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  • Author or Editor: Patricia Branch x
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Lateral branches of poinsettia tend to break from the main stem as plants reach maturity. The cause of poor stem strength is not known; however, suggested factors implicated in poor stem strength are: rate of nitrogen fertilizer used, type of plant growth regulator used, crowding of plants, or stem diameter of the cutting. Four different experiments were conducted to determine if these factors affected stem strength of poinsettia. Experiment 1: `Freedom Red', `Success', `V-17 Angelika Red', `Red Sails', `Nutcracker Red', `Cortez', `Maren', and `Red Splendor' poinsettia were fertilized with 20N–1P0–20K at 75, 75/125, 125/200, or 200 ppm N drip fertigation with zero leachate. Experiment 2: Three plant growth regulators were applied to `Pearl' and `Jolly Red' poinsettias. Experiment 3: `Freedom Red' plants were grown in a 625, 900, 1225, or 1600 cm2 area. Experiment 4: Rooted `Freedom Red' cuttings with stem diameters of 4.5, 5.5, 6.5, or 7.5 mm were used. A force meter was used to determine the strength of each lateral on the main stem of the six replications in each experiment. The lower laterals had the least stem strength and the top lateral had the highest stem strength for all treatments in all experiments. The stem strengths of some cultivars in experiment 1 were stronger at the lower fertilizer rates. Type of plant growth regulator had no significant affect on most poinsettia cultivars. The stem strengths of poinsettias in experiments 3 and 4 varied according to which lateral was measured.

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Three slow-release fertilizer formulations (Osmocote 14–14–14, 18–6–12, and Nutricote 17–6–10) at three rates (1, 2, and 3 lb/yd3) were incorporated into 4 pine bark: 1 sand (by volume) media filling 1-gal nursery containers. Additional treatments included slow-release fertilizer formulations at 1 lb/yd3 fertigated with 100 ppm N 20–10–20 fertilizer. As fertilizer rates increased, vegetative height, width, and dry-weight accumulation generally increased for both pinched and no-pinch mum crops. Fertigated pinch and no-pinch mums were the largest plants with the greatest dry-weight accumulation for each fertilizer formulation. The high rate for all slow-release fertilizers produced the greatest vegetative growth for nonfertigated treatments. This research suggest that higher rates for incorporated slow-release fertilizers and/or fertigation are required to produce maximum vegetative growth.

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Abstract

The timing of the crop is probably the most important thing that Easter lily (Lilium longiforum thunb) forcers must accomplish, and the variable date of Easter complicates scheduling (6, 12). The influence of bulb maturity and treatments prior to being placed in the greenhouse, often not under the grower’s control, makes forcing a challenge (2, 11, 17). Several methods are used to monitor progress of the crop, but adjusting temperatures is the actual means of controlling the rate of growth and development. Measurements of time and temperature, expressed as heat units or degree-days, are used to monitor the growth and development of many crops (1, 13, 21) and to predict with a high level of precision certain stages of their development. Degree-days or heat units offer little advantage over time alone as indicators of crop progress under conditions where temperature can be controlled to eliminate or minimize variations. Variations in greenhouse temperatures, greater during daytime hours than at night, especially in southern U.S. locations, are largely responsible for timing problems with Easter lilies. Heat unit summations may be reliable indicators where such variations occur. There are apparently no reports of attempts to use heat units or degree-days to monitor Easter lily shoot development.

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Irrigation water quality is an important factor in ornamental plant production; however, there is little information in this area. Saline (NaCl) and alkaline (NaHCO3) water have been shown to cause general chlorosis, tip burn, and defoliation of plants. The growing medium used in crop production may be an important factor when irrigating with saline and alkaline water. Our objectives were to determine the effects of increasing concentrations of NaCl: CaCl2 and NaHCO3 in irrigation water on growth and development of spring and fall bedding plants grown in peat, peat/pine bark, and pine bark media. Plant dry weight, height, and width were significantly lower at 300 and 400 ppm NaCl: CaCl2 and NaHCO3 levels. Early visible symptoms were necrosis of leaf tips, some leaf discoloration and finally plant death in the NaCl: CaCl2 experiment. The leaves of plants in the NaHCO3 experiment became water soaked and chlorotic, and some leaf abscission occurred. The best plant growth in the NaHCO3 experiment occurred in peat and the best plant growth in the NaCl: CaCl2 experiment occurred in pine bark. Decreased uptake of K+, Ca++, and Mg++ occurred when high levels of sodium were present.

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Eight bedding plant species were grown from plugs obtained from two sources. The plugs were transplanted into jumbo six packs and sprayed with a solution of chlormequat/daminozide with concentrations of 1000/800, 1250/1250, or 1500/5000 mg·L-1 when new growth was ≈5 cm in height or width. Three different species were grown in the fall (Dianthus chinensis L., `Telstar Mix', Petunia ×hybrida Hort. Vilm.-Andr., `Dreams Red', and Viola ×wittrockiana Gams., `Bingo Blue'), winter [Antirrhinum majus L., `Tahiti Mix', Matthiola incana (L.) R. Br., `Midget Red', and P. × hybrida, `Dreams Mix'], and spring [Catharanthus roseus (L.) G. Don, `Cooler Pink', Salvia splendens F. Sellow ex Roem. & Schult., `Empire Red', and Begonia ×semperflorens-cultorum Hort., `Cocktail Mix']. The treatments significantly reduced finished plant size of all species for each season. There was a significant difference in finish size between sources for Dianthus, Antirrhinum, Matthiola, Catharanthus, Salvia, and Begonia. The efficacy of chlormequat/daminozide also differed for each source of Dianthus, Matthiola, and Begonia, but the treatments minimized the differences in finish size between sources for Petunia and Viola. Chemical names used: (2-chlorethyl) trimethylammonium chloride (chlormequat); (N-dimethylaminosuccinamic acid) (daminozide).

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Plug production has increased the finished quality and uniformity of bedding plants, making them one of the most important greenhouse crops grown. The wide range of cultural practices used by different growers to produce plugs, may influence the efficacy of plant growth regulators applied to the same crop in postplug production. Ten bedding plant species were grown from plugs obtained from two sources using different cultural practices. The plugs were transplanted to jumbo six packs and sprayed with either chlormequat/daminozide tank mix, ancymidol, or paclobutrazol at three concentrations at three times of year. The effect of each plant growth regulator varied by plant species and time of year applied. Source of plug material did have a significant effect on height and time of flowering of finished bedding plants and the use of plant growth regulators did not minimize the differences in height between sources in most cases.

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Zantesdeschia has been grown for cut-flower production for many years, but more recently it has been grown as a containerized plant. Problems with height control and disease, however, have limited Zantesdeschia production in warmer climates. Our objectives were to evaluate paclobutrazol and uniconazole on control of plant growth of three Zantesdeschia species and evaluate four preplant treatments for preventing Erwinia infection on rhizomes. Paclobutrazol at 1 mg a.i. gave the best control of flower height, foliage height, and plant width. After 20 d in a postharvest chamber, plants drenched with paclobuturazol at 2 mg a.i. and uniconazole at 6 mg a.i. were still suitable plants, plants drenched at 3 and 4 mg a.i. paclobutrazol remained short, and plants drenched at 2 and 4 mg a.i.uniconazole became tall and weak, with flower stems breaking over. Rhizomes were dipped in dimethylbenzyl ammonium chlorides, sodium hypochlorite, 4% formaldehyde, or streptomycin. Streptomycin provided the best control against Erwinia infection followed by formaldehyde. Dimethylbenzyl ammonium chlorides and sodium chloride provided the poorest protection.

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Nitrate nitrogen has been recommended as the best form of nitrogen for the production of poinsettia while ammonium and urea have been reported to be deleterious to poinsettia growth. Recent studies have indicated that lower nitrogen and leaching levels will produce quality poinsettias. Poinsettias were grown with 21–7–7 Acid Special (9.15% NH4, 11.85% urea), 20–10–20 Peat-lite Special (7.77% NH4, 12.23% NO3), 15-220 plus Ca and Mg (1.5% NH4, 12.7% NO3, 0.8% urea), and 15–5–15 Excel CalMag (1.2% NH4, 11.75% NO3, 2.05% urea) applied at 200 mg·L-1. Plants were fertigated by drip irrigation with zero leachate. There were no significant differences between fertilizer treatments for plant height, width, bloom diameter, and dry weight. Electrical conductivity and pH did vary significantly between treatments; however, this did not effect plant growth. Thus, by using lower nitrogen levels and zero leachate, quality poinsettias can be grown with commercial fertilizers high in ammonium/urea or high in nitrate nitrogen, or ammonium and nitrate in combination.

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Dimethyl ammonium chloride (DAC, `Triathlon'), sodium hypochlorite, formaldehyde, and streptomycin (`Agri-mycin 17') were used as dips to treat Zantedeschia rehmannii superba Engl., Zantedeschia elliotiana ×maculata (Hook.) Engl., and Zantedeschia albomaculata (W.Wats.) Baill. rhizomes to control Erwinia soft rot. A 30 min 200 ppm (mg·L−1) streptomycin dip provided the best control of Erwinia soft rot for all three Zantedeschia species and a 1-hour 10% formaldehyde dip provided the second best control of inoculated rhizomes. Rhizomes inoculated with Erwinia required more days to emerge. Chemical treatments did not affect days to emergence or final plant growth.

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