epiphytotic

from The American Heritage® Dictionary of the English Language, 5th Edition.

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

from The Century Dictionary.

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

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective (of plants) epidemic among plants of a single kind especially over a wide area