthetic analogs of indole-3-acetic acid were screened for herbicidal activity in order to select anti-plant agents for military use–clearing vegetation and destroying food crops–leading to the choice of a mixture of the isopropyl esters of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid. Produced in quantity but not used during the war, such anti-plant agents were first used for destroying crops and reducing vegetation by the UK in Malaya during the 1940s and 1950s and later by Portugal in Angola. Agent Orange, a mixture of the n-butyl esters of 2,4-D and 2,4,5-T, and other herbicides, were used on a large scale by the US for defoliation and crop destruction in the Republic of Vietnam during 1961-70. Toward the end of that period, faced with increasing public and official concern over possible health effects and environmental damage and with skepticism regarding military utility, US President Richard Nixon in December 1970 ordered a rapid „phase-out“ of herbicide operations.
In this talk I will address some of the factors that led to large-scale anti-plant chemical warfare in the Vietnam war and to its eventual termination.