During the war, U.S. forces used defoliants, substances that cause leaves to fall off plants when applied, as a weapon against North Vietnamese forces. These defoliants were sprayed en masse over forests to deprive the enemy of cover. The most infamous defoliant used during the war was Agent Orange, a mixture of two compounds called 2,4,5-T and 2,4-D in a 1:1 ratio. Exposure to Agent Orange led to major illnesses in over a million people in Vietnam after the war.
Britain was the first country to use defoliants as a weapon of war during the Malayan Emergency in 1950s. They used a substance similar to Agent Orange but with the addition of a toxicant called Dioxin. Dioxin was responsible for the Seveso disaster of 1976 in Italy where it contaminated soil and water sources leading to cancer cases among people living nearby.
Alongside Agent Orange, the U.S developed a mixture of cacodylic acid, sodium cacodylate, and water to destroy rice plants during World War II. These plants were difficult even with fire as they could easily regenerate from their roots if not killed completely by this method.
The use of defoliants against civilian populations has been banned since 1980 under international law due to its devastating effects on human health and environment but unfortunately, civilians were affected during wars such as Vietnam War where napalm was famously photographed by Nick Ut which caused burns and severe injuries on those exposed to it