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Ornamental cabbage and kale (Brassica oleracea var. acephala) plants of cultivars Osaka White and Nagoya Red were treated with paclobutrazol and uniconazole as foliar sprays or substrate drenches. These treatments were compared to the industry standard of daminozide foliar sprays. Applying drenches of paclobutrazol (a.i.) at 4 mg/pot or uniconazole (a.i.) at 1 mg/pot (28,350 mg = 1.0 oz) resulted in 6% or 17%, respectively, shorter `Osaka White' plants while a 2 mg/pot paclobutrazol drench or a uniconazole drench at 0.25 mg/pot resulted in 25% shorter `Nagoya Red' plants. Although effective, the expense of substrate drenches for both plant growth regulators (PGRs) would not be economically feasible for growers to use. Paclobutrazol foliar sprays at concentrations of up to 80 mg·L-1 (ppm) were ineffective in controlling plant height and diameter of either `Osaka White' or `Nagoya Red'. A uniconazole foliar spray of 16 mg·L-1 resulted in 17% shorter `Nagoya Red' plants and 6% shorter `Osaka White' plants. A daminozide foliar spray of 2500 mg·L-1, sprayed twice, resulted in 21% shorter plants for both cultivars. Spraying daminozide would provide optimal height control for the retail grower. Although spraying daminozide twice controlled plant height and costs half the amount of an uniconazole spray at 16 mg·L-1, plant diameter was not affected with daminozide, therefore a wholesale grower who would desire a smaller diameter plant should use a uniconazole spray of 16 mg·L-1.
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.
Plant growth retardant (PGR) substrate drench treatments (mg a.i./1.5-L pot) of ancymidol at doses of 0.5 to 8, paclobutrazol from 1 to 16, and uniconazole from 0.125 to 2 were applied to tuberous-rooted dahlias (Dahlia variabilis Willd.) to compare their effectiveness for controlling height. When the first inflorescence opened, the number of days from potting until flowering, leaf canopy height, inflorescence height above the foliage, and plant diameter were recorded. Total height control achieved using PGRs was primarily due to reduced inflorescence height, rather than leaf canopy height. Paclobutrazol, ancymidol, and uniconazole at all doses reduced total plant height of the less-vigorous `Red Pigmy' by >21% compared to the untreated control, with a height of 43.5 cm for the untreated control plants. Marketable potted plants were produced with doses of 2 to 4 mg of paclobutrazol, 0.25 to 0.5 mg of uniconazole, or 0.5 mg of ancymidol. All paclobutrazol, ancymidol, and uniconazole doses reduced total plant height of the more-vigorous `Golden Emblem' by >11% compared to the untreated control, with a height of 82.1 cm for the untreated control. Marketable potted plants were produced with 4 to 8 mg of paclobutrazol, 0.5 to 1 mg of uniconazole, or 2 mg of ancymidol.
Plant growth retardant (PGR) foliar sprays (in mg·L−1) of daminozide at concentrations from 1,000 to 16,000; paclobutrazol from 5 to 80; and uniconazole from 2 to 32 were applied to `Pacino' potted sunflowers (Helianthus annuus L.) to compare their effectiveness at chemical height control. Plants were grown in 650-mL or 1.2-L pots. When the first inflorescence started to shed pollen, number of days from seeding until anthesis, total plant height measured from the pot rim to the top of the inflorescence, inflorescence diameter, and plant diameter were recorded. There was no significant difference in plant height between `Pacino' plants grown in 650-mL or 1.2-L pots. Total plant height, plant diameter, inflorescence diameter, and days until flowering were significant for the PGR treatment main effect. Marketable-sized plants grown in the 1.2-L pots were produced with uniconazole concentrations from 16 to 32 mg·L−1 or with daminozide concentrations from 4,000 to 8,000 mg·L−1. Paclobutrazol foliar sprays up to 80 mg·L−1 had little effect, and higher foliar spray concentrations or substrate drench treatments may be needed to effectively control height.
Vigorous osteospermum (Osteospermum ecklonis) cultivars Congo and Wildside received foliar sprays of daminozide or daminozide + chlormequat (Expt. 1). Both cultivars responded similarly to the plant growth regulator (PGR) treatments. Only a limited amount of plant height control occurred using 5,000 mg·L-1 (ppm) daminozide + 1,500 mg·L-1 chlormequat or 5,000 mg·L-1 daminozide + 3,000 mg·L-1 chlormequat. Flowering was delayed, phytotoxicity was observed, while peduncle length increased, suggesting that higher concentrations of daminozide or chlormequat may or not be effective at any concentration and may result in increased phytotoxicity. In Expt. 2, `Lusaka' received foliar sprays or substrate drenches of paclobutrazol or uniconazole. Foliar sprays ≤80 mg·L-1 paclobutrazol or ≤24 mg·L-1 uniconazole were ineffective in controlling plant growth. Substrate drenches of paclobutrazol (a.i.) at 8 to 16 mg/pot (28,350 mg = 1.0 oz) produced compact plants, but at a cost of $0.23 and $0.46/pot, respectively, would not be economically feasible for wholesale producers to use. Uniconazole drenches were effective in producing compact `Lusaka' osteospermum plants. Uniconazole drench concentrations of 0.125 to 0.25 mg/pot were recommended for retail growers, while wholesale growers that desire more compact plants should apply a 0.25 to 0.5 mg/pot drench. Applying uniconazole would cost $0.06 for a 0.25 mg drench or $0.12 for a 0.5 mg drench.
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.
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.
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.
Flurprimidol was applied as a foliar spray (12.5, 25.0, 37.5, 50.0, or 62.5 mg·L-1) or as a substrate drench (0.015, 0.03, 0.06, 0.12, or 0.24 mg/pot a.i.) to determine its efficacy on `Blue Champion' exacum (Exacum affine). Flurprimidol substrate drenches were more consistent in controlling plant growth than foliar sprays. Substrate drenches of 0.03 mg/pot a.i. or foliar sprays ≥50 mg·L-1 resulted in smaller plant heights and diameters than the untreated control. With the use of flurprimidol, exacum growers have another plant growth regulator (PGR) available to control excessive growth.
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.