The effects of trinexapac-ethyl (TE) on the anatomical and biochemical composition of turfgrasses and their implications for its field use are poorly understood. Two greenhouse experiments were conducted to determine if application of TE increased Kentucky bluegrass (Poa pratensis L.) leaf blade cell density, chlorophyll concentration, or structural carbohydrate content. Kentucky bluegrass (KB) sod was harvested from the field, established in greenhouse pots, and sprayed with 0.27 kg·ha-1 a.i. TE. Leaf blade samples were collected 4 weeks after treatment (WAT), fixed in glutaraldehyde, and embedded in Spurr resin. Photomicrographs of longitudinal leaf blade sections were used to determine cell density, cell length, and cell width. Chlorophyll and structural carbohydrate contents were determined at 2 and 4 WAT. Treatment with TE increased cell density and chlorophyll-b concentration, while reducing cell length, but structural carbohydrate content was unaffected. Chemical name used: 4-cyclopropyl-α-hydroxy-methylene-3,5-dioxo-cyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl).
A growth chamber and a greenhouse study were conducted to determine if successive applications of trinexapac-ethyl (TE) to developing perennial ryegrass (Lolium perenne L.) plants would reduce leaf elongation rate (LER) while increasing tiller number and root mass. Growth parameters measured were LER, tiller number, and root mass. In the growth chamber, developing perennial ryegrass plants were sprayed twice with TE at 0.24 kg·ha-1 a.i. at 20 and 40 days after emergence. Leaf elongation rate was reduced by ≈35% following two applications of TE in both growth chamber experiments. This treatment increased the number of tillers per plant in the growth chamber at 60 days after emergence and in the greenhouse at 150 days after emergence, but had no effect on root or shoot mass in either location. Multiple applications of TE to developing perennial ryegrass turfs may favor quicker establishment in terms of tillering, while substantially reducing mowing requirement. Chemical names used: 4-cyclopropyl-α-hydroxy-methylene-3,5-dioxo-cyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl).
Creeping bentgrass (Agrostis palustris Huds.) is an extensively used cool-season grass for fine turf areas such as golf course putting greens, but suffers from poor summer stress tolerance. These studies were conducted to investigate the influences of natural plant growth regulators (NPGR) and Fe on creeping bentgrass photochemical activity (PA), antioxidant superoxide dismutase (SOD) activity, root growth and leaf color under two fertilization regimes. The bentgrass was maintained in well-watered field conditions or water-stressed glasshouse conditions. A mature bentgrass was treated monthly during the field season with seaweed (Ascophyllum nodosum Jol.) extract (SWE) at 50 mg·m-2 or humic acid (HA) at 150 mg·m-2 or in combination with or without FeSO4 at 520 mg·m-2 and grown under a low or a high fertilization regime. Foliar application of SWE + Fe increased PA (14% to 15%), while applications of SWE + HA or SWE + HA + Fe increased SOD activity (49% to 114%) of creeping bentgrass in Summer 1997 and Summer 1998. There was no significant fertilization × NPGR interaction for PA and SOD activity. Bentgrass PA was increased by 13% to 46% when treated with NPGR with or without Fe compared to the control measured in May. The addition of Fe with each NPGR application improved fall and winter leaf color. All NPGR and Fe treatments increased root mass (17% to 29%) in Aug. 1997 and 1998, except HA alone in 1998. Under sustained low soil moisture (-0.5 MPa) conditions, application of NPGR with or without Fe increased PA and SOD activity. The data indicate that SWE and HA enhance the physiological function of `Southshore' creeping bentgrass, resulting in improved root growth regardless of low or high fertilization regime. However, addition of Fe to these NPGR served primarily to improve late season leaf color. The results suggest that, in addition to maintaining adequate plant-available nutrients, applications of natural PGRs, such as SWE and HA, prior to and during summer abiotic stresses would be beneficial.
Decline of sod quality during the transportation, storage, and transplant stages of sale is a primary economic concern of sod producers. However, the mechanisms of extending sod quality during storage, transportation, and transplantation remain unclear. This study was conducted to investigate the influences of selected plant metabolic enhancers (PMEs) seaweed (Ascophyllum nodosum Jol.) extract (SWE), humic acid [93% a.i. (HA)], and propiconazole (PPC), on sod tolerance to stress during storage and posttransplant root growth of tall fescue (Festuca arundinacea Schreb.) sod. The SWE + HA, and PPC were applied alone, or in a combination, to tall fescue 2 weeks before harvest. Photochemical efficiency (PE) of photosystem II was measured immediately before harvest. The harvested sod was subjected to high temperature stress (40 °C) for 72 or 96 hours. The heated sod was replanted in the field and posttransplant injury and root strength were determined. On average over 1999 and 2000, application of SWE (50 mg·m-2) + HA (150 mg·m-2), PPC (0.30 mL·m-2), and a combination of SWE + HA with PPC (0.15 mL·m-2), enhanced PE of preharvest sod by 8.5%, 9.1%, and 11.2%, respectively, and increased posttransplant rooting by 20.6%, 34.6%, and 20.2%, respectively. All PME treatments reduced visual injury except SWE + HA and SWE + HA + PPC in 1999. Extension of heat duration from 72 to 96 hours caused significantly more injury to the sod and reduced posttransplant rooting by 22.9% averaged over 2 years. The data suggest that foliar application of SWE + HA, PPC alone, or in a combination with SWE + HA, may reduce shipment heat injury and improve posttransplant rooting and quality of tall fescue sod. Chemical name used: 1-(2-(2,4-dichloropheny)-4-propyl-1,3-dioxolan-2yl)methyl-1-H-1,2,4-triazole [propiconazole (PPC)].
Bermudagrass [Cynodon dactylon (L.) Pers.] is widely used along its northern limit of adaptation. However, cold hardiness and winter survival are common concerns facing turfgrass managers in these areas. The objective of this study was to determine the effects of moderate salinity applications on bermudagrass cold hardiness. Two trials were conducted in Summer 2002. The cultivar Princess was seeded into pots in a glasshouse at a rate of 24 kg·ha-1. Pots received a weekly solution of 20-20-20 at a rate of 4.9 kg·ha-1 N. Bi-weekly salinity treatments began ≈2 months after germination and consisted of 0, 5, 20, and 40 dS·m-1 in the form of NaCl. These treatments continued for ≈8 weeks. Weekly quality ratings and chlorophyll fluorescence measurements showed similar results, with the high salinity treatments having the poorest quality. Soil electrical conductivity measurements showed a significant increase for the high salinity rates over the lower rates at the end of the trials. Proline concentrations increased with increasing salinity treatments in Trial 1 and were highest with the 20 dS·m-1 rate in Trial 2. Plants were acclimated in a growth chamber, and artificial freezing tests revealed that the 5 and 20 dS·m-1 treatments had the highest percentage of regrowth after freezing. These results indicate that moderate applications of salt or the use of effluent water prior to hardening may be an important way to increase bermudagrass cold hardiness.
'Meyer' zoysiagrass (Zoysia japonica Steud.) is a popular turfgrass species for transition zone golf course fairways and tees because it is generally winter hardy while providing an excellent playing surface with minimal chemical and irrigation inputs. However, its functionality declines readily on many of the shaded areas on these courses. Reduced irradiance causes excessive shoot elongation, reduced tillering, and weak plants that are poorly suited to tolerate or recover from traffic and divoting. Trinexapac-ethyl (TE) effectively reduces gibberellic acid (GA) biosynthesis and subsequent shoot cell elongation. The objective of this study was to determine if monthly applications of TE would reduce shoot elongation of 'Meyer' zoysiagrass and improve stand persistence under two levels of shade. Shade structures were constructed in the field that continuously restricted 77% and 89% irradiance. A mature stand of 'Meyer' was treated with all combinations of three levels of shade (0%, 77%, and 89%) and three levels of monthly TE application [0, 48 g·ha-1 a.i. (0.5×), and 96 g·ha-1 a.i. (1×)] in 1998 and 1999. In full sun, the 0.5×-rate reduced clipping production by 17% to 20% over a four-week period and the 1×-rate by 30% to 37%. Monthly application of TE at the 1×-rate increased 'Meyer' tiller density in full sun and under 77% shade. Both rates of TE consistently reduced shoot growth under shade relative to the shaded control. Only the monthly applications at the 1×-rate consistently delayed loss of quality under 77% shade. The zoysiagrass persisted very poorly under 89% shade whether treated or not with TE and plots were mostly dead at the end of the experiment. Our results indicate TE can be an effective management practice to increase 'Meyer' zoysiagrass persistence in shaded environments. Chemical name used: 4-cyclopropyl-α-hydroxy-methylene-3,5-dioxocyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl)