A blight is a disease affecting plants that causes sudden death. The term can also be used to refer to any sudden disease.
In 2373, Keiko O'Brien worked to try and get a blight under control on Bajor. (DS9: "Business as Usual")
The con artists Dala and Mobar, posing as clerics, told Neelix and Tom Paris a story about the crops grown in hydroponic pods for the orphans on Narva being infected by a blight. (VOY: "Live Fast and Prosper")