In the War
While almost all of the 20 million gallons of herbicides were sprayed in southern Vietnam, the U.S. war effort spilled over into neutral Cambodia. Little is known about the extent of the spraying and the present-day impacts.
Unlike Laos, Cambodia was not systematically sprayed, though the HERBS database does show records of spray runs conducted in Cambodian territory. There were incidences of spray drift of herbicides that carried over into where the Ho Chi Minh Trail was established on the Cambodian side that bordered South Vietnam, likely a consequence of the spraying of over 1 million gallons of herbicides in neighboring parts of the latter.
Between April 18 and May 2, 1969, about 270 square miles of French and Cambodian rubber plantations in Kampong Cham Province in Cambodia were sprayed. Gardens and trees in nearby villages were also impacted, including 45,000 jackfruit trees that were either completely destroyed or severely damaged. Kampong Cham, up until recently, in 2013, previously extended eastward towards the border with southern Vietnam. The damage was too far from the border and too extensive to be caused by spray drift.
It was unclear exactly the entity or forces that carried out the spraying over the plantations; it was purported at the time that the spraying missions, flown by Air America aircraft, were led by the CIA. In 1969, the Cambodian government filed a claim for $12.2 million in damages, though there was never any admission of responsibility by the U.S. Ultimately, however, the U.S. made plans to pay the claim by 1972, in order to promote “broader interests.”
Anecdotal reports from residents of Mondulkiri and Ratanakiri provinces in northeast Cambodia, though unsubstantiated, have alleged that herbicides were sprayed in these regions as well, during the war. More research is needed to confirm these reports, as well as the reports of spraying in the Prey Veng and Svay Rieng in southern Cambodia.
Operation Ranch Hand: The Air Force and Herbicides in Southeast Asia, 1961-1971
By William Buckhingham (1982). This book is a model study of the process by which military policy was made in Southeast Asia.
Agent Orange in Cambodia: The 1969 Defoliation in Kampong Cham
By Andrew Wells-Dang, PDF, Expanded Version.