Primocane Growth in 'Chester Thornless∑ Blackberry Trained to the Rotatable Cross-arm Trellis

Primocane Growth in 'Chester Thornless∑ Blackberry Trained to the Rotatable Cross-arm Trellis,Fumiomi Takeda,Ann K. Hummell,Donald L. Peterson

Primocane Growth in 'Chester Thornless∑ Blackberry Trained to the Rotatable Cross-arm Trellis   (Citations: 2)
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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. Eastern thornless blackberry (Rubus subgenus Rubus Watson) cultivars, such as 'Chester Thornless∑ , 'Hull Thornless∑ , and 'Triple Crown∑ , are grown commercially on "I"-shaped hedgerows and on narrow divided canopy trellis systems in the middle Atlantic coast, middle South, lower Midwest, and Pacific Northwest areas of the United States (Galletta et al., 1998). The yield of blackberries is dependent, in part, on the number of bud nodes left on the floricanes after winter pruning (Takeda, 2002). Pruning lateral branches gener- ally decreases yields but often improves fruit quality (Crandall and Daubeny, 1990; Moore and Skirvin, 1990). However, node number per plant is not correlated with yield because not all axillary buds produce a flowering shoot (Takeda, 2002). Yet, yield per floricane remains high in severely pruned plants due to increased budbreak of secondary axillary buds and fruit numbers per raceme. Improved knowledge of the relationship between node number distri- bution and yield will help determine the best pruning method. Alternative trellis systems and primocane training techniques are needed in the production of eastern thornless blackberries to maximize yield, minimize labor and to improve machine harvestability (Peterson et al., 1992). A modi- fied, "Y"-shaped trellis (Fig. 1) with a rotatable cross-arm (RCA) was developed to facilitate an over-the-row mechanical harvester (Takeda and Peterson, 1999). Detailed descriptions of trellis components and primocane training practices for the RCA trellis system are pro- vided elsewhere (Takeda and Peterson, 1999). The RCA trellis, like the Lincoln canopy trellis system (Dunn et al., 1976) and the variations of shift trellis (Stiles, 1999), expands the canopy surface area, spatially separates the floricanes and primocanes into two canopies and potentially improves machine harvest efficiency (Harper et al., 1999; Peterson and Takeda, 2003). Our technique of training pri- mocanes onto the RCA trellis system involves bending and tying the primocane tips as they reach a height of ß 1.2 m onto a training wire that runs through the web of angle iron under- neath the short stationary catch arm (Fig. 1). This technique forces the primocanes to grow horizontally in the direction that the mechanical harvester travels. When primocane terminals reach the adjacent plant, the primocanes are tipped. The rationale for training primocanes to grow horizontally is to promote the develop- ment of lateral branches from the portion of the primocane that is tied to the training wire at 0.9-m height. The bending of the main canes also facilitates the rotation of the cross-arm without causing main cane breakage. Mature plants of 'Chester Thornless∑ blackberry can produce as many as six or seven primocanes. The canes emerge from the crown of the plant over a 2-month period, beginning in mid-April. The diameters, heights, and numbers of lateral branches that develop from these primocanes are highly variable. If all primocanes are retained, then the need for labor to train them will continue into July and August at the time when fruit is being harvested. Blackberry management strategies that will not conflict with the labor-intensive harvest opera- tion, mitigate labor costs, and help compensate for the scarcity of labor are needed. Bell et al.
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