Epidemiology / Épidémiologie The development of a dynamic disease- forecasting model to control Entomosporium mespili on Amelanchier alnifolia

Entomosporium leaf and berry spot, which is caused by the fungal pathogen Entomosporium mespili, can cause up to 100% yield loss in Amelanchier alnifolia (saskatoon) in years when weather conditions are conducive to disease development. In an effort to optimize the effectiveness and minimize the use of fungicides, a dynamic diseaseforecasting model was developed. The model uses a disease pressure index equation, which integrates information regarding the phenological development of saskatoon, the relationship of disease to inoculum potential and production, leaf-wetness duration and temperature, inoculum release, and host susceptibility, to provide an estimate of disease pressure. When the model was evaluated, a strong correlation was found between predicted disease pressure and observed disease symptom development. After the field data were combined, the model could account for 82% of the variation in the increase of mean lesion number per leaf observed during the preharvest period. Control thresholds, together with application and control guidelines for use of the fungicide propiconazole, were added to the model, which was then evaluated in a field trial. A preliminary field test of the model showed that its use resulted in reduced disease development prior to the completion of fruit harvest.