The correct answer is (D) To strip (a tree, bush, or other plant) of (leaves. To destroy an area of forest, jungle, etc. by chemical spray or other means in order to do away with places of concealment. To remove leaves from trees.

Examples of use:

• Agent Orange was used to defoliate the jungles of Viet Nam.
• Defoliating any area of vegetative area by chemical means is probably a serious error.