Epidemiologists use specific terminology to accurately 
communicate magnitudes and potentials for disease 
Incidence: the number or proportion of plant units diseased 
Severity; the proportion of area or amount of plant tissue 
that is diseased 
Yield loss; the proportion of yield that a grower will not 
be able to harvest due directly to the disease 
Economic loss; the reduction in economic returns due to 
disease. What about compensation of plants which results in 
no yield loss though one has up to 50% plants lost due to 
disease? Think about the "Green Revolution". 
Economic threshold; when the amount of gain from control 
equals the amount of estimated loss from the disease