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S.C. Myers

Micropropagated plants of `Heritage' primocane-fruiting (PF) red raspberry (Rubus idaeus L.) were planted at in-row spacings of 100, 50, or 25 cm. Yield per unit area during the first season was positively correlated with initial plant in-row spacing. During the first season of growth, initial plant in-row spacing did not affect the total number of primocanes that developed but was positively associated with the numbers of primocanes that fruited. Yield per primocane, primocane yield efficiency, total nodes per primocane, and number of fruiting nodes per primocane were not affected by plant in-row spacing in the first year. Average fruit weight and fruiting primocane diameter in the first year were negatively associated with plant in-row spacing. Photosynthetic photon flux density (PPFD) penetrating the row canopy as measured in the first season was not affected by treatment. Treatment did not influence percentage of fruit exhibiting solar injury, shattering, or infection by Botrytis cinerea. Plant in-row spacing did not influence yield during the second and third production seasons.

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David G. Himelrick, Robert C. Ebel, and Floyd M. Woods

`Navaho' erect thornless blackberry plants were subjected to a combination of three primocane summer topping heights and two winter lateral length pruning treatments. Plants were topped at 91, 122, 152 cm tall, and laterals were shortened to either 30 or 61 cm in length. Treatment effects on yield and plant structure were examined for four growing seasons. Lateral length had little effect on yield and any pruning height. Yield generally increased with increasing plant height. The 122-cm height appeared to optimize yield while still allowing for manageable floricane architecture.

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Jean-Pierre Privé, J.A. Sullivan, and J.T.A. Proctor

Leaf removal, cane girdling, and 14C translocation patterns were used to study source-sink relationships of primocane-fruiting (PF) red raspberries. Although the leaves in the reproductive zone were most important for vegetative and reproductive development, compensatory effects between the cane leaves were evident. When 14C translocation was studied in the reproductive portion of the cane, the lateral closest to the 14C-treated leaf was the major sink for carbohydrate from that leaf, independent of leaf position or reproductive development. Thereafter, partitioning to leaves and/or flowers or fruits above the 14C-treated leaf was related to leaf phyllotaxy 75% of the time.

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Pedro B. Oliveira, Cristina M. Oliveira, Luís Lopes-da-Fonseca, and António A. Monteiro

The spring shoots of `Autumn Bliss' red raspberry (Rubus idaeus L. var. idaeus; primocane-fruiting type) were cut on 2, 16, 31 July and 15 and 30 Aug. with the objective of delaying fruit harvest into the off-season under mild winter climatic conditions. Cutting shoots in August delayed fruit harvest until February and April of the following year, but shoot growth was weak and fruit yield low (4.8 and 2.1 g/cane). July cuttings delayed harvest until October to January with acceptable fruit yield (63.5, 52.8, and 26.5 g/cane for 2, 16, and 31 July, respectively). The differences in cane height and total node and fruiting node count between the three cutting dates of July were small, but there was a constant decrease in leaf area per cane from the first to the third date and a sharp decrease in fruit yield from the second to the third date. Vegetative shoot growth was less affected than yield when summer cutting was delayed until the end of July to induce a later harvest. Fruit quality always reached acceptable standards. This study confirms the practicability of using summer-cutting of primocane-fruiting red raspberries to induce off-season fruit production under protected cultivation in mild winter climates.

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Stenhen F. Klauer, J. Scott Cameron, and Paul W. Foote

Results from previous cultural and physiological studies of red raspberry suggest that primocanes compete with floricanes for light, nutrients and/or photoassimilates. This study was undertaken to determine whether this competition might be reflected in the actual translocation of photoassimilates between the two types of canes. In 1993, pairs of greenhouse grown, potted red raspberry (Rubus idaeus L.) plants contaming one or two floricanes and numerous primocanes were labeled with 14CO2 on four dates corresponding with early anthesis, green fruit, red fruit and post fruit maturity stages of the growing season. For each experiment, either a floricane or a primocane was exposed to 92.5μCi 14CO2 within a sealed bag. After 24 hours, the bag was removed and the presence of label was monitored for up to 11 days. Activity was determined using liquid scintillation. At all developmental stages 14C moved from the labeled floricane to primocanes that were from 2.5 cm to 1.5 m tall and to the roots. Movement was quickest and relatively greatest at early anthesis, dccreascd during fruiting, and was still occuring at 2 months after fruit maturity. Small amounts of label were detected in roots of labeled primocanes at all stages, but trace amounts were present in fruit and other primocanes only at post fruit maturity.

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J.A. Sullivan, B.A. Hale, and D.P. Ormrod

Factorial experiments in two growing seasons in open-top field chambers with two or three O3 concentrations and two primocane-fruiting raspberry (Rubus idaeus L.) cultivars were used to obtain dose-response relationships describing the effects of seasonal O3 exposure on raspberry plant vegetative and reproductive growth. At the lower concentration (0.12 μl·liter-1), the response to O3 was nonsignificant. However, at 0.24 μl·liter-1, `Heritage' showed a significant decline relative to the control in cane height, node count, cane diameter, and dry weight. These changes were accompanied by a 52% decrease in yield, caused mainly by a reduction in fruit count. In contrast, vegetative and yield characters of the `Redwing' were not affected by O3.

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T. Kostman, J. S. Cameron, C. Chen, and S. F. Klauer

The red raspberry industry of the Pacific Northwest depends upon chemical primocane suppression to temporarily reduce competing vegetation during fruit development. This practice increases yield and harvest efficiency, but can reduce cane vigor, number and diameter over time. Few chemicals are available for this purpose and thus the potential of nonchemical alternatives is being explored. The purpose of this project was to evaluate the potential of blown air as a thigmic stress to temporarily suppress primocane growth.

Blown air treatments were applied once (12 PM) or twice (12\4pm) per day, five days per week using a portable leaf blower generating winds of 273 km per hr. Treatments also included several rates of three experimental herbicides and an untreated control. All treatments were applied when primocanes were 10-15 cm in length and blown air treatments continued through fruit development. Primocane development was monitored over the course of the season.

Blown air reduced primocane length by 15-30% prior to harvest giving control equivalent to current chemical methods. Blown air increased cane diameter but reduced yield by reducing fruit numbers. Reductions in fruit numbers are likely due to flowering\fruiting points removed by blown air.

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Fumiomi Takeda, D. Michael Glenn, and Thomas Tworkoski

Three experiments were performed to determine the effect of amending the soil surface layer and mulching with hydrophobic kaolin particle on weeds and blackberry (Rubus subgenus Rubus Watson) plants. In the first study a processed kaolin material (product M-96-018, Engelhard Corporation, Iselin, N.J.), was incorporated in August into the top 3 cm of freshly roto-tilled field that had been in pasture the previous 5 years. The following spring, dry weight of weed vegetation in the control treatment was 219 g·m–2 and was significantly higher (P = 0.05) than the 24 g·m–2 harvested from the treated soil. In two other studies, planting holes for blackberry transplants were either 1) pre- or postplant mulched with a 2- or 4-cm layer of 5% or 10% hydrophobic kaolin in field soil (w/w), or 2) postplant treated with a) napropamide, b) corn gluten meal, c) a product comprised of hydrous kaolin, cotton seed oil, and calcium chloride in water (KOL), d) hand weeded, or e) left untreated. Although untreated plots had 100% weed cover by the end of July, herbicide treatments, 4-cm deposition of hydrophobic kaolin particle/soil mulch, and KOL all suppressed weeds the entire establishment year. Preplant application of hydrophobic kaolin mulch and postplant application of KOL reduced blackberry growth and killed transplants, respectively. In year 2, blackberry plants produced more primocanes that were on average 10-cm taller in weed-free plots (herbicide, 4-cm kaolin soil mulch, and mechanical weeding) than in weedy plots (control and 2-cm kaolin soil mulch). In year 3, yield was significantly lower in control plots (1.5 kg/plant) than in plots that were treated with napropamide and 2- and 4-cm hydrophobic kaolin mulch, or hand weeded during the establishment year (4 kg/plant). The results showed that 4-cm hydrophobic kaolin mulch applied after planting can suppress weeds without affecting blackberry productivity. These kaolin products are excellent additions to the arsenal of tools for managing weeds in horticultural crops.

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Joseph A. Fiola, Robert Lengyen, and Harry J. Swartz

A major objective of the MD/NJ/VA/WI Cooperative Raspberry Breeding Program is to develop new primocane-fruiting raspberry cultivars that are early, with large fruit size, and good fresh flavor, relative to the `Heritage' standard. Step I seedling selections were made and tissue culture-propagated. The Step III advanced selection trial, planted in 1993, consisted of two advanced selections, JCR-F1 [Geo-1 (Autumn Bliss × Glen Moy) × Heritage–red], and JEF-B1 (Amity × Glen Eagles–golden), with a `Heritage' check. The planting was a RCB (four replications), with 3-m plots, 60-cm plant spacing, on raised beds with black plastic mulch (establishment year), and trickle irrigation. The 1994 season started dry, and mid-summer was warm and wet, inducing an early harvest overall. JCR-F1 was >2 weeks earlier, 40% higher yielding, with 18% larger fruit size than `Heritage'. JCR-F1 fruit was tall conic, cohesive, and had good flavor; plant vigor was very good. JEF-B1 was 10 days earlier than `Heritage', had 40% larger fruit size, but was 25% lower yielding; plant vigor was also good. The flavor was described as banana and apricot. The planting will be fruited for multiple seasons for continued comparison.

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Neil C. Bell, Bernadine C. Strik, and Lloyd Marti

Primocanes were cut at ground level at one-month intervals from late April to late July 1991 and 1992. An uncut control was included. Four canes per plant were trained either in August or the following February, the others being removed and measured. Yield data were collected and yield components measured in 1992 and 1993. Cane diameter, main cane length and branch cane length per plant generally declined with later suppression date. Consequently, yield per meter of cane declined with later suppression date. However, cane number and total plant main cane length were greater for all suppression treatments and percent budbreak increased with later suppression date. As a result, April- and May-suppressed plants had increased-yields compared to control plants in both 1992 and 1993, as did June-suppressed plants in 1993. August-trained plants had significantly higher yields than February-trained in both years, primarily because of increased budbreak. The basal section of canes was the most productive, because of increased budbreak and branch cane production.