An organism, chemical, or agent that causes leaves to fall off plants or trees.
From defoliate + -or (agent noun). Applied to insects, chemicals, or any entity whose primary effect is removing foliage from vegetation.
The gypsy moth is North America's most famous defoliator, but tent caterpillars are close seconds—in bad years, their silk tents completely shroud entire trees, and the caterpillars inside can cause 100% defoliation.
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