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  • Author or Editor: Haibo Liu x
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Aluminum toxicity is a major limiting factor for turfgrass establishment and growth when soil pH is <5.0. Limited information on aluminum resistance is available among warm-season turfgrasses and these turfgrasses often grow in the areas with acid soil conditions. The objectives of this study were 1) to evaluate seeded bermudagrass (Cynodon dactylon L.) cultivars for the ability to tolerate a high level of aluminum and 2) to measure the extent of aluminum damage to the root systems. In total, 16 bermudagrass cultivars were evaluated under greenhouse conditions using a solution culture and an acid Tatum soil (Clayey, mixed, thermic, typic, Hapludult). The soil had pH 4.4% and 69% exchangeable aluminum. A concentration of 640 μm aluminum and a pH 4.0 was used for solution culture. The grasses were grown for 28 days in solution culture; 28 days in the acid Tatum soil; and 78 days in the acid Tatum soil before harvesting. Aluminum resistance was determined by measuring the longest root length, the longest shoot length, dry root weight, dry shoot weight, and shoot to root ratio in comparing the control to obtain the relative Al resistance among the cultivars. The results indicate that seeded bermudagrass cultivars differ in their aluminum resistance.

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Economic and environmental concerns over nitrogen (N) fertilization of turfgrasses are prompting serious considerations of how to best use various N pools in turf-soil ecosystems. Nitrogen in clippings is receiving special consideration but information on how large and variable this N source might be for different turfgrasses is limited. Therefore, a field study investigated growth of and N recovery in clippings from 10 cultivars each of kentucky bluegrass (Poa pratensis L.), perennial ryegrass (Lolium perenne L.), and tall fescue (Festuca arundinacea Schreb.) turf at the University of Rhode Island Turfgrass Research Station, Kingston, during 1990 and 1991 growing seasons. All turf had been established in 1985, 1986 or 1987 on an Enfield silt loam (Coarse loamy over sandy skeletal, mixed, mesic, Typic Dystrochrepts) and maintained under N fertilization rate of 147 kg N ha/year. Daily clipping growth rate (DCG), leaf blade N concentration (NC), and daily N recovery rate (DNR) in clippings were compared across species and cultivars. Seasonal clipping yields ranged from 5152 kg dry weight/ha for tall fescue to 3680 kg·ha–1 for perennial ryegrass. Significant species differences in the amount and seasonal pattern of N recovery were identified. Cultivar differences in N recovery were greatest for kentucky bluegrass but much less for perennial ryegrass and tall fescue. Total N recovery in clippings ranged from 260 to 111 kg N/ha/year generally exceeded N supplied as fertilizer, thus emphasizing potential importance of clipping N in turf management.

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Centipedegrass [Eremochloa ophiuroides (Munro) Hack] is a native grass of China, and information on soil adaptation ranges, including acid soils, among centipedegrass cultivars is limited. Therefore, objectives of this study were 1) to conduct a preliminary evaluation of relative aluminum tolerance of 48 centipedegrass accessions plus a cultivar, TifBlair, and a common centipedegrass under aluminum (Al) stress (0 and 1500 μM Al) by using a solution culture method; and 2) to determine Al effects on nutrient uptake between resistant-group and sensitive-group accessions among the 50 accessions and cultivars. Differences were found among accessions and cultivars, and the CV of relative root weight, relative shoot weight, and relative total weight were 39.9%, 32.9%, and 33.6%, respectively. After growing 28 days in an acid subsoil, the resistant-group accessions showed much better growth than the sensitive-group accessions. The Al concentrations in roots and shoots of the two groups of accessions were increased under Al treatment, but most absorbed Al remained in roots with greater Al absorption among the sensitive group compared with the resistant group. The concentrations of phosphorus (P), magnesium (Mg), calcium (Ca), and potassium (K) in the two groups were reduced under Al stress with reductions of 59.3%, 54.8%, 47.9%, and 41.3% in shoots and reductions of 8.70%, 52.5%, 43.2%, and 34.4% in roots, respectively. Under Al stress, differences in P, Mg, and Ca concentrations were found between the two groups; however, differences were not found for K. The resistant-group accessions maintained higher concentrations of Mg and Ca than the sensitive group.

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Research was conducted in two studies at the Clemson University Greenhouse Complex, Clemson, S.C., with the objective of evaluating `TifEagle' bermudagrass (Cynodon dactylon × C. transvaalensis) response to paclobutrazol. TifEagle bermudagrass plugs were placed in 40 cm polyvinylchloride containers, with 20.3-cm-diameters and built to U.S. Golf Association specifications with 85 sand: 15 peatmoss (by volume) rootzone mix. Paclobutrazol was applied to separate containers at 0, 0.14, 0.28, and 0.42 kg·ha-1 (a.i.) per 6 weeks. Minor phytotoxicity occurred with 0.14 kg·ha-1 applications, but turf quality was unaffected. Severe bermudagrass phytotoxicity occurred from paclobutrazol at 0.28 and 0.42 kg·ha-1. Total clipping yield from 12 sampling dates was reduced 65%, 84%, and 92% from 0.14, 0.28, and 0.42 kg·ha-1, respectively. Root mass after 12 weeks was reduced 28%, 45%, and 61% for turf treated 0.14, 0.28, and 0.42 kg·ha-1, respectively. Paclobutrazol reduced root length 13%, 19%, and 19% by 0.14, 0.28, and 0.42 kg·ha-1, respectively. Turf discoloration and negative rooting responses advocate caution when using paclobutrazol on `TifEagle' bermudagrass. Chemical names used: (+/-)-(R*,R*)-ß-[(4-chlorophenyl) methyl]-alpha-(1, 1-dimethyl)-1H-1,2,4,-triazole-1-ethanol (paclobutrazol).

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Trinexapac-ethyl (TE) is an effective plant growth retardant for hybrid bermudagrass; however, growth responses of various dwarf-type bermudagrass cultivars to TE have not been reported. Two 60-day greenhouse experiments were conducted at the Clemson Greenhouse Research Complex, Clemson, S.C., to evaluate the response of `Champion', `FloraDwarf', `MiniVerde', `MS Supreme', `Tifdwarf', and `TifEagle' bermudagrass with and without TE at 0.0125 kg·ha-1 a.i. per 10 days. From 20 to 60 days after initial treatments, TE enhanced visual quality 9% to 13% for all cultivars. From four samples, TE reduced clippings 63%, 63%, 69%, 62%, 64%, and 46% for `Champion', `FloraDwarf', `MiniVerde', `Tifdwarf', and `TifEagle', respectively. Trinexapac-ethyl enhanced root mass 23% and 27% for `MiniVerde' and `FloraDwarf' bermudagrass, respectively. `Champion', `MS Supreme', `Tifdwarf', and `TifEagle' bermudagrass treated with TE had similar root mass to the untreated respective cultivars. Among untreated cultivars, `FloraDwarf', `MiniVerde', `MS Supreme', and `Tifdwarf' had similar root masses; however compared to these cultivars, `Champion' and `TifEagle' had 33% and 81% less root mass, respectively. Root length was unaffected by TE; however, `Champion' and `TifEagle' averaged 20% and 36% less root length compared to `Tifdwarf' bermudagrass, respectively, while `FloraDwarf', `MiniVerde', and `MS Supreme' had similar root length to `Tifdwarf'. Trinexapac-ethyl safely enhanced turf quality and reduced clipping yield at 0.0125 kg·ha-1 per 10 days without inhibiting root growth of six dwarf-type bermudagrasses. Chemical name used: [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (trinexapac-ethyl).

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Plant growth regulators (PGRs) are commonly used to enhance putting green quality and ball roll distances but their effects with various mowing operations have not been reported. Three experiments were conducted and repeated at Clemson University, Clemson, SC, on an `L-93' creeping bentgrass putting green to evaluate the effects of mowing operations and PGRs on diurnal ball roll distances. The PGRs tested included ethephon at (a.i.) 3.8 kg·ha-1, flurprimidol at (a.i.) 0.28 kg·ha-1, paclobutrazol at (a.i.) 0.28 kg·ha-1, and trinexapac-ethyl at (a.i.) 0.05 kg·ha-1. Mowing operations tested included rolling vs. mowing, morning mowing vs. morning plus afternoon mowing, and single vs. double morning mowing, all with and without PGRs. PGR by mowing operation interactions did not occur in any experiments. Ball roll distances decreased from 12:00 hr to evening observations in all experiments. In Experiment 1, rolling the green without mowing reduced ball roll distance 4% (5 cm) compared to mowing. Turf rolled without mowing in the morning and treated with flurprimidol, paclobutrazol, and trinexapac-ethyl produced similar ball roll at 12:00, 15:00, and 18:00 hr to mowed untreated turf. In Experiment 2, all plots were mowed at 08:00 hr and half of each plot was remowed at 12:30 hr. The second mowing at 12:30 hr enhanced ball roll distances 6% (8 cm) over the day. Turf mowed only at 08:00 and treated with paclobutrazol and trinexapac-ethyl had greater or equal ball roll distances at 12:30, 15:30, and 18:30 hr to untreated turf that had a second mowing at 12:30 hr. Turf receiving ethephon and 08:00 hr mowing had 4% to 12% (4 to 17 cm) shorter ball roll distances throughout the day compared to untreated turf mowed at 8:00 and 08:00+12:30 hr, respectively. In the third experiment, mowing twice in the morning increased ball roll 3% (4 cm) compared to mowing once. Trinexapac-ethyl and paclobutrazol treated turf mowed once in the morning had greater or equal ball roll distances throughout the day to untreated turf mowed twice in the morning. Overall, PGR use may provide putting green ball roll distances similar to or greater than untreated turf despite additional mowing; however, ethephon reduced ball roll distances regardless of mowing operations. Chemical names used: [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (trinexapac-ethyl); {α-(1-methylethyl)-α-[4-(trifluoro-methoxy) phenyl] 5-pyrimidine-methanol} (flurprimidol); (+/-)-(R*,R*)-β-[(4-chlorophenyl) methyl]-α-(1, 1-dimethyl)-1H-1,2,4,-triazole-1-ethanol (paclobutrazol); [(2-chloroethyl)phosphonic acid] (ethephon).

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Dwarf bermudagrass morphological characteristics following the use of plant growth regulators have not been reported. The objective of this greenhouse study was to determine short-term effects of seven plant growth regulators on clipping yield, chlorophyll concentration, and root mass of `TifEagle' bermudagrass. Growth regulators tested included ethephon, fenarimol, flurprimidol, maleic hydrazide, mefluidide, paclobutrazol, and trinexapac-ethyl. Two applications of each compound were made over a 6-week period. Root mass was reduced 39% by fenarimol and 43% by flurprimidol, while other PGRs had root mass similar to untreated turf. `TifEagle' bermudagrass treated with paclobutrazol, mefluidide, fenarimol, and flurprimidol averaged 45% less root mass than trinexapac-ethyl-treated turf. Trinexapac-ethyl was the only compound to reduce clippings and enhance turf quality without negative rooting effects. Chemical names used: [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (trinexapac-ethyl); {α-(1-methylethyl)-α-[4-(trifluoro-methoxy) phenyl] 5-pyrimidine-methanol} (flurprimidol); (+/-)-(R*,R*)-β-[(4-chlorophenyl) methyl]-α-(1, 1-dimethyl)-1H-1,2,4,-triazole-1-ethanol (paclobutrazol); (N-[2,4-dimethyl-5 [[(trifluoro-methyl)-sulfonyl] amino]phenyl]acetamide) (mefluidide); [1,2-dihydro-3,6-pyridazine-dione] (maleic hydrazide); [(2-chloroethyl)phosphonic acid] (ethephon); and (2-(2-chlorophenyl)-2-(4-chlorophenyl)-5-pyrimidinemethanol) (fenarimol).

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Plant growth regulators (PGRs) are often applied in combinations to reduce turf clippings, enhance turf quality, and suppress Poa annua L.; however, effects of PGR combinations on putting green ball roll distances have not been reported. Two field experiments were conducted on an `L-93' creeping bentgrass (Agrostis stolonifera var. palustris Huds.) putting green in Clemson, S.C., to investigate effects of four PGRs with and without a subsequent application of ethephon at 3.8 kg·ha–1 a.i. 6 days after initial treatments. The PGRs initially applied included ethephon at 3.8 kg·ha–1 a.i., flurprimidol at 0.28 kg·ha–1 a.i., paclobutrazol at 0.28 kg·ha–1 a.i., and trinexapac-ethyl at 0.05 kg·ha–1 a.i.. Ball roll distances were enhanced 3% to 6% (4 to 8 cm) by exclusive flurprimidol, paclobutrazol, and trinexapac-ethyl treatments. The additional ethephon application reduced ball distances 2% to 9% (2 to 11 cm). Paclobutrazol and trinexapac-ethyl treated turf receiving the additional ethephon application had longer or similar ball roll distances to non-PGR treated turf. The additional ethephon treatment reduced turf quality to unacceptable levels 1 and 2 weeks after applications. However, bentgrass treated previously with trinexapac-ethyl and paclobutrazol had 8 to 16% higher visual quality following the additional ethephon treatment relative to non-PGR treated turf receiving the subsequent ethephon application. Overall, ethephon may have deleterious effects on monostand creeping bentgrass putting green quality and ball roll distances; however, applying ethephon with GA inhibitors could mitigate these adverse effects. Chemical names used: [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (trinexapac-ethyl); {α-(1-methylethyl)-α-[4-(trifluoro-methoxy) phenyl] 5-pyrimidine-methanol} (flurprimidol); (+/-)–(R*,R*)-β-[(4-chlorophenyl) methyl]-α-(1, 1-dimethyl)-1H-1,2,4,-triazole-1-ethanol (paclobutrazol); [(2-chloroethyl)phosphonic acid] (ethephon).

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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).

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Plant growth regulators are applied to inhibit uneven shoot growth of putting green turf but research is limited on responses of dwarf-type bermudagrass cultivars to growth inhibition. Experiments were conducted at the Clemson University Greenhouse Complex with `Champion' and `TifEagle' bermudagrass grown in polyvinylchloride containers with 40 cm depths and 177 cm2 areas built to United States Golf Association specification. Flurprimidol was applied at 0.14, 0.28, and 0.48 kg·ha–1 a.i. and paclobutrazol at 0.14 kg·ha–1 a.i. on separate containers. Flurprimidol at 0.28 and 0.42 kg·ha-1 caused 17% and 31% reduction in turf color 5 weeks after treatment (WAT), respectively. `Champion' exhibited unacceptable turf injury (>30%) 2 WAT from paclobutrazol and all flurprimidol rates. `TifEagle' had unacceptable turf injury from flurprimidol at 0.42 kg·ha–1 2 WAT, 0.28 kg·ha–1 3 WAT, and 0.14 kg·ha–1 4 WAT that did not recover. Moderate injury (16% to 30%) was observed from paclobutrazol on `TifEagle' but ratings were acceptable. After 6 weeks, flurprimidol at 0.14, 0.28, and 0.42 kg·ha–1 reduced bermudagrass green shoot density (GSD) per square centimeter by 20%, 40%, and 40%, respectively, while paclobutrazol reduced GSD 12%. `TifEagle' total clipping yield was reduced 60%, 76%, and 86% from flurprimidol at 0.14, 0.28, and 0.42 kg·ha–1, respectively, and 37% from paclobutrazol. `Champion' total clipping yield was reduced 82%, 90%, and 90% from flurprimidol at 0.14, 0.28, and 0.42 kg·ha–1, respectively, and 58% from paclobutrazol. After 6 weeks, flurprimidol reduced `Champion' total root mass by 44% over all three rates. `Champion' treated with paclobutrazol had similar total root mass to the untreated. `TifEagle' treated with all PGRs had similar rooting to the untreated. Overall, flurprimidol will likely not be suitable for dwarf bermudagrass maintenance at these rates; however paclobutrazol may have potential at ≤0.14 kg·ha–1. Chemical names used: Flurprimidol {α-(1-methylethyl)-α-[4-(trifluoro-methoxy) phenyl] 5-pyrimidine-methanol}; Paclobutrazol, (+/-)–(R*,R*)-β-[(4-chlorophenyl) methyl]-α-(1, 1-dimethyl)-1H-1,2,4,-triazole-1-ethanol.

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