Leaf and Flower Blight Caused by Monilinia vaccinii-corymbosi on Lowbush Blueberry: Effects on Yield and Relationship to Bud Phenology.

ABSTRACT Naturally established lowbush blueberry clones in four fields were evaluated for the incidence of leaf and flower blight, proportion of mummy berries, and yield reductions caused by Monilinia vacciniicorymbosi. The relationship between the phenology of flower and leaf bud development and susceptibility also was examined. Three fields were examined over one crop year and one field was studied in two subsequent crop years. The incidence of stems with blight was correlated to incidence of leaf blight in all fields and to incidence of flower blight in one field. Incidence of leaf and flower blight and the proportion of mummy berries produced were not correlated. Lowbush blueberry clones with higher incidence levels of leaf blight had reduced fruit set and lower berry weights. For healthy stems, leaf-to-fruit ratios had no effect on berry weight in most fields. In contrast, blighted stems with higher leaf-to-fruit ratios had higher berry weights in three fields. Stems with slowerdeveloping leaf and flower buds had less leaf and flower blight, respectively, than stems with faster bud development. Some blueberry clones may avoid infection by delaying production of susceptible tissue until after ascospore release by M. vaccinii-corymbosi.