Epidemiology / Épidémiologie Leaf-wetness duration and temperature required for infection of saskatoon leaves by Entomosporium mespili under controlled conditions

The influence of leaf-wetness duration and temperature on infection of Amelanchier alnifolia (saskatoon) by Entomosporium mespili was quantified in controlled-environment studies. Plants were inoculated with a conidial suspension and then subjected to a period of leaf wetness (0, 6, 12, and 24 h), after which they were moved to a growth room set at a fixed temperature (10, 15, 20, 25, and 30°C) for a period of 14 d. Infection levels rose as the leaf-wetness duration increased for combined temperature treatments up to 24 h. Temperatures between 10 and 20°C promoted optimal leaf infection for leaf-wetness periods longer than 6 h. Above the optimal temperature range, mean disease levels decreased. ANOVA with orthogonal contrasts and stepwise regression were used to create a regression equation that describes the relationship of E. mespili infection on saskatoon to both temperature and leaf-wetness duration. Combinations of temperatures between 10 and 25°C and leaf-wetness periods between 6 and 24 h were optimal for lesion development on younger saskatoon leaves.