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Sarah A. White, Holly L. Scoggins, Richard P. Marini, and Joyce G. Latimer

Little information is available on cultural requirements for greenhouse production of Tradescantia virginiana L. We tested three plant growth regulators (PGRs) at ascending rates on T. virginiana `Angel Eyes,' `Blue Stone,' and `Red Cloud' in an effort to find appropriate application levels for height suppression. Treatments applied two weeks after transplant. Each PGR was applied once at the following rates: paclobutrazol at 0, 40, 80, 120, or 160 mg·L-1, uniconazole at 0, 15, 30, 45, or 60 mg·L-1, or flurprimidol at 0, 15, 30, 45, 60, or 75 mg·L-1. Repeated measures experimental design and multivariate analysis was used to examine plant responses to PGRs over time. The most effective paclobutrazol rate for adequate height suppression was 120 mg·L-1. Uniconazole at 30 to 45 mg·L-1 and flurprimidol at 45 to 60 mg·L-1 resulted in adequate height control. `Blue Stone' and `Red Cloud' appeared more responsive (greater suppression of height at rates applied) to both uniconazole and flurprimidol than `Angel Eyes.' These results suggest that cultivars respond in a different manner to PGRs applied to them; more compact growth can be obtained for cultivars tested using these suggested rates. Chemical names used: trifuloromethoxy phenyl-5-pyrimidinemethanol (flurprimidol); [(±)-(R*,R*)-ß-((4-chlorophenyl) methyl)-?-(1,1,-dimethylethyl)-1H-1,2,4,-triazole-1-ethanol)] (paclobutrazol); uniconazole.

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Juan P. Brigard, Richard L. Harkess, and Brian S. Baldwin

Tomato seedling hypocotyls elongate rapidly after germination resulting in weak seedlings. The effects of 0, 250, 500, 750, or 1000 mg paclobutrazol (PB)/L seed soak and soaking times from 1 to 12 hours on tomato (Solanum lycopersicum L.) seed germination, seedling growth, and plant growth were tested. Adequate height control was obtained with 250 mg PB/L while soaking time did not affect seedling growth. In a second experiment, PB was tested at 0, 50, 100, 150, 200, or 250 mg PB/L soaking the seed for 1 hour. A concentration of PB at 100 mg·L–1 provided optimum control of hypocotyl elongation with minimal residual effect on subsequent plant growth. In a third experiment, seed soaked at the different PB concentrations were germinated and grown under light intensities of 0.09, 50, 70, or 120 μmol·m–2·s–1. Seedlings grown under 0.09 μmol·m–2·s–1 were not affected by PB treatment and did not develop an epicotyl. PB seed soak treatment gave greater growth suppression under 50 μmol·m-2·s-1 than under the two higher light levels. Soaking tomato seeds in 100 mg PB/L for 1 hour prevented early hypocotyl stretch of tomato seedlings with no long term effects on plant growth. This treatment effectively prevented excessive hypocotyl elongation when seeds were germinated under low PAR while not over controlling elongation under high PAR conditions.

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Gary J. Keever and William J. Foster

`Redwings' and `Gloria' azaleas (Rhododendron × `Redwings' and `Gloria') were treated with foliar sprays of uniconazole, paclobutrazol, or daminozide to suppress bypass shoot development and promote flower initiation and development. Uniconazole at 5 and 25 mg·liter-1 suppressed bypass shoot development of `Redwings' and `Gloria', respectively. Flowering of `Gloria', but not `Redwings', was delayed slightly with uniconazole sprays up to 25 mg·liter-1 ; with the highest uniconazole concentration, 200 mg·liter-1, flowering was delayed as much as 18 days. Flower count of `Gloria' was not affected by lower concentrations of uniconazole, but it was greatly reduced in both cultivars with concentrations above 75 mg·liter-1. Uniconazole was more active than paclobutrazol sprays of similar concentrations or than two daminozide sprays of 3000 mg·liter–1 . Chemical names used: (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (uniconazole); (2RS,3RS)-1-(4-chlorophenyl)-2-(1,1-dimethylethyl)-(1H-1,2,4,-triazol-l-yl-)pentan-3-ol (paclobutrazol); butanedioic acid mono(2,2-dimethylhydrazide (daminozide),

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Brian A. Krug, Brian E. Whipker, Ingram McCall, and John M. Dole

Three experiments were conducted to determine the effectiveness of plant growth regulators (PGRs) on `Tete a Tete', `Dutch Master', and `Sweetness' narcissus (Narcissus pseudonarcissus). Ethephon foliar sprays (500 to 2500 mg·L-1) and substrate drenches of flurprimidol and paclobutrazol (0.25 to 4 mg/pot a.i.) did not control height during greenhouse forcing of `Tete a Tete' at any concentration trialed. Stem stretch was controlled during postharvest evaluation with ethephon foliar sprays ≥1000 mg·L-1, flurprimidol substrate drenches ≥0.5 mg/pot a.i., and paclobutrazol substrate drenches of 4 mg/pot a.i. A second experiment investigated preplant bulb soaks of flurprimidol (10 to 40 mg·L-1) applied to `Dutch Master' and `Tete a Tete' narcissus bulbs. Flurprimidol preplant bulb soaks controlled postharvest stretch on `Tete a Tete' and `Dutch Master' at concentrations ≥15 and ≥10 mg·L-1, respectively. A third experiment was conducted with paclobutrazol (75 to 375 mg·L-1) on `Tete a Tete' and `Dutch Master' and three concentrations of flurprimidol on `Sweetness' to determine optimal soak recommendations. Paclobutrazol preplant bulb soaks ≥75 mg·L-1 controlled postharvest stretch of `Tete a Tete' and `Dutch Master', while 37.5 mg·L-1 of flurprimidol controlled postharvest stretch of `Sweetness'. Based on the results of these experiments, growers can now select a PGR to help control excessive plant growth.

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Johnny Carter, B.P. Singh, and W. Whitehead

During the fall of 1993 and 1994, four commonly used growth retardants (B-nine, Cycocel, A-rest, and Bonzi) were compared for their effect on the growth and development of three ornamental flowering cabbage cultivars (white, red, and pink) and two ornamental flowering kale cultivars (frizzy red and red peacock). Two weeks after transplanting, seedlings of each cultivar were sprayed with aqueous solutions of the four growth retardants. Treatments for each cultivar were arranged in a randomized complete block design with 6 replications. Plant height, plant width, and dry weight were the parameters used to measure growth and development. Treatments for each cultivar were rated for head formation and color development. Results showed that all the growth retardants except for Cycocel significantly affected growth and development without any effect on head formation and color development. Bonzi caused the greatest growth suppression.

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Johnny Carter and Sauveur Mahotiere

During the Fall of 1993, four commercial growth retardants (B-nine, Cycocel, A-rest and Bonzi) were compared for their effectiveness in controlling the growth and development of three ornamental cabbage cultivars (white, red and pink) and two flowering ornamental kale cultivars (frizzy red and red peacock). Two weeks after transplanting; seedling of each cultivar were sprayed with aqueous solutions of the four commercial growth retardants. Treatments for each cultivar were arranged in a randomized complete block design with 6 replications. Plant height, plant width and dry weight were the parameters used to measure growth and development. Results showed that all the growth retardants except for cycocel significantly affected growth and development without any effect on head formation and color development. Bonzi caused the greatest growth suppression.

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Paul A. Thomas and Joyce G. Latimer

Perennial growers experience marketing difficulty when the stem length, or height of their perennial stock is excessive. Both wholesale and retail outlets desire to keep height to a minimum, while still promoting the production of flowers. The objective of this study was to screen containerized, spring-planted perennials for response to the growth retardants Sumagic, Bonzi, and B-Nine. Each perennial variety used was treated with B-Nine (Daminozide at 5000 ppm Bonzi (paclobutrazol) at 240 ppm, and Sumagic (uniconizole-P) at the following rates: 0, 40, 80, 120, and 160 ppm.Pre-cooled plugs of cultivars were selected from the genera Achillea, Coreopsis, Echinaceae, Digitalis, Gaillardia, Phlox, Rudbeckia, Alcea, Veronica, and Monarda. A randomized complete block design was implemented. Eight of the nine cultivars were responsive to Sumagic, with a 12% to 79% range of reduction in height. Seven cultivars were responsive to Bonzi with a 20% to 61% range of reduction. Only one cultivar was responsive to B-Nine, requiring two applications of 5000 ppm, to yield a 22% reduction in height at 4WAT. Based upon growers' desire for up to 50% height reduction, a 30% height reduction assessment point was established as a minimum rate for production, and a 50% to 60% reduction was established as the maximum landscape rate (based upon in-landscape persistence).

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George J. Wulster and Thomas M. Ombrello

Growth and flowering of Ixia hybrids as potted plants can be controlled environmentally by cool preplant storage of corms, regulation of greenhouse forcing temperatures, and application of a growth retardant. Paclobutrazol applied as a preplant corm soak, a postemergent drench, or a postemergent spray in combination with a 2- to 4-week preplant storage of corms at 7 °C, and an 18 °C day/10 °C night forcing temperature produced attractive and marketable plants. Chemical name used: β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol, Bonzi®).

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George J. Wulster and Thomas M. Ombrello

Growth and flowering of Ixia hybrids as potted plants can be controlled environmentally by cool preplant storage of corms, regulation of greenhouse forcing temperatures, and application of a growth retardant. Paclobutrazol applied as a preplant corm soak, a postemergent drench, or a postemergent spray in combination with a 2- to 4-week preplant storage of corms at 7 °C, and an 18 °C day/10 °C night forcing temperature produced attractive and marketable plants. Chemical name used: β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol, Bonzi®).

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Jianjun Chen, Russell D. Caldwell, and Cynthia A. Robinson

Gynura aurantiaca is a colorful foliage plant with creeping stems and velvety purple hairs that cover the green leaves. It grows rapidly, but is cultivated primarily for those attractive purple leaves. Annually during the spring, this plant produces prominent flowers both in appearance and smell, gaudy and malodorous. Flowering coupled with acquiring an over-grown leggy appearance have been key limitations in its production and use in interiorscaping. This study was undertaken to determine if an available commercial plant growth regulator could inhibit flowering. A-Rest (ancymidol), B-Nine (daminozide), Bonzi (paclobutrazol), cycocel (chlormequat chloride) and florel (ethephon) each diluted to three different concentrations were sprayed in two applications in early spring at 2-week intervals. Flowering and bud numbers and plant growth (number of lateral shoots, vine lengths and internode lengths) were recorded. Results indicated that applications of A-Rest, B-Nine, Bonzi and Cycocel, regardless of treatment concentrations, were ineffective in suppressing the flowering of this plant; whereas, florel completely suppressed flowering at the three concentrations used. The florel-treated plants also grew more lateral shoots, which produced a compact and dense bush-look, indicating that appropriate concentrations of florel application not only will stop flowering of purple passion but can also improve and prolong its aesthetic value as a potted or hanging-basket interior plant.