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Youping Sun, Guihong Bi, Genhua Niu, and Christina Perez

an optimized concentration of PGR for producing compact plants. Dikegulac sodium [18.5% dikegulac sodium (Augeo ® ; OHP, Mainland, PA)] is a PGR labeled to reduce or break apical dominance in plant shoots and to enhance lateral branching by disrupting

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Luis Pozo, Ana Redondo, Ulrich Hartmond, Walter J. Kender, and Jacqueline K. Burns

Two formulations of the plant growth regulator dikegulac (2,3:4,6-di-O-isopro-pylidene-α-L-xylo-2-hexulofuranosoic acid), consisting of dikegulac-sodium (Atrimmec) or dikegulac:ascorbic acid (1:1) (DAA), as well as 5-chloro-3-methyl-4-nitro-pyrazole at 200 mg·L-1, were applied as foliar sprays to `Hamlin' and `Valencia' orange trees (Citrus sinensis L. Osbeck) at two dates during the harvest season for each cultivar (11 Nov. and 10 Jan. for `Hamlin', 22 Mar. and 25 May for `Valencia'). Fruit detachment force was evaluated 10 days after application, whereas cumulative leaf abscission was monitored up to 60 days after application. In both cultivars, Atrimmec and DAA at 3,000 mg·L-1 induced moderate fruit loosening when applied at the earlier application date, but fruit loosening improved when applied at the later application date. In `Hamlin', both formulations caused higher leaf abscission when applied at the later date. DAA applications resulted in low leaf loss in `Valencia' regardless of application time, whereas Atrimmec caused unacceptably high leaf loss at either application date. No differences in internal fruit quality were found as a result of any abscission material treatment. The results indicate that DAA could be a promising option to induce fruit loosening in late harvested `Valencia' orange trees with minimal undesirable side effects.

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Diana R. Cochran, Amy Fulcher, and Guihong Bi

lack of consistency across plant species. Cohen (1978) reported 4400 ppm dikegulac sodium increased mean number of shoots of ‘Formosa’ indica azalea ( Rhododendron indicum ) compared with manually pinching yet there was no difference in shoot number

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Amir Rezazadeh, Richard L. Harkess, and Guihong Bi

different modes of action have been developed to suppress apical dominance and enhance branching. Dikegulac sodium is translocated in the phloem to the apical meristem, inhibiting DNA synthesis resulting in a chemical pinching effect. Benzyladenine, a

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J.G. Norcini, J.H. Aldrich, and J.M. McDowell

Foliar spray application of dikegulac at 1600 mg·liter-1 during production of Bougainvillea glabra Choicy `Mauna Kea White', and Bougainvillea `Raspberry Ice', `Royal Purple', `Summer Snow', and `Temple Fire' in 4.5-liter hanging baskets (25.4 cm in diameter) was investigated in relation to flowering. The effect of foliar-applied dikegulac at 0, 400, 800, 1200, and 1600 mg·liter-1 on bracteole size of `Mauna Kea White' was also determined. Liners of `Temple Fire' pruned at transplanting (0 weeks) and sprayed with dikegulac at, 0 and 4 weeks had increased flowering and a slightly more compact, pendulous growth habit than plants that had only been pruned at 0 and 4 weeks. Dikegulac had little to no effect on flowering of the other cultivars. Under late-spring to early summer conditions (generally increasing temperatures), bracteole size of `Mauna Kea White' was reduced ≈25 % by 400 mg dikegulac/liter compared to nontreated plants; 800 to 1600 mg dikegulac/liter reduced bracteole size ≈37%. Under late-summer to mid-fall conditions when the weather was cooler and wetter, dikegulac had little to no effect on bracteole size; however, bracteoles of nontreated plants were ≈25% smaller than those of plants grown under the warmer and drier conditions of late spring to early summer. Chemical name used: sodium salt of 2,3:4,6-bis -O- (1-methylethylidene) -α-l-xylo- 2-hexulofuranosonic acid (dikegulac).

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Mara Grossman, John Freeborn, Holly Scoggins, and Joyce Latimer

species was conducted as a separate experiment and included an untreated control, DS (Augeo, 18% dikegulac sodium; OHP, Inc., Mainland, PA) at 400 mg·L −1 , 800 mg·L −1 , or 1600 mg·L −1 ; BA (Configure, 2% benzyladenine; Fine Americas, Inc., Walnut Creek

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J.G. Norcini, J.M. McDowell, and J.H. Aldrich

The use of dikegulac foliar sprays in production of 4.5-liter hanging baskets (25.4-cm in diameter) of `Barbara Karst' bougainvillea [Bougainvillea ×buttiana (Bougainvillea glabra Choicy X Bougainvillea peruviana Humb. & Bonpl.) `Barbara Karst'] and `Rainbow Gold' bougainvillea (Bougainvillea `Rainbow Gold') was investigated under high temperatures (27.5-32C) and two production seasons (late spring to early summer and midsummer to early fall). During the late production season, liners pruned at transplanting (0 weeks) and treated with 1600 mg dikegulac/liter at 0 and 4 weeks resulted in plants with more flowers than that of controls (pruned only at 0 and 4 weeks), with `Barbara Karst' having a slightly compact, pendulous growth habit similar to that of controls. Dikegulac enhanced flowering compared with controls during midspring to early summer, but it did not result in plants with a slightly compact pendulous growth habit. These results suggest that a foliar spray of 1600 mg dikegulac/liter could substitute for the second pruning during hanging basket production of `Barbara Karst'. Chemical name used: sodium salt of 2,3:4,6-bis-O-(1-methylethylidene)-α-xylo-2-hexulofuranosonic acid (dikegulac-sodium).

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Sauveur Mahotiere, Clarence Johnson, and Philamenia Howard

On Sept. 23, 1988, 12-month-old greenhouse-grown `Mary Washington', `Emerald', `UC 157 F1' and `UC 157 F2' asparagus seedlings were sprayed with dikegulac solutions ranging from 0 to 750 mg·l-1 with 150 mg·l-1 increments. The potted plants were then transferred to a lathhouse to simulate the weather conditions in the field. No significant shoot emergence occurred prior to killing frosts and low temperatures in December. The rise of the temperature in Jan. and Feb. 1989, promoted shoot emergence in all cultivars; but `Mary Washington' did not respond to the treatments. At 600 mg·l-1, the chemical increased shoot emergence in `Emerald', `UC 157 F1' and `UC 157 F2' by a respective cumulative average of 310, 161 and 305% over the control on 2 Feb. After intervening killing frosts and low temp, at the resumption of growth in late February 1989, `UC 157 F,' and `Mary Washington' were first to respond to the residual effects of the chemical, giving at 750 mg·l-1 a respective cumulative increase of 65 and 77% over the control. Dikegulac did not affect the height and dry weight of `Mary Washington' ferns. But it reduced the height of `Emerald' without affecting its dry weight.

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Michelle L. Bell, Roy A. Larson, and Douglas A. Bailey

Dikegulac, dikegulac + GA4+7, BA, and Promalin (GA4+7 + BA) were evaluated as lateral shoot-inducing agents on greenhouse forcing azalea, Rhododendron cultivars Gloria and Prize. The addition of GA4+7 (1000 or 2000 mg.L-1) to a commercial rate of dikegulac (3900 mg.L-1) did not effectively increase plant diameter or leaf width compared to plants sprayed with dikegulac alone. The combination of dikegulac and GA4+7 (3900 + 2000 mg.L-1, respectively) was more phytotoxic than dikegulac alone. Foliar sprays of BA and Promalin at 1000 and 2000 mg.L-1 and 1000 and 1816 mg.L-1, respectively, did not increase lateral shoot count. Neither the addition of GA4+7 to dikegulac nor the use of Promalin is a viable alternative to dikegulac application for inducing lateral branch development of dikegulac-sensitive cultivars. Chemical names used: Na 2,3:4,6-Bis-0-(l-methylethylidene)-α-L-xylo-2-hexulofuranosonic acid (dikegulac), (lα,2β,4aα,4bβ,10β)-2,4a,7-trihydroxy-l-methyl-8-methylenegibb-3-ene-l,10-dicarboxylic acid l,4a-lactone (GA4+7),N-(phenylmethyl)-lH-purin-6-amine (BA), and Promalin [1:1 (wt/wt) GA4+7 and BA].

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Johnny Carter, Bharat P. Singh, and Wayne Whitehead

Greenhouse studies conducted in 1990 and 1991 evaluated the influence of dikegulac and benzyladenine on frond initiation and vegetative growth of Boston fern [Nephrolepsis exaltata (L.) Schott `Compacta']. Four weeks after transplanting, fern liners were sprayed with aqueous solutions of dikegulac (0, 250, 500, or 750 mg·L–1) or benzyladenine (BA; 0, 50, 100, or 150 mg·L–1). The effect of dikegulac and BA on the number of shoots, frond length, leaf area, and dry weight was measured. Dikegulac stimulated shoot initiation and increased leaf area and dry weight without affecting frond length. BA reduced frond length and had no effect on shoot initiation and dry weight. This study suggests dikegulac has potential to improve the appearance and aesthetic quality of Boston fern. Chemical names used: 2,3:4,6-bis-0-(1-methylethylidene)-α-l-Xylo-2 hexulofuranosonic acid (dikegulac); N-(phenylmethyl)-1H-purine-6-amine (benzyladenine).