HORTSCIENCE, VOL. 29(11), NOVEMBER 1994 1368 NOTES HORTSCIENCE 29(11):1368. 1994. Chemical Growth Retardant Application to Lisianthus Brian E. Whipker, Robert T. Eddy, and P. Allen Hammer Department of Horticulture, 1165 Horticulture Building, Purdue University, West Lafayette, IN 47907-1165 Additional index words. Eustoma grandiflorum, daminozide, paclobutrazol, uniconazole plied from KNO 3 , Ca(NO 3 ) 2 , and NH 4 NO 3 , at concentrations of 71, 65, and 65 mg•liter –1 , respectively. In addition, plants received K at 200 mg•liter –1 from KNO 3 and P at 46 mg•liter –1 supplied from 75% (w/w) technical grade H 3 PO 4 in the irrigation system. Greenhouse night/day set points were 18/24C. The plants were grown under natural daylengths. Plants were pinched, leaving four to six nodes on 14 May. On 2 June, five PGR treatments (mg•liter –1 ) were applied as foliar sprays using a volume of 204 ml •m –2 : daminozide at 2500 and 5000, paclobutrazol at 20, and uniconazole at 5 and 10, plus a nontreated control. A completely randomized design of six single-plant repli- cates was used. When the first inflorescence opened, plant height was measured from the pot rim to the top of the plant, and the number of days from transplanting until flowering was recorded. Data for all three cultivars were analyzed together using analysis of variance by general linear model procedures (SAS In- stitute, 1990). Significantly different means were separated by least significant differences (LSD) at P ≤ 0.05. The results of the PGR applications were significant at the treatment × cultivar interac- tion. Foliar spray applications of 5000 mg daminozide and 5 or 10 mg uniconazole/liter had the greatest effect on plant height of ‘Yo- del Blue’, with a reduction of 32%, 40%, and 36%, respectively, compared to the control (Table 1). For ‘Yodel Pink’ and ‘Yodel White’, 5000 mgdaminozide/liter reduced plant height by 30% and 37%, respectively, compared to the control. Uniconazole at 5 and 10 mg• liter –1 also reduced ‘Yodel Pink’ plant height by 27% and 28%, respectively, compared to the con- trol. For ‘Yodel White’, 10 mg uniconazole/ liter reduced plant height by 23%, compared to the control. At the concentration used, paclobutrazol had little effect on reduc- ing plant height for any of the cultivars. The effects of the PGR treatments on the number of days from transplanting to flower- ing were similar for all three cultivars. The use of 5000 mg daminozide and 5 or 10 mg uniconazole/liter significantly delayed flow- ering by at least 3 days [85.1, 82.9, and 83.2 days, respectively (LSD = 2.33)] when com- pared to the control (79.8 days). The variations in cultivar response to the PGRs we observed are probably due to differ- ences in vigor of the three cultivars. Signifi- cant differences in overall plant height existed among the cultivars. ‘Yodel White’ was the most vigorous cultivar, growing to 46.8 cm when untreated, while ‘Yodel Pink’ (39.9 cm) and ‘Yodel Blue’ (32.6 cm) were shorter. Rates of PGRs higher than those used in this study may be more effective in producing suitable pot-sized plants for the vigorous cul- tivars. The degree of height control achieved with uniconazole agrees with earlier work done with ‘Yodel Blue’ by Starman (1991a, 1991b), although our study resulted in plants that were 52% and 34% shorter, respectively, for 5 and 10 mg uniconazole/liter than Starman’s. The 5000-mg daminozide and 5- and 10-mg uniconazole/liter treatments were the most effective in controlling plant height and pro- duced the most marketable-sized plants, with only a minimal delay in flowering. Paclobutra- zol at 20 mg•liter –1 had little effect on lisianthus plant height. Further research will need to be conducted to determine optimal rates for paclobutrazol as an effective PGR on lisianthus. Literature Cited Halevy, A.H. and A.M. Kofranek. 1984. Evaluation of lisianthus as a new flower crop. HortScience 19:845–847. Hammer, P.A. and C. Fultz. 1985. The effect of B- Nine SP on height of lisianthus. Focus on Flori- culture 13(4):1–3. Roh, M.S.M. and R.H. Lawson. 1984. The lure of lisianthus. Greenhouse Manager 2(11):103–106, 112–121. SAS Institute. 1990. SAS/STAT user’s guide, vol. 2, version 6, 4th ed. SAS Inst., Cary, N.C. Starman, T.W. 1991a. Lisianthus growth and flow- ering responses to uniconazole. HortScience 26:150–152. Starman, T.W. 1991b. Corrigendum. HortScience 26:333. Tjia, B. and T.J. Sheehan. 1986. Chemical height control of Lisianthus russellianus. HortScience 21:147–148. Lisianthus [ Eustoma grandiflorum (Shinn.)] is an annual with blooms that range from purple to white. Evaluators at the U.S. Dept. of Agriculture Florist and Nursery Crops Laboratory of Beltsville, Md., found lisianthus to be an ideal pot plant when grown as a pinched plant treated with chemical plant growth retardants (PGRs) (Roh and Lawson, 1984). Several researchers have conducted stud- ies with PGRs to control lisianthus height; foliar sprays of 2500 mg butanedioic acid mono(2,2-dimethylhydrazide) (daminozide)/ liter, applied twice at a 7- and 14-day interval, and single 5000- or 7500-mg•liter –1 sprays are effective in controlling plant height (Halevy and Kofranek, 1984; Hammer and Fultz, 1985; Starman, 1991a, 1991b; Tjia and Sheehan, 1986). Ancymidol applied as a 0.5-mg a.i./pot soil drench was effective in controlling height of a white cultivar (Halevy and Kofranek, 1984). [(E)-1-(4-chlorophenyl)-4,4-dimethyl- 2-(1,2,4-triazol-yl)penten-3-ol] (uniconazole) sprays of 5 and 10 mg•liter –1 and 0.2 mg a.i./pot as a drench also were effective (Starman, 1991a, 1991b). Varietal differences did exist in studies that tested more than one cultivar, but to our knowledge, limited information is available on the effectiveness of [(2RS, 3RS)- 1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4- triazol-yl)penten-3-ol] (paclobutrazol) or the response of the three lisianthus color cultivars to PGRs. This study was conducted to com- pare the effectiveness of paclobutrazol, daminozide, and uniconazole on plant height and days to flowering for blue, pink, and white lisianthus cultivars. Seedling plugs of lisianthus cultivars Yo- del Pink, Yodel Blue, and Yodel White were planted into 0.45-liter round pots on 14 Apr. 1993. The root medium contained 1 soil : 2 sphagnum peat : 2 perlite (by volume) amended with (all per cubic meter of mix) 890 g Ca(H 2 PO 4 ) 2 , 593 g KNO 3 , 593 g MgSO 4 • 7H 2 O, 4.75 kg ground limestone, and 74 g Peter’s fritted trace elements no. 555 (Peters, Allen- town, Pa.). Plants were fertilized at each wa- tering with N at 201 mg•liter –1 ; this was sup- Table 1. Plant growth retardant (PGR) effect on height of lisianthus cultivars Yodel Blue, Yodel Pink, and Yodel White. Cultivar Yodel Yodel Yodel Concn Blue Pink White PGR (mg•liter –1 ) ht (cm) ht (cm) ht (cm) None --- 32.6 39.9 46.8 Daminozide 2500 31.9 34.1 38.1 5000 22.2 27.8 29.6 Paclobutrazol 20 29.8 40.1 42.1 Uniconazole 5 19.7 29.2 45.1 10 20.9 28.7 35.8 Significance ** LSD (α = 0.05) 6.24 ** Significant at P ≤ 0.01 for the treatment × cultivar interaction. Received for publication 3 May 1994. Accepted for publication 2 July 1994. Journal paper no.14202 of the Agricultural Experiment Station of Purdue Univ., West Lafayette, Ind. Thanks to Vaughan’s Seed Co. for supplying the seedlings and Uniroyal and Valent Chemical companies for grant support. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked adver- tisement solely to indicate this fact.