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

Flurprimidol preplant soaks, foliar sprays, and substrate drenches were compared to commercially recommended concentrations of uniconazole as a preplant bulb soak and a foliar spray for height control of `Star Gazer' oriental lily (Lilium hybrids). Foliar sprays of uniconazole at 10 mg·L–1 (ppm) did not control plant height and foliar sprays of flurprimidol concentrations ≥80 mg·L–1 provided only minimal height control. Substrate drenches of flurprimidol at 0.5 mg/pot a.i. (28,350 mg = 1 oz) controlled plant height, resulting in plants 45.3 cm (17.83 inches) tall, which were 24% shorter than the untreated control. Uniconazole preplant bulb soaks of 5 and 10 mg·L–1 controlled plant height, resulting in plants 41.8 cm (16.46 inches) and 37.8 cm (14.88 inches), respectively. Preplant bulb soaks of flurprimidol (25 to 400 mg·L–1) were applied and a concentration of 25 mg·L–1 resulted in plants 47.7 cm (18.78 inches) tall, which were 23% shorter than the untreated control. Flurprimidol substrate drenches and preplant bulb soaks at concentrations of 0.5 mg/pot a.i. and 25 mg·L–1, respectively, were effective in controlling height in `Star Gazer' lily. In Expt. 2, flurprimidol substrate drenches were applied as either a single or two split applications. A one-time flurprimidol substrate drench of 0.5 mg/pot a.i. provided similar control as two split applications of 0.25 mg/pot a.i.

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Anuradha Tatineni, Nihal C. Rajapakse, R. Thomas Fernandez, and James R. Rieck

Responses to selected chemical growth retardants (daminozide, paclobutrazol, and prohexadione-Ca) and GA1 and GA3 under photoselective greenhouse covers with various phytochrome photoequilibrium estimates (φe) were evaluated using `Bright Golden Anne' chrysanthemum [Dendranthema ×grandiflora Kitam. (syn. Chrysanthemum morifolium Ramat.)] as the model plant to better understand the height control mechanism by far red (FR) light depleted environments. Plant height linearly decreased as φe increased from 0.72 to 0.83. The rate of height decrease of daminozide treated plants was less than that of water (control) or GA3-treated plants. The rate of height reduction was not different between control and GA3-treated plants among chambers with various φe. Both paclobutrazol and prohexadione-Ca reduced plant height regardless of φe, but the height reduction by paclobutrazol was more than that by prohexadioneCa. The combination of paclobutrazol and prohexadione-Ca reduced plant height more than either alone. GA1 reversed the height reduction caused by paclobutrazol and prohexadione-Ca regardless of φe, but the height increase by GA1 was more when it was applied with prohexadione-Ca than when applied alone. Results show that photoselective covers with high φe were effective in controlling height of chrysanthemums without chemical growth retardants. The linear relationship between plant height and φe suggests that effectiveness of photoselective covers increased as φe increased. The photosynthetic photon flux (PPF) transmission of photoselective covers decreased as the φe increased because of the increasing dye concentration. Identifying photoselective covers that effectively filter out FR light from sunlight and reduce plant height while minimizing the PPF reduction is critical for commercial success of photoselective covers. Gibberellins are, at least partially, involved in height control by photoselective covers. Photoselective greenhouse covers did not reduce responsiveness to gibberellins, and it appears that the mechanism may be to suppress gibberellin biosynthesis. Results also suggest that increased metabolism of GA1 to GA8 was not the mechanism of height control by photoselective covers. Chemical names used: butanedioic acid mono (2,2-dimethylhydrazide) [daminozide]; (±)-(R*,R*)-b-((4-chlorophenyl)methyl)-a-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol [paclobutrazol]; 3,5-dioxo-4-(1-oxopropyl)cyclohexanecarboxylic acid [prohexadione-Ca]; gibberellic acid [GA].

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Terri Woods Starman

Single and multiple sprays of uniconazole at 0, 5, 10, or 20 mg·liter-1 were compared with daminozide sprays at 2500 mg·liter-1 applied twice for height control of Dendranthema × grandiflorum (Ramat.) Kitamura (Chrysanthemum × morifolium Ramat.) `Puritan' and `Favor'. A single uniconazole spray at 20 mg·liter-1 applied 2 weeks after pinching or two uniconazole applications at 10 mg·liter-1 applied 2 and 4 weeks after pinching were as effective as daminozide for reducing height. Drenches of uniconazole at 0, 0.025, 0.05, or 0.10 mg a.i./pot were compared with ancymidol drenches at 0.45 mg a.i./pot for controlling height of `Bright Golden Anne'. Although ancymidol was more effective, a 0.10-mg uniconazole drench adequately reduced height.

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Jodi Benson and John Kelly

Height control is a major concern when growing bedding plants. Growth regulating chemicals are often applied to regulate height of bedding plant species. However, reductions in plant height have been observed when plants were grown under light with a high ratio of red to far red light. Light passing through clear double walled, acrylic panels filled with copper sulfate solution has a high red to far red ratio. This work examined the effect of growing tomatoes, peppers, pansies, petunias, geraniums, and impatiens under panels filled with 4, 8, and 16 percent copper sulfate solution. Plants were grown for approximately 3 weeks in cell packs, then data were taken on plant height, number of leaves, leaf area, fresh and dry weight, and chlorophyll content. Significant reductions in height (40-66%) were achieved by growing bedding plants under any of the copper sulfate concentrations.

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Terri Woods Starman, Teresa A. Cerny, and Tracy L. Grindstaff

Height control and flowering responses to uniconazole spray or drench treatments were measured for `Multibloom Scarlet' and `Red Elite' geranium (Pelargonium ×hortorum L.H. Bailey). Total plant height of both cultivars was reduced proportionately to the height of a 10-cm container when the uniconazole drench concentration was 0.025 mg a.i./pot. Used as a spray, uniconazole was not as effective in restricting total plant height of either cultivar. Foliage height was shortened more than inflorescence height. Inflorescence diameter was decreased with increasing uniconazole drench concentrations. Sprays did not affect inflorescence diameter of either cultivar. Uniconazole effect on days to flower varied with cultivar and application method. Chemical name used: (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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Terri Woods Starman

This study investigated the effects of concentration and application time of uniconazole as a spray for single- or double-pinched ornamental pepper (Capsicum annuum L. `Holiday Cheer'). Concentrations from 5.0 to 15.0 mg·liter-1 gave adequate height control, except that 15.0 mg·liter-1 reduced height excessively when applied 8, but not 10, weeks after sowing. Increasing uniconazole concentration increased red fruit percentage when applied at 10, but not 8, weeks after sowing. These results indicate that the later application was beneficial and may lessen the overdosing problem associated with triazole growth regulators. Chemical name used: (E)-(S)-1-(4-chlrophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pent-1-ene-3-oll(uniconazole).

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Thomas J. Banko and Marcia A. Stefani

Russian sage (Perovskia atriplicifolia) grown in a pine bark medium in 1-gal containers were sheared to a height of 15 cm on 20 June 1997. One day later the plants were treated with foliar sprays of Florel (ethephon) at 0, 500, or 1000 ppm. One week later, sprays of B-Nine (daminozide, 5000 ppm) or Sumagic (uniconazole, 15 ppm) were applied to some of the plants previously treated with Florel, or previously nontreated. Three weeks after initial treatments, the Florel (500 and 1000 ppm) and the Sumagic treatments, applied individually, reduced plant height by 26%. The B-Nine treatment reduced height by 18%. Combination treatments (Florel followed by Sumagic or Florel followed by B-Nine) provided additional height control Florel at 500 or 1000 ppm significantly increased branching of Perovskia. Additional treatments with B-Nine or Sumagic had little effect on this response. Florel delayed flowering by ≈7 to 10 days.

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David A. Gilbertz

Spray applications of 15 or 30 mg uniconazole or 30 or 60 mg paclobutrazol/liter (20 ml/1.5-liter pot) were sprayed 0, 2, or 4 weeks after pinching of Dendranthema × grandiflorum (Ramat.) Kitamura `Bright Golden Anne' plants. Plants were shorter the earlier growth regulators were applied. Plants were more responsive to uniconazole, requiring paclobutrazol at up to four times the uniconazole concentration to achieve the same height control. Time to flowering was also lengthened the earlier applications were made, up to 3 days compared to nontreated plants. Flower diameter was only minimally affected by the treatments. Chemical names used (2RS,3RS)-1-(4-chlorophenyl)-2-1,1-dimethylethyl)-(1H-1,2,4-triazol-1-yl)pentan-3-ol(-paclobutrazol);(E)-l(p-chlorophenyl) -4,4-dimethyl-2-(1,2,4-triazol-1-yl-1-penten-3-ol) (uniconazole).

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Brian E. Whipker and Shravan Dasoju

Plant growth retardant (PGR) foliar spray treatments (mg•liter–1) of daminozide at 1000 to 16,000; paclobutrazol from 5 to 80; and uniconazole from 2 to 32 were applied to `Pacino' pot sunflowers (Helianthus annuus) to compare their effectiveness at chemical height control. When the first inflorescence opened, the number of days from seeding until flowering, total plant height measured from the pot rim to the top of the inflorescence, inflorescence diameter, and plant diameter were recorded. Total plant height, plant diameter, inflorescence diameter, and days until flowering were significant for the PGR treatment interaction. Marketable-sized plants grown in the 1.2-liter pots were produced with uniconazole concentrations between 16 and 32 mg•liter–1 or with daminozide concentrations between 4000 and 8000 mg•liter–1. Paclobutrazol foliar sprays up to 80 mg•liter–1 had little effect and higher concentrations or medium drench treatments should be considered.

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Robert Berghage

Temperature management has emerged as an important tool for plant height control in greenhouse production systems. This is particularly important in vegetable transplant production where chemical controls for plant height are limited or not legal. Plant height is a function of the number of nodes and the length of each internode, and both are strongly influenced by greenhouse temperatures. Node number, or formation rate, is primarily a function of the average greenhouse temperature, increasing as the average temperature increases. Internode length is strongly influenced by the relationship between the day and night temperature, commonly referred to as DIF (day temperature - night temperature). As DIF increases, so does internode length in most plant species studied. Although the nature and magnitude of temperature effects vary with species, cultivar, and environmental conditions, these two basic responses can be used to modify transplant growth. Although data are limited, controlling transplant height with temperature does not appear to adversely influence plant establishment or subsequent yield.