Substrate pH Impacts Efficacy of Ethephon Drenches on Growth of Herbaceous Perennials

Abstract

<jats:p>Ethephon [(2-chloroethyl) phosphonic acid] is widely used as a growth regulator in floricultural crop production, with foliar sprays as the typical application method. Ethephon efficacy is determined by rate of uptake and subsequent ethylene evolution, which can be influenced by a number of factors, including solution pH. This study examines whether an ethephon substrate drench (100 mg⋅L<jats:sup>−1</jats:sup> at a volume of 296 mL per 2.8-L container) would allow for plant uptake in two herbaceous perennials, <jats:italic>Verbena bonariensis</jats:italic> (L.) ‘Lollipop’ and <jats:italic>Veronica spicata</jats:italic> (L.) ‘Goodness Grows’, as measured by subsequent effects on shoot growth and days to flower. We also investigated substrate pH effects on ethephon drench efficacy by analyzing the shoot responses to ethephon applied at a range of starting substrate pH (4.5 to 7.0) compared with untreated plants grown under the same substrate pH conditions (controls). One or more measurements of shoot growth (height, width, shoot dry weight) were reduced in both taxa treated with ethephon as compared with controls. <jats:italic>Veronica</jats:italic> plant growth was not influenced by substrate pH in either the control or ethephon-drenched plants. For <jats:italic>Verbena</jats:italic> plants receiving the ethephon drench, as substrate pH increased, height and width increased. For example, when ethephon was applied at substrate pH 4.5, finished plant height averaged 32.0 cm, compared with 43.5 cm for those plants that received the drench at a substrate pH of 7.0. Increasing substrate pH conditions also influenced the days to flower in <jats:italic>Verbena</jats:italic> plants. Ethephon-treated plants at a substrate pH of 4.5 required an average of 6.5 days longer to flower than those at a substrate pH of 7.0. In summary, ethephon drench applications can result in significant growth regulation effects, as seen in both <jats:italic>Veronica</jats:italic> and <jats:italic>Verbena.</jats:italic> Furthermore, increasing substrate pH can reduce the efficacy of ethephon drench applications.</jats:p>

Concentration and Timing of Ethephon Drench Applications Interact to Affect Growth and Flowering of Containerized Angelonia and Geranium

“…Our results agree with previous reports on the effects of ethephon drenches on annuals (Aiken et al, 2015;Miller et al, 2012). Miller et al (2012) reported time to flower for numerous annuals treated with ethephon at different institutions.…”

“…In addition to flowering, ethephon drenches controlled size (heights and widths) and growth (dry weight) of angelonia and geranium. This work agrees with previous research on ethephon drenches which reported successful growth control of containerized annuals and perennials (Aiken et al, 2015;Miller et al, 2012). Aiken et al (2015) reported that veronica treated with ethephon drenches were narrower than untreated plants with no differences in plant height, whereas height and width of treated verbena were consistently smaller than untreated plants.…”

“…This work agrees with previous research on ethephon drenches which reported successful growth control of containerized annuals and perennials (Aiken et al, 2015;Miller et al, 2012). Aiken et al (2015) reported that veronica treated with ethephon drenches were narrower than untreated plants with no differences in plant height, whereas height and width of treated verbena were consistently smaller than untreated plants. Variation in plant responses to ethephon across study locations was reported by Miller et al (2012).…”

“…Interestingly, the same osteospermum cultivar (Zion Copper Amethyst) and cell size was used at both Cornell and Michigan State and, whereas flowering was delayed for plants treated 2 d after transplanting at Cornell, time to flower was unaffected by ethephon applied 10 d after transplanting at Michigan State. Aiken et al (2015) reported that while veronica (Veronica spicata) flowering was unaffected by ethephon drenches, verbena (Verbena bonariensis) flowered up to 2 weeks later than untreated plants; though flowering delays were greater when substrate pH was more acidic.…”

“…Spray applications are easy to apply and can provide adequate growth control, though substrate drenches can increase growth control uniformity and duration (Currey et al, 2010;Currey and Lopez, 2011;Currey et al, 2012). Ethephon is not currently labeled for application via substrate drenches, though recent research reports the promise of using drenches for growth control (Aiken et al, 2015;Miller et al, 2012). Miller et al (2012) noted that ethephon drench activity appeared to vary when plants were treated early (2 d after transplanting) as opposed to later (10 d after transplanting); however, application times were not a controlled factor and varied across locations.…”