Estimating inoculum production relative to percent leaf area infected and environmental conditions required for stimulating release ofEntomosporium mespiliconidia onAmelanchier alnifolia

Amelanchier alnifolia, commonly known as saskatoon, is a fruit-bearing shrub native to the Canadian Prairies. Currently, production is limited by the fungal pathogen Entomosporium mespili. It was found that there is a positive linear relationship between the relative concentration of E. mespili conidia (X) and the percent of saskatoon leaf area that is infected (Y), as represented by the equation Y = 0.0534X. In a field study, initial disease symptoms appeared 5 d after the first precipitation event that occurred 1 d or more after the date of flowering. A splash-dispersed-conidia trap was constructed and used to trap conidia within the canopy of a saskatoon plant and, in both years of this study, conidia were first trapped on the 184th day of the year, which coincided with the exponential increase of percent leaf area infected. Conidia were primarily released during the first 2 h of precipitation events. Information on inoculum production and release will eventually be integrated into a dynamic disease-forecasting model for entomosporium leaf and berry spot caused by E. mespili on saskatoon.