Timing of Benzyladenine and Dikegulac Sodium Application Affects Branching of Liners and Finished Herbaceous Perennial Plants

Abstract

<jats:p>Foliar spray applications of plant growth regulators (PGRs) benzyladenine (BA) and dikegulac sodium (DS) on herbaceous perennial liners and transplants were evaluated to determine effects on branching and quality. PGRs were applied three times (main plot): liner (24 h after removal from mist), post-transplant (5 to 7 days after transplant), or both (applications at liner and post-transplant). PGRs (subplots) were applied at concentrations of 400, 800, or 1600 mg·L<jats:sup>−1</jats:sup> DS; 600 mg·L<jats:sup>−1</jats:sup> BA; or a combination of 400 mg·L<jats:sup>−1</jats:sup> DS and 600 mg·L<jats:sup>−1</jats:sup> BA (DS/BA). All studies included an untreated control. <jats:italic>Sedum spectabile</jats:italic> ‘Autumn Joy’ treated with PGRs at both application times had a 100% increase in branching compared with either single application time. Applied post-transplant, 800 mg·L<jats:sup>−1</jats:sup> DS, BA, or DS/BA increased branching. Applied at both times, all DS concentrations or BA tripled the number of lateral branches per plant, whereas DS/BA resulted in a 4-fold increase in number of branches. <jats:italic>Sedum</jats:italic> treated with 1600 mg·L<jats:sup>−1</jats:sup> DS at liner, post-transplant, or both application times was shorter than controls; plants sprayed with 1600 mg·L<jats:sup>−1</jats:sup> DS at both application times were stunted. Phytotoxicity (yellow, narrow leaves) was present in finished plants treated with 800 or 1600 mg·L<jats:sup>−1</jats:sup> DS or DS/BA post-transplant or with 1600 mg·L<jats:sup>−1</jats:sup> DS applied both times. <jats:italic>Gaillardia aristata</jats:italic> ‘Gallo Red’ treated with PGRs at both application times had increased branching compared with plants subjected to a single application. Number of branches was increased by liner application of 400 mg·L<jats:sup>−1</jats:sup> DS, post-transplant applications of DS/BA, or applications both times of BA or DS/BA, whereas applications both times of 1600 mg·L<jats:sup>−1</jats:sup> DS decreased branching and caused stunting and chlorotic foliage. In application as liners or at both times, all PGRs except 400 mg·L<jats:sup>−1</jats:sup> DS caused 16- to 33-day delays in flowering. Branching of <jats:italic>Phlox paniculata</jats:italic> ‘Bright Eyes’ was unaffected by application time. Only <jats:italic>Phlox</jats:italic> treated with BA or 1600 mg·L<jats:sup>−1</jats:sup> DS at both application times had increased branches, although plants treated with 1600 mg·L<jats:sup>−1</jats:sup> DS were shorter than controls and had phytotoxicity in the form of narrow, yellow leaves. <jats:italic>Nepeta racemosa</jats:italic> ‘Walker’s Low’ treated with PGRs post-transplant or both application times had more branches than plants treated with PGRs once as liners. Number of branches was increased with BA or 800 mg·L<jats:sup>−1</jats:sup> DS applied post-transplant or 1600 mg·L<jats:sup>−1</jats:sup> DS, BA, or DS/BA applied both times, but the plants treated with 1600 mg·L<jats:sup>−1</jats:sup> DS were stunted and had yellow leaves. Neither BA nor DS affected branching in <jats:italic>Delosperma</jats:italic> ‘Table Mountain’. Application time did not affect branching in <jats:italic>Achillea</jats:italic> ‘Moonshine’; only both applications of BA increased the number of branches in <jats:italic>Achillea,</jats:italic> whereas either single application of 1600 mg·L<jats:sup>−1</jats:sup> DS or both applications of 800 or 1600 mg·L<jats:sup>−1</jats:sup> DS caused phytotoxicity and stunting. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)], sodium 2,3:4,6-bis-<jats:italic>O-(1-methylethylidene)-α-L-xylo-2</jats:italic>-hexulofuranosonate (DS)</jats:p>

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

“…An increase in DS concentration or pinch number resulted in a reduction in GI (Table 1). This result was in agreement with Grossman et al (2013), who reported two applications of DS at 1600 ppm reduced plant growth in all of the crops studied. Growth index also decreased as BA concentration increased up to the 1250 ppm (Table 1).…”

“…Reduction in leaf area of plants treated with 2400 ppm DS likely contributed to the decreased dry weight observed at the same DS concentration. An increase in shoot dry weight following BA application has been reported previously in 'Autumn Joy' sedum (Grossman et al, 2013).…”

“…In both experiments, phytotoxicity was observed for all plants treated with 1600 or 2400 ppm DS as yellow foliage or narrow branches (data not shown). Phytotoxicity following 1600 ppm DS treatment has also been reported in 'Autumn Joy' sedum [Sedum spectabile (Grossman et al, 2013)], in 'Scarlet Flame' zinnia (Zinnia elegans) at 750 ppm (Arzee et al, 1977), and in blanket flower at 800 to 3200 ppm (Latimer and Freeborn, 2010).…”

“…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). The reduction in inflorescence length may be useful in height control of red firespike if it causes no reduction in floret number or floret size.…”

“…To achieve better uniformity, growers often use cultural practices including hand pinching and PGRs to release apical dominance. This allows dormant, lateral buds to grow resulting in well-branched plants (Grossman et al, 2013). Pinching promotes lateral branch development and more synchronous flowering (Larson, 1985).…”