VERB
（尤指战时）使落叶，去掉…的叶子，毁坏(某一地区)的绿色植物
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.
例句
Dioxin was the ingredient in Agent Orange, used to defoliate Vietnam.
越南战场上用于毁灭林区的“橙剂”，其成分是二氧杂芑。