Modeling phenology and entomosporium leaf and berry spot disease development in Amelanchier alnifolia Nutt

The improper timing of harvest efforts and entomosporium leaf and berry spot disease, which is caused by the fungal pathogen Entomosporium mespili (D.C.) Sacc., are two important factors limiting growers from achieving optimal Amelanchier alnifolia Nutt. (saskatoon) fruit yield. In order to overcome these limitations and improve the quality and quantity of saskatoon fruit yielded, phenological and disease forecasting models based on orchard microclimate were created. Temperature, leaf wetness, and precipitation data used in the models were collected real-time using Adcon Telemetry weather stations. A heat unit model for predicting the dates of flowering, fruit harvest and the cessation of axillary vegetative shoot expansion from the date of bud break was created for saskatoon (SASK-Day) using critical temperatures for plant growth and development. When historical SASK-Day heat unit data were incorporated with actual SASK-Day heat unit data it was possible to predict the dates of flowering and fruit harvest, 9 and 57 d before they occurred in the field, respectively. A dynamic disease-forecast model was created to estimate disease pressure based on epidemiological studies regarding the relationship of disease to inoculum potential and production, inoculum release, leaf wetness duration and temperature, and host susceptibility. When compared to disease observations in the field, the model was able to account for 82% of the variation in the increase of average lesion number per leaf (LESNO) during the pre-harvest period. Regression analysis was used to create an equation (Y = 8.0 x 10-3 X + 1.01) that estimates LESNO 5 d before symptoms developed based on cumulative disease pressure. To make the dynamic disease-forecasting model useful for controlling disease in the field, control thresholds together with application and control guidelines for Topas 250E were added to the model. When tested in 2002 at an orchard near Carman, Manitoba, disease was controlled using two fungicide applications as recommended by the model. A future study should be used to establish economic thresholds when validating the model on different cultivars and in different geographic regions. With properly set economic thresholds, it is still possible to further reduce the number of fungicide spays used.