defoliation (?), n. [LL. defoliare, defoliatum, to shed leaves; L. de- + folium leaf: cf. F. défoliation.] The separation of ripened leaves from a branch or stem; the falling or shedding of the leaves.
[1913 Webster]
2. the act or process of causing plants to lose their leaves, especially by application of a chemical agent. The deliberate defoliation of plants has been used in war (as in Vietnam) to deprive an enemy of cover and allow attack from the air; also, to destroy narcotic-producing plants as a tactic against illegal drug production. The chemical defoliating agents are often sprayed over large areas from airplanes.
[PJC]