Efficacy of Dikegulac Sodium Applied to Pruned and Unpruned ‘Limelight’ Hydrangea Grown at Two Locations in the Southeastern United States

Abstract

<jats:p>Pruning is commonly performed during production of nursery crops to produce symmetrical, compact plants that are pleasing to the consumer’s eye. To achieve the desired results, nursery growers hand prune or apply plant growth regulators (PGRs). However, hand pruning is expensive and is not always effective, and efficacy of PGRs can depend on cultural practices, environmental conditions, irrigation, cultivar, and rate. Therefore, the objective of these experiments was to evaluate the effect of dikegulac sodium applied to pruned or unpruned ‘Limelight’ hardy hydrangea (<jats:italic>Hydrangea paniculata</jats:italic>). Plants were grown at two locations, Tennessee (TN) and Mississippi (MS). The pruned treatment consisted of hand pruning, leaving three nodes followed by applications of dikegulac sodium (400, 800, or 1600 ppm). Applications of dikegulac sodium to pruned or unpruned plants were made the same day using a carbon dioxide backpack sprayer. There were two additional control treatments: hand-pruned untreated (hand-pruned) and unpruned untreated (untreated). Plants were grown outdoors under full sun in TN and under 40% shade in MS. Data were collected at the close of the experiment on the number of branches over 1 inch, final growth index (FGI), floral attributes, branch symmetry, and phytotoxicity. At both locations, pruned and unpruned plants treated with 800 or 1600 ppm dikegulac sodium had more branches than the hand-pruned and unpruned plants. Flower number and size tended to be greater for unpruned plants than pruned plants. Phytotoxicity was observed at 2 and 6 weeks after treatment (WAT). For plants grown in TN, symptoms were more pronounced on plants following treatment with 800 (pruned plants) and 1600 ppm (pruned and unpruned) dikegulac sodium compared with the untreated plants. There were no visible phytotoxicity symptoms at 6 WAT for plants grown in MS, regardless of treatment.</jats:p>

Stimulation of Lateral Branching of Red Firespike Using Dikegulac Sodium, Benzyladenine, and Pinching

“…The highest concentrations of DS decreased inflorescence numbers. Similar results were found in unpruned panicle hydrangea (Cochran et al, 2013), where the plants treated with 1600 ppm DS had fewer branches and flowers compared with lower concentrations of DS. However, following application of 1600 ppm DS in bougainvillea (Bougainvillea) flower numbers increased (Norcini et al, 1993(Norcini et al, , 1994.…”

“…Plants treated with 800, 1600, and 2400 ppm DS had shorter inflorescences than the control plants (Table 1). Cochran et al (2013) reported DS at 800 and 1600 ppm reduced inflorescence length of panicle hydrangea. Treatment with 1600 ppm DS to garden phlox (Phlox paniculata) plants resulted in shorter flower stalk height compared with the control (Grossman et al, 2013).…”

“…Dikegulac sodium and BA have been used to effectively enhance branching in bigleaf hydrangea [Hydrangea macrophylla (Hester et al, 2013)]. Foliar sprays of 400 or 800 ppm DS increased branching of 'Gallo Yellow' blanket flower [Gaillardia aristata (Latimer and Freeborn, 2010) (Cochran et al, 2013)]. The foliar application of DS between 4000 and 6000 ppm suppressed dominant shoots and enhanced uniform regrowth without causing marked chlorosis or shoot distortion in orange jessamine [Murraya paniculata (Kawabata and Criley, 1996)].…”

Growth and Flowering of Salvia nemorosa ‘Ostfrieland' in Response to Reduced Irrigation1

“…Hand pruning and plant growth regulators (PGRs) are currently used to control plant growth and to promote increased branching (Cochran et al 2013). Hand pruning is time consuming and is labor intensive, leading to increased production costs (Holland et al 2007).…”

“…Hand pruning is time consuming and is labor intensive, leading to increased production costs (Holland et al 2007). Plant growth regulators may be effective, but their efficacy may vary across ornamental plant species, environmental conditions, substrates, irrigation practices, and method of application (Cochran et al 2013, Cole et al 2013, Keever 2003, Kessler and Keever 2008. Potential restrictions on the use of PGRs in some countries (Clifford et al 2004), and growing concerns about agrochemical use in plant production and their presence in runoff, are causing an increased interest in alternative means of plant growth control (Kaufmann et al 2000).…”