Premature loss of leaves or needles due to airborne pollution or other factors interfering with vital processes in trees Used to refer to trees that have lost over 20% of their leaves or needles
causing the leaves of trees and other plants to fall off (as by the use of chemicals)
To defoliate an area or the plants in it means to cause the leaves on the plants to fall off or be destroyed. This is done especially in war to remove protection from an enemy. Dioxin was the ingredient in Agent Orange, used to defoliate Vietnam. + defoliation de·fo·lia·tion preventing defoliation of trees by caterpillars. to use defoliant on a plant or tree