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  • Author or Editor: Ingram McCall x
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Plant growth retardant (PGR) foliar sprays of daminozide at 4,000 or 8,000 mg·L-1 (ppm) and paclobutrazol drenches of 2 or 4 mg a.i. per pot were applied to `Big Smile', `Pacino', `Sundance Kid', `Sunspot', and `Teddy Bear' pot sunflowers (Helianthus annuus L.) to compare their chemical height control. Plant height varied among the cultivars due to genetic variation. The percentage reduction in plant height from the untreated control only was significant at the PGR level, indicating similar responses of all five cultivars to each PGR rate. Paclobutrazol drenches at 2 mg and daminozide foliar sprays at 4,000 or 8,000 mg·L-1 reduced plant height by about 24% when compared to the control. Paclobutrazol drenches at 4 mg produced plants that were 33% shorter than the control. Plant diameter of `Big Smile', `Pacino', or `Sundance Kid' was unaffected by daminozide, whereas `Sunspot' plants were smaller than the controls. Paclobutrazol drenches at 2 or 4 mg decreased plant diameter for all cultivars except `Teddy Bear', with the reduction being greater as paclobutrazol drench rates increased. The number of inflorescence buds increased by ≥18% with the use of daminozide sprays, while paclobutrazol drenches at 2 or 4 mg had no effect when compared to the untreated control. Paclobutrazol drenches of 2 or 4 mg offer the economic advantage to growers of increased plant density on greenhouse benches, while plants treated with daminozide had an increased bud count but would require a greater amount of bench space.

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Experiments were conducted to evaluate the appropriate concentration of flurprimidol for ‘Orange Tiger’ tiger lily (Lilium lancifolium), the persistence of residual effects the following year with ‘Orange Tiger’, and differences in flurprimidol’s effect between tiger lily cultivars. In Expt. 1 flurprimidol was applied as a preplant bulb soak to determine its efficacy on height control of ‘Orange Tiger’ tiger lily. Bulbs were hydrated in 17 °C water for 1 h, allowed to drain 1 h, given 10 min soaks of 0, 5, 10, 20, 40, 80, and 160 mg·L−1 flurprimidol, and then allowed to drain for 1 h before potting. In Expt. 2 ‘Orange Tiger’ tiger lilies from Expt. 1 were then planted into outdoor beds to evaluate residual carryover effects of flurprimidol. Expt. 3 involved comparison trials of ‘Pink Tiger’, ‘White Tiger’, and ‘Yellow Tiger’ tiger lilies to determine if cultivars responded differently to flurprimidol drenches. Flurprimidol at 10 to 20 mg·L−1 effectively controlled stem elongation of ‘Orange Tiger’. No residual effect of flurprimidol on ‘Orange Tiger’ plant growth was observed a year after application. Optimal concentrations of flurprimidol for ‘Pink Tiger’ and ‘White Tiger’ were 2 to 5 mg·L−1 and for ‘Yellow Tiger’ 20 to 30 mg·L−1. Results showed that preplant bulb soaks prevented excessive height and provided plants that were more suitable in height for retail sales. Differential responses of ‘Pink Tiger’, ‘White Tiger’, and ‘Yellow Tiger’ tiger lilies to flurprimidol indicate that trials are required to customize optimal concentrations for other cultivars.

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Three plant growth regulators (PGRs) were applied as substrate drenches; paclobutrazol (1, 2, 4, or 8 mg/pot), flurprimidol (0.5, 1, 2, or 4 mg/pot), or ethephon (125, 250, 500, or 1000 mg·L−1), plus an untreated control, to determine the efficacy of controlling excessive growth of ‘Imperial Dark Blue’ plumbago (Plumbago auriculata). No delay in flowering occurred with any of the PGR drenches, as compared with the untreated control. Plumbagos were responsive to both paclobutrazol and flurprimidol drenches. Concentrations of paclobutrazol and flurprimidol ≥1 mg/pot resulted in shorter plant heights than the untreated control. For producers desiring a moderate to high degree of control, 1 mg/pot drenches of either PGR could be suitable. All flurprimidol and paclobutrazol concentrations greater than 1 mg/pot resulted in excessive stunting and should be avoided. All ethephon drench concentrations were more consistent in controlling diameter, and increasing branching and flowering than paclobutrazol or flurprimidol. Based on the results of this study, the growth suppression of ethephon drenches was gradual, limiting overdose risks. Although plant diameters were not as small as plants treated with paclobutrazol or flurprimidol, diameter control was still adequate, and plants treated with ethephon drenches had a higher aesthetic appeal due to a more full appearance and increased flowering. With the use of an ethephon drench at 125 to 250 mg·L−1, plumbago producers have another PGR available to control excessive stem elongation and improve the flowering of plumbago.

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To produce floriculture crops like mealy-cup sage (Salvia farinacea), growers must be equipped with cultural information including the ability to recognize and characterize nutrient disorders. ‘Evolution’ mealy-cup sage plants were grown in silica-sand culture to induce, describe, and photograph symptoms of nutritional disorders. Plants received a complete modified Hoagland's all-nitrate solution of (macronutrient concentrations in millimoles) 15 nitrate-nitrogen (N), 1.0 phosphorus (P), 6.0 potassium (K), 5.0 calcium (Ca), 2.0 magnesium (Mg), and 2.0 sulfur (S) plus (micronutrient concentrations in micromoles) 72 iron (Fe), 18 manganese (Mn), 3 copper (Cu), 3 zinc (Zn), 45 boron (B), and 0.1 molybdenum (Mo). Nutrient-deficient treatments were induced with a complete nutrient formula minus one of the nutrients. The B-toxicity treatment was induced by increasing the element 10-fold higher than the complete nutrient formula. Reagent-grade chemicals and deionized (DI) water of 18 million ohms per centimeter purity were used to formulate treatment solutions. We monitored plants daily to document and photograph sequential series of symptoms as they developed. Typical symptomology of nutrient disorders and corresponding tissue concentrations were determined. Out of 13 treatments, 12 exhibited symptomology; Mo was asymptomatic. Symptoms of N, P, S, Ca, and K deficiencies and B toxicity manifested early; therefore, these disorders may be more likely problems encountered by growers. Unique symptoms were observed on plants grown under N-, Cu-, and Zn-deficient conditions. Necrosis was a common symptom observed, but use of other diagnostic criteria about location on the plant and progression of the disorder can aid growers in diagnosing nutrient disorders of mealy-cup sage.

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Plant growth retardant (PGR) substrate drenches (in milligrams active ingredient) of ancymidol at 0.25, 0.5, 1, 2, or 4; paclobutrazol at 1, 2, 4, 8, or 16; and uniconazole at 0.25, 0.5, 1, 2, or 4 were applied to pampas grass (Cortaderia argentea Nees) to compare their effectiveness at chemical height control during greenhouse forcing and evaluate the residual effect on plant growth in the landscape. Cortaderia argentea plant height exhibited a quadratic dose response to paclobutrazol and uniconazole, while ancymidol-treated plants showed a linear dose effect. During greenhouse production, all rates of uniconazole reduced plant height by 56% to 71% compared to the untreated control, whereas paclobutrazol and ancymidol treatments reduced plant height by 14% to 61% and 0% to 34%, respectively. Severe height retardation was evident at 2 mg of uniconazole. By week 5 in the field all plants treated with uniconazole, paclobutrazol doses of 4, 8, or 16 mg, and with 4 mg of ancymidol were shorter than the untreated control. By week 24 in the field, all plants exhibited similar heights except plants treated with uniconazole at 1, 2, or 4 mg remained shorter than the untreated control. In conclusion, each PGR was effective in controlling plant height of Cortaderia argentea during greenhouse forcing. Furthermore, plants treated with low to moderate rates of ancymidol or paclobutrazol grew out of the regulating effect by week 5 in the landscape. These results demonstrate that PGR can be effectively and economically employed in the production of Cortaderia argentea.

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High relative humidity (RH) can cause lower concentrations of boron (B) accumulating in plants. The common greenhouse practice of controlling excess temperatures by applying mist irrigation to young plants (plugs) can result in elevated RH levels, especially with plugs grown in high heat and humidity conditions of summer. ‘Dynamite Yellow’ pansy (Viola ×wittrockiana Gams.), ‘White Storm’ petunia (Petunia ×hybrida Vilm.), and ‘Festival Apricot’ gerbera (Gerbera jamesonii Bolus) plugs were grown in high or ambient RH conditions to determine the effect RH had on B uptake. Results indicate that an increase in RH decreased the amount of water the plant lost as a result of transpiration resulting in lower concentrations of B in shoot tissue. Boron concentrations in leaf tissue were 9.43, 10.56, and 17.81 mg·L−1 in pansy, petunia, and gerbera plants, respectively, grown in high RH conditions. These values were significantly lower than pansy, petunia, and gerbera plants grown in ambient RH conditions (19.94, 25.49, and 42.71 mg·L−1, respectively). Leaf distortion, consistent with B deficiency symptoms, was present in petunia and gerbera plants. Similar trends were observed when the experiment was repeated and leaf distortion was present in all species. This provides convincing evidence that the distorted growth observed in pansy, petunia, and gerbera plug production is the result of limited B caused by excessive humidity.

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A series of experiments investigated the effects of increasing phosphate–phosphorus (P) concentrations on the growth and development of four horticultural species. In experiment 1, petunia [Petunia atkinsiana (Sweet) D. Don ex W.H. Baxter] plants were grown using eight P concentrations, and we found that the upper bound for plant growth was at 8.72–9.08 mg·L−1 P, whereas concentrations ≤2.5 mg·L−1 P caused P deficiency symptoms. Experiment 2 investigated P growth response in two cultivars each of New Guinea impatiens (Impatiens hawkeri W. Bull) and vinca [Catharanthus roseus (L.) G. Don]. Growth for these plants was maximized with 6.43–12.42 mg·L−1 P. In experiment 3, ornamental peppers (Capsicum annuum L. ‘Tango Red’) were given an initial concentration of P for 6 weeks and then switched to 0 mg·L−1 P to observe whether plants could be supplied with sufficient levels of P, and finished without P to keep them compact. Plants switched to restricted P began developing P deficiency symptoms within 3 weeks; however, restricting P successfully limited plant growth. These experiments indicated that current P fertilization regimens exceed the P requirements of these bedding plants, and depending on species, concentrations of 5–15 mg·L−1 P maximize growth.

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Pansy (Viola ×wittrockiana Gams.), petunia (Petunia ×hybrida hort. Vilm.), and gerbera daisy (Gerbera jamesonii Bol. ex Adlam.) plants were grown hydroponically to characterize the deficiency symptoms caused by the absence of calcium (Ca) or boron (B). Primary symptoms occurred on the youngest tissue for both elements, but distinct differences between Ca and B deficiencies were observed. Plants responding to Ca deficiency exhibited discoloration and upward rolling of leaves and ultimately necrosis. Plants responding to B deficiency exhibited minor chlorosis, upward curling, and thickening of leaves, distorted meristems, and strap-like leaves. A second experiment investigated how a temporary disruption of Ca or B affects the plant throughout the crop cycle. Either Ca or B was removed from the nutrient solution for a 7-day period from Day 15 to Day 21, Day 22 to Day 28, or Day 29 to Day 35 after sowing. After the 7-day disruption, the respective element was reintroduced to the plants. Regardless of when the plants were deprived of Ca or B, the symptoms of the respective deficiency were present at the end of the experiment. These studies have shown that a temporary disruption of either Ca or B can cause lasting symptoms throughout the plug production cycle. Also, the symptoms that have been observed in plug production were most similar to those symptoms caused by B deficiency, not Ca deficiency.

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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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Flurprimidol preplant tuber soaks (1.25 to 40 mg·L−1) and substrate drenches (0.25 to 4 mg/pot a.i.) were applied to ‘Red Flash’ caladium (Caladium bicolor) plants for growth control. Flurprimidol was compared with the industry recommendations of paclobutrazol preplant tuber soaks (2.5 to 40 mg·L−1) and paclobutrazol and uniconazole substrate drenches (0.25 to 4 mg/pot a.i.). At the concentrations used, neither flurprimidol nor paclobutrazol preplant tuber soaks controlled plant height or diameter. Longer soaking time or higher concentrations of flurprimidol and paclobutrazol may be required for growth control of vigorous caladium cultivars. Uniconazole substrate drenches did not provide height or diameter control. Both flurprimidol and paclobutrazol substrate drenches at 2 mg/pot a.i. provided acceptable height control resulting in plants that were 17% and 15%, respectively, shorter than the untreated control. The 4 mg/pot a.i. drench of flurprimidol or paclobutrazol provided excessive control.

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