A Model for Temporal Dynamics of Brown Rot Spreading in Fruit Orchards

Brown rot, caused by Monilinia spp., is a major disease of stone fruit and, in favorable environmental conditions and in the absence of fungicide treatments, it causes important economic losses. In the present work, we propose a modification of classical susceptible, exposed, infectious and removed compartmental models to grasp the peculiarities of the progression of brown rot epidemics in stone fruit orchards in the last stage of the fruit growth (i.e., from the end of the pit hardening to harvest time). Namely, we took into account (i) the lifespan of airborne spores; (ii) the dependence of the latent period on the cuticle crack surface area, which itself varies in time with fruit growth; (iii) the impossibility of recovery in infectious fruit; and (iv) the abrupt interruption of disease development by the elimination of the host fruit at harvest time. We parametrized the model by using field data from a peach Prunus persica orchard infected by Monilinia laxa and M. fructicola in Avignon (southern France). The basic reproduction number indicates that the environmental conditions met in the field were extremely favorable to disease development and the model closely fitted the temporal evolution of the fruit abundance in the different epidemiological compartments. The model permits us to highlight crucial mechanisms undergoing brown rot build up and to evaluate the consequences of different agricultural practices on the quantity and quality of the yield. We found that winter sanitation practices (which decrease the initial infection incidence) and the control of the fruit load (which affects the host fruit density and the single fruit growth trajectory) can be effective in controlling brown rot in conjunction with or in place of fungicide treatments.