1981: Alexander Haig announced that the United States was in possession of “physical evidence” that the Soviet Union was supplying its Southeast Asian allies with biological warfare agents for military use against their opponents. According to the Secretary of State, the Soviet Union was providing Laos and Vietnam with mycotoxins – poisonous compounds synthesized by fungi.
The “physical evidence”? Hmong villagers, refugees from fighting in Laos, had seen low-flying aircraft spraying what the Hmong called “yellow rain”, an oily liquid that left a residue of yellow spots on leaves, rocks and rooftops. Villagers caught in these chemical showers exhibited symptoms that included blurred vision, breathing difficulties and skin burns. Between 10 and 20 per cent of victims died.