Plant Growth Retardant Drench Efficacy Is Not Affected by Substrate Containing Parboiled Rice Hulls

Abstract

<jats:p>Parboiled rice hulls have become a more common component of soilless growing substrates. While there have been reports that some organic substrate components reduce the efficacy of plant growth retardant (PGR) drenches, the influence of rice hulls on PGR drenches is unknown. ‘Callie Deep Yellow’ calibrachoa (<jats:italic>Calibrachoa</jats:italic> ×<jats:italic>hybrid</jats:italic>) and ‘Delta Orange Blotch’ pansy (<jats:italic>Viola wittrockiana</jats:italic>) were planted in containers filled with substrate containing (v/v) 80% peat and 20% perlite or parboiled rice hulls. After planting, 2.5-fl oz drenches containing deionized water or ancymidol, paclobutrazol, or uniconazole were applied to plants grown in each substrate. Plant growth retardants, but not substrate, affected growth rate, and final stem length of calibrachoa and plant height of pansy. There were no differences in regression model coefficients between substrates within PGR applications for plant height (pansy) or stem length (calibrachoa) over the course of the experiment. Paclobutrazol (2.0 or 4.0 ppm) and uniconazole (1.0 or 2.0 ppm), but not ancymidol (1.0 or 2.0 ppm) suppressed final stem length of calibrachoa. Final height of pansy was suppressed by each concentration of paclobutrazol and uniconazole and 2.0 ppm ancymidol, but not 1.0 ppm ancymidol. Based on these results, rice hulls did not reduce PGR drench efficacy when included as a substrate component comprising (v/v) 20% of a substrate.</jats:p>

Ethephon Substrate Drenches Inhibit Stem Extension of Floriculture Crops

“…Plant growth regulators (PGRs) are commonly used in greenhouse production to produce uniform, compact plants that can be easily shipped and marketed to consumers (Currey et al, 2010). Foliar sprays, substrate drenches, liner dips, or bulb, tuber, and rhizome soaks or dips are common application methods for PGRs and one or more of these techniques are appropriate for nearly every active ingredient (Barrett, 2004;Blanchard and Runkle, 2007;Currey et al, 2010;Whipker and McCall, 2000). The majority of synthetic PGRs suppress stem elongation by inhibiting gibberellin biosynthesis (Davis et al, 1988;Rademacher, 2000).…”

“…Substrate drenches of many PGRs provide more uniform results and increase the duration of effectiveness compared with foliar sprays (Boldt, 2008;Gent and McAvoy, 2000). Applying antigibberellin substrate drenches containing flurprimidol, paclobutrazol, or uniconazole early in the production of Euphorbia, Lilium longiflorum, and bedding plants is a PGR application strategy for height control (Barrett, 2004;Currey et al, 2010;Currey and Lopez, 2011;Lopez and Runkle, 2007;Runkle et al, 2006).…”

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

“…The majority of PGR applications are administered using either foliar sprays or substrate drenches (Gent and McAvoy, 2000). 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).…”

Quantifying the Effects of Crop-cultural Practices on Growth and Development of Herbaceous Annuals and Perennials in Novel Bioplastic Biocontainers

“…Triazoles are the most effective class of PGR labeled for use on flowering ornamental plants; growth control of flowering plants can be achieved when using substrate drench concentrations as low as 0.05 mg•L -1 (Currey and Lopez, 2011). Efficacy of PGR applications can be affected by plant genetics (Currey et al, 2016a), active ingredient (Currey et al, 2016b), application method (Hawkins et al, 2015), and, in the case of substrate drenches, substrate components (Barrett, 1982;Bonaminio and Larson, 1978;Currey et al, 2010). Triazole PGRs are readily absorbed by organic substrate components such as sphagnum peat moss (Barrett, 1982), and the addition of organic substrate amendments affects drench efficacy differently.…”

“…Triazole PGRs are readily absorbed by organic substrate components such as sphagnum peat moss (Barrett, 1982), and the addition of organic substrate amendments affects drench efficacy differently. When pine bark is included as a substrate component, the efficacy of PGR drenches is reduced (Bonaminio and Larson, 1978), whereas the presence of parboiled rice hulls in substrate does not affect efficacy (Currey et al, 2010).…”