HORTSCIENCE 26(7):877-880. 1991. plant heights have been observed in willows, forsythias, and roses but not spirea or wei- gela that were treated with this growth reg- Pyracantha coccinea ‘Kasan’ and ulator (Grzesik and Rudnicki, 1985). Pyracantha is used widely as an informal ‘Lalandei’ Response to Uniconazole hedge and as espaliers. This species can, however, grow out of control if it is not and Chlormequat Chloride properly pruned and maintained. The use of growth regulators to control the growth habit Janet C. Henderson and Thomas H. Nichols of pyracantha during production and after Department of Horticulture and Landscape Architecture, Oklahoma State planting into the landscape could lead to wider University, Stillwater OK 74078 use of this species and reduced maintenance costs. The objectives of this research were Additional index words. growth regulator, growth retardant, firethorn to determine uniconazole application rates that would decrease growth of two pyracantha Abstract. Pyracantha coccinea M.J. Roem. ‘Kasan’ and ‘Lalandei’ were treated with cultivars while maintaining a desirable ap- a soil drench of 30 mg a.i. chlormequat chloride per container or 0, 0.25, 0.50, or 1.00 pearance, and to determine whether unicon- mg a.i. uniconazole per container or with a foliar application of 3000 mg a.i. chlor- azole controls the height of woody plants mequat chloride/liter or 0, 25, 50, or 100 mg a.i. uniconazole/liter. Chlormequat chlo- better than chlormequat chloride, a growth ride applied as a drench did not affect growth of ‘Kasan’ or ‘Lalandei’ until 17 weeks regulator currently used in the floriculture after application, when ‘Kasan’ was taller and ‘Lalandei’ shorter than untreated plants. industry to reduce height of seasonal flow- ‘Kasan’ plants drenched with chlormequat chloride had more leaves with greater total ering plants. leaf area and higher leaf and stem dry weights than untreated plants. However, area One hundred 7.5-cm-long rooted cuttings per leaf, root dry weight, and root : shoot ratio were not affected by the chlormequat of Pyracantha coccinea ‘Kasan’ and ‘La- chloride drench. In ‘Lalandei’, the chlormequat chloride drench did not affect any of landei’ were planted in 3.8-liter containers these criteria, except stem dry weight. Foliar applications of chlormequat chloride had of 3 pine bark :1 peat :1 sand (by volume) little effect on either cultivar. Height of ‘Kasan’ and ‘Lalandei’ decreased with increas- amended with 17N-3. 6P-10K slow release ing uniconazole rates for both application methods. Area per leaf increased in ‘Kasan’ fertilizer at 8.3 g·m-3) (Osmocote, Sierra but decreased in ‘Lalandei’ receiving a drench applied to the medium. Foliar and Chemical, Milpitas, Calif.), Micromax at 1.9 drench applications of uniconazole both resulted in decreased stem dry weight of both kg·m-3 (Sierra Chemical), and dolomite at cultivars. Chemical names used: 2-chloro-N,N,N-trimethylethanaminium chloride 2.3 kg·m-3. Plants were grown in a green- (chlormequat chloride); (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1- house for 6 weeks at 30/15C day/night, then penten-3-ol (uniconazole). pruned to a 20-cm final shoot length. Plants then were treated with 30 mg chlormequat Uniconazole and chlormequat chloride are the floriculture industry. The response of chloride per container or 0, 0.25, 0.50, or plant growth regulators that reduce plant woody plants to uniconazole has been vari- 1.00 mg uniconazole per container as a soil growth by inhibiting gibberellin biosynthesis able, depending on species and application drench, or 3000 mg chlormequat chloride/ (Henry, 1985). These chemicals have been rate. Extremely short internodes resulted when liter or 0, 25, or 50 mg uniconazole/liter as used to restrict the height of floricultural crops uniconazole was applied at 2.5 mg a.i. per a foliar spray and placed outside in full sun. such as chrysanthemum (Holcomb et al., container as a soil drench to ibolium privet Soil drenches were applied in 100 ml of so- 1983; Wilfret, 1986), poinsettia (Conover and and ‘Wonderberry’ pyracantha (Norcini and lution to each container, and foliar applica- Vines, 1972; White and Holcomb, 1974; Knox, 1989). Uniconazole-treated hibiscus tions were applied as a spray to runoff. The Wilfret, 1986) and several bedding plant were shorter than untreated hibiscus, but fo- soil surface of plants receiving a foliar spray species (Barrett and Nell, 1986). liar distortion reduced plant quality as ap- was covered with plastic before spraying to The use of growth regulators on woody plication rate increased (Newman et al., assure that no uniconazole would enter the ornamental plants is less widespread than in 1989). In contrast, forsythia (Vaigro-Wolff growing medium. Plastic was removed when and Warmund, 1987) and Fraser photinia the foliage had dried. (Norcini and Knox, 1989) treated with sim- Plant height from the medium surface to Received for publication 1 Oct. 1990. Oklahoma ilar uniconazole rates were more compact, the top of the tallest shoot was measured Agricultural Experiment Station Journal Series no. periodically beginning 3 weeks after appli- 5849. The cost of publishing this paper was de- plant appearance was more desirable, and frayed in part by the payment of page charges. photinia flowers were showier than for con- cation. Plant widths were determined by Under postal regulations, this paper therefore must trols. Although chlormequat chloride has not measuring plant diameter at the widest point be hereby marked advertisement solely to indicate been as widely tested on woody plants, in- and perpendicular to this point and then av- this fact. creased shoot lengths, plant diameters, and eraging the values. Seventeen weeks after

HORTSCIENCE, VOL. 26(7), JULY 1991 877 treatment, plants were harvested and leaves sis of variance procedures and paired t tests creased plant height in willow, forsythia, and counted, leaf areas were measured with a LI- were used to determine differences among roses treated with chlormequat chloride 3100 area meter (LI-COR, Lincoln, Neb.), chlormequat chloride and uniconazole treat- (Grzesik and Rudnicki, 1985). Plants receiv- and leaves, shoots and roots were dried at ments within each application method. Or- ing foliar treatments also did not differ ex- 45C for 7 days and weighed. Average area thogonal contrasts were used to determine cept at week 13, when chlormequat chloride per leaf for each plant was calculated by di- linear, quadratic, and cubic relationships plants were shorter than control plants. viding total leaf area by leaf number. among uniconazole application rates. Chlormequat chloride applied as a drench Root : shoot ratios were calculated as (leaf ‘Kasan’ plants treated with a chlormequat resulted in more leaves, larger plant leaf areas, dry weight + shoot dry weight)/root dry chloride medium drench did not differ sig- and higher leaf and stem dry weights in ‘Ka- weight. nificantly from controls in height or width san’ than the control treatment (Table 2). A randomized complete-block design with until 17 weeks after application when treated The foliar application of chlormequat chlo- 10 single-plant replications and 10 treat- plants were taller than controls (Table 1). ride did not affect these measurements. ments within each cultivar was used. Analy- These results agree with observations of in- ‘Lalandei’ plants drenched with chlorme-

878 HORTSCIENCE, VOL. 26(7), JULY 1991 quat chloride were smaller than controls after dium drenches beginning 13 weeks after linearly decreased stem dry weights. 17 weeks (Table 3). The foliar chlormequat treatment. Similar results were obtained by Decreased stem and leaf dry weight with chloride application resulted in larger plants Norcini and Knox (1989), with ibolium privet, uniconazole was also noted by Norcini and at week 13, but this difference was not sig- fraser photinia, and ‘Wonderberry’ pyracan- Knox (1989) on ‘Wonderberry’ pyracantha, nificant at week 17. Application of chlor- tha, all being shorter when treated with un- fraser photinia, and ibolium privet. The in- mequat chloride as a medium drench to iconazole, particularly when environmental creased individual leaf areas were in contrast ‘Lalandei’ reduced stem dry weights, but fo- conditions favored rapid growth. to the decrease in total foliage areas observed liar applications had no effect (Table 4). Uniconazole did not affect the number of in treated privet seedlings and American sy- ‘Kasan’ height decreased as the unicona- leaves per plant or plant leaf area, leaf and camore when uniconazole was injected into zole concentration increased for the medium root dry weights, or the root : shoot ratio of plants (Sterrett, 1988); however, individual drench and foliar applications (Table 1). The ‘Kasan’ (Table 2). The medium drench re- leaf areas were not measured in that study. effect was curvilinear for foliar sprays, be- sulted in a curvilinear increase in area per Height and width of ‘Lalandei’ decreased ginning 8 weeks after treatment and for me- leaf, while both application methods curvi- beginning 8 weeks after drench applications

HORTSCIENCE, VOL. 26(7), JULY 1991 879 (Table 3). At this time, there was a curvilin- green foliage and were considered more de- on chrysanthemum and poinsettia. HortScience ear relationship between application rates and sirable in appearance than those not treated 18:364-365. height and width. Foliar applications de- with the growth regulator or with chlorme- Newman, S.E., S.B. Tenney, and M.W. Follett. r creased plant height curvilinearly by 3 weeks quat chloride. 1989. Influence of uniconazole (Sumagic ) on after application. There was a linear rela- Hibiscus rosa-sinensis L. Mississippi Agr. Expt. Sta. Res. Rpt. 14(4):1-3. tionship between foliar application rate and Literature Cited width at week 3, but it was curvilinear by Norcini, J.G. and G.W. Knox. 1989. Response Barrett, J.E. and T.A. Nell. 1986. Evaluation of week 5. of Ligustrum ´ ibolium, Photinia ´ fraseri, and XE-1019 and paclobutrazol for height control Pyacantha koidzumii ‘Wonderberry’ to XE-1019 Both application methods decreased leaf of flowering annuals. Proc. Plant Growth Reg- and pruning. J. Environ. Hort. 7:126-128. count and stem dry weight curvilinearly in ulat. Soc. Amer. 13:62-64. ‘Lalandei’ (Table 4). The drench resulted in Sterrett, J.P. 1988. XE-1019: Plant response, Conover, C.A. and H.M. Vines. 1972. Chlor- translocation, and metabolism. J. Plant Growth a curvilinear decrease in area per leaf, while mequat drench and spray applications to poin- Regulat. 7:19-26. the foliar treatment resulted in a curvilinear settias. J. Amer. Soc. Hort. Sci. 97:316-320. Vaigro-Wolff, A.L. and M.R. Warmund. 1987. decrease in root dry weight. Grzesik, M. and R.M. Rudnicki. 1985. The use Suppression of growth and plant moisture stress In this study, chlormequat chloride had of growth regulators in nursery production of of forsythia with flurprimidol and XE-1019. little effect on plant growth and visual ap- woody ornamental plants. Acta Hort. 167:401– HortScience 22:884-885. pearance of either Pyracantha coccinea ‘Ka- 415. White, J.W. and E.J. Holcomb. 1974. Height san’ or ‘Lalandei’. In contrast, uniconazole Henry, M.J. 1985. Plant growth regulating activ- control methods for poinsettia. HortScience decreased height of both. ‘Kasan’ was most ity of sterol and gibberellin biosynthesis inhib- 9:146-147. affected by the soil drench, while ‘Lalandei’ itors. Bul. Plant Growth Regulat. Soc. Amer. Wilfret, G.J. 1986. Growth retardation of chry- responded more to foliar applications. Uni- 13(2):9-11. santhemum and poinsettia with Ortho XE-1019. conazole-treated plants of both cultivars had Holcomb, E.J., S. Ream, and J. Reed. 1983. The Proc. Plant Growth Regulat. Soc. Amer. 13:65. a desirably compact growth habit and darker effect of BAS 106, ancymidol, and chlormequat (Abstr.)

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