van den Bosch et al. [6] use the endemic equilibrium to determine a threshold given by I = (1/α)(μq−μ+αK) so that I > 0 if μq − μ + αK > 0 (where I represents infected plants at the endemic equilibrium, α is the transmissibility, μ is the death rate, q is the fraction of infectious seeds, and K is the total plant population density). They show that two different rearrangements of this inequality give