Fresh market blackberry production has increased in the United States in the last 10 years. Commercial acreage of erect and trailing blackberry has expanded most notably in California (M. Jimenez, personal communication) and of erect blackberry in Georgia (G. Krewer, personal communication) and North Carolina (G. Fernandez, personal communication). However, western trailing blackberry is rarely planted in mid-Atlantic coast region because temperatures <−12 °C are common during the winter [U.S. Department of Agriculture (USDA), 2004]. Current commercial trailing blackberry, grown mainly in USDA Plant Hardiness Zones 8 and 9 (Cathey, 1990), such as Willamette Valley, OR, and San Joaquin Valley, CA, suffers winter injury when temperatures drop below −10 °C (Crandall, 1995), and this has limited the expansion of trailing blackberry outside Oregon, Washington, and California where winter conditions are mild. In controlled freezing studies, Cortell and Strik (1997) reported that canes and buds of western trailing ‘Marion’ blackberry survived temperatures as low as −22 °C in one year, but only to −10 °C in another year. In Oregon, ‘Siskiyou’, a western trailing blackberry, did not show visible injury after a winter when temperatures dropped to −12 °C on several nights (Finn et al., 1999). In the upper Piedmont region of North Carolina (USDA Plant Hardiness Zone 7b), where fluctuating sub-0 °C temperatures in winter are common, ‘Siskiyou’ blackberry did not produce a crop (J. Ballington, personal communication). However, in the eastern United States, the interest in growing trailing blackberries still exists among small and part-time farmers looking for a niche market and an early-season crop.
For blackberry production to expand into areas with more severe winter conditions, cultivars with increased winterhardiness and systems to protect blackberry plants from winter injury are needed. Improved trellis design and cane-training techniques along with enhanced winter protection strategies and improved harvest efficiency have enabled diversification for small farms and opened up niche markets (Takeda et al., 2008). A wide variety of techniques, such as RCs, coldframes, plasticulture, plastic-covered and glass greenhouses, and high tunnels, have been used to modify the environment for vegetable (Lamont, 2005; Wells and Loy, 1985) and berry crops (Demchak, 2009; Pritts et al., 1999) and for extending the production season. Besides modifying soil and air temperatures, these techniques also protect plants from wind damage and may limit pests.
At the Appalachian Fruit Research Station (AFRS) in Kearneysville, WV, a novel trellis system called the rotating cross-arm trellis and unique cane-training technique aided mechanical harvesting of fresh market quality fruit of eastern thornless blackberries (Harper et al., 1999; Takeda and Peterson, 1999). The RCA trellis design is similar to the shift trellis system described by Stiles (1999). The RCA system has a short upright post (24 inches) with a 5-ft-long cross-arm at the top of the post that rotates as much as 180° (Takeda and Peterson, 1999) and is now commercially marketed by Trellis Growing Systems [TGS (Fort Wayne, IN)]. The drawings of RCA trellis are available at their website (TGS, 2010). The details of cane training technique developed for this trellis system are provided elsewhere (Takeda et al., 2003, 2008). In the fall, the lateral canes that were tied to the wires on RCA trellis during the growing season are inclined to a horizontal position. Inclination of the lateral canes close to the ground (≈20 inches) creates a plant shape conducive for the placement of winter protection material over the plant. In spring, the RC is removed and after flowering shoots emerge from buds on the lateral canes and grow upward, the cross-arm is rotated through the vertical and to an additional 30° so that much of the fruit hangs on one side of a narrow canopy below the cross-arm without causing cane breakage. ‘Siskiyou’ plants that were low to the ground and covered with one layer of RC produced ≈5 kg of fruit per plant while plants in the open produced <2 kg fruit/plant during all previous 6 years (2003–2008) (Takeda et al., 2008). On the basis of these findings, we hypothesized that the combination of having canes close to the ground and covering them with RC would be more effective in reducing winter injury than covering the upright canes. The objective of this study was to determine the effect of lateral cane orientation and winter RC application on bud survival, cane injury, and productivity of ‘Siskiyou’ trailing blackberries.
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Trellis Growing System 2010 Overview of the RCA (rotating cross-arm) trellis system 19 Nov. 2010 <http://www.trellisgrowingsystems.com/resources/RCA_Overview.pdf>.
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