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Brent L. Black

Balancing vegetative growth with fruiting is a primary concern in strawberry (Fragaria ×ananassa Duch.) production. Where nursery plant selection and preconditioning are inadequate for runner control, additional approaches are needed. The gibberellin biosynthesis inhibitor prohexadione-Ca (commercial formulation Apogee) was tested over two seasons for suppressing fall runners of `Chandler' plug plants in a cold-climate annual hill production system. Prohexadione-Ca was applied as a foliar spray at active ingredient concentrations ranging from 60 to 480 mg·L-1, either as a single application 1 week after planting, or repeated at 3-week intervals. The lowest rate resulted in inadequate runner control, with some runners producing malformed daughter plants. Higher rates resulted in 57% to 93% reductions in fall runner numbers, with a concomitant increase in fall branch crown formation. There were no effects of the prohexadione-Ca treatments on plant morphology the following spring, and no adverse effects on fruit characteristics or yield. Chemical names used: prohexadione-calcium, calcium 3-oxido-4-propionyl-5-oxo-3-cyclohexene-carboxylate.

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Brent L. Black

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Brent L. Black and Mark K. Ehlenfeldt

Precocious varieties of highbush blueberry (Vaccinium corymbosum L.) may overcrop during the first few seasons in the fruiting field, adversely affecting plant establishment. Reducing or preventing bloom in the nursery and during establishment would be beneficial in preventing early cropping and reducing the risk of infection by pollenborne viruses. We investigated the efficacy of foliar applications of GA4+7 for suppressing flower bud initiation in blueberry. One-year-old rooted cuttings of ‘Bluecrop’ were obtained from a commercial nursery and established in 11-L pots at the Philip E. Marucci Blueberry and Cranberry Research Center, Chatsworth, N.J. Three separate experiments were conducted over three seasons with ‘Bluecrop’ (and ‘Duke’ in 2005) highbush blueberry where foliar applications of GA4+7 were made at concentrations ranging from 50 to 400 mg·L−1 a.i., with timing treatments ranging from 7 July to 15 Sept., with 10 replicate plants per treatment. Floral and vegetative buds were counted the following spring. In the first study, the greatest degree of flower bud suppression resulted from applications at 400 mg·L−1 repeated weekly from 7 July to 1 Sept. However, these treatments also reduced total vegetative bud number and plant height. In the two subsequent studies, the largest treatment effect resulted from three weekly applications in late August and early September, where flower bud numbers were suppressed by 70% to 85% for ‘Bluecrop’ and 95% for ‘Duke’ while total vegetative growth was unaffected.

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Kylara A. Papenfuss and Brent L. Black

Mature tart cherry (Prunus cerasus L. ‘Montmorency’) trees in a commercial orchard were subjected to irrigation deficits from pit hardening to harvest during the 2007 and 2008 seasons. Irrigation treatments ranged from 30% to 100% of a commercially managed application rate during the deficit period. Midday stem water potential measurements were significantly different among treatments before harvest. However, fresh weight yield at harvest did not differ significantly among irrigation treatments in either year (P = 0.64). In 2008, the amount of undersized fruit eliminated during packout was significantly higher in the treatments replacing 30% and 47% of the commercial irrigation level (P < 0.001), but only amounted to 2.0% and 1.4% of total yields, respectively. This small increase in undersized fruit did not significantly affect packout. Soluble solids concentration and chroma of intact fruit increased with the severity of the irrigation deficit and were inversely correlated with fruit water content.

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Brent L. Black and Richard H. Zimmerman

Highbush blueberry plants require low-pH, well-drained sandy soils. To increase the range of sites available for highbush blueberry production, by-products were tested as constituents in soilless media and as soil amendments. By-products, including coal ash, municipal biosolid compost, leaf compost, and acid peat, were combined in different proportions and compared to Berryland sand (alone) and Manor clay loam (alone and compost-amended) for a total of 10 media treatments. The pH of all treatment media was adjusted to 4.5 with sulfur. One-year-old tissue-cultured plants of `Bluecrop' and `Sierra' were planted in 15-L pots containing the pH-adjusted treatment media in 1997, producing their first substantial crop in 1999. For the 1999 crop, ripe fruit was harvested at weekly intervals over 5 weeks. ANOVA for yield indicated a significant cultivar × media interaction. `Bluecrop' appeared more sensitive to media treatment as yields on Manor clay loam were 80% less than on Berryland sand. Yields of `Bluecrop' on coal ash-compost mixes were similar to that of Berryland sand, and 1:1 coal ash:compost mixes produced significantly higher yields than did the 3:1 mixes. Yield of `Sierra' on Manor clay loam was 41% less than on Berryland sand, and plants growing on soilless mixes yielded 17% to 58% more than those on Berryland sand. `Bluecrop' fruit size was greatest for Berryland sand, but did not differ significantly among coal ash-compost mixes. For all media treatments, `Sierra' fruit size was inversely correlated with yield. Fruit from `Bluecrop' plants on coal ash-compost mixes ripened slightly earlier than on Berryland sand, but ripening date of `Sierra' did not vary significantly with soil treatment. The potential for employing these by-product mixes in small-scale commercial blueberry production will be discussed.

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Brent L. Black and Richard H. Zimmerman

Bottom ash from a coal-fired power plant and two composts were tested as components of soil-free media and as soil amendments for growing highbush blueberry (Vaccinium corymbosum L.). Combinations of ash and compost were compared to Berryland sand, and Manor clay loam, and compost amended Manor clay loam. The pH of all treatment media was adjusted to 4.5 with sulfur at the beginning of the experiment. In 1997, plants of `Bluecrop' and `Sierra' were planted in 15-dm3 pots containing the pH-adjusted treatment media. The first substantial crop was harvested in 1999. At the end of the 1999 season, one half of the plants were destructively harvested for growth analysis. The remaining plants were cropped again in 2000. Yield and fruit size data were collected in both seasons, and leaf and fruit samples were collected in 1999 for elemental analysis. The presence of coal ash or composted biosolids in the media had no detrimental effect on leaf or fruit elemental content. Total growth and yield of both cultivars was reduced in clay loam soil compared to Berryland sand, whereas growth and yield of plants in coal ash-compost was similar to or exceeded that of plants in Berryland sand.

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Jerome Hull Jr., Martin J. Bukovac, and Brent L. Black

The effect of Accel concentration and time of application on fruit size and yield was studied using `Delicious' (Redchief), `Empire', `Jonathan', and `Gala'. High-volume sprays of Accel were applied at 25 to 150 mg·liter–1 to `Delicious' and `Empire' at king fruit diameter (KFD) of 5 to 20 mm. `Jonathan' and `Gala' were treated at KFD of 5 to 20 mm with 10 to 40 g/A. The effect of spray volume (500 to 2000 liters·ha–1) and surfactant (Regulaid) was studied using `Jonathan'. Response was indexed by yield and fruit size distribution at harvest. Although yield in `Delicious' was reduced with all concentrations of Accel, the percentage of fruits in the larger-size classes (3”+) was not significantly increased. In contrast, with `Empire', Accel reduced fruit load similar to hand-thinning (HT) and percentage of large fruit equaled or exceeded that of the HT treatment. Increasing concentration of Accel was related to an increase in fruit size; early application (5 mm KFD) was more effective than late (10, 20 mm KFD) application. There was no significant effect of spray volume or Regulaid. Increasing Accel rate (10 to 20 g/A) resulted in significant yield reduction and increase (4% to 9%) in mean fruit weight in `Gala'.

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Martin J. Bukovac, Brent L. Black, and Jerome Hull Jr.

NAA and Accel are used for fruit thinning of apples. However, when combined, many small (<65 mm) fruit were produced in `Delicious'. We extended our studies using Redchief `Delicious' and `Empire', and, since BA is common to both Accel and Promalin, to study the effect of NAA-thinning sprays on Promalin-treated Redchief trees. NAA (10–15 mg·liter–1) and Accel (25–100 mg·liter–1) were applied to Redchief and `Empire' at 100-mm king fruit diameter (KFD). NAA interaction with Promalin was studied using Redchief. Promalin (1.5 pt/A) was applied as a single spray (80% king bloom, KB) and as a split application (0.75 pt/A, 80% KB and repeated at 10-mm KFD) with NAA (15 mg·liter–1) at 10-mm KFD. In `Delicious', 2% to 9% of the fruit from Accel-treated trees was <65 mm in diameter, compared to 11% for NAA alone. However, when NAA was applied with Accel, 22% to 30% of the fruit was <65 mm and percentage of large fruit (75 mm+) was reduced by 24% to 36%. There was no strong interaction for fruit size in `Empire', but the combination decreased yield. NAA applied to Promalin-treated `Delicious' increased percentage of small fruit dramatically (14% to 25%). No increase in small fruit was observed with Accel of Sevin.

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Brent L. Black, Martin J. Bukovac, and Matej Stopar

Apple fruit size is influenced by position on the spur, and location and number of competing fruits. King fruit appear to have the greatest potential to size and grow best in the absence of intraspur fruit competition (ISFC). Accel (A) and NAA (N), commercial thinning chemicals, influence fruit size beyond their effects on crop load. A 2-year study was conducted to determine the effect of ISFC and position (king, K, or lateral, L) on fruit growth in response to A and N. Branches from `Redchief Delicious' were thinned, after petal fall, to one K, one L, one K + one L, or two L fruits per spur. Whole-tree treatments of N (15 mg·liter–1), A (50 mg·liter–1, 1993; 25 mg·liter–1), and a combination (N+A) were applied at 10-mm king fruit diameter. A nontreated control was included. In 1993, N and N+A reduced fruit size only with ISFC, while A increased fruit size in the absence of ISFC. In 1994, A had no effect, but N and N+A reduced fruit growth with ISFC. In both seasons, A and N decreased the frequency of spurs bearing multiple fruit, while N+A dramatically increased number of spurs with multiple fruits (branch survey).

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Brent L. Black, Tiffany Maughan, Christina Nolasco, and Blake Christensen

Winter injury to raspberry floricanes commonly limits productivity in cold climates. Primocane-fruiting raspberries avoid winter injury by fruiting on first year canes, but fruit production in the high-elevation valleys of the Intermountain West is later than needed for local markets, and may be limited by early fall freezes. High tunnels were used for early spring heat to advance primocane growth and the fruiting season of two primocane-fruiting red raspberry cultivars. Tunnels were covered with plastic in March and April. Then, they were covered with shade cloth during fruit ripening. Tunnel-covered plots were compared with field plantings for primocane growth rate, fruiting season, yield, and fruit quality over two seasons. High tunnels increased cane growth rate, with the harvest season advanced by 18 to 26 days depending on season and cultivar, but they did not consistently affect the total season yield or fruit size. Low-cost two-season tunnels used in conjunction with early-season primocane-fruiting raspberries may provide a viable method for small acreage producers in harsh climates to reliably supply high-value seasonal raspberry markets.