Trinexapac-ethyl Application Research Articles

Influence of Sequential Trinexapac‐Ethyl Applications on Cytokinin Content in Creeping Bentgrass, Kentucky Bluegrass, and Hybrid Bermudagrass

Trinexapac‐ethyl (TE) is a popular plant growth regulator in the turfgrass industry not only for its effectiveness in reducing mowing requirements but for its positive effects on turf density and appearance. We hypothesized that reported side effects of TE such as increases in color, photochemical efficiency (PE) of photosystem II, tillering, and chlorophyll, may be related to changes in leaf cytokinin content. Our objective was to determine if TE influences leaf trans‐zeatin riboside (t‐ZR) content of three common turfgrass species. Sods of Kentucky bluegrass (Poa pratensis L.), creeping bentgrass (Agrostis stolonifera L.), and hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) were transplanted and grown in flats under a greenhouse mist system. Label‐rate TE treatments were applied every 2 wk for 2 mo. Canopy PE, leaf color, canopy height, and leaf t‐ZR contents were measured every 2 wk in 2003, with leaf total nonstructural carbohydrates (TNC) measurements added in 2004. A significant increase in t‐ZR content was measured following sequential TE treatment in all three species in both years. Leaf TNC was consistently increased following the second TE application in creeping bentgrass and hybrid bermudagrass. While our data are nonspecific as to how TE increases leaf t‐ZR, it appears that a shift in assimilate partitioning to basal organs could be a contributing factor. Whatever the mechanism, increased leaf t‐ZR is likely to confer aesthetic, as well as functional, advantages to treated turfgrasses.

Effects of Trinexapac‐Ethyl Foliar Application on Creeping Bentgrass Responses to Combined Drought and Heat Stress

Simultaneous drought and heat stress is detrimental to turfgrass growth. Growth regulators may influence plant responses to stresses. The objective of this study was to determine effects of pretreatment with trinexapac‐ethyl (TE) on creeping bentgrass (Agrostis stolonifera L.) responses to subsequent exposure to combined heat and drought stress. Plants were treated with TE (1.95 mL L−1 [v/v], Primo Maxx) every 14 d for 42 d and then exposed to combined drought and heat (35°C) in growth chambers. Application of TE increased turf quality and relative water content and chlorophyll content during 21 d of stress. Trinexapac‐ethyl–treated plants had increased growth rate and maintained constant canopy photosynthetic rate (Pn) and photochemical efficiency (Fv/Fm) during the stress period, while these parameters declined for the untreated control. Trinexapac‐ethyl–treated plants maintained lower evapotranspiration rate (ET) under nonstressed control conditions, but higher ET at 21 d of stress. Trinexapac‐ethyl–treated plants showed no differences from untreated plants in osmotic adjustment, and had lower levels of total nonstructural carbohydrates during the stress period. The study suggests that TE application enhanced turf performance under stress, as demonstrated by maintenance of higher turf quality and growth rate during a prolonged period of com bined stress. The beneficial effects of TE on bentgrass stress responses could be related to the maintenance of photosynthetic activities and greater level of cellular hydration. These and other published data indicate that use of TE on creeping bentgrass that seasonally experiences heat and drought stresses could benefit its performance.

PRODUTIVIDADE DE CULTIVARES DE TRIGO EM FUNÇÃO DO TRINEXAPAC-ETHYL E DOSES DE NITROGÊNIO

Visando determinar a dose e a época de aplicação do redutor de crescimento trinexapac-ethyl em cultivares de trigo realizaram-se experimentos na Fazenda Escola da Universidade Estadual de Ponta Grossa, no ano de 2005. O delineamento experimental foi de blocos ao acaso, em esquema fatorial 2 x 2 x 6 com três repetições para cada cultivar de trigo. Os tratamentos constaram de doses de nitrogênio (50 e 240 kg ha-1), épocas de aplicação de trinexapac-ethyl (entre o 1o e o 2o nó e entre o 2o e o 3o nó perceptível) e de doses de trinexapac-ethyl (0; 31,2; 62,5; 93,7; 125,0 e 156,2 g ha-1). Foram utilizadas quatro cultivares de trigo de diferentes respostas ao acamamento: CD-104 (resistente), Vanguarda (moderadamente resistente), Supera (moderadamente suscetível) e CEP-24 (suscetível). Avaliaram-se características agronômicas, severidade de doenças e produtividade. O aumento da dose de nitrogênio resultou em maior produtividade para a cultivar CEP-24; a aplicação mais tardia do trinexapac-ethyl afetou positivamente a produtividade das cultivares CD-104 e CEP-24; o trinexapac-ethyl reduziu a altura das plantas de todas as cultivares; para todas as cultivares a equação de ajuste da produtividade em relação às doses de trinexapac-ethyl foi quadrática ocorrendo um aumento da produção com o aumento da dose do redutor, até um limite (de 63,8 a 132,5 g ha-1), variável com a cultivar.

Plant Growth Regulators Alter Kentucky Bluegrass Canopy Leaf Area and Carbon Exchange

ABSTRACTTurf managers apply plant growth regulators (PGRs) throughout the growing season to reduce clipping production, provide a uniform canopy, and increase color. Reduced efficacy of trinexapac‐ethyl (TE) [4‐(cyclopropyl‐α‐hydroxy‐methylene)‐3,5‐dioxocyclohexanecarboxylic acid ethyl ester] and paclobutrazol (PAC) [(2RS, 3RS)‐1‐(4‐chlorophenyl)‐4,4‐dimethyl‐2‐(1H‐1,2,4‐triazol‐1‐yl) pentan‐3‐ol] has been reported during warmer summer months. Plant growth regulator dissipation and Kentucky bluegrass (KBG; Poa pratensis L.) clipping production, canopy leaf area, and carbon exchange rates (CERs) were measured following single TE or PAC applications applied at three rates and three application timings. Warmer summer conditions reduced the intensity and duration of TE and PAC growth suppression compared to spring applications. Plant growth regulator applications above the manufacturers label rate provided no additional suppression. Residues of PGRs were analyzed by HPLC‐UV. Warmer temperatures increased TE and PAC uptake, but accelerated the rate of PGR dissipation. Carbon exchange rates were measured weekly on ground (CERG) and leaf (CERL) area bases. Treatment with PGRs resulted in decreased leaf area early during inhibition followed by increased rate of leaf area production. Changes in canopy leaf area were greatest in spring and PAC caused the greatest change in leaf area. Changes in CERG reflected changes in leaf area. Paclobutrazol generally increased CERL during periods of clipping suppression, while TE had no effect on CERL.

Doses e épocas de aplicação de redutor de crescimento afetando cultivares de trigo em duas doses de nitrogênio

Os redutores de crescimento têm sido utilizados com sucesso em trigo, evitando o acamamento, mas a recomendação de uso não diferencia cultivares quanto ao porte. Visando determinar a dose e a época de aplicação mais adequadas de trinexapac-ethyl (Moddus), em cultivares de trigo, realizaram-se experimentos na Fazenda Escola da Universidade Estadual de Ponta Grossa, no ano de 2005. O delineamento experimental foi de blocos ao acaso, em esquema fatorial 2 x 2 x 6, com três repetições para cada cultivar de trigo. Os tratamentos constaram de duas doses de nitrogênio (50 e 240 kg ha-1), duas épocas de aplicação de trinexapac-ethyl (entre o 1º e o 2º nó e entre o 2º e o 3º nó perceptível) e de seis doses de trinexapac-ethyl (0, 31,2, 62,5, 93,7, 125,0 e 156,2 g ha-1). Foram utilizados oito cultivares de trigo com diferentes respostas ao acamamento: OR-1, CD-104 e CD-105 (resistentes), Alcover, Ônix e Vanguarda (moderadamente resistentes), Supera (moderadamente suscetível) e CEP24 (suscetível). Avaliaram-se características agronômicas, componentes da produção e produtividade. O clima ameno não foi favorável à ocorrência de acamamento, que foi observado somente para as menores doses de trinexapac-ethyl no cultivar CEP-24. A dose de nitrogênio afetou características da planta e a produtividade de alguns cultivares. O estádio de aplicação de trinexapac-ethyl não afetou de forma substancial a produtividade, e sim a altura das plantas, que foi menor quanto mais tardia a aplicação. Em geral, a equação de ajuste da produtividade em relação às doses de trinexapac-ethyl foi quadrática, ocorrendo aumento da produção com o aumento da dose do redutor, até um limite, variável de acordo com o cultivar.

Effects of Trinexapac-Ethyl on the Salinity Tolerance of Two Ultradwarf Bermudagrass Cultivars

Studies on bermudagrasses (Cynodon spp.) have demonstrated variability in salinity response among species and cultivars. However, information on ultradwarf bermudagrass cultivars in relative salinity tolerance associated with trinexapac-ethyl (TE) [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester], a cyclohexanedione type II plant growth regulator (PGR), remains unknown. Therefore, two replicated greenhouse studies were conducted to determine the salinity tolerance of two ultradwarf bermudagrass cultivars treated with TE on turfgrass quality (TQ), total root biomass, and root and shoot tissue nutrient concentration. Turfgrasses included `TifEagle' and `Champion' bermudagrass (Cynodondactylon(L.) Pers. × C. transvaalensisBurtt-Davy). Daily sodium chloride (NaCl) exposure was 0, 12.90 (8,000 ppm), 25.80 (16,000 ppm), and 38.71 dS·m–1 (24,000 ppm). Biweekly TE applications (active ingredient 0.02 kg·ha–1) were initiated 2 weeks after salinity exposure. `Champion' was more salt-tolerant than `TifEagle' based on TQ and root mass. At 12.90, 25.80, and 38.71 dS·m–1 of NaCl, nontreated (without TE) `Champion' consistently outperformed nontreated `TifEagle' with greater TQ on most rating dates. At 12.90 dS·m–1, TE treated `Champion' (8.0) had greater TQ than nontreated `TifEagle' (6.1) at week 10. Regardless of TE application, after 2 weeks of applying 25.80 dS·m–1 of NaCl, both cultivars fell below acceptable TQ (<7). When averaged across all salinity treatments, applying TE four times at 0.02 kg·a.i./ha in two week intervals enhanced root growth for both bermudagrass cultivars by 25%. Also, both cultivars decreased root mass as salinity levels increased. Non TE-treated `TifEagle' had 56% and 40% less root and shoot Na uptake compared to TE treated cultivars at 25.80 dS·m–1. In conclusion, the two bermudagrass cultivars responded differently when exposed to moderate levels of NaCl.

Response of ‘TifEagle’ Bermudagrass (Cynodon dactylon×C. transvaalensis) to Fenarimol and Trinexapac-Ethyl

Fall applications of fenarimol on hybrid Bermudagrass (Cynodon dactylon×C. transvaalensis) provide effective preemergencePoa annua(L.) control and suppressOphiosphaerellaspp. pathogens; however, concerns exist for turf injury and root growth restrictions. Two 60-d greenhouse studies were conducted to evaluate the effects of fenarimol at 0, 1.6, and 3.2 kg ai/ha per 30 d with and without trinexapac-ethyl (TE) at 0.017 kg ai ha/15 d on ‘TifEagle’ Bermudagrass. Turf color was enhanced by TE 14 d after initial treatment (DAIT) and was continually superior throughout the experiment. Fenarimol at 3.2 kg/ha per 30 d decreased turf color 14 DAIT, but was similar to nontreated turf on all other observation dates. Increased fenarimol rates applied twice caused approximately 10% injury at 42, 49, and 56 d after treatment; however, injury was acceptable after initial and repeat applications. TE reduced clipping yield an average 39% from six sampling dates. Initial fenarimol applications (without TE) reduced clippings by 37% 20 DAIT and repeated applications reduced clippings 40, 50, and 60 DAIT. Increased fenarimol rate linearly decreased root mass for turf treated with and without TE; however, Bermudagrass receiving TE averaged 23% enhanced root mass 60 DAIT over all fenarimol rates. Bermudagrass receiving fenarimol at 0, 1.6, and 3.2 kg/ ha per 30 d with TE averaged 27, 24, and 16% higher root mass, respectively, compared to turf receiving fenarimol without TE. Treatments had no influence on root length. Results indicate that two consecutive fenarimol applications at 1.6 and 3.2 kg/ha per 30 d may cause minor injury to TifEagle Bermudagrass and restrict root growth. Repeated TE applications, however, could decrease injury from fenarimol and enhance rooting relative to fenarimol applied exclusively.

Trinexapac-ethyl Application Regimens Influence Creeping Bentgrass Putting Green Performance

Trinexapac-ethyl (TE) is a plant growth regulator registered for periodic applications on creeping bentgrass greens but ball roll as affected by various TE regimens have not been reported. Field experiments were conducted in Clemson, S.C., from May to July 2003 and 2004 on an `L-93' creeping bentgrass putting green. Turf received a total of 0.2 kg·ha–1 a.i. of TE over 12 weeks in three application regimens: 0.017 kg·ha–1 per week, 0.033 kg·ha–1 per 2 weeks, and 0.05 kg·ha-1 per 3 weeks plus a control. Ball roll distances were measured weekly with a stimpmeter in the morning (900 to 1100 hr) and evening (>1700 hr). Morning ball roll distances were generally longer than evening. Ball roll distances increased from June to July 2003 and from May to July 2004, likely resulting from greater bentgrass summer heat stress during the test period. Turf treated with biweekly and triweekly TE regimens had enhanced ball roll on three and four dates, respectively, but inconsistencies occurred likely from reduced efficacy with greater time between repeated applications. Weekly TE applications enhanced ball roll distances from the untreated by 5% to 8% on six dates. Turf injury did not occur following TE applications regardless of regimen. Overall, weekly TE applications increased ball roll distances more frequently than biweekly and triweekly regimens, but enhancements were inconsistent over the 2 years. Chemical name used: [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (trinexapac-ethyl); (tetrachloroisophthalonitrile) (chlorothalonil); [methyl(E)-2-(2-(6-(2-cyanophenoxy) pyrimidin-4-yloxy)phenyl)-3-methoxyacrylate] (azoxystrobin); [aluminum tris(0-ethyl phosphonate)] (fosetyl-al); [N-(2,6-Dimethylphenyl)-N-(methoxyacetyl) alanine methyl ester] (metalaxyl); [(1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl) -methyl]-14-1,2,4-triazole] (propiconazole).

Growth Response of Three Turfgrass Species to Nitrogen and Trinexapac-ethyl in Shade

Previous research on the potential of the gibberellin inhibiting growth regulator trinexapac-ethyl (TE) [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester] to improve quality and density of shaded turfgrass has been conducted under neutral-density shade. However, some phytochrome-mediated growth responses of turfgrass, such as tillering, are different under deciduous shade versus neutral-density shade. The objectives of this study were to investigate 1) whether TE would result in improved stand density and quality of turfgrass grown under deciduous shade as has been observed under neutral-density shade and 2) the shade tolerance of sheep fescue (Festuca ovina L. `Quatro') compared to tall fescue (Festuca arundinacea Schreb. `Plantation'), and rough bluegrass (Poa trivialis L.). Trinexapac-ethyl at either 0 or 29 kg·ha–1 a.i. and nitrogen at 12 or 36 kg·ha–1 were applied on 23 May, 3 July, and 15 Aug. 2003 and 21 May 2004 to each species in a randomized complete block design under deciduous shade (about 9% of full sun). Clipping yield, color, and density data were collected for 6 weeks after the May applications in each year. Visual quality was assessed for 6 weeks after application in 2004 only. In 2003, TE significantly reduced clipping yields by 35% to 50% on sheep fescue, 58% to 76% on tall fescue and 55% to 80% on rough bluegrass. However, in 2004, yield reduction was 0% to 50% for all three species and there was no interaction between week, TE, and species. `Plantation' tall fescue had the highest overall visual quality and density. Sheep fescue also provided an acceptable quality turf stand. TE application did not significantly impact the quality of these species. Rough bluegrass performance was unacceptable, and high rate applications of TE to this species in shade resulted in significant (P < 0.05) losses in density. Trinexapac-ethyl application, based on the results of this study, may not enhance turf quality of cool season grasses grown under dense tree shade.

Trinexapac-ethyl Affects Kentucky Bluegrass Root Architecture

Trinexapac-ethyl (TE) [4-(cyclopropyl-a-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester] effects on turfgrass root architecture are not known. It has been postulated that PGR application could cause photoassimilate that is normally used for shoot growth to be funneled to root growth. This study evaluated the effects of a single TE application on kentucky bluegrass (KBG) root and shoot growth for seven weeks. Individual KBG plants were grown in a hydroponic system and harvested weekly. At each harvest, tiller height, tiller number, and color ratings were recorded. Estimates of total root length (TRL), root surface area (SA), and average root diameter were measured using the WinRhizo system. Trinexapac-ethyl reduced plant height for 4 weeks followed by a period of postinhibition growth enhancement. Trinexapac-ethyl increased tiller number over the course of the study and slightly enhanced plant color. Trinexapac-ethyl reduced TRL and SA 48% and 46% at 1 week after treatment (WAT) followed by an accelerated growth rate 1 to 4 WAT. Trinexapac-ethyl had no effect on root diameter. On a tiller basis, TE initially reduced TRL and SA 30% and 31%, respectively. Total root length per tiller and root surface area per tiller were reduced by TE treatment, but by 7 WAT, those differences were no longer significant. Initial reductions in TRL and SA per tiller may reduce tiller competitiveness for water and nutrients. Based on data for TRL and SA per tiller, shoot and root growth must be considered in total to fully understand TE effects on plant growth. Field research is needed to corroborate results from hydroponic-studies and examine the effect of various TE rates and multiple applications on turfgrass root and shoot growth.

Use of Trinexepac-ethyl for Growth Regulation of Chrysanthemum (Dendranthema ×grandiflora)

Trinexapac-ethyl (TE) [4-(cyclopropyl-α-hydroxy-methylene)-3, 5-dioxocyclohexanecarboxylic acid ethyl ester] is a plant growth regulator registered for use in turfgrass. The objective of the research reported in this paper was to determine if TE could be used in the production of florist chrysanthemums (Dendranthema ×grandiflora) to produce more compact, higher value plants. Foliar applications of TE to non-pinched plants of the tall cultivar `Billings' reduced canopy height 8% to 40% as the amount of applied TE was increased from 6.25 × 10–5 to 2.0 × 10–3 g. The effects of TE varied among chrysanthemum cultivars. Growth inhibition of pinched plants among the various cultivars ranged from 7% (`White Viewtime') to 23% (`White Graceland') 28 days following a single application of 1.0 × 10–3 g TE. In most cultivars, the inhibitory action of TE was not observed after 28 days. In fact some cultivars exhibited a rebound effect during the post-suppression growth phase in which internode extension rates were greater in TE-treated plants than controls. Both the number and timing of the TE application affected efficacy. A second TE application 5 weeks after the first treatment, or application of TE at the appearance of flower buds produced the highest quality crop in terms of uniformity and compactness, with overall height reduction generally 15% to 20%. No differences in flower color, number, or mass per flower were observed due to TE application.

Total Nonstructural Carbohydrate Storage in Creeping Bentgrass Treated with Trinexapac-ethyl

Total nonstructural carbohydrates (TNC) are important for summer recuperation from injury for cool-season turfgrass. The objectives of this study were to determine if trinexapac-ethyl (TE) [4-(cyclopropyl-a-hydroxy-methylene)-3,5-dioxo-cyclohexane-carboxylic acid ethyl ester] affects TNC content and turf quality of a creeping bentgrass at various application frequencies and rates and to investigate any interactions between the effects of TE and traffic treatments on TNC content. Field experiments were conducted in 1995 and 1996 on a mature stand of `Pennlinks' creeping bentgrass grown on a Flanagan silt loam soil maintained at a height of 1.9 cm. Treatments included a single application (0.28 kg·ha-1) or repeat applications at 2 (0.06 kg·ha-1) or 4 (one at 0.28 kg·ha-1 and one at 0.09 kg·ha-1) week intervals during the first 8 weeks of each experiment. Treatments were arranged in a strip-plot design with TE applications as whole plots and traffic treatments as strip plots. Traffic treatments began at 2 weeks and 2 days after initial applications in 1995 and 1996, respectively and continued until the last evaluation date. Traffic treatments consisted of 4 passes of a 102.2 kg smooth roller, 2 days·week-1 in 1995 and 8 passes daily in 1996. A single aqueous extraction method was used for quantification of glucose, fructose, sucrose, and fructan. TNC was the total of all analyzed fractions. Single applications of TE at 0.28 kg·ha-1 significantly reduced turf quality for 4 weeks in both experiments. Sequential applications of TE at 0.06 kg·ha-1 exhibited reduced quality compared to the control at 4 and 8 weeks in 1995 and 2 weeks in 1996. When TE was applied once at 0.28 kg·ha-1, there was a significant reduction in TNC from 4 to 8 weeks after treatment. In 1996 when TE applications were repeated at 2 and 4 week intervals at 0.06 and 0.09 kg·ha-1, a reduction of TNC from week 4 to week 14 was observed. After 14 weeks the TNC content showed incremental increases. There was no interaction effect between traffic treatments and TE applications in the verdure TNC in either year. In 1996, verdure TNC content was 6% to 17% lower in plots receiving traffic from weeks 4 to 18. These results suggest that high rates of TE, either sequential or single applications, might reduce turf quality or carbohydrate content. While this study has not examined if this is detrimental, multiple TE applications at low rates may minimize any TNC reduction while providing effective growth suppression for extended periods.

Nitrogen Use in Tifway Bermudagrass, as Affected by Trinexapac‐Ethyl

Nutrient movement from turfgrass systems into surface and ground water is a public concern. Data indicate that actively growing turf rapidly immobilizes applied N, thus restricting nutrient movement. It is possible, however, that growth suppression with plant growth regulators (PGRs) could reduce N demand and thus N uptake, resulting in greater leaching losses. An experiment was conducted with column lysimeters to investigate the effects of trinexapac‐ethyl (TE) on nitrate leaching and N‐use efficiency in Tifway bermudagrass (Cynodon dactylon × C. transvaalensis). The experiment was conducted in a growth chamber with day/night temperature set at 29/24°C and a 12‐h photoperiod. Trinexapac‐ethyl was applied twice at 4‐wk intervals at 0.11 kg a.i. ha−1 Ammonium nitrate (AN) was applied at 50 kg N ha−1 2 wk after each TE application, and again 6 wk after the second TE application. Separate sets of columns received 15N‐labeled AN for the first two applications. Irrigation was scheduled to provide a leaching fraction of ≈50%; leachate was collected after each irrigation and analyzed for nitrate and ammonium. Cumulative nitrate leaching was unaffected by TE after the first two N applications, but was reduced ≈60% by TE following the third N application. Trinexapac‐ethyl reduced 15N allocation to clippings by ≈25% and increased 15N allocation to roots and rhizomes; total recovery of applied 15N in tissues was ≈65%. Results demonstrate chemical growth suppression with TE does not reduce N uptake or increase nitrate leaching from bermudagrass.

Shade performance of a range of turfgrass species improved by trinexapac-ethyl

The increased use of enclosed sports stadiums produces shade conditions that seriously affect the quality of turfgrass surfaces, by encouraging undesirable excess vertical succulent growth. Plant growth regulators offer an opportunity to modify a plant’s growth habit, to enable it to be better adapted to a shady environment. To examine growth response to the plant growth regulator, trinexapac-ethyl, cool-season temperate turfgrasses (Kentucky bluegrass–perennial ryegrass, Poa pratensis L./Lolium perenne L.; creeping bentgrass, Agrostis palustris Huds.; supina bluegrass, Poa supina Schrad.; and tall fescue, Festuca arundinacea Schreb.) and a warm-season species (Bermudagrass, Cynodon dactylon L.) were established in a field experiment. Main treatments were 4 levels of shade (0, 26, 56 or 65% shade), with or without trinexapac-ethyl at a rate of 0.5 kg/ha. A pot experiment measured the vertical shoot growth rates of Kentucky bluegrass–perennial ryegrass and tall fescue under 0, 56 or 65% shade, with and without trinexapac-ethyl. Both experiments were conducted under ambient conditions. Light readings taken in full sunlight, at midday through summer and autumn (major period of assessment), ranged from 1350 to 1950 μmol/m2.s. Trinexapac-ethyl reduced vertical growth of all turfgrass species. This resulted in decreased clipping weights and in clipping material having an increased dry matter percentage (i.e. reduced succulence). The impact of trinexapac-ethyl on sward quality and colour was dependent on shade level, for all species. At 56 and 65% shade, quality and colour improvement was maximised with trinexapac-ethyl application; the magnitude of improvement was dependent on species, with Kentucky bluegrass–perennial ryegrass and bentgrass showing the most benefit. It was concluded that trinexapac-ethyl improved the shade performance of a number of turfgrass species commonly used in high quality turf surfaces. It may offer the potential to reduce costs of managing turf in such an environment.

Trinexapac-ethyl, Propiconazole, Iron, and Biostimulant Effects on Shaded Creeping Bentgrass

Creeping bentgrass (Agrostis stolonifera) is used extensively on temperate zone golf course greens, tees, and fairways, but often performs poorly in shade. Previous research has indicated that sequential applications of gibberellic acid (GA) inhibiting plant growth regulators (PGRs) such as trinexapac-ethyl (TE) increase cool-season turfgrass performance in 70-90% shade. This research was conducted to: 1) confirm appropriate TE application rates and frequencies for maintaining `Penncross' creeping bentgrass in dense shade in the mid-Atlantic region of the U.S.; 2) determine the efficacy of other PGRs, biostimulants, and iron (Fe); and 3) assess whether the addition of a biostimulant with TE would have additive, synergistic, or negative effects. The other compounds tested against TE and the control were: propiconazole (PPC), iron sulfate, CPR (a seaweed and iron containing biostimulant), and a generic seaweed extract (SWE) (Ascophyllum nodosum) plus humic acid (HA) combination. These treatments were applied to 88% shaded bentgrass every 14 days from May or June through October in 2001 and 2002, with turf quality, leaf color, root strength, photochemical efficiency, and antioxidant enzyme superoxide dismutase (SOD) activity being determined. While the quality of control plots fell below a commercially acceptable level by the second month of the trial, repeated foliar TE application provided 33% to 44% better quality throughout the experiment. Propiconazole resulted in 13% to 17% better quality through September of each year. Trinexapac-ethyl and PPC resulted in darker leaf color and increased mid-trial root strength by 27% and 29%, respectively. Canopy photochemical efficiency and leaf SOD activity were also increased due to TE in August of both years. Treatment with Fe, CPR, or SWE+HA did not have an effect on quality, root strength, SOD, or photochemical efficiency, but periodic increases in color were observed. The addition of CPR to TE in 2002 provided results that were not different from those of TE-alone. This and previous studies indicate that restricting leaf elongation with anti-GA PGRs is of primary importance for improving shade tolerance, while treatments that increase leaf color or chlorophyll levels without restricting leaf elongation are relatively ineffective.

Light Intensity Affects Gibberellic Acid Content in Kentucky Bluegrass

Turfgrasses grown under low light conditions generally exhibit increased shoot elongation. Gibberellic acids (GAs), GA1 in particular, promote stem elongation in grass species. GA20 is the immediate precursor of GA1. However, a direct quantitative measurement of GA1 and GA20 has not been reported for turfgrass under different light intensities. This study was conducted in a greenhouse to quantify the endogenous levels of GA1 and GA20 of `KenblueTimes', `Livingston', and `NuGlade' Kentucky bluegrass (Poa pratensis L.) under two light intensities with and without trinexapacethyl (TE) application. GA1 and GA20 content in leaf tissue were analyzed using gas chromatography-mass spectrometry with deuterium-labeled GA1 and GA20 as internal standards. Light reduction of 73% under greenhouse conditions increased GA1 by 44% to 47% and GA20 by 16% to 50%. `NuGlade' had a GA1 content 20% lower than that of `Kenblue', suggesting that the dwarf characteristics of `NuGlade' may be related to its low GA1 content. The application of TE (0.1 kg·ha-1) reduced GA1 concentration by 47%, but increased GA20 concentration by 146%, supporting the contention that TE inhibited GA1 biosynthesis by blocking the conversion of GA20 to GA1. Chemical names used: 4-(cyclopropyl- -hydroxy-methylene)-3,5-dioxo-cyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl); gibberellic acid (GA).

Efeito de regulador de crescimento na cultura de trigo submetido a diferentes doses de nitrogênio e densidades de plantas

Com o objetivo de avaliar os efeitos de um regulador de crescimento no cultivar de trigo IAPAR-53, em diferentes densidades de plantas e submetido a diferentes doses de nitrogênio, instalou-se um experimento na Fazenda-Escola da UEPG em Ponta Grossa-PR, no ano de 1999. O delineamento experimental foi o de blocos ao acaso, em esquema fatorial 2 x 3 x 4, com quatro repetições. Os tratamentos constaram da aplicação de 125 g i.a. ha-1 de trinexapac-ethyl e testemunha sem aplicação, em densidades de 44, 60 e 75 plantas m-1, no espaçamento de 0,17 m entre fileiras e nas doses de 0, 45, 90 e 135 kg ha-1 de nitrogênio em cobertura. A aplicação de trinexapac-ethyl resultou em plantas com menor massa seca, entrenós mais curtos, maior diâmetro do caule e aumento do número de espigas m-1, de grãos por espiga e produtividade. Com o aumento da dose de nitrogênio ocorreu aumento da estatura das plantas, do número de espigas m-1, do peso de mil grãos e da produtividade. Com o aumento da densidade de plantas, o diâmetro do caule, a massa seca das plantas e o número de grãos por espiga diminuíram e o número de espigas m-1 e o peso de mil grãos aumentaram, sem efeitos na produtividade. Não foi observado acamamento em nenhum dos tratamentos.

Turf Quality and Freezing Tolerance of ‘Tifway’ Bermudagrass as Affected by Late‐Season Nitrogen and Trinexapac‐Ethyl

Bermudagrass [Cynodon dactylon (L.) Pers.] is the most widely used species for intensively managed turf sites in the southern United States and in the transition zone. However, the lack of cold tolerance in many cultivars can result in significant winter injury. There is a limited body of information in the literature regarding management of bermudagrass to enhance cold tolerance, especially as it relates to N nutrition and the use of plant growth regulators (PGRs). As such, a 2-yr field study (1998-1999 and 1999-2000) was conducted to examine the effects of late season N fertilization and trinexapac-ethyl (TE) applications on morphology, quality, and freezing tolerance of 'Tifway' bermudagrass. During both years, monthly N applications were terminated on either 15 July, 15 August, or 15 September, while applications of TE were made on 15 August; 15 August and 15 September; or 15 August, 15 September, and 15 October. Late season applications of N and TE enhanced the fall green color retention of bermudagrass and promoted early spring green-up (SGU). Neither N nor TE had a consistent effect on growth and development of bermudagrass rhizomes or stolons, and neither treatment had a consistent effect on the freeze tolerance of rhizomes. However, a positive attribute of these treatments is a significant increase in the overall green period of bermudagrass (20-25 d), which can prolong the playability of high maintenance sports facilities. From these studies we have concluded that, contrary to what is commonly believed, late season applications of N did not affect the freeze tolerance of bermudagrass rhizomes.

Lack of Competitive Success of an Intraseeded Creeping Bentgrass Cultivar into an Established Putting Green

Intraseeding is a popular approach for converting established golf course putting greens to a more desirable cultivar of the same species without killing the existing turf. This study was conducted to determine the competitive success of an intraseeded creeping bentgrass (Agrostis palustris Huds.) cultivar in an established putting green using random amplified polymorphic DNA (RAPD) markers. Two replicate, United States Golf Association (USGA) specification greens, established with ‘Penncross’ creeping bentgrass, were arranged in a randomized complete block design with five conversion treatments as follows: control, scalping, coring, a trinexapac-ethyl application, and a glyphosate application. Vertical mowing and topdressing were followed by subsequent seeding with ‘Penn G-2’ creeping bentgrass (G-2) in two directions at 12.2 kg seed ha−1 Treatments were performed in October 1998, April 1999, and September 1999. Pretreatment samples taken from each plot on 22 Sept. 1998 and posttreatment samples taken on 28 May 1999 and 24 Mar. 2000 were evaluated for changes in population dynamics using RAPD markers. By the end of the study, both glyphosate-treated plots had completely shifted to G-2, while plots subjected to other treatments showed no evidence of the cultivar. The detection of G-2 in samples collected on 28 May 1999 suggested that a transient change occurred in the scalp (Exp. 2) treatment; however, evidence of G-2 was no longer evident on 24 Mar. 2000. Data indicated that the effectiveness of the intraseeding techniques and timings used in this study to convert putting greens to a new cultivar were quite limited. This may have been due to unsuccessful elimination of root competition from the existing turf. Until more effective intraseeding methods are developed, chemical renovation remains the most effective way to ensure the establishment of new cultivars.

Trinexapac-ethyl Restricts Shoot Growth and Prolongs Stand Density of 'Meyer' Zoysiagrass Fairway Under Shade

'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)