Phase diagram of pair approximation showing the three regions of the equilibrium state.

<p>In the epidemic region, plants and pathogens coexist and the equilibrium is stable. In the oscillation region, plants and pathogens coexist, but the equilibrium is unstable. Therefore, Hopf bifurcation occurs and oscillation is observed. The solid line indicates the bifurcation threshold, and the dashed line the epidemic threshold, respectively. In the disease-free region, pathogens become extinct because of the too low mortality cost.