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Robert M. Frymire and Janet C. Henderson

Uniform liners of pyracantha (Pyracantha coccinea Roem `Lalandei'), photinia (Photinia × fraseri Dress) and dwarf Burford holly (Ilex cornuta Lindl. and Paxt. `Burfordii Nana') were potted into 3.8 liter containers in a pine bark:sand medium. Ten weeks later, plants received uniconazole treatments as a media drench or foliar spray. The uniconazole drench rates were 0, 0.5, 1.0, and 3.0 mg ai per container for all three plant species. The foliar application rates were 0, 50, 100 and 150 ppm for pyracantha, 0, 25, 50 and 100 ppm for photinia, and 0, 10, 25, and 50 ppm for dwarf Burford belly. Plant heights and widths were recorded at 3 week intervals, and leaf chlorophyll content was determined by calorimeter at the same time as height and weight measurements. At harvest, leaf counts, leaf areas, and shoot, leaf and root dry weights were determined. Initial results indicate that both foliar and media drench treatments of uniconazole reduced growth of pyracantha and photinia at all rates. Only the two highest rates decreased growth of dwarf Burford holly when applied as either a media drench or a foliar spray.

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Emily A. Clough, Arthur C. Cameron, Royal D. Heins, and William H. Carlson

Influences of vernalization duration, photoperiod, forcing temperature, and plant growth regulators (PGRs) on growth and development of Oenothera fruticosa L. `Youngii-lapsley' (`Youngii-lapsley' sundrops) were determined. Young plants were vernalized at 5 °C for 0, 3, 6, 9, 12, or 15 weeks under a 9-hour photoperiod and subsequently forced in a 20 °C greenhouse under a 16-hour photoperiod. Only one plant in 2 years flowered without vernalization, while all plants flowered after receiving a vernalization treatment, regardless of its duration. Thus, O. fruticosa had a nearly obligate vernalization requirement. Time to visible bud and flower decreased by ≈1 week as vernalization duration increased from 3 to 15 weeks. All plants flowered under 10-, 12-, 13-, 14-, 16-, or 24-hour photoperiods or a 4-hour night interruption (NI) in a 20 °C greenhouse following 15-weeks vernalization at 5 °C. Time to flower decreased by ≈2 weeks, flower number decreased, and plant height increased as photoperiod increased from 10 to 16 hours. Days to flower, number of new nodes, and flower number under 24 hour and NI were similar to that of plants grown under a 16-hour photoperiod. In a separate study, plants were vernalized for 15 weeks and then forced under a 16-h photoperiod at 15.2, 18.2, 20.6, 23.8, 26.8, or 29.8 °C (average daily temperatures). Plants flowered 35 days faster at 29.8 °C but were 18 cm shorter than those grown at 15.2 °C. In addition, plants grown at 29.8 °C produced only one-sixth the number of flowers (with diameters that were 3.0 cm smaller) than plants grown at 15.2 °C. Days to visible bud and flowering were converted to rates, and base temperature (Tb) and thermal time to flowering (degree-days) were calculated as 4.4 °C and 606 °days, respectively. Effects of foliar applications of ancymidol (100 mg·L-1), chlormequat (1500 mg·L-1), paclobutrazol (30 mg·L-1), daminozide (5000 mg·L-1), and uniconazole (15 mg·L-1) were determined on plants vernalized for 19 weeks and then forced at 20 °C under a 16-h photoperiod. Three spray applications of uniconazole reduced plant height at first flower by 31% compared with that of nontreated controls. All other PGRs did not affect plant growth. Chemical names used: α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol); (2-chloroethyl) trimethylammonium chloride (chlormequat); butanedioic acid mono-(2,2-dimethyl hydrazide) (daminozide); (2R,3R+2S,3S)-1-(4-chlorophenyl-4,4-dimethyl-2-[1,2,4-triazol-1-yl]) (paclobutrazol); (E)-(S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pent-1-ene-3-ol (uniconazole).

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J. C. Vlahos

Plants of Achimenes cv Hilda were treated with foliar sprays of Ancymidol, Paclobutrazol and Uniconazole at 3 different concentrations each, and were placed in a greenhouse at 21°C under 2 light levels (0 and 40% light exclusion) for 12 weeks. Reduced light level decreased plant height, number of axillary shoots and flowers. The three growth retardants in any concentration, supressed development of axillary shoots and flowers. Ancymidol at 25 and 50 mg.1-1, Uniconazole at 5 mg.1-1 and Paclobutrazol at 25, 50 or 100 mg.1-1 decreased plant height and number of leaf whorls. Number of rhizomes was reduced by the 3 chemicals at the highest concentration only. Paclobutrazol was most effective than the other 2 growth retardants. Effects of treatments were more pronounced under shade rather than in full sunlight. Days to anthesis was not affected by any of the treatments except by Paclobutrazol at 100 mg.1-1. The use of these growth retardants in concentration and mode of application similar to those used in this study is not recommended for “Hilda” as height retardation significantly reduces number of flowers

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Brian A. Krug, Brian E. Whipker, and Ingram McCall

Eight experiments were conducted to develop height control protocols for greenhouse-forced hyacinth (Hyacinthus orientalis) bulbs. `Pink Pearl' hyacinth bulbs were treated with flurprimidol preplant bulb soaks to determine optimal timing of treatment, soak duration, quantity of bulbs that could be treated before the solution lost efficacy, bulb location of solution uptake, and if higher concentrations of flurprimidol can be used to overcome stretch that occurs with extended cold treatment. No difference in height control occurred when bulbs were soaked in flurprimidol the day of, 1 day before, or 7 days before potting; therefore, growers can treat bulbs up to 1 week before potting with no difference in height control. All preplant bulb soak durations of 1, 5, 10, 20, or 40 min controlled plant height. Any soak durations ≥1.3 min resulted in similar height control, which would provide growers with a flexible time frame of 2 to 40 min in which to soak the bulbs. When 1 L of 20 mg·L-1 flurprimidol solution was used repeatedly over 20 batches of five bulbs, solution efficacy was similar from the first batch to the last batch, indicating the soak solution of flurprimidol can be used repeatedly without loss of efficacy. Soak solution temperature was also tested to determine its effect on flurprimidol and paclobutrazol uptake. Temperature of the soak solution (8, 16, or 24 °C) had no effect on flurprimidol and only at a temperature of 8 °C was the efficacy of paclobutrazol lower. Postharvest heights of `Pink Pearl' hyacinths were similar whether only the top, bottom, or the entire bulb was soaked. Control provided by flurprimidol, paclobutrazol, or uniconazole preplant bulb soaks varied among the three hyacinth cultivars Delft Blue, Jan Bos, and Pink Pearl, so growers will have to conduct their own trials to determine optimal cultivar response to preplant bulb soaks. Also, `Pacino' sunflowers (Helianthus annuus) were treated with residual soak solution of flurprimidol to determine if substrate drenches could be used as a disposal method. Fresh and residual solutions of flurprimidol (1.18, 2.37, or 4.73 mg/pot a.i.) applied to `Pacino' sunflowers were similar in their efficacy of controlling height, which would enable growers to avoid disposal problems of residual soak solutions.

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James L. Gibson and Brian E. Whipker

Twenty-six ornamental cabbage and kale (Brassica oleracea var. acephala) cultivars were grown in 8-inch (20.8-cm) diameter pots during Fall 1998 to classify their foliage traits and determine their response to the plant growth regulator (PGR) daminozide. Cultivar vigor was classified by height. Foliage characteristics were described and cultivars of ornamental cabbage, notched ornamental kale, and curly ornamental kale were selected for retail or wholesale markets based on the shortest number of days until a significant center color change, the largest center color diameter, and attractive foliage characteristics. Two cultivars treated with 2,500 ppm (mg·L-1) daminozide and eight cultivars treated with 5,000 ppm were significantly smaller in height compared to nontreated plants. Plants were treated 6 weeks after sowing, and the response to the PGRs may have been diminished by the age of the plant. Therefore, to further investigate PGR efficacy, seven outstanding cultivars selected in 1998 were treated with 5,000 ppm daminozide or 5 ppm uniconazole 14 days after potting (4 weeks after sowing) in Fall 1999. Greater control was observed with daminozide at 5,000 ppm in 1999 with a 13% smaller plant height as compared to 9% in 1998, when compared to the nontreated control. For greater height control, PGR applications to ornamental cabbage and kale should be applied 4 weeks after sowing.

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Norman B. Best, Xingang Wang, Scottie Brittsan, Eric Dean, Seth J. Helfers, Ryan Homburg, Mariah L. Mobley, Tiffeny L. Spindler, Bofan Xie, Menglu Zhang, Paul M. Hasegawa, Robert J. Joly, David Rhodes, and Brian P. Dilkes

sunflower cultivar Sunspot. Comparisons of responses to GA 3 and uniconazole (UCZ), a GA biosynthetic inhibitor, application with the tall cultivar of sunflower Mammoth Grey indicated that ‘Sunspot’ is GA insensitive. Recently, Ramos et al. (2013) mapped

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Jesse R Quarrels and Steven E. Newman

A study was conducted to determine the effects of pine bark grind size and pine bark levels on the activity of two growth regulators on poinsettia Two bark grinds (≤ 6 mm and >10 mm) were used with four media combinations within each grind: vermiculite:bark:peat moss at 2:0:3, 2:1:2, 2:2:1, and 2:3:0 (by volume). Two growth regulators, paclobutrazol and uniconazole, were applied at 0, 0.125, and 0.250 mg/15 cm container in 250 ml water. Two poinsettia cultivars, `Freedom' and `Gutbier V-14 Glory', were planted September 2, 1993, pinched September 16, and growth regulators applied September 30. There were five single plant replications for each treatment. Stem length and bract area were effected by bark grind, bark level, growth regulator, and growth regulator rate. Plants treated with uniconazole had the shortest stems and the least bract area. Plants grown in the smaller grind and at higher bark levels were less effected. Plants treated with paclobutrazol had longer stems than those treated with uniconazole.

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Seung-Hyun Kim, A.A. De Hertogh, and P.V. Nelson

Two experiments were conducted to determine the effects of applied ancymidol, chlormequat, daminozide, paclobutrazol, and uniconazole on early spring (March) and late (May) spring forcing of Dutch-grown Bleeding Heart [Dicentra spectabilis (L.) Lem.] as a flowering pot plant. Most of the plant growth regulator (PGR) treatments delayed flowering, however, the average time to flower after planting was from 17 to 21 days for untreated plants and delays were only 3 to 6 days with PGR treatments. Thus, the effect is not important commercially. Acceptable plant quality and height control not only at flowering but also 14 days later was obtained with two sprays of 3000 mg·L-1 (ppm) daminozide or two sprays of 50 mg·L-1 paclobutrazol. Uniconazole reduced total plant height, however, because the inflorescence did not elongate, plant quality was greatly reduced. Most ancymidol sprays were phytotoxic producing a chlorosis of the leaf margins. Media drenches of ancymidol or chlormequat did not control total plant height. Sprays and media drenches of ancymidol, daminozide, paclobutrazol, and uniconazole produced plants with a very deep green leaf color, but chlormequat did not. The total number of shoots per tuberous root, the number of shoots with flowers, and stem strength were not significantly affected by PGR treatments. If the tuberous roots have been properly cold treated, they initiate growth rapidly after planting. Thus, the first PGR spray must be applied immediately after shoot growth is initiated, which was 6 to 8 days after planting, followed by a second spray 5 days later. Two applications are necessary because of uneven shoot emergence and growth from the tuberous roots.

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M.W. Duck, B.M. Cregg, R.T. Fernandez, R.D. Heins, and F.F. Cardoso

Tabletop Christmas tree growers whose greenhouse-grown conifers have undesirable shoot growth may alleviate this problem by applying plant growth retardants (PGRs). Some of the most common PGRs in the horticulture industry were evaluated to determine their effectiveness in controlling plant height: ancymidol at 100 μL·L-1 (ppm), daminozide at 5000 μL·L-1, paclobutrazol at 60 μL·L-1, chlormequat at 1500 μL·L-1, uniconazole at 15 μL·L-1, and ethephon at 500 μL·L-1 compared to a nontreated control. The following conifer species were used: colorado blue spruce (Picea pungens), black hills spruce (P. glauca var. densata), serbian spruce (P. omorika), noble fir (Abies procera), grand fir (A. grandis), fraser fir (A. fraseri), concolor fir (A. concolor), arborvitae (Thuja occidentalis), port orford cedar (Chamaecyparis lawsoniana), and douglas-fir (Pseudotsuga menziesii). Chlormequat was the only PGR that caused phytotoxicity and damage to the foliage was minimal. Noble fir, douglas-fir, colorado blue spruce, and arborvitae were unaffected by any PGR treatment. Daminozide reduced growth of port orford cedar and concolor fir; uniconazole reduced growth of black hills spruce and serbian spruce; paclobutrazol reduced growth of fraser fir; and ethephon reduced growth of grand fir.

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E. Jay Holcomb, Loren D. Tukey, and Mark A. Rose