or uniconazole doses increased up to drenches. Foliar applications of Vegetatively 0.02 mg. However, doses of ≥0.02 mg at 15 mg·L–1, applied Propagated had little additional effect on total twice, or uniconazole at 10 mg·L–1, height and canopy height. applied twice, resulted in effective Most of the total height control height control and the production of Geraniums achieved by the use of PGRs was primarily due to a reduction of leaf marketable (Tayama and Carver, Respond canopy height, rather than inflores- 1990). The same doses of these PGRs cence height. Doses of 0.005 to 0.01 applied as substrate drenches resulted Similarly to mg of either PGR produced market- in excessive suppression of growth able sized potted plants of ‘Medallion (Tayama and Carver, 1990). A similar Drench Dark Red’ and ‘Pink Satisfaction’. study indicated that uniconazole ap- Applications of ‘Aurora’, which was the most vigorous plied at 0.6 to 1.2 mg as a substrate cultivar, required doses of 0.01 or 0.02 drench was excessive on vegetatively Paclobutrazol or mg of either paclobutrazol or propagated geraniums, however this uniconazole to produce marketable study did not include lower doses and sized potted plants. Uniconazole a recommended commercial rate was not given (Tayama and Carver, 1992). While some studies have involved ei- Brian E. Whipker,1 hemical plant growth ther paclobutrazol or uniconazole, regulators (PGRs) are none have directly compared similar 2 Shravan K. Dasoju, and C applied to both seed and veg- doses of both chemicals over a wide Michael R. Evans3 etatively propagated geraniums to con- range of concentrations on vegeta- trol plant height and improve overall tively propagated geraniums. This appearance. Paclobutrazol ((+)- study was conducted to compare the (R*,R*)-β([4-chlorophenyl]methyl)- effectiveness of paclobutrazol and ADDITIONAL INDEX WORDS. Pelargonium α-(1,1-dimethylethyl)-1H-1,2,4- uniconazole drenches at similar doses × hortorum, growth retardant triazole-1-ethanol) (Bonzi, Uniroyal on plant growth of vegetatively propa- Chemical, Middlebury, Conn.) gated geraniums. SUMMARY. Drench applications of drenches of 0.01 to 0.5 mg a.i./pot paclobutrazol or uniconazole were Materials and methods applied at doses of 0, 0.0025, 0.005, suppressed plant height of seed propa- 0.01, 0.02, or 0.04 mg a.i./pot gated geraniums (Shanks, 1980). Cox Rooted vegetative cuttings of ‘Au- (28,350 mg = 1.0 oz) to vegetatively and Keever (1988) conducted studies rora’, ‘Medallion Dark Red’, and ‘Pink propagated ‘Aurora’, ‘Medallion Dark with paclobutrazol to control height Satisfaction’ geraniums were potted into Red’, and ‘Pink Satisfaction’ geranium of seed propagated geraniums and 0.6-L (0.16-gal), 10-cm-diameter (4- (Pelargonium ×hortorum L.H. Bailey). found substrate drenches of inch), square pots on 18 Feb. 1996. The Geranium total plant height, leaf 0.0075 or 0.015 mg or a single foliar root substrate contained 2 soil : 5 sph- canopy height, and plant diameter spray of 20 or 40 mg·L–1 (ppm) were agnum peat : 3 perlite (by volume) and responded similarly to drench applica- effective in controlling height and pro- was amended with ground dolomitic tions of either paclobutrazol or ducing a marketable plant. Excessively limestone to pH 5.1. Plants were fertil- uniconazole. There was a significant –1 quadratic relationship between plant short plants resulted when higher ized at each watering (mg·L ) with 155 growth regulator (PGR) dose and total drench or foliar spray doses were used. N, 21 P, and 127 K. Greenhouse day/ plant height and leaf canopy height for Nørremark and Andersen (1990) also night set points were 24/18 °C (75/ ‘Aurora’ and ‘Medallion Dark Red’, found paclobutrazol drench applica- 65 °F), and the plants were grown with total plant height and leaf canopy tions of ≥0.05 mg resulted in seed under natural daylength with average height being shorter as paclobutrazol geraniums which were excessively short light levels of 250 µmol·m–2·s–1 at 12:00 and new growth continued to be re- HR. Growth retardants were applied Iowa Agriculture and Home Economics Experiment tarded throughout the summer. to the root substrates 21 d after plant- Station journal paper J-18079, project 3345. Sup- Uniconazole ((E)-1-(p-chlorphenyl)- ing. A volume of 89 mL (3 oz) of ported by Hatch Act and State of Iowa funds. This 4,4-dimethyl-2-(1,2,4-triazol-1-yl-1- solution containing 0, 0.0025, 0.005, research was funded in part by the North Carolina Agricultural Research Service (NCARS), Raleigh. Use penten-3-ol)) (Sumagic, Valent USA, 0.01, 0.02 or 0.04 mg paclobutrazol of trade names in this publication does not imply Marysville, Ohio) drenches of 0.025 or uniconazole was applied per con- endorsement by the NCARS of products named nor tainer. The experiment was a com- criticism of similar ones not mentioned. Thanks to to 0.1 mg were applied to two cultivars Oglevee Ltd., Connellsville, Pa., for supplying cuttings of seed geraniums and doses of 0.025 pletely randomized design with 10 and to Uniroyal Chemical Co. and Valent Chemical were found to be effective for growth single-plant replications of the 11 treat- Co. for grant support. The cost of publishing this paper was defrayed in part by the payment of page charges. control, while higher doses were ex- ments. On 8 May, leaf canopy height Under postal regulations, this paper therefore must be cessive (Starman et al., 1994). (measured from the pot rim to the top hereby marked advertisement solely to indicate this fact. Vegetatively propagated gerani- of the foliage), total plant height (mea- 1Assistant professor, Dept. of Horticultural Science, ums are typically more vigorous than sured from the pot rim to the top of the Box 7609, North Carolina State Univ., Raleigh, NC 27695-7609. seed propagated geraniums. A limited inflorescence), and plant diameter (measured at the widest dimension, 2Former research associate, Department of Horticul- number of scientific studies have been ture, Iowa State Univ., Ames, IA 50011-1100. conducted on the response of vegeta- measured again after a turn of 90°, 3Assistant professor, Department of Horticulture, Iowa tively propagated geraniums to then averaged) were recorded for all State Univ., Ames, IA 50011-1100. paclobutrazol or uniconazole substrate plants.

● January–March 2000 10(1) 151 RESEARCH REPORTS

Table 1. Regression coefficients of models for total plant height and leaf canopy height of ‘Aurora’, ‘Medallion Dark Red’ and ‘Pink Satisfaction’ vegetatively propagated geraniums.z

Plant part Adjusted Regression and cultivary Regression equation r2 r2 F statistic Total plant height (cm) Aurora y = 28.1*** – 480.46 (conc)*** + 6431.45 (conc2)*** 0.714 0.709 146.2 Medallion Dark Red y = 24.17*** – 369.25 (conc)*** + 4567.14 (conc2)** 0.531 0.523 66.2 Pink Satisfaction y = 23.48*** – 170.98 (conc)*** 0.552 0.548 145.4 Leaf canopy height (cm) Aurora y = 19.13*** – 446.26 (conc)*** + 6331.45 (conc2)*** 0.641 0.635 104.6 Medallion Dark Red y = 14.31*** – 246.2 (conc)*** + 3299.46 (conc2)*** 0.523 0.515 64.1 Pink Satisfaction y = 13.79*** – 112.11 (conc)*** 0.477 0.473 107.8 zThe plants were drenched with 0, 0.0025, 0.005, 0.01, 0.02, or 0.04 mg a.i./pot of paclobutrazol or uniconazole. Total plant height and leaf canopy height were not significantly influenced by plant growth regulator (PGR) type (paclobutrazol or uniconazole) and therefore the data were pooled across PGR type; 28,350 mg = 1.0 oz. y2.54 cm = 1.0 inch. **,***Significant at P ≤ 0.01 or 0.001, respectively.

DATA ANALYSIS. Data for the total dures outlined above to determine the Total plant height of ‘Aurora’ was plant height, leaf canopy height, and best fit linear or quadratic model. reduced as paclobutrazol or plant diameter were analyzed using uniconazole dose increased up to 0.02 analysis of variance by general linear Results and discussion mg. However, additional increases in model procedures (SAS Institute, Cary, There were significant cultivar × dose had little effect on total plant N.C.). Means were separated by least dose interactions for total plant height height. ‘Aurora’ plants treated with significant differences (LSD) at P ≤ 0.05. and leaf canopy height (P ≤ 0.001). 0.01 mg of paclobutrazol or Total plant height and leaf canopy Therefore, the height data were ana- uniconazole were 15% shorter than height were not significantly influenced lyzed by cultivar. the untreated plants. Untreated con- by PGR type (paclobutrazol or There was a significant quadratic trol plants of ‘Aurora’ were 27.8 cm uniconazole) and therefore, data were relationship between the dose and to- (10.8 inches), while ‘Medallion Dark pooled across PGR type. Total plant tal plant height for ‘Aurora’ and ‘Me- Red’ and ‘Pink Satisfaction’ were height and leaf canopy height values dallion Dark Red’, while ‘Pink Satis- shorter [23.9 cm (9.3 inches) and 23.3 were regressed using the PROC REG faction’ responded linearly (Table 1). cm (9.1 inches), respectively]. ‘Medal- procedure (SAS Institute, Cary, NC) to determine the best fit linear or qua- dratic model. Variables in the model were PGR concentration (conc) and indicator variables for cultivar (cult), with the full model being as follows: Concentration = β + β Cult + β Cult β β i 0 × 1 2 2 3 + 3Conc + 4Conc Cult2 + β × β 2 β 2 × 5Conc Cult3 + 6Conc + 7Conc β 2 × Cult2 + 8Conc Cult3 where concentrationi = PGR concen- tration (0, 0.0025, 0.005, 0.01, 0.02, or 0.04 mg), i = variable being re- gressed (total plant height or leaf canopy height); Cult2 = 1 if cultivar = ‘Medallion Dark Red’, 0 otherwise (for ‘Aurora’ or ‘Pink Satisfaction’);

Cult3 = 1 if cultivar = ‘Pink Satisfac- tion’, 0 otherwise (for ‘Aurora’ or

‘Medallion Dark Red’) (when Cult2 = 0 and Cult = 0, then Cult = ‘Aurora’); β 3 k = estimated coefficients (k = 0 to 8). Terms of the model were judged to be significant or nonsignificant and included in the final model based on a comparison of F values at α = 0.05. Fig. 1. Effect of paclobutrazol or uniconazole (mg a.i./pot) on plant diameter Plant diameter was not signifi- of vegetatively propagated geraniums. Data pooled across plant growth regula- cantly influenced by either PGR type tor (PGR) type and cultivar. Plant diameter significant at P ≤ 0.001 for the or cultivar and the data was pooled. PGR dose and LSD (α ≤ 0.05) is 1.0 cm (0.39 inch). The adjusted r2 for plant The concentration values were re- diameter was 0.59. ***Significant at P ≤ 0.001. L = linear and Q = quadratic; gressed using the PROC REG proce- 28,350 mg = 1.0 oz.

152 ● January–March 2000 10(1) lion Dark Red’ and ‘Pink Satisfaction’ smaller than the untreated control. Plants $74/L ($78/qt) for uniconazole, the were shorter cultivars, however they treated with 0.04 mg of paclobutrazol 0.02-mg drench would also cost less had a response similar to ‘Aurora’ for or uniconazole had smaller, darker green than $0.001 per 0.6-L (0.16-gal) pot. total plant height as the PGR dose and stunted growth. With a similar degree of growth control increased. Excessive height retarda- and similar costs per pot available with tion of all three cultivars was evident at Conclusions either paclobutrazol or uniconazole doses of 0.04 mg, with plants being The vigor and responsiveness of drench doses of 0.005 to 0.02 mg or 31%, 30%, and 28% shorter than the vegetatively propagated geranium cul- paclobutrazol foliar sprays between 5 untreated control, respectively, for tivars should be considered when de- and 15 mg·L–1, growers would find the ‘Aurora’, ‘Medallion Dark Red’, and termining the optimal drench dose of chemical cost of any of these PGR appli- ‘Pink Satisfaction’. These results were a PGR. ‘Aurora’ was the most vigor- cation methods to be economical. similar to other experiments which ous cultivar, with a total plant height indicated excessively short plants of of 27.8 cm (10.8 inches) for the un- seed or vegetatively propagated gera- treated control. Drench doses of Literature cited niums resulted from drench applica- paclobutrazol or uniconazole of 0.01 Barrett, J.E., M.E. Peacock, and T.A. Nell. tions of either paclobutrazol to 0.02 mg per container produced 1986. Height control of exacum and chry- (Nørremark and Anderson, 1990; marketable sized potted plants. Both santhemum with paclobutrazol, XE-1019, Tayama and Carver, 1990) or ‘Medallion Dark Red’ and ‘Pink Satis- flurprimidol and RSW-0411. Proc. Fla. uniconazole (Starman et al., 1994; faction’ were less vigorous, and lower State Hort. Soc. 99:254–255. Tayama and Carver, 1990; 1992) at paclobutrazol or uniconazole drench Cox, D.A. and G.J. Keever. 1988. doses of ≥0.05 mg. rates of 0.005 to 0.01 mg/container Paclobutrazol inhibits growth of zinnia At 19.5 cm (7.6 inches), the leaf produced marketable plants. Our rec- and geraniums. HortScience 23:1029– canopy height of untreated control ommendation of 0.01 to 0.02 mg of 1030. plants of ‘Aurora’ were taller than ei- paclobutrazol or uniconazole per con- Nørremark, I. and A. Andersen. 1990. ther ‘Medallion Dark Red’ or ‘Pink tainer on vegetatively propagated ‘Au- Effect of paclobutrazol on seed propa- Satisfaction’, which were 14.8 cm (5.8 rora’ geraniums is similar to those for gated Pelargonium ×hortorum L.H. Bailey. inches) and 13.9 cm (5.4 inches), re- seed propagated geraniums of 0.025 Gartenbauwissenschaft 55:1–8. mg of uniconazole recommended by spectively (Table 1). Leaf canopy height Shanks, J.B. 1980. Chemical dwarfing of of ‘Aurora’ and ‘Medallion Dark Red’ Starman et al. (1994) and the range of several ornamental greenhouse crops with were 32% and 26% shorter than the 0.0075 or 0.015 mg of paclobutrazol PP333, p. 46–51. Proc. VII Annu. Meet- untreated control, respectively, as by Cox and Keever (1988). Based ing of the Plant Growth Regulat. Working paclobutrazol or uniconazole doses upon our results and those of Cox and Group. Great Western Sugar Co., increased up to 0.02 mg. However, Keever (1988), and Starman et al. Longmont, Colo. (1994), we have concluded that veg- additional increases in dose had little Starman, T.W., T.A. Cerny, and T.L. effect on leaf canopy height of ‘Au- etative and seed propagated gerani- Grindstaff. 1994. Seed geranium growth rora’ and ‘Medallion Dark Red’. Most ums respond similarly to paclobutrazol and flowering responses to uniconazole. of the height control achieved by the or uniconazole drenches. This conclu- HortScience 29:865–867. use of PGRs was primarily due to a sion is in contrast to the responses of reduction of leaf canopy height, rather many ornamental species in which an Tayama, H.K. and S.A. Carver. 1990. Zonal equivalent dose of uniconazole resulted geranium growth and flowering responses than inflorescence height and similar to six growth regulators. HortScience results were reported with uniconazole in greater height reduction compared 25:82–83. drenches on seed propagated gerani- to paclobutrazol (Barrett et al., 1986; ums (Starman et al., 1994). Wilfret, 1990). Tayama, H.K. and S.A. Carver. 1992. Plant diameter of vegetatively Growers have a number of PGRs Concentration response of zonal geranium propagated geraniums was significantly available for controlling plant growth. and potted chrysanthemum to uniconazole. HortScience 27:126–128. different (P ≤ 0.001) only for PGR dose, The type of PGR used to control growth therefore the data was pooled across of vegetatively propagated geraniums Whipker, B.E., P.A. Hammer, and J. cultivars and PGR type. There was a should be based on the response of the Connell. 1997. Vegetatively propagated significant quadratic relationship for plant and the cost of the PGR. In foliar geranium response to single and multiple plant diameter as the PGR dose in- PGR experiments, Whipker et al. (1997) applications of chemical growth retardants. creased (Fig. 1). Plant diameter was recommended paclobutrazol foliar Plant Growth Regulat. Soc. Amer. Quart. 25(3):131–133. smaller as the PGR dose increased, with sprays between 5 and 15 mg·L–1 at a plants treated with 0.02 mg were 22% PGR cost of less than $0.001 per 0.6-L Wilfret, G.J. 1990. Height control of pot- smaller than the untreated control, and (0.16-gal) pot. Based on the cost of ted Easter lilies in Florida. Fla. Ornamental those treated with 0.04 mg were 31% $97/L ($102/qt) for paclobutrazol or Growers Assn. Nwsl. 13(1):1–3.

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