1) Epidemic 
See epidemic. 
A virulent, widespread disease in a plant population. Often called anepidemic. ... (09 Oct 1997) ... 
An epidemic in a plant (as opposed to epizootic, an epidemic disease in an animal) the study of which is sometimes known as epiphytotiology.
[adj] - (of plants) epidemic among plants of a single kind especially over a wide area
adjective (of plants) epidemic among plants of a single kind especially over a wide area; `an epiphytotic blight of potatoes`; `epiphytotic conditions associated with a single-plant agriculture`
(of a disease) destroying a large number of plants in an area at the same time.