Does Position in the Canopy Affect Fruit Bud and Berry Development in Highbush Blueberry?

The study was conducted in a 7-year-old field of certified organic highbush blueberry. Plants were grown on raised beds, and treatments included ‘Duke’ and ‘Liberty’ plants mulched with weed mat or compost topped with sawdust and fertilized with feather meal or fish emulsion. One-year-old fruiting laterals, ranging from 0.5−0.7 m, were randomly-selected at three heights (top, middle, and bottom) on the east and west side of the plants. The third flower bud from distal end of each lateral was tagged, and bud, flower, and fruit development were monitored through fruit harvest. Fruit harvest occurred ≈8 d after the fruit were fully blue and ranged from 2−25 July 2012 and 26 June−3 July 2013 in ‘Duke’ and from 1−20 Aug. 2012 and 17 July−7 Aug. 2013 in ‘Liberty’. Proportionally more fruit buds occurred on upper laterals than on lower laterals [1:2, 2:1, 2:1 (‘Duke’); 1:2, 1:1, 1:1 (‘Liberty’)]. Bud swell and bud break dates were not affected by cultivar or lateral position, but ‘Duke’ reached the early pink stage before ‘Liberty’. ‘Duke’ produced 6–8 and ‘Liberty’ produced 7–9 flowers/bud. Fruit set was high and averaged ≈95% in both cultivars. However, 10–20% of the flowers aborted or remained relatively small in ‘Liberty’. Laterals in the upper canopy were longer (≈65 cm) and had a greater diameter (4–5 mm in ‘Duke’ and 2–3 mm in Liberty) than those in the lower canopy (35–45 cm long and 2–3 and 1.5–2 mm diameter in ‘Duke’ and ‘Liberty’, respectively). The first shoot flush produced only vegetative buds while the second and third flushes produced vegetative and flower buds. Fruit ripening was more uniform within clusters in ‘Duke’ than in ‘Liberty’, and average fruit diameter was similar among harvests in ‘Duke’ but decreased by 25–40% between the first and last harvest in ‘Liberty’. Fruit ripening was faster and berries were larger at harvest in clusters on partially-shaded laterals than in those on completely-shaded laterals. The berries matured 3−5 d earlier on the east side of the canopy than on the west side. The first fruit coloring stage in 2012 started in the upper east laterals in plants fertilized with fish emulsion and mulched with weed mat in ‘Duke’ and sawdust+compost in ‘Liberty’. The results suggest that more pruning on the lower part of the canopy will result in larger fruit at harvest than uniform pruning of the canopy.