Modelling rubber-tree root diseases, simulations of various inoculum rates and methods of control

Two root-rot fungi, Rigidoporus lignosus and Phellinus noxius are the causal agents of severe damage in Ivory Coast rubber tree (Hevea brasiliensis) plantations. Mathematical investigations were made using data from a previous 6 year long epidemiological survey. Modelling of spatial spread of the pathogens and mortality of the infected trees, lead to simulations of the quantitative evolution vs. rime of root diseases. The theoretical kinetics obtained revealed intra- and interspecific variability among the studied stands with respect to the damage caused. Using this model, different phytosanitary scenarios were simulated in relation ro the density of the initial inoculum, the control measures, the specificity of the fungicide, the efficiency of the treatment, and che optimal time for application. Their influence on root-disease dynamics was quantified. The characteristics of the model, its applicability in plantations and its use in predicting disease or stand development are discussed.