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J.M. Mutisya, J.A. Sullivan, S. Couling, J.C. Sutton, and J. Zheng

The relationship between severity of leaf scorch epidemics, caused by Diplocarpon earlianum, and components of vegetative growth and fruit yield was examined in `Kent' strawberry (Fragaria ×ananassa Duch.). Plants were treated in July with six densities of initial inoculum of the pathogen, and severity of leaf scorch was assessed at 2-week intervals from late July to late October. After an analysis of vegetative growth in late October, plants were overwintered in the field or grown in a greenhouse, and later assessed for yield components. Relationships between area under the disease progress curve (AUDPC) and plant growth and yield components were examined by regression analysis. Significant negative linear relationships were found between AUDPC values and number of green leaves, leaf area, leaf dry weight, crown number, crown dry mass, and root dry weight. Significant negative relationships were also found between AUDPC values and number of flowers and inflorescences, and total and marketable berries in the subsequent season, in plants maintained in the field or in the greenhouse. Mean berry weight was not significantly affected. Reduction in the number of crowns in plants affected by leaf scorch was a major factor limiting the yield of diseased plants. In an analysis of regrowth at seven weeks after fruit harvest, a significant negative linear relationships was found between AUDPC values and each growth component except crown dry weight. Collectively, the data provide a rationale to optimize timing of treatments, such as chemical fungicides or microbial agents, to control leaf scorch in August, September and October and thereby promote berry yield in the subsequent season.