Blueberry (Vaccinium spp.) summer pruning can increase yield by promoting healthy fall foliage to support the reproductive development. However, there has been little research to examine the effects of timing and intensity of summer pruning in subtropical conditions. The objective of this study was to determine the effects of summer pruning timing and intensity on reproductive traits of mature ‘Jewel’ and ‘Emerald’ southern highbush blueberry (SHB) plants (V. corymbosum L. interspecific hybrid) in subtropical Florida. The effect of pruning time was evaluated by removing 30% of the canopy in June or July. The effect of intensity was evaluated by pruning either 30% or 60% of the canopy in June, followed by removal of the upper 5 cm of regrowth (“tipping”) in July. Both timing and intensity used nonpruned plants as a control. The same plants were evaluated over three consecutive seasons (June 2011–May 2014). Main effects of pruning time, intensity, and tipping were evaluated. Tipping did not affect the reproductive traits evaluated. ‘Emerald’ reproductive traits were unaffected by either summer pruning time or intensity over the 3-year study. ‘Jewel’ yield was unaffected in the first year, but was increased by 48% and 65% in years 2 and 3, respectively, in the 30% pruning treatment compared with the nonpruned control. Lack of pruning in ‘Jewel’ decreased inflorescence bud number compared with moderate pruning likely due to more diseased foliage that increased defoliation. Thus, pruning effects on reproductive traits were cultivar dependent. Leaving ‘Jewel’ plants unpruned for two or more seasons reduced inflorescence bud number and yield.
Vaccinium arboreum Marsh is a wild species adapted to high pH (above 6.0) and low organic matter soils (below 2.0%). The use of V. arboreum rootstocks may be a viable option to increase soil adaptation of southern highbush blueberry (SHB) (Vaccinium corymbosum interspecific hybrid) under marginal soil conditions. The objective of this research was to evaluate the vegetative and reproductive traits of ‘Farthing’ and ‘Meadowlark’ SHB own-rooted or grafted onto V. arboreum and grown in pine bark–amended or nonamended soil. The study was conducted from 2012 through 2014 at a research center in Citra, FL, and a grower’s farm in Archer, FL. Vaccinium arboreum rootstock generally induced the same effects in both cultivars. Grafted plants in both soil treatments had reduced canopy growth in the first year after field planting compared with own-rooted plants in amended soil. However, canopy volume of grafted plants was greater than own-rooted plants in nonamended soil and similar to own-rooted plants in amended soil 2 years after field planting for ‘Meadowlark’ and 3 years after planting for ‘Farthing’. Fruit yield was lower in grafted plants compared with own-rooted plants in the first fruiting year (2 years after field planting). By the second fruiting year, yields of grafted plants were similar to or greater than yields of own-rooted plants when grown in nonamended soil, whereas in amended soil, yields of grafted plants were similar to yields of own-rooted plants. Grafted plants had greater mean berry weight, but lower berry firmness; however, the firmness values were still considered acceptable (greater than 160 g⋅mm−1). Internal fruit quality [total soluble solids (TSS) and total titratable acidity (TTA)] was not consistently affected by the rootstock or soil treatments. These results suggest that grafting SHB onto V. arboreum does not increase yield in the establishment years compared with own-rooted SHB when grown in amended soils, but may have the ability to increase yield with no negative effects on fruit quality when grown in nonamended soils.
The profitability of the fresh market blueberry industry in many areas is constrained by the extensive use and cost of soil amendments, high labor requirements for hand harvesting, and the inefficiencies of mechanical harvesters. Vaccinium arboreum Marsh is a wild species that has wide soil adaptation and monopodial growth habit. It has the potential to be used as a blueberry rootstock, expanding blueberry production to marginal soil and improving the mechanical harvesting efficiency of cultivated blueberry. The objectives of this research were to compare yield, berry quality, and postharvest fruit storage of own-rooted vs. grafted southern highbush blueberry (SHB) cultivars (Farthing and Meadowlark) grown on amended vs. nonamended soil and either hand or mechanical harvested. Yields of hand-harvested SHB during the first two fruiting years were generally greater in own-rooted plants grown on amended soil compared with own-rooted plants on nonamended soil or grafted plants on either soil treatment. However, by the second fruiting year, hand-harvest yields of grafted SHB were ≈80% greater than own-rooted plants when grown in nonamended soil. Yields of mechanical-harvested SHB grafted on V. arboreum and grown in either soil treatment were similar to yields of mechanical-harvested own-rooted plants in amended soil the second fruiting year, and greater than yields of own-rooted plants in non-amended soil. In general, mechanical harvesting reduced marketable yield ≈40% compared with hand harvesting. However, grafted plants reduced ground losses during harvest by ≈35% compared with own-rooted plants for both cultivars. Mechanical-harvested berries had a greater total soluble solids:total titratable acidity ratio (TSS:TTA) than hand-harvested berries, and berries harvested toward the end of the harvest season had a greater TSS:TTA than those from early-season harvests. As postharvest storage time increased, berry appearance ratings decreased and berry softness and shriveling increased, particularly in mechanical-harvested compared with hand-harvested berries. Firmness of mechanical-harvested berries decreased during storage, whereas firmness of hand-harvested berries remained relatively stable. However, fruit quality at harvest and during postharvest storage was unaffected by V. arboreum rootstocks or lack of pine bark amendment. This study suggests that using V. arboreum as a rootstock in an alternative blueberry production system has the potential to decrease the use of soil amendments and increase mechanical harvesting efficiency.
Pruning is a recommended practice for blueberry (Vaccinium spp.) production and is usually done in the summer in warm subtropical climates with long growing seasons. Summer pruning promotes healthy vegetative growth during the remainder of the growing season; however, research-based recommendations for summer pruning strategies are lacking. The objective of this study was to determine effects of summer pruning timing and intensity on vegetative growth in ‘Jewel’ and ‘Emerald’ southern highbush blueberry (V. corymbosum-interspecific hybrid), two cultivars of the primary species grown in subtropical areas. To determine effects of pruning time, 30% of the canopy was removed in June or July. To determine pruning intensity effects, either 30% or 60% of the canopy was removed in June, both followed by shoot tipping in July. Both timing and intensity treatments were compared with a non-pruned control. Lack of pruning in the first year had no negative effects on growth; however, lack of pruning for two or more seasons decreased regrowth volume and shoot length of both cultivars. By the third season, canopy regrowth volume in both cultivars decreased in the non-pruned control compared with the 30% and 60% pruning treatments and compared with the June pruning treatment. Disease infection in ‘Jewel’ was also increased in the non-pruned control compared with these pruning treatments. Summer pruning, regardless of timing or intensity, generally increased vigor of vegetative growth for both cultivars and decreased incidence of leaf disease in ‘Jewel’.