The 2012 ASHS Annual Conference

Pruning is an essential component of blueberry management and in the southeastern U.S. summer pruning is done soon after harvest to stimulate growth. However, blueberry stem blight (Botryosphaeria spp.)—a major cause of decline and death of blueberry in the Southeast—can be spread from infected to non-infected canes by summer pruning. Therefore, summer pruning plays an important role in growth, yield, and survival of blueberry and research-based recommendations for pruning in the southeastern U.S. are needed. The objective of this study is to determine the effects of timing and severity of summer pruning on vegetative and reproductive growth, and the incidence of stem blight in ‘Jewel’ southern highbush blueberry. The following treatments were applied to mature plants of ‘Jewel’: 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). At the end of the growing season, non-pruned plants had the greatest canopy volume, averaging 0.80 m³, while 60% June+tip had the smallest volume, averaging 0.41 m³. All 30% pruning treatments, regardless of timing or tipping, had similar canopy volumes, averaging 0.61 m³. Flower bud formation began between 6 Oct 2011 and 20 Oct 2011 for all treatments, and there was no clear differentiation among the treatments for timing of initiation. Flower bud density was greatest in the 30% July pruning treatment (0.32 buds/cm), compared with all other treatments, in which density ranged from 0.22–0.26 buds/cm. Flower bud number per shoot was greatest in the non-pruned treatment and least in the 30% and 60% pruning treatments, regardless of timing or tipping. Bud break started in early January 2012 for all treatments and 50% bloom occurred by early February. None of the treatments were affected by stem blight. The non-pruned plants produced the greatest new shoot growth and the greatest number of flower buds compared with all other treatments. The 30% July pruning resulted in the least amount of regrowth and was among the lowest in total flower bud number, probably as a result of the later timing that limited the ability for new flower bud initiation on the late regrowth.