Optimization of pollination and fruit set in northern highbush blueberry

TL;DR: Calcium (Ca) and boron (B) are of particular interest for reproductive developmental processes and increased honey bee stocking densities and provision of supplemental bumble bees (Bombus vosnesenskii) may improve pollination.

Abstract: by Matthew Alan Arrington, Ph.D. Washington State University December 2017 Chair: Lisa Wasko DeVetter Fruit set in northern highbush blueberry (Vaccinium corymbosum L.) can be low under certain climatic conditions, contributing to reduced yields in northwestern Washington. Little is known about the mechanisms of reduced fruit set and yields in this important production region, but it may be associated with inadequate pollination, and/or nutrient deficiencies. Enhanced nutrient availability during critical stages of flowering, ovule fertilization, and fruit development may lengthen the pollination window or improve pollen germination and tube growth. Calcium (Ca) and boron (B) are of particular interest for reproductive developmental processes. Additionally, increased honey bee (Apis mellifera) hive stocking densities and provision of supplemental bumble bees (Bombus vosnesenskii) may improve pollination. Commercially available fertilizers containing Ca and B were applied to ‘Draper’ and ‘Bluecrop’. In another experiment, the recommended honey bee stocking density of 10 hives/ha was compared to a high stocking density (20 hives/ha) in ‘Duke’ and to bumble bee supplemented pollination (10 honey bee hives + 8 colonies of bumble bee/ha) in ‘Draper’. Flower morphology and the impact of shade and Ca on fruit drop were also studied. No significant increases were observed for fruit set, estimated yield, fruit firmness or berry weight in the Ca and B study. Honey bee visitation was increased