Dynamics of Epidemics of Plant Disease: Population bursts of fungi, bacteria, or viruses in field and forest make an interesting dynamical study.

In the context of this discussion an epidemic is defined as an increase of disease in a field, forest, or other population of host plants. The susceptibility of the host plants, the virulence of the fungus or other pathogen, and the weather and other environmental conditions all affect the relative rate of increase. They do so by affecting the time it takes newly infected tissue to become infectious, the time tissue remains infectious, the infectiousness of infectious tissue, and the susceptibility of healthy tissue to infection. These factors operate throughout the epidemic. Two other factors become increasingly important as the epidemic proceeds: the proportion of healthy susceptible tissue remaining available for infection, and the degree of uniformity of the population of host plants and of their environment.