epiphytotic

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Of, relating to, or characterized by a sudden or abnormally destructive outbreak of a plant disease, usually over an extended geographic area.

Century Dictionary and Cyclopedia

1. In botany, noting an epidemic of a plant-disease.

WordNet 3.0

1. adj. (of plants) epidemic among plants of a single kind especially over a wide area