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Donald L. Peterson

Hand-harvesting fruit crops is labor-intensive, and the supply of dependable, skilled labor is a concern of the fruit industry. Only a small portion of all fruit crops is harvested mechanically, primarily for processing. Public funding of mechanical harvesting research on fruit crops has reached a low level. However, there is renewed interest in mechanical harvesting research due to the potential scarcity of hand-harvest labor and new federal laws that may deplete further the labor pool. Much of the research expertise in mechanical harvesting of fruit crops has been lost, since most projects have been discontinued. Considerable lead time will be required to develop facilities, personnel, and projects if the decision is made to initiate publicly funded harvest mechanization research. More time will be required before commercially acceptable techniques and methods will be available. A majority of the research described in this paper was conducted outside the United States. The United States will not remain competitive in the world market for fruit crops with the present lack of mechanical harvesting research.

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Fumiomi Takeda and Donald L. Peterson

There is increased interest in growing blackberries in the United States for the fresh fruit market. For fresh market blackberry production, >350 h/acre (900 h·ha-1) of work is required to hand pick blackberries over a season that lasts 5 weeks with harvest every 2 days. Existing bramble mechanical harvesters can detach fruit from plants trained on a vertically oriented I trellis and harvest more cheaply than when harvested by hand, but the harvested fruit does not have fresh-market quality. We developed a cane training and trellis system for semierect blackberries to orient canes horizontally with the fruit positioned below the canes. Also, we developed an over-the-row mechanical harvester that uses vibrating nylon rods on a drum to shake fruit from horizontally trained canes onto a moving fruit-catching surface directly under the canopy to minimize impact damage to fruit. A new trellis design, new cane training practices, and new harvesting technologies have allowed fruit to be removed efficiently and be acceptable for fresh-market sales. This production system has been evaluated economically and appears to be profitable. It could overcome the high cost of handpicking, which has limited the expansion of fresh-market blackberries.

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D. Michael Glenn, Donald L. Peterson, Daniela Giovannini, and Miklos Faust

Hand-thinning (Prunus persica L. Batsch) “Y”-trained peach trees at bloom and 51 days after full bloom (DAFB) was compared to mechanical fruit thinning 51 DAFB using a spiked-drum and an impact shaker. The spiked-drum shaker removed more fruit from horizontal branches than from vertical branches, yet did not selectively remove either large or small fruit. Bloom thinning by hand increased fruit size compared to postbloom thinning 51 DAFB, and both postbloom mechanical thinning techniques were as effective as postbloom hand thinning. The spiked-drum shaker may be a better thinning technique than the impact shaker because it transfers less shaking energy to the fruit, can be used in high-density plantings, and does not contact the trunk, lessening the potential for tree damage.

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Fumiomi Takeda, Ann K. Hummell, and Donald L. Peterson

A study was conducted to characterize vegetative growth of mature 'Chester Thornless' blackberry plants trained to the rotatable cross-arm (RCA) trellis in which up to six primocanes were retained. Cane emergence occurred from mid-April to late-May. The first (oldest) primocane attained a sufficient height to be trained in early May in 40% of plants, but younger primocanes could not be trained until late July. However, only 94%, 73%, 60%, and 42% of plants developed three, four, five, and six primocanes, respectively. In primocanes that were trained from 14 May to 3 June, eight or nine medium (0.7-1.3 m) to long (>1.3 m) lateral branches developed. Primocanes tied from 4 June to 16 July averaged less than six lateral branches that were mostly of medium and short (<0.7 m) categories. Primocanes trained after 16 July produced only two short lateral branches. The results indicated that training primocanes from mid-May to mid-June for 'Chester Thornless' blackberry on the RCA trellis would be advantageous to minimize labor costs.

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Fumiomi Takeda, Ann K. Hummell, and Donald L. Peterson

Mature 'Chester Thornless' blackberry plants were trained to the rotatable cross-arm (RCA) trellis to determine the effect of retaining two, four, or six primocanes on plant productivity. Retention of only the two oldest primocanes and generally the most vigorous primocanes per plant yielded 14.1 kg of fruit compared to 17.1 kg per plant in which as many as six primocanes were retained. Increasing the number of canes did not result in significant yield increase (P = 0.09) because the primocanes trained in late-June and July produced only a few, and, in some cases, no lateral branches. Thus, retaining only those canes that become trainable early in the season decreased labor inputs and allowed primocane training to be completed prior to the onset of harvest. As a result, the effort to train and retain only those primocanes that reach the trainable height before mid-June may be advantageous to minimize labor costs, but will not effect plant productivity.

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Fumiomi Takeda, Gerard Krewer, Elvin L. Andrews, Benjamin Mullinix Jr, and Donald L. Peterson

Mechanical harvesting systems for processed blueberries (Vaccinium spp.) are available. However, low harvest efficiency and high fruit damage have limited the use of mechanical harvesters for picking blueberries for fresh market to specific cultivars under good weather conditions. New harvesting technology for fresh-market blueberries is needed. The V45 harvester was developed by the U.S. Department of Agriculture in 1994 to harvest fresh-market-quality northern highbush (V. corymbosum) blueberries in Michigan. The current study was performed in Georgia to evaluate the V45 harvester on specially pruned rabbiteye blueberry [V. virgatum (syn. V. ashei)] and southern highbush blueberry (V. darrowi × V. corymbosum) and included analysis of harvest efficiency and fruit quality (percent blue fruit, percent bloom, percent split skin, and internal bruise damage). Six-year-old, 6- to 8-ft-tall ‘Brightwell’ and ‘Powderblue’ rabbiteye blueberry plants were winter pruned to remove vertically growing and overarching canes in the center of the bush in Jan. 2004 and Feb. 2005 respectively. Three-year-old, 3- to 5-ft-tall ‘FL 86-19’ and ‘Star’ southern highbush blueberry plants were similarly pruned in summer (June 2004) or in winter (Feb. 2005). Pruning removed an estimated 30% to 50% of the canopy and opened the middle, resulting in V-shaped plants in both rabbiteye and southern highbush blueberries. Yield of winter-pruned ‘Brightwell’ rabbiteye blueberry was lower compared with unpruned plants during both years, but winter-pruned ‘Powderblue’ rabbiteye blueberry plants produced as much as unpruned plants in 2005. In ‘FL 86-19’ southern highbush blueberry, plants that were summer pruned in June 2004 produced as much as unpruned plants in 2005, but plants that were winter pruned in Feb. 2005 had lower yields than unpruned plants in 2005. The V45 harvester caused little cane damage on pruned blueberry plants. In rabbiteye blueberries, internal fruit damage and skin splitting was less in V45-harvested fruit than in fruit harvested by a sway harvester and nearly that of hand-harvested fruit. However, in ‘FL 86-19’ southern highbush blueberry, the V45 harvester detached a lower percentage of blue fruit and excessive amounts of immature and stemmed fruit. These findings suggest that the V45 harvester has the potential to harvest some rabbiteye blueberry cultivars mechanically with fruit quality approaching that of hand-harvested fruit.