The Effect of Timing and Intensity of Summer Pruning on Vegetative and Reproductive Traits of Southern Highbush Blueberry

Summer pruning is a major practice for blueberry management in the southeastern United States, but research-based recommendations are lacking. The objective of this study is to determine the effects of timing and intensity of summer pruning on vegetative and reproductive growth, and the incidence and severity of leaf spots in ‘Jewel’ and ‘Emerald’ southern highbush blueberry. The following treatments were applied to mature plants of both cultivars for two years: 1) control—no pruning; 2) control—detailed hand pruning; 3) pruning 30% of existing foliage in early June (30% June); 4) pruning 30% of existing foliage in mid-July (30% July); 5) pruning 30% of existing foliage in early June followed by shoot tipping in mid-July (30% June+tip); and 6) pruning 60% of existing foliage in early June, followed by shoot tipping in mid-July (60% June+tip). Plant volume was similar across years within treatments for both cultivars, with the non-pruned plants having the greatest canopy volume at the end of each growing season, averaging 1.57 m³ and 1.26 m³ for ‘Jewel’ and ‘Emerald’, respectively, across both years. However, regrowth volume of the non-pruned plants decreased significantly from the first to second year, while regrowth in the other treatments either increased or had no differences between years. Flower bud formation in ‘Emerald’ started in early August for the non-pruned plants, but not until late August for the other treatments. For ‘Jewel’, flower bud formation began in mid-October for all treatments. Flower bud number per shoot was least in the 30% July pruning, reflecting decreased regrowth compared with the other treatments. The non-pruned and the 60% June+tip had the greatest average number of flower buds per shoot. Full bloom (50%) in ‘Jewel’ occurred 3 days earlier in the hand-pruned compared with the 30% June and 60% June+tip treatments and one week earlier than in the other treatments. Leaf spot in ‘Jewel’ non-pruned plants was greater than in the other treatments, which likely resulted in the greatest defoliation for this treatment. ‘Emerald’ was not affected by leaf spots. Shoot length in the non-pruned plants was reduced by 30% to 50% and flower bud number by 50% from the first to second year, while the other treatments were stable or increased for these traits, reflecting the reduction of vigor caused by the lack of pruning. Early pruning (June) resulted in increased vegetative growth and flower bud number compared to later pruning (July), regardless of severity and tipping.