defoliant, a chemical dust or spray applied to plants to cause their leaves to drop off prematurely. Defoliants sometimes are applied to crop plants such as cotton in order to facilitate harvesting. They are also used in warfare to eliminate enemy food crops and potential areas of concealment by enemy forces. Defoliants were employed for these purposes by South Vietnamese and U.S. forces in the Vietnam War; among the more controversial of these substances was the chemical compound known as Agent Orange (q.v.).