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Fumiomi Takeda and Ann K. Hummell

A new trellis system called the “rotatable cross-arm” (RCA) trellis was developed to ease mechanical fruit harvesting of eastern thornless blackberries. The rotation of the cross-arm following bloom 1) positions all the fruit to one side of the trellis in a plane underneath the cross-arm and 2) permits primocanes to be trained to side without the fruit. To maintain productivity, the number of lateral shoots that arise from primocanes must be maximized. In this study, we examined the growth and development of individual primocanes within plants and the number of lateral canes that developed on them to decide which canes should be retained during the growing season. In `Chester Thornless' blackberry, primocanes trained early in the season produced more laterals per cane, had higher percentage of buds forming laterals, and were much larger in diameter than primocanes trained later in the season. Field observations suggested high sink strength and less light competition probably contributed to the increased productivity of early canes. These results indicated that the canes that become trainable early in the season must be retained for the success of the RCA trellis. Conversely, the primocanes that become trainable later in the season do not develop sufficiently and should be removed.

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Ann K. Hummell and David C. Ferree

A 2-year field study was initiated in 1994 to examine the interactions between crop load and cluster exposure and their influences on the yield and fruit quality of mature, own-rooted `Seyval blanc' grapevines. Light, moderate, and heavy crop loads were established near bloom by cluster-thinning vines planted at 2.6 × 3.0-m spacing to around 20, 40, and 80 clusters per vine, respectively. At veraison, three clusters per vine were given one of three natural shaded treatments: fully exposed, partially shaded, and densely shaded. Vines with the heavy crop load produced higher yields per vine and lower cluster and berry weights. Heavy vine clusters tended to be more green in 1994 and possessed lower pH and soluble solid concentrations in both years compared to other crop loads. Compared to densely shaded clusters, fully exposed clusters had smaller average cluster and berry weights, lower titratable acidity, higher pH and soluble solid concentrations, and more yellow coloration. In 1994, no significant interactions were found for any fruit quality or yield characteristics. In 1995, significant interactions were found for soluble solids and hue angle, but not for yield, pH, or titratable acidity. These results suggest that the crop load of the vine and microclimate around the cluster, in addition to their individual effects, sometimes interact to affect fruit quality in `Seyval blanc' wine grapes.

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Ann K. Hummell and David C. Ferree

`Seyval blanc' grapevines (Vitis spp.) were cluster thinned 7 days after full bloom to 20, 40, and 80 clusters per vine to create light, moderate, and heavy crop levels. Vines were also shoot positioned at veraison to create exposed, partially shaded, and densely shaded cluster microclimates to examine the interactions between crop level and light exposure on fruit composition during stage III of berry development. Clusters were harvested using one of two criteria: on the same date or at similar soluble solids concentrations. Cluster mass and berries per cluster decreased with increasing crop level regardless of harvesting criterion. When harvested on the same date, soluble solids concentration, pH and malic acid concentration of juice decreased with increasing crop level. When harvested at similar soluble solids concentrations, increasing crop level delayed harvest and reduced titratable acidity (TA), tartaric acid, and malic acid. As cluster light exposure increased, soluble solids and pH increased and TA and malic acid decreased when clusters were harvested on the same date. When harvested at similar soluble solids concentration, increasing light exposure advanced harvest date and pH, TA, tartaric acid, and malic acid decreased. If clusters were harvested on the same date, significant interactions were found between crop level and light exposure for soluble solids concentration and the hue angle of berries. Significant interactions were found for berry mass, pH, TA, and tartaric acid when clusters were harvested at similar soluble solids. When harvested on the same date in 1995, soluble solids concentration of densely shaded clusters declined as crop level increased, whereas the soluble solids of exposed and partially shaded clusters declined as cluster number increased from 20 to 40 clusters per vine but remained constant from 40 to 80 clusters. In 1995, the hue angles of exposed clusters decreased with increasing crop level, while those of partially shaded and densely shaded clusters increased. When harvested at similar soluble solids concentration, berry mass of exposed and partially shaded clusters was similar across crop levels, whereas berry mass of densely shaded clusters declined as crop levels increased. Based on contribution to treatment error, crop level influenced pH more, and TA less, than did light exposure if harvested at the same date. Conversely, crop level influenced TA more, and pH less, than did light exposure if harvest was done at similar soluble solids concentrations. Regardless of harvest criterion, crop level influenced yield components, and soluble solids concentration to a greater extent and hue angle to a lesser extent than did light exposure.

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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.