H ort S cience 22(5):884—885. 1987. Suppression of Growth and Plant Moisture Stress of Forsythia with Flurprimidol and XE-1019 A.L. Vaigro-Wolff1 and M.R. Warmund2 Department of Horticulture, University of Missouri, Columbia, Mo 65211 Additional index words, mefluidide, growth regulator, growth retardant, transpiration, xylem pressure potential, Forsythia spectabilis Abstract . Flurprimidol and XE-1019, applied at 15.0 and 2.5 mg/plant respectively, suppressed shoot dry weight and increased xylem pressure potential of Forsythia spec - tabilis Spaeth when drought was induced but did not affect leaf size or root dry weight. XE-1019 did not suppress growth when applied on 28 Aug. 1985. Plants treated with flurprimidol in late August had less shoot growth and higher xylem pressure potential than untreated controls or plants treated with XE-1019. Mefluidide applied as a foliar spray at 5000 mg-liter-1 on 25 June 1985 did not suppress growth or affect plant moisture status of forsythia. None of the growth regulators reduced the transpiration rate of forsythia plants. Chemical names used: A^-[2,4-dimethyl-5-[[(trifluoro- methyl)sulfonyl]amino]phenyl]acetamide (mefluidide); a-(l-methylethyl)- a-[4-trifluo- romethoxy)phenyl]-5-pyrimidinemethanol (flurprimidol); (E)-(p-chlorophenyl)-4,4- dimethyl-2-(l,2,4-triazol-l-yl)-l-penten-3-ol (XE-1019). Container-grown nursery stock treated with a growth retardant has a compact form that can increase the retail value of plants and reduce shipping costs. Growth regulators also may reduce water consumption of plants. For example, applications of a-cyclopropyl-a-(4- methoxyphenyl)-5-pyrimidinemethanol (an- cymidol) and 2 -chloro-A-/V-/V-trimethyl- ethanaminum chloride (chlormequat) reduced leaf area and water consumption of poinset- tia (Euphorbia pulcherrima Willd. ex Klotzsch) and bean (Phaseolus vulgaris L.) plants (3). A similar effect of chlormequat on hydrangea (Hydrangea macrophylla Thunb.) has been demonstrated (14). Mefluidide is a growth regulator currently labeled for the growth suppression of nursery stock (15). Flurprimidol and XE-1019 also have been tested as experimental growth re tardants on ornamental plants (2, 6 , 10). Ah rens ( 1) observed that terminal growth of flowering dogwood (Cornus florida L.) and sugar maple (Acer saccharum Marsh.) was only 10 % that of untreated plants the year after a soil application of the growth regu lator. Additionally, flurprimidol provided growth suppression of an evergreen hybrid holly (Ilex X meserveae S. Y. Hu) for 9 months (6 ). Barrett and Nell (4) reported that bed ding plants treated with XE-1019 were shorter than untreated controls. Forsythia is cumbersome and expensive to transport due to the rank growth of arching canes and drought stress suffered during shipment. The objectives of this study were to evaluate flurprimidol and XE-1019 for growth suppression at two different dates of application and to determine the effect of these growth regulators on plant moisture status. Expt. 1 . Eleven-week-old rooted cuttings of forsythia were transplanted into 1 peat : 1 sand : 1 soil (by volume) medium in 15.9- cm-diameter plastic pots (3.1-liter volume) on 11 Sept. 1984 and grown in a nursery throughout the fall. Plants were overwin tered underneath microfoam in a coldframe from 29 Nov. 1984 to 12 Apr. 1985 and then placed back in the nursery, pruned to a 25- cm height, fertilized with Osmocote (14N- 6.2P-11.6K, 6 g/pot), and routinely irri gated until treatment of 25 June 1985. Treat ments included an untreated control, flurprimidol at 15 mg/plant, and XE-1019 at 2.5 mg/plant applied as drenches. A foliar spray (20 ml/plant) of mefluidide at 500 mg-liter-1 also was included in this experi ment as a standard treatment of comparison. After treatment, plants were grown in a greenhouse at 18° (day)/13°C (night) and ir rigated with 300 ml of water every 24 hr. The experimental design was a randomized complete block design with seven one-plant replicates of each treatment. New shoot growth that occurred after treatment and in- temodal length and number per shoot were recorded on 30 July, 20 Aug., and 26 Sept. Xylem pressure potential was estimated from fully expanded apical leaves with a pressure chamber (PMS Instruments, Cor vallis, Ore.) at 2, 24, and 32 hr after the final irrigation on 27 Aug. Two leaves per node located at four positions (5%, 35%, 65%, and 95% of the total shoot length) were sampled from three shoots per plant and measured with a LI-COR Area Meter (Model 3050) on 4 Sept, to determine the effect of treatments on leaf size. Shoots were re moved and roots were washed free of soil for dry weight determinations. Plant material was oven-dried at 50°C for 48 hr. Data were subjected to an analysis of variance, and means were compared by Duncan’s multiple range test. All forsythia treated with mefluidide ex hibited foliar injury on the apical pair of leaves 4 days after treatment, but subsequent growth was not affected. Similar injury has been re ported on other ornamentals (7, 8 ). Even though mefluidide caused injury to the for sythia, it did not significantly reduce shoot dry weight as compared to the controls (Ta ble 1). Bloomberg and Wax (5) reported that Table 1. Effect of a June application of mefluidide, XE-1019, or flurprimidol on the growth and xylem pressure potential of Forsythia spectabilis (Expt. l).z Total no. Shoot elongation (cm) Dry wt (g) Xylem pressure potential (MPa)x Treatment Dosage of intemodes Shoots Roots Control ... 11.9 a> 46.0 a 47.1 a 45.4 a -2.11 a Foliar spray (m g-liter1) Mefluidide 5000 8.8 a 33.3 a 49.0 a 48.9 a -2.17 a Soil drench (mg/pot) XE-1019 2.5 9.0 a 31.7 a 37.6 b 48.0 a -1.82 b Flurprimidol 15.0 2.1 b 1.0 b 26.9 c 43.7 a -1.49 c zMeans represent seven replications of each treatment. yMean separation within columns by Duncan’s multiple range test, P = 5%. xRecorded 32 hr after irrigation on 27 Aug. 1985. Table 2. 2)*z Effect of an August application of XE-1019 or flurprimidol on Forsythia spectabilis (Expt. Received for publication 11 Aug. 1986. Contri bution from the Missouri Agricultural Experiment Station, Journal Series no. 10141. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regula tions, this paper therefore must be hereby marked advertisement solely to indicate this fact. 'Graduate student. Assistant Professor. Treatment Rate (mg/pot) Shoot elongation (cm) No. internodes Length of internodes Xylem pressure potential (MPa)x Transpiration rate (|ig-cm-2-s-1)x Control — 25.7 ay 10.2 a 2.8 a -1.53 a 3.69 a XE-1019 2.5 24.7 a 9.8 a 2.6 a -1.33 a 3.37 a Flurprimidol 15.0 13.0 b 9.4 a 1.4 b -0.73 b 3.65 a zMeans represent five replications of each treatment. yMean separation within columns by Duncan’s multiple range test, P = 5%. xMeans represent five replications of each treatment. 884 HortS cience , V ol . 22(5), October 1987