To remove all the leaves from a plant, tree, or forest.
From de- (remove) + Latin 'folium' (leaf) + -ate (verb suffix). The term became prominent in military and ecological contexts during the 20th century, though botanical use is older.
Trees naturally defoliate in autumn, but when chemicals force defoliation in summer, it's catastrophic—the tree has already invested energy in those leaves and can't recover before winter dormancy.
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