Blight, a general term for any plant disease that causes withering, decay, or premature death of the plant or any of its parts. The word blight has been used loosely to describe any condition of this nature, whether due to fungus disease, insects, or insufficient food supply. More specifically, the word is used for a kind of mildew that affects fruits and vegetables. The more common varieties are apple, pear, grape, tomato, and potato blights.