2017 ASHS Annual Conference

Fruit set in northern highbush blueberry (Vaccinium corymbosum) can be low under certain climactic conditions and contributes to reduced yields, particularly in western Washington. The mechanisms influencing fruit set are complex, but poor fruit set can be associated with inadequate nutrient availability during critical stages of flower and fruit development. Boron (B) and calcium (Ca) and may be of specific importance for reproductive developmental processes, but little research has been done to evaluate their influence on improving fruit set and yield in Washington blueberry. The objective of this project was to evaluate if foliar-applied B and Ca increase fruit set and resultant yields of highbush blueberry. Specific sub-objectives were to: 1) evaluate the effects of foliar applied B and Ca, alone or in combination, on fruit set, yield, and fruit quality (berry firmness and weight) of blueberry; and 2) measure the effects of B and Ca application on blueberry pollen germination, tube growth, and fertilization of ovules. Commercially available fertilizers containing these nutrients were applied either alone or in combination as foliar sprays during the 2015 and 2016 growing season in western Washington. Nutrient were applied as: calcium chloride, calcium sulfate, and tetra borate foliar sprays, repeated 6 times per year, 7-10 days apart. Applications were timed from pink bud through petal fall in ‘Draper’ and ‘Bluecrop’. No significant increases were observed in fruit set, estimated yield, or fruit quality (berry firmness and weight) across any of the treatments, however year and cultivar effects were observed. Increased B was observed in leaf tissue nutrient analyses in 2015 and 2016, suggesting foliar nutrient applications of B were effectively taken up by the plants. However, elevated levels did not lead to increased fruit set or yield. Results indicate that foliar applications of B and Ca, either alone or in combination under the conditions of the experiment, do not increase fruit nutrient levels, fruit set, yield, and attributes of berry quality in Washington blueberry.