The vegetative establishment of warm-season turfgrasses is achieved by spreading large quantities of propagation material at the soil surface and subsequently encouraging growing points to generate new plants (Dunn and Diesburg, 2004). A more efficient use of the propagation material by placing sprigs at a pre-established precise depth in the soil and with defined spacing is expected to produce a higher percentage of buds converted into new stems and a more uniform plant density. Precision seeding is routinely adopted for several field crops. Properly sized sprigs could fit precision seeding machinery thus with the potential of being planted at a defined depth and spacing.
Gibberellic acid inhibitors such as TE and PB routinely are used in fine turfs. Treatments are carried out to reduce leaf growth or seed head formation while preserving stolon growth (McCarty, 2011). Volterrani et al. (2012) reported a significant reduction of stolon length when TE was applied on ‘Patriot’ hybrid bermudagrass over the labeled rate. The available data on hybrid bermudagrass for PB only refers to the effects on clipping yield, root mass, root length, and shoot density of dwarf types (McCullough, 2005a, 2005b).
Chlormequat chloride also belongs to the group of GA inhibitors but is currently labeled for grain crops and ornamental plants. Its use on hybrid bermudagrass was reported by Youngner and Nudjie (1974) who recorded a slight delay in root growth, a decrease in internode elongation, and a nodal branching stimulation.
The potential use of triazoles as plant growth regulators, such as PB and PPC, was first attributed to their interference with the GA synthesis pathway (Fletcher et al., 2000). Brassinosteroids were then identified as phytohormones involved in several growth responses such as cell and stem elongation, and PPC has been recognized as a specific suppressor of their synthetic pathway (Hartwig et al., 2012; Sekimata et al., 2002). The application of PPC as a plant growth regulator on turfgrasses was reported by Ervin et al. (2004) who recorded an increase in quality and color when 0.22 kg·ha−1 PPC were applied to a creeping bentgrass (Agrostis stolonifera) sward grown in shaded conditions.
In addition to products intended for growth regulation, several other compounds are known to induce growth suppression. A number of active ingredients that are listed in herbicides share a similar mode of action with PGRs and, when applied to plants at rates far below the recommended rate for herbicidal action, they produce sublethal effects that result in growth suppression (Ervin and Zhang, 2008).
DQ is listed as a growth inhibitor herbicide, but little is known about its use on turfgrasses. Suppression of flower initiation in sugarcane (Saccharum officinarum) (Meyer et al., 2013) seems to be the only current use of DQ as a growth regulator. FS belongs to the sulfonylurea herbicides, some of which are listed as growth regulators (Watschke et al., 1992). McCullough et al. (2011) tested FS for the plant growth regulation of seashore paspalum (Paspalum vaginatum), achieving up to 75% clipping reduction and up to 86% seed head suppression compared with the untreated control.
Glyphosate inhibits the aromatic amino acid biosynthesis, which ultimately leads to a slow cessation of growth (Arteca, 1996). Johnson (1990) documented plant growth reduction on bahiagrass (Paspalum notatum) treated with the isopropylamine GP salt at 0.2 kg·ha−1.
EP and GA are classified as hormonal compounds because they are phytohormones or mimic the action of phytohormones (Ervin and Zhang, 2008). GA is labeled for turfgrass use with the aim of initiating or maintaining growth and preventing color changes in bermudagrasses (Cynodon sp.) during periods of cold stress (Ervin and Zhang, 2008). Besides these effects, the increase in stolon growth has been reported for common bermudagrass (Cynodon dactylon) (Juska, 1958).
EP is labeled for annual bluegrass (Poa annua) seed head suppression and for regulating the growth of cool season turfgrasses; however, experimental applications on bermudagrasses have been reported by several authors (Brosnan et al., 2010; McCarty et al., 2011; McCullough et al., 2004). Results obtained by Shatters et al. (1998) indicated an increase in the rate of shoot formation from crowns of ‘Tifton 85’ common bermudagrass treated with EP.
Most information on PGRs is related to field applications for biomass reduction, and little is known about stolon growth regulation in pot-grown turfgrasses. We carried out a preliminary screening on products known to act as PGRs to explore their potential use for controlling stolon development and elongation in pot-grown hybrid bermudagrass. We also assessed the effects of tested treatments on sward characteristics to identify the products or application rates that are potentially harmful to plants.
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