Trinexapac-ethyl Application Research Articles

Bacterial etiolation of creeping bentgrass as influenced by biostimulants and trinexapac-ethyl

Bacterial etiolation, caused by Acidovorax avenae and Xanthomonas translucens, has become a widespread problem in turfgrass throughout the U.S. Various management tactics are used in managing this disease and differ among turfgrass managers. The use of biostimulants and trinexapac-ethyl (TE) has become a staple in putting green management and many products have been associated with etiolation outbreaks. Experiments performed in field and controlled environments evaluated the impact of commercial biostimulants and TE on etiolation of creeping bentgrass (Agrostis stolonifera L. c.v. ‘Penn A-1’) caused by both A. avenae and X. translucens. In the field, a factorial study was arranged as a split-plot randomized complete block design with 4 replications. The main plot consisted of biostimulants (Knife Plus, CytoGro, Astron, Nitrozyme, PerkUp, BioMax, and none) applied at label rates while the subplot treatments consisted of TE application frequency (0.049 kg ha−1 applied at 7 d, 14 d, and none). For controlled environment experiments, biostimulant and TE treatments were arranged in a randomized complete block design with 4 replications. Bacterial etiolation was measured regularly when present using a grid count to determine the percent area exhibiting etiolation in the field while etiolated turfgrass plants were counted individually in controlled environments. Turf quality was also rated using a scale of 1–9 with 1 = completely dead, 9 = best, and 5 = minimum acceptable turf quality for all experiments. Biostimulant treatments did not have a significant effect on etiolation caused by either bacterium. Trinexapac-ethyl decreased etiolation caused by X. translucens and increased etiolation caused by A. avenae. These results support the necessity of identifying bacteria associated with etiolation as variable effects were observed with TE treatments. These factors should be considered when developing plant growth regulator programs if etiolation is problematic. Future research to evaluate phytohormone production in these bacteria may improve our understanding of etiolation development while improving methods for control.

Regulation with Trinexapac-ethyl and Dew Removal at the Time of Fungicide Application Did Not Influence Dollar Spot Control

Dollar spot, caused by Sclerotinia homoeocarpa F.T. Bennett, is an important disease of creeping bentgrass (Agrostis stolonifera L.) on golf courses in the northern United States. Canopy moisture in the form of dew plays an important role in the development of dollar spot and routine displacement has been shown to reduce disease severity. The use of plant growth regulators (PGRs) is a common management practice for maintaining creeping bentgrass fairways, but their influence on dollar spot is unclear. The objective of this field study was to elucidate the influence of dew removal at the time of fungicide application on dollar spot control in creeping bentgrass regulated by trinexapac-ethyl (TE). Main factors in the study included three dew removal strategies (non-treated, dew removed–mowed, and dew removed–not mowed) before the application of four fungicide treatments (non-treated, chlorothalonil, propiconazole, and iprodione). All fungicide treatments were applied once to turfgrass previously treated with TE or not treated. The presence or absence of dew at the time of fungicide application generally had no influence on fungicide performance with respect to dollar spot control. Based on the results of this study, dew removal before the application of fungicides targeting dollar spot is unnecessary. Applications of TE before fungicides reduced dollar spot severity in some cases, but reductions in symptom expression were limited and did not result in markedly improved dollar spot control.

Influence of trinexapac-ethyl in improving drought resistance of wheatgrass and tall fescue

Various methods are available for improving drought resistance in turfgrasses. Several studies have reported the application of plant growth regulators as an effective method for reducing drought stress effects. A factorial experiment based on a randomized complete block design with three replications was performed in 2011 and 2012 to investigate the effects of the gibberellic acid (GA) inhibitors trinexapac-ethyl (TE) and drought stress on the physiological responses of wheatgrass (Agropyron desertorum) and tall fescue (Festuca arundinacea) to drought stress. The foliage of wheatgrass and tall fescue were sprayed with 1.95 ml L−1 TE at 0.113 % a.i. 14 days prior to and at the beginning of the drought stress. Both TE-treated and untreated plants were placed to well-watered and no water circumstances for 45 days in field conditions. Results indicated that drought stress reduced turf quality (color, density, and uniformity), relative water content (RWC), and total chlorophyll content, but increased proline content, electrolyte leakage (EL), malondialdehyde (MDA) and soluble sugar content (SSC) in both species. Superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and peroxidase (POD) activities in the two turfgrass species initially increased transiently, but declined subsequently. TE application increased SOD, APX, POX, and CAT activities, especially under drought stress conditions. Correlation analysis showed that there were significantly positive correlation between turf quality and RWC and negative correlation between turf quality and proline content, EL, MDA and SSC in both species. The use of TE seems to have enhanced resistance to drought stress in both species by improving proline, SSC and antioxidant activities.

Trinexapac-ethyl rate and application timing effects on seed yield and yield components in tall fescue

Trinexapac-ethyl (TE) has been used for lodging control and seed yield enhancement in several grass seed crop species but little is known about how this plant growth regulator (PGR) performs in tall fescue [Schedonorus arundinaceus (Shreb.) Dumort.]. The objective of this study was to determine how TE application rate and timing influences seed productivity over six diverse lodging environments in Oregon's Willamette Valley. Three field trials were conducted to examine TE effects on seed yield and yield components. Stem length, a key factor in lodging control, was reduced incrementally with increasing TE rate from 17% reduction at 200gTEha−1 to a maximum of 39% reduction at 600gTEha−1. Lodging was consistently reduced by TE but had no effect on above-ground biomass and paniclesm−2. Over environments, TE increased seed yield by an average 40% over the untreated control. However, TE rate or application timing did not differentially affect seed yield across environments. Increases in tall fescue seed yield attributable to TE were the result of increased seed numberm−2 and improved harvest index (HI), but not seed weight. A better understanding of TE-induced seed yield increases will aid in improving use efficiency and economy of this important PGR.

English

The objective of this work was to evaluate the effects of three plant growth inhibitors on the development and emission of floral rachis of Saint Augustine grass [ Stenotaphrum secundatum (Walt.) Kuntzel] plants. The study was carried out in a 15 month old lawn with the experimental plots being distributed in accordance with a complete randomized block design with four replications. The treatments consisted of sole application of trinexapac-ethyl (113, 226, 452, 678, and 904 g ai ha -1 ), prohexadione-calcium (100 and 200 g ai ha -1 ), and bispyribac-sodium (40 and 60 g ai ha -1 ) plus a check treatment in which the plants were not submitted to any of the plant growth inhibitors. The effects of those products were evaluated in terms of visual signs of plant intoxication, plant height, emission and height of floral rachises, and chip total dry matter production. All the plant growth inhibitors resulted in visible injury to the plants but these intoxication signs practically disappeared 28 days after the application. Trinexapac-ethyl at the dose of 904 g ai ha -1 reduced plant height by 59.7%, the emission of floral rachis by 96.4%, and the amount of chip dry matter production by 87.7%. Plant growth inhibitors may reduce the number of times of lawn plants cutting up to 119 days after their application with no harmful effects on the plants visual aspect.

Plant Growth Regulator and Soil Surfactants’ Effects on Saline and Deficit Irrigated Warm‐Season Grasses: I. Turf Quality and Soil Moisture

ABSTRACTA study was conducted at New Mexico State University in Las Cruces, NM, from 2010 to 2012 to investigate the effects of deficit irrigation on bermudagrass (Cynodon dactylon L.) cultivar Princess 77 and seashore paspalum (Paspalum vaginatum Swartz) cultivar Sea Spray treated with either soil surfactants [Revolution (modified methyl capped block copolymer) or Dispatch (alkyl polyglucoside blended with a straight block copolymer)] or a plant growth regulator [Trinexapac‐ethyl (TE); 4‐(cyclopropylhydroxymethylene)‐3,5‐dioxocyclohexanecarboxylic acid]. Irrigation was applied daily at 50% reference evapotranspiration from either a sprinkler or a subsurface drip system with either potable (electrical conductivity [EC] = 0.6 dS m−1) or saline (2.3 dS m−1) water. Normalized Difference Vegetation Index (NDVI) and visual ratings were determined monthly to assess stand quality and turf stress. Princess 77 treated with TE showed the highest quality and the highest NDVI (0.655) on 10 out of 15 sampling dates. Positive effects of TE applications were also observed on Sea Spray quality, NDVI, and fall color retention. Subsurface drip irrigation resulted in higher quality and NDVI during the third year of the study when compared with sprinkler irrigation. Salinity buildup in the root zone did not negatively affect visual quality of the tested warm‐season species. Generally, sprinkler irrigation system and turf treated with Revolution promoted higher water distribution uniformity (lower standard deviations) than the other treatments. Further research is needed to investigate if greater drought tolerance of subsurface drip–irrigated turf is the result of increased water‐use efficiency due to altered root morphology.

Nitrogen and Trinexapac-ethyl Applications for Managing ‘Diamond’ Zoysiagrass Putting Greens in the Transition Zone, U.S.

As a result of the increasing popularity of fine-leafed zoysiagrasses on golf courses, a 2-year field study was conducted to assess ‘Diamond’ zoysiagrass [Zoysia matrella (L.) Merr.] putting green performance at The Cliff’s Communities Turfgrass Research Facility in Marietta, SC. Factors included four nitrogen (N) fertility rates and two trinexapac-ethyl (TE) regimes. Foliar applications of 0, 4.9, 9.8, and 14.7 kg·ha−1 N were made once weekly for 7 and 15 weeks in 2009 and 2010, respectively. Trinexapac-ethyl was tank-mixed and applied weekly for 7 weeks during July to August at 0 or 0.017 kg a.i./ha totaling 0.120 kg a.i./ha for both growing seasons. Putting green performance was measured by assessing turf quality (TQ), ball roll distance (BRD), surface firmness (SF), leaf tissue nutrient concentrations, and thatch accumulation. Turfgrasses receiving 4.9 kg N/ha weekly exhibited acceptable TQ and greater SF and BRD than plots receiving 14.7 kg N/ha weekly on all rating dates in 2010 before seasonal dormancy. Trinexapac-ethyl reduced clipping yield by 15% to 43% and influenced BRD, SF, and tissue nutrient concentration across the 2-year study. Surface firmness decreased as total N input increased during the 2010 growing season and is presumably the result of an increase in leaf tissue causing a cushioned putting surface. Linear regression of thatch accumulation and SF were analyzed and found to be significant at four rating dates in 2010 indicating that as thatch organic matter increased, SF decreased. Nitrogen input for ‘Diamond’ zoysiagrass putting greens grown in the transition zone should begin at 73.5 kg·ha−1/year with supplemental N applications applied as needed.

Trinexapac‐Ethyl and Burning Effects on Seed Yield Components in Strong Creeping Red Fescue

Open‐field burning has been used to remove post‐harvest residue for high seed yield and quality in strong creeping red fescue (CRF) (Festuca rubra L. subsp. rubra) but concern over air pollution and safety issues has resulted in legislatively mandated reductions of this practice in Oregon. The effects of spring and fall applications of the plant growth regulator trinexapac‐ethyl (TE), and burning (burn) and mechanical removal (flail) of post‐harvest residue on seed yield components, were evaluated in strong CRF over a 4‐yr period. Response to treatments was different among years but burn was critical for maintaining high potential seed yields as the stand aged. Burn increased panicles m−2 and spikelets panicle−1 by up to 120 and 22%, respectively, over flail, and in turn, resulted in higher seed yields. Spring TE applications increased florets spikelet−1 by up to 14% in Years 1, 3, and 4. Fertile tiller height and lodging were reduced by spring‐applied TE. The combination of burn and spring TE produced highest seed yields in Years 3 and 4 as a result of increased seed number m−2 and seed weight. Fall TE did not affect seed yield components or yield and therefore, is not an effective management tool in strong CRF seed production.

Alterações nas características fisiológicas da cana-de-açúcar causadas por trinexapac-ethyl

The use of plant growth regulators has been performed frequently, especially in the large sugarcane or sugar alcohol plants in Brazil, due to the need for early harvest and optimization of agricultural planning. However, incorrect applications of these products may adversely affect the physiological processes of the plant resulting in the failure of this technology. This research evaluated the effects of trinexapac-ethyl applications in different seasons on the physiological characteristics of sugarcane to improve the management of this crop. The treatments were arranged in a randomized block factorial design (3 x 2 + 2), with four replications. The factor A corresponded to times of application of plant growth regulator (120, 200 and 240 days after budburst (DAB) of sugarcane) and factor B the number of applications (one or two applications). In addition, two controls (one with three applications and other without application of the regulator) were added. The mode of application of trinexapac-ethyl (number and time of application) affected differently the physiological characteristics of sugarcane plants. The one at 120 DAB and sequentially at 120, 200 and 240 DAB application increased the consumption of CO2, stomatal conductance, transpiration rate and photosynthetic rate. It was concluded that the application of trinexapac-ethyl may result in agronomic benefit to sugarcane growth, because when applied to 120 or sequentially at 120, 200 and 240 DAB promotes increments in the variable component of the process of photosynthesis which can result in better development and growth of crops.

Effects of Sequential Application of Plant Growth Regulators and Osmoregulants on Drought Tolerance of Creeping Bentgrass (Agrostis stolonifera)

ABSTRACTPlant growth regulators and osmoregulants may be involved in protection against drought stress, but their additive effects are not well documented in turfgrass. The objective of this study was to determine physiological effects of trinexapac‐ethyl (TE) and glycine betaine on drought tolerance in creeping bentgrass (Agrostis stoloniferaL.) under field conditions. The experiment was conducted in 2010 and 2011 on mature field plots of creeping bentgrass cultivar 007 planted on a Nixon sandy loam soil. The application of TE before drought in conjunction with glycine betaine at drought onset and during water withholding significantly improved turf performance evaluated as turf quality (TQ) and normalized difference vegetation index (NDVI). Enhanced turf performance was associated with greater osmotic adjustment promoting water retention in leaves and improved cellular membrane stability, indicating less membrane damage during drought stress. Furthermore, the combined TE plus glycine betaine treatment was more effective in maintaining high TQ during soil‐water deficit than when either TE or glycine betaine was applied alone. The results suggested that the sequential application of TE before drought onset and glycine betaine during water withholding effectively promoted creeping bentgrass tolerance to prolonged periods of drought stress. Cultural methods to maintain acceptable TQ with limited water resources are of major concern in the turfgrass industry, and this study provided promising results as to the effects of TE and glycine betaine for promoting creeping bentgrass drought tolerance.

Performance of trinexapac-ethyl on Lolium perenne seed crops in diverse lodging environments

Application of trinexapac-ethyl (TE) plant growth regulator (PGR) for lodging control in perennial ryegrass (Lolium perenne L.) is a widespread practice, but information on how this PGR increases yield is limited. The objective of this study was to determine how TE application rate and timing influences seed productivity over nine diverse lodging environments in Oregon's Willamette Valley. Four field trials were conducted to examine TE effects on seed yield and yield components. Stem length, a key factor in lodging control, was reduced incrementally with increasing rate of TE to a maximum of 28%. TE consistently reduced lodging but had no effect on the seed yield components spikes m−2, spikelets spike−1, and florets spikelet−1. Over environments, TE increased seed yield by an average 43% over the untreated control at 400gaiha−1 TE. Best seed yield results across environments were attained with TE applied between BBCH 32 and 51. The number of seeds spikelet−1, seed mass spikelet−1, and seed set were increased by TE. TE-induced seed yield increases were attributable to increased seed number m−2 and improved seed set, but not seed weight. A better understanding of TE-induced seed yield increases will aid in improving use efficiency and economy of this important PGR.

Effects of the Simulated Drift of Ripeners on Eucalyptus urograndis

The objective of this study was to evaluate the effects of the drift of ripeners (sulfometuron-methyl, ethephon and trinexapac-ethyl) on the initial growth of Eucalyptus urograndis. The experimental design was a randomized block with seven treatments (control; sulfometuron-methyl 0.9 and 1.2 g i.a. ha-1; ethephon 28.8 and 38.3 g i.a ha-1; trinexapac-ethyl 15 and 20 g i.a. ha-1) with four replicates using each plant as an experimental plot. We evaluated the effects 7, 14, 21, 28, 35 and 42 days after application, when we determined the length, diameter, total leaf area and total dry mass of the stem. The application of sulfometuron-methyl may have resulted in an effect known as “hormesis” due to an increasing trend in stem growth. The application of trinexapac-ethyl resulted in greater increases in the leaf dry mass and leaf area compared with those caused by the other ripeners that were used in this study, most likely due to the loss of apical dominance. The application of ethephon had no significant effect on the plants.

Effect of plant regulators on growth and flowering of 'Meyer' zoysiagrass

This trial aimed to evaluate the effect of sequential applications of different plant regulators over growth and flower rachis emission of 'Meyer' zoysiagrass (Zoysia japonica). The study was conducted on 15-month old green turfgrass under a randomized complete block design with four replications. The following plant regulator and doses were tested: trinexapac-ethyl (113+113, 226+113, 226+226, 452+113, 452+226, 452+452, 678+339 e 904+452 g a.i./ha-1), prohexadione-calcium (100+100 e 200+200 g a.i. ha-1) and bispyribac-sodium (40+40 e 60+60 g a.i. ha-1), as well as an untreated control. The turfgrass was mowed again at 3.0 cm aboveground and the second plant regulator was applied when 'Meyer' zoysiagrass was between 5.0 and 6.0 cm high. The effect of the treatments was visually rated for visual injury, plant height, height and number of flower rachis, and total dry mass production of clippings. Only bispyribac-sodium had visual symptoms of injury on 'Meyer' zoysiagrass, and no intoxication was observed at 28 days after the second application (DAAB). The sequential applications of trinexapac-ethyl, prohexadione-calcium and bispyribac-sodium reduced by more than 80% the total clipping dry mass produced by 'Meyer' zoysiagrass. All the plant regulators tested also showed promising results in reducing the height and emission of rachis, especially when trinexapac-ethyl was applied at the doses 452+452, 678+339 and 904+452 g a.i. ha-1. 'Meyer' zoysiagrass turfgrass can be handled with the sequential application of a plant regulator, which reduces the need for mowing over a period up to 110 days after the application of the second plant regulator, and it also avoids deleterious visual effects over turfgrass.

A Split Application Approach to Nitrogen and Growth Regulator Management for Perennial Ryegrass Seed Production

ABSTRACTExperiments were conducted during 2009 and 2010 in first year perennial ryegrass (Lolium perenne L.) fields under limiting or adequate spring N. Three N application methods (single, two‐split, and three‐split), five growth regulators (split and single applications of prohexadione Ca or trinexapac ethyl) and two spring N rates (56 or 100 kg N ha−1) were evaluated in a split‐split plot design. Under adequate spring N, all N application methods resulted in similar seed yields but when spring N was limiting, a single application of N resulted in up to 14% greater yield vs. the three‐split. The three‐split N application improved relative chlorophyll index (RCI) 6 to 20% late in the harvest season and reduced stem rust (Puccinia graminis Pers. subsp. graminicola) area under the disease progress curve (AUDPC) by 18 to 39% vs. the single N application. Other effects of three‐split N applications observed in 2010 were 8 to 19% less biomass, 2 to 3% greater harvest index (HI), 4% greater seedling vigor, and 25% less lodging. The split prohexadione Ca treatment gave the most consistent results and when vegetative growth was greatest it resulted in a 36% increase in seed yield, a 5.5% increase in HI, 14 cm shorter plants, 70% less lodging, 30% greater RCI, 13% lower stem rust incidence, and 3% lower stem rust severity. Development of a model to optimize rates and timings for split N and growth regulator applications based on growth stage, soil N availability, and growing degree days (GDD) could improve efficacy of split applications.

Doses e épocas de aplicação de regulador de crescimento em híbridos de milho

A fim de avaliar o efeito do regulador de crescimento trinexapac-ethyl em diferentes doses e épocas de aplicação em dois híbridos de milho, instalaram-se dois experimentos em Ponta Grossa, PR, Brasil, no ano agrícola de 2010/11. O delineamento experimental foi o de blocos ao acaso, em esquema fatorial 4 x 4 (doses x épocas de aplicação), com quatro repetições. Os tratamentos constaram da aplicação do trinexapac-ethyl (Moddus®) nas doses de 0,0, 187,5, 375,0 e 562,5 g ha-1 nos estádios V2, V4, V6 e V8 do milho, nos híbridos Status TL e Maximus TLTG. Avaliaram-se características agronômicas, componentes de produção e produtividade. A época de aplicação do trinexapac-ethyl não afetou características agronômicas e a produtividade dos dois híbridos de milho. Em relação à dose do regulador, somente o Maximus TLTG mostrou aumento da largura e diminuição do comprimento das folhas com o incremento da dose do produto, sem efeitos substanciais nos componentes da produção e na produtividade. Os resultados mostraram pouca resposta dos híbridos avaliados à dose e época de aplicação do trinexapac-ethyl; ao contrário do trigo, o uso na cultura deve ser mais bem avaliado, especialmente em relação à dose do produto e à reação de híbridos.

Gas exchange rates, plant height, yield components, and productivity of upland rice as affected by plant regulators

The objective of this work was to evaluate gas exchange rates, plant height, yield components, and productivity of upland rice, as affected by type and application time of plant growth regulators. A randomized block design, in a 4x2 factorial arrangement, with four replicates was used. Treatments consisted of three growth regulators (mepiquat chloride, trinexapac-ethyl, and paclobutrazol), besides a control treatment applied at two different phenological stages: early tillering or panicle primordial differentiation. The experiment was performed under sprinkler-irrigated field conditions. Net CO2 assimilation, stomatal conductance, plant transpiration, and water-use efficiency were measured four times in Primavera upland rice cultivar, between booting and milky grain phenophases. Gas exchange rates were neither influenced by growth regulators nor by application time. There was, however, interaction between these factors on the other variables. Application of trinexapac-ethyl at both tillering and differentiation stages reduced plant height and negatively affected yield components and rice productivity. However, paclobutrazol and mepiquat chloride applied at tillering, reduced plant height without affecting rice yield. Mepiquat chloride acted as a growth stimulator when applied at the differentiation stage, and significantly increased plant height, panicle number, and grain yield of upland rice.

Trinexapac-ethyl Effects on Stolon Activity and Node Vitality of ‘Tifway’ Hybrid Bermudagrass

The stoloniferous-rhizomatous growth habit of bermudagrass [Cynodon dactylon (L.) Pers.] is a key feature for fast turf establishment and effective recovery from wear and divots. Trinexapac-ethyl (TE) is a plant growth regulator used extensively to reduce the need for mowing. However, vertical growth suppression of vertical growth has the potential to reduce horizontal growth. Furthermore, side effects reported on several physiological functions could affect node ability to generate new plants. In a greenhouse trial, ‘Tifway’ hybrid bermudagrass (C. dactylon × C. transvaalensis Burtt Davy) grown in pots was treated with increasing rates of TE (untreated control, 0.015, 0.075, 0.150, and 0.300 g·m−2). The treatment effects on the number of stolons produced and their linear growth rate, node production, node vitality, and daughter plant characteristics were investigated. The effects of growth inhibition because of TE application on nodes and daughter plants and the relative duration were also assessed. Starting from 2 weeks after treatment (2 WAT), TE application resulted in reductions of stolon length of 24.6% and 52.9% compared with the untreated control, while at 3 and 4 WAT only 0.150 and 0.300 g·m−2 application rates produced significant reductions in stolon length with values of 37.1% and 52.9% at 3 WAT and of 34.1% and 48.3% at 4 WAT, respectively. The number of nodes per stolon was unaffected by treatments. No effect was observed in node vitality but daughter plants showed a postinhibition growth enhancement when nodes were excised at 4 WAT. TE application at the labeled rate did not affect the number of stolons produced by ‘Tifway’ hybrid bermudagrass compared with untreated control, while a reduction in stolon growth rate was recorded only at 2 WAT. Application at higher rates reduced stolon growth rate longer than labeled rate but not stolon production. None of the treatments reduced the number of vital nodes. Application rates higher than labeled rate produced a postinhibition growth enhancement in plants that originated from nodes excised at 4 WAT.

Improvement of Salt Tolerance in Kentucky Bluegrass by Trinexapac-ethyl

Trinexapac-ethyl (TE) is a popular plant growth regulator in the turfgrass industry that inhibits gibberellic acid (GA) biosynthesis and effectively reduces leaf elongation and subsequent clipping production. This greenhouse sand culture experiment was conducted to determine effects of TE application on kentucky bluegrass (Poa pratensis L.) responses to salinity stress. The five salinity levels (0, 20, 40, 60, and 80 mm NaCl) were applied in nutrient solutions and TE treatments (0, 1, and 1.7 g/100 m2) were applied twice at 4-week intervals. Under non-saline conditions and low level salinity conditions, application of TE at 1 g/100 m2 (TE1) increased turf quality (TQ), leaf total non-structural carbohydrates (TNC), and chlorophyll (Chl) content. In high salinity, TE1 alleviated the decline in TQ, antioxidant enzyme activities, leaf TNC, Chl, and K+ content. In addition, treated turf with TE at 1 g/100 m2 had lower proline, Na+, and malondialdehyde (MDA) contents. However, the adverse effects of high salinities were more pronounced when turf was treated by TE at 1.7 g/100 m2 (TE1.7), suggesting that effects of TE on salt tolerance vary with its dosages and salinity levels. We concluded that moderate inhibition of GA biosynthesis by TE enhances salt tolerance in kentucky bluegrass and suggest that enhancement is the result of the maintenance of antioxidant activities, leading to more root growth and greater levels of TNC and Chl content. Chemical names used: 4-(cyclopropyl-β-hydroxymethylene)-3, 5-dioxocyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl).

Diamond Zoysiagrass Golf Green Response to Reduced Light Environments with the Use of Trinexapac‐Ethyl

A 2‐yr study was conducted to determine the tolerance of a mature Diamond zoysiagrass [Zoysia matrella (L.) Merr.] golf green to reduced light environments (RLE) treated with trinexapac‐ethyl (TE) at 0 and 0.013 kg ha−1 wk−1. Three levels of RLE, 0, 60, and 90%, were imposed to coincide with maximum seasonal growth of zoysiagrass. Plant growth measurements included turf quality (TQ), chlorophyll concentration, clipping yield, and total nonstructural carbohydrates. Zoysiagrass grown in full sunlight and 60% RLE maintained commercially acceptable TQ (≥7) with and without TE throughout Year 1 while 90% RLE treatments fell below an acceptable level 2 mo after study initiation. Sixty percent RLE treatments without TE demonstrated unacceptable TQ during Year 2. Application of TE sustained turf viability in 90% RLE through Year 2. Clipping yield increased in 60% RLE without TE compared to full sunlight treatments. Application of TE to 60% RLE treatments reduced clipping yield 30 to 76% in Year 1. Chlorophyll concentration in 60% RLE treatments was similar 10 wk after RLE implementation compared to full sunlight treatments in Year 1 and higher in Year 2. Total nonstructural carbohydrate concentration of roots, rhizomes, and stolons was similar in full sun and 60% RLE treatments at the end of both years and between 47 and 100% lower in 90% RLE treatments compared to full sun treatments. These results support the use of Diamond zoysiagrass in up to 60% reduced light putting green environments with concurrent use of a gibberellin biosynthesis inhibiting product such as TE.

Impact of Nitrogen Source and Trinexapac-ethyl Application on Creeping Bentgrass (Agrostis stolonifera L.) Physiology under Neutral Shade, Deciduous Tree Shade, and Full Sunlit Conditions

Decreased light quantity or quality affects the growth of turfgrass plants. Shade causes thinning of turfgrass stands and loss in surface quality. Plant changes include increased chlorophyll levels, lower soluble sugars, and loss of canopy cover. The objective of this research was to investigate if applications of foliar nitrogen and trinexapac-ethyl [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (TE) would result in beneficial biochemical changes in creeping bentgrass (Agrostis stolonifera L. cv. Penncross) grown in different shaded environments. Foliar applications of three nitrogen treatments, (NH2)2CO, Ca(NO3)2, or (NH4)2SO4, were made weekly at 0.43 g N/m2. Growth regulator treatments consisted of an untreated control or TE applied biweekly at an a.i. rate of 0.057 kg·ha−1. Plots were established in full sun (FS), neutral shade (NS), and deciduous shade (DS). Chlorophyll content, soluble carbohydrates, flavonoids, clipping yield, and color were measured. Nitrogen treatments caused some variation in levels of soluble carbohydrates in shaded conditions. Chlorophyll (Chl) levels varied between TE treatments, with increased levels of chlorophyll b (Chl b) found in TE-treated plots under FS. Application of TE resulted in higher flavonoid concentrations in leaf tissue in shaded conditions. Repeated applications of (NH2)2CO significantly improved color (P = 0.05). Turfgrass managers maintaining creeping bentgrass in shade may benefit from applications of TE and (NH2)2CO.