Plant disease epidemiology

Epidemiology (=epiphytology) is the study of the outbreak of a disease, its course, intensity, causes, effects and various factors governing it.
On the basis of of occurrence and geographical distribution, diseases are categorized as follows:


Sporadic disease occurs at irregular intervals in a limited area. Only a few individuals in a population are infected.
e.g., Bunt of wheat caused by Telletia barclyana.
Karnal bunt of wheat
Bunted grain (left) healthy grain (right)


Endemic diseases are confined in a particular locality. These occur in moderate to sever form year after year.
e.g., Wart disease of potato caused by Synchytrium endobioticum is endemic in Darjeeling of India.

Epidemic or epiphytotic

Epiphytotic is a sudden outbreak of a disease over a widespread area. It results in heavy losses to complete destruction of the entire population. Favorable environmental conditions are responsible for the rapid outbreak.
Outbreak of the epidemic plant disease can be best understood by studying three factors in disease triangle.
e.g., Late blight of potato caused by Phytophthora infestans become epiphytotic when environmental conditions become favorable.
late blight of potato
Photographs showing the potato crops. a: healthy plants of potato, b: late blight affected potato in the field, and c: abaxial surface of infected leaves.


When an epidemic disease spreads over a large geographical area or over a subcontinent or at more than one continent at a time span and involves mass mortality is considered as pandemic.
e.g., Black or stem rust of wheat caused by Puccinia graminis tritici in the Indian subcontinent during 1947.
Black rust of wheat
Wheat plants infected with black or stem rust

Content first created on 25-01-2023
last updated on 25-01-2023