Mildew, e.g.

BLIGHT

["This plant disease often causes crops to wither and fail to thrive."]

"Mildew, e.g." hints at a word meaning a plant disease, with "e.g." suggesting the answer is an example of such a condition. "Blight" fits because it refers to a disease that harms plants, much like mildew does. The clue is straightforward, using "e.g." to indicate the answer is a synonym or related term.