Modelling dynamics of airborne conidia of Stemphylium vesicarium, the causal agent of brown spot of pear

The BSPcast model has been validated in the pear-growing areas of the Emilia-Romagna region (North Italy) and it gave satisfactory results in identifying infection periods of brown spot, so that it is now in use for advising farmers. Nevertheless, this model produces unjustified alarms when the airborne inoculum of S. vesicarium is absent or at low densities. To improve the accuracy of BSPcast, a model (BSPspor) able to simulate the dynamic of inoculum density (i.e. airborne spores) was elaborated. This model allows daily estimation of the potential for inoculum availability, using meteorological data. The model was elaborated using data collected from volumetric spore samplers in several epidemiological conditions (years and locations) and from laboratory experiments. BSPspor calculates an index, cumulated over a 3-day period, based on favourable conditions of temperature and moisture, and corrected by an index of seasonality. To reduce early unjustified alarm, BSPcast outputs can be considered for warnings only when the BSPspor model in the previous days had signalled a peak of inoculum.