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Richard H. Zimmerman and George L. Steffens

Paclobutrazol was provided by ICI Americas. uniconazole by Chevron Chemical Co., and daminozide and ethephon by Uniroyal. We thank Larry Douglass for advice and useful discussion\ on cxperimental design and statistical analysis and Charles Mischke

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Ioannis C. Porlingis and Demetrios G. Voyiatzis

Anthesis of an important staminate pistachio (Pistacia vera L.) cultivar (B) in Greece was delayed by foliar paclobutrazol (PBZ) sprays applied in June or July the previous season. A September spray was ineffective. The amount of delay depended on dose (50 to 1000 mg PBZ/liter applied to incipient runoff). Using the same total amount of chemical, one spray was as effective as two sprays 1 month apart. There were no effects on inflorescence fresh weight, pollen production, and pollen germination. Stem elongation was inhibited strongly, but the number of nodes and flower buds per shoot was reduced only slightly. In Expt. 2, two other staminate cultivars (A and C) responded similarly to cultivar B. Treatment effects appeared only during the treatment year, whereas a soil drench was effective for 2 years. PBZ may be able to synchronize the blooming of staminate and distillate pistachio cultivars and result in good fruit set without artificial pollination. Chemical name used: B[(4-chlorophenyl)methyl] -α-(1,1 dimethylethyl)-l H -1,2,4-triazole-l-ethanol (paclobutrazol).

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Alexander G. Litvin, Marc W. van Iersel, and Anish Malladi

plant GA content ( Vettakkorumakankav et al., 1999 ). Paclobutrazol (PAC), a triazole, inhibits ent -kaurene oxidase, reducing its ability to convert ent -kaurene to ent -kaurenoic acid, an important early step in the biosynthesis of GA precursors

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Rachael E. Pepin and Janet C. Cole

increased with subirrigation compared with foliar applications, since most plant growth regulators are absorbed by plant roots more readily than by leaves. For example, Wang et al. (1986) showed that root-applied paclobutrazol was translocated throughout

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C.M. Roberts, G.W. Eaton, and F.M. Seywerd

Paclobutrazol treatments of 0, 0.125, 0.250, and 0.500 mg/plant improved the form of Tibouchina urvilleana (DC.) standards and eliminated the need for pruning during the display season. Paclobutrazol did not improve the form of Fuchsia × hybrida Hort. ex Vllm. Paclobutrazol inhibited trunk caliper development in both species. Paclobutrazol at 0.125 mg/plant slightly increased Tibouchina flower size. Chlormequat at 0, 1000, or 2000 mg/plant did not hasten flowering of Tibouchina. Chemical names used: ß-[(4-chlorophenyl) methyl]-α- (1,1-dimethylethyl) -1H-1,2,4-triazole-1-ethanol (paclobutrazol); α-chloro-N,N,N-trimethylethanammonium chloride (chlormequat).

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Xiaojuan Wei, Siyu Wu, Xiaojing Liang, Kun Wang, Yuejuan Li, Baocai Li, Jinlin Ma, and Haiying Liang

( Wei et al., 2018 ). No references regarding flower size were found for naturally occurring C. tamdaoensis flowers. Fig. 1. Camellia tamdaoensis plants and their paclobutrazol (PBZ)-induced reproductive buds and flowers. ( A ) Untreated shoots

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Genhua Niu, Royal Heins, and Will Carlson

Late-season height control of poinsettia (Euphorbia pulcherrima) is difficult since most chemical growth retardants adversely reduce bract size when applied after first bract color. Paclobutrazol (Bonzi) controls stem elongation late in poinsettia crop development but can excessively reduce bract size if improperly applied. Two experiments were conducted to quantify how paclobutrazol application influenced height and bract area of `Freedom' poinsettia. In the first experiment, paclobutrazol was applied at 1 mg·L-1 (ppm) in 118-mL (4.0-fl oz) volumes per pot [(a.i.) 0.12 mg/pot (28,350 mg = 1.0 oz)] as a drench to a new group of plants weekly from the initiation of short days until 1 week before anthesis. Maximum reduction in height and bract area was obtained when paclobutrazol was applied immediately after short days, and the response to paclobutrazol decreased as application time was increasingly delayed toward anthesis. In the second experiment, paclobutrazol was applied weekly after first bract color as either a drench or subapplication at various concentrations. Plant height and bract area were reduced by 23% when 2 mg·L-1 [(a.i.) 0.24 mg/pot) paclobutrazol was applied through subapplication at first color. The effects of paclobutrazol on height and bract area reduction decreased as application time was progressively delayed. Concentrations lower than 1 mg·L-1 had no significant effect on height or bract area reduction, regardless of application time or method. Generally, the reduction in height and bract area was larger when paclobutrazol was applied through subapplication. The combined results from both experiments indicate that paclobutrazol drench applications after flower initiation concomitantly reduce plant height (internode extension) and bract area. Therefore, drench applications should be delayed as long as possible to limit reduction in bract size.

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Claudio C. Pasian and Daniel K. Struve

The effectiveness of two application methods of the growth regulator paclobutrazol on the growth of Chrysanthemum plants, Dendranthema ×grandiflora (Ramat) (cv. `Fina' and `Cream Dana') were compared. Plants were grown in containers with their interior covered by a mixture of flat latex paint and several concentrations of paclobutrazol (0, 5, 10, 20, 40, 80, 100, 150, 160, and 200 mg·L–1) or were treated with a soil drench of the growth regulator according to label recommendations (59 ml/container of paclobutrazol solution at 4 mg·L–1). Plants grown in containers with the paint–paclobutrazol mix at concentrations >80 mg·L–1 were shorter than plants given the control and paint only treatments but taller than plants given the drench treatment. Increasing paclobutrazol concentrations in paint from 100 to 150 and 200 mg·L–1 did not produce proportionately shorter plants. Paint alone had no effect on growth and development. Plants subject to growth regulator treatments appeared greener than the control plants. None of the plants given treatments with paint with or without paclobutrazol showed any sign of phytotoxicity. These results suggest the possibility of a new application method for systemic chemicals with the potential of reducing or eliminating worker protection standard restricted entry intervals and reducing the release of chemicals to the environment. Chemical name used: beta-[(4-chlorophenyl)methyl]-α-(1,1-dimethyl)-1H-1,2,4,-triazole-1-ethanol (paclobutrazol).

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J. Million, J. Barrett, D. Clark, and T. Nell

A broccoli seedling bioassay was used to compare the activity of paclobutrazol applied at six concentrations to 20 media component samples mixed 1:1 (v:v) with vermiculite. Results indicated that 4-, 5-, and 10-fold higher media paclobutrazol concentrations were required in old composted pine bark, fresh pine bark, and composted pine bark samples, respectively, to achieve the same activity observed in sphagnum peatmoss. Paclobutrazol bioassay activity in coir was similar to the activity observed in peat, while activity in vermiculite and perlite was greater than in peat. In a second trial, paclobutrazol activity was reduced more in the fine (<2 mm) fraction of fresh and composted bark samples than in medium (2–4 mm) or coarse (>4 mm) fractions. In a third trial, petunias grown in a 60% composted pine bark:0% peat mix required a »14-times higher drench paclobutrazol concentration to achieve the same size control as petunia grown in a 0% composted bark:60% peat mix. It was concluded that media components differed greatly in their influence on paclobutrazol activity and that the bioassay procedure might serve as a useful tool for predicting media–paclobutrazol interactions.

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Osman Karaguzel, Ibrahim Baktir, Sadik Cakmakci, and Veli Ortacesme

The effects of method of application and dose of paclobutrazol on the growth and flowering characteristics of Lupinus varius L. were studied. On 17 Dec., seeds were sown into 18-cm pots (three seeds per pot) filled with a mixture consisting of 2 peat: 1 river sand (by volume). On 25 Mar., when 5% of the plants had elongated first internodes, doses of paclobutrazol at 0 (control), 0.625, 1.250, and 2.500 mg a.i./plant were applied to plants as a foliar spray or media drench. The application of paclobutrazol led to a slight shortening of the time to flowering, especially when applied as a foliar spray. Plant height and internode length, length, and internode length of the main inflorescence significantly decreased with increased doses of paclobutrazol and this also happened with the number of branches per plant, branch length, and length and internode length of branch inflorescence. On the contrary, stem, main, and branch inflorescence diameters significantly increased with increased doses of paclobutrazol, whether applied as a foliar spray or media drench. However, drench applications of paclobutrazol were consistently more effective than foliar spray treatments on most of the growth characteristics investigated. Paclobutrazol, in particular when applied as a foliar spray, also increased the number of flowers on main and branch inflorescences relative to the control, but media drenched applications of paclobutrazol at doses of 1.250 and 2.500 mg a.i./plant resulted in consistent significant reductions in the number of flowers on branch inflorescences. Chemical name used: (±)-(R*,R*)-β[(4-chlorophenyl)methyl]-α-(1,1-dimethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).