Golf Greens Research Articles

Trinexapac‐Ethyl Application Regimens Influence Growth, Quality, and Performance of Bermuda Grass and Creeping Bentgrass Putting Greens

Dwarf bermudagrass (Cynodon dactylon × C. transvaalensis Burtt‐Davy) and creeping bentgrass (Agrostis stolonifera L.) are planted for golf greens in the U.S. transition zone, but management regimes, such as the use of a plant growth regulator (PGR), often vary for long‐term culture of the two species. The objective of this experiment was to investigate application regimens of the PGR trinexapac‐ethyl (TE), on growth, quality, and performance of creeping bentgrass and bermudagrass putting greens in Clemson, SC. ‘L‐93’ creeping bentgrass and ‘TifEagle’ bermudagrass putting greens, established in summer 2002 and mowed at 3.2 mm, received TE over 12 wk in three regimens: 0.017 kg ha−1 wk−1, 0.033 kg ha−1 2 wk−1 (biweekly), or 0.05 kg ha−1 3 wk−1 (triweekly) from May to August 2003 and 2004. Creeping bentgrass was not discolored from TE, but unacceptable bermudagrass discoloration (>20%) occurred on one, two, and six dates for weekly, biweekly, and triweekly regimens, respectively. All TE regimens reduced bermudagrass clippings approximately 50% from nontreated bermudagrass across all dates, while creeping bentgrass clipping reductions, approximately 20 to 35% from nontreated grass, were inconsistent. The root masses of both species treated with TE regimens were similar to nontreated turf. Bermudagrass aerification recovery was reduced on two, two, and four dates after weekly, biweekly, and triweekly TE regimens, respectively. All TE regimens increased morning and evening bermudagrass golf ball roll distance approximately 25 cm from morning distances of nontreated turf.

Dwarf Bermudagrass Tolerance to Preemergence Herbicides

Preemergence herbicides are applied to prevent summer annual weed infestations in turf, but safety to dwarf-type bermudagrass golf greens has not been determined for many of these materials. Field experiments tested ‘TifEagle’ bermudagrass response to bensulide at 11.2 kg·ha−1 (a.i.), dithiopyr at 0.56 kg·ha−1 (a.i.), napropamide at 2.2 kg·ha−1 (a.i.), oxadiazon at 2.2 kg·ha−1 (a.i.), oxadiazon plus bensulide at 1.7 + 6.7 kg·ha−1 (a.i.), and pendimethalin at 1.7 kg·ha−1 (a.i.). All herbicides reduced root mass from the nontreated, but only losses incited by oxadiazon plus bensulide were acceptable (less than 20%). Dithiopyr, napropamide, and pendimethalin delayed spring greenup in 2003 and 2004, whereas oxadiazon plus bensulide delayed spring greenup in 2004. In greenhouse experiments, ‘TifEagle’ bermudagrass root mass was reduced 19% to 37%, 30% to 33%, 4% to 26%, 28% to 37%, and 24% to 30% from various rates of bensulide, dithiopyr, napropamide, and pendimethalin, respectively. Oxadiazon and oxadiaxon plus bensulide reduced root mass by only 2% to 15% and 15% to 22%, respectively. In another experiment, oxadiazon plus bensulide at 1.7 + 6.7 kg·ha−1 did not injure shoots or roots of ‘Champion’, ‘FloraDwarf’, ‘MiniVerde’, ‘Tifdwarf’, or ‘TifEagle’ bermudagrass. Overall, dwarf-type bermudagrass golf greens do not appear to tolerate mitotic inhibitor preemergence herbicides, whereas oxadiazon or oxadiazon plus bensulide caused minimal injury.

Turf Covers for Winter Protection of Bermudagrass Golf Greens

Research trials were conducted on a bermudagrass (Cynodon magennissii Hurc. ‘MS-Express’) putting green at the Mississippi State University Golf Course over the winter months of 2000-2001, 2001-2002, and 2002-2003 to evaluate how various turf covers modify surface temperatures and turfgrass growth when applied for temporary cold temperature protection. Average daily maximum, minimum, and mean temperatures were recorded, as well as the average daily range in temperatures under covers. Temperature responses varied with cover composition, permeability, color, and to a lesser extent, thickness. An experimental translucent overwintering blanket provided the highest average daily maximum temperatures, but also had the greatest temperature range, indicating the potential for excessive heating under the cover. A commercially available interwoven polyethylene cover also provided high daily mean soil surface temperatures, but its mean daily minimum temperatures were not significantly different from the uncovered control in two of the three years, apparently indicating much of the energy acquired during the day was lost after sundown. Doubled layers of commercially available white or black polypropylene covers had only slightly increased mean daily minimum temperatures as compared to single layers. All covers provided some degree of potentially desirable temperature modifications, but selection and use would depend on the particular needs of the turf manager.

Heat Resistance Enhanced by Trinexapac-Ethyl and Benzyladenine Combination in Creeping Bentgrass

Creeping bentgrass (Agrostis stolonifera var. palustrisHuds) is one of the most widely used turfgrasses for golf greens and fairways. The optimum temperature for creeping bentgrass ranges between 15 to 24 C for shoot growth and 10 to 18 C for root growth (Beard, 1973). However, temperatures during summer months often exceed the optimal ranges for prolonged periods. High-temperature stress is one of the major factors limiting use of creeping bentgrass in transitional and warmer climatic regions (Beard, 1997; Beard and Daniel, 1966; Carrow, 1996; Wang et al., 2003). Typically, grasses are exposed to high temperatures more than 35/30 C (day/night) for 20 to 30 d during the summer in many areas of China. Such prolonged high temperatures severely limit shoot and root growth, and survival of plants. Many physiological factors are involved in heat stress injury. Heat stress reduces photosynthesis (Carrow and Duncan, 2003; Paulsen, 1994; Xu and Huang, 2001), and increases respiration, which exhausts carbohydrate reserves (Xu and Huang, 2003). Carbohydrate metabolism is among the key physiological processes controlling plant growth. High-quality turf is often cultivated under a frequent mowing program. Clipping removal is one of the main concerns in reduction of energy reserves and leaf area required for photosynthesis in creeping bentgrass. Trinexapac-ethyl (TE) is a plant growth regulator that inhibits gibberellin (GA) synthesis by blocking the transformation of GA20 to GA1 (Rademacher, 2000). TE reduces vertical growth of many turfgrass species, which results in decreased clipping weights (Fagerness et al., 2004; McCullough et al., 2004, Tegg and Lane, 2004). TE has been shown to reduce sod heating through reducing plant respiration, resulting in enhanced stress resistance in Kentucky bluegrass (Poa pratensis) (Ervin and Koski, 2001a,b; Heckman et al., 2001), indicating its effects on energy conservation from respiratory consumption. Cytokinin, a phytohormone, may regulate plant response to high-temperature stress. A period of heat stress reduced the level of cytokinins in roots in many plants (Itai et al., 1973; Liu et al., 2002; Udomprasert et al., 1995). Application of cytokinins (Liu and Huang, 2002) or products containing cytokinins (Zhang et al., 2003) to the root system or shoot (Zhang and Schmidt, 2000) could enhance the heat resistance of turfgrasses. The positive effects of cytokinins on stress resistance of plants are related to protection from oxidative stress by preventing the formation of free radicals or by the regulation of antioxidant enzyme activities (Caers et al., 1985; Liu and Huang, 2002; Wang et al., 2003; Zhang and Schmidt, 2000). Although many plant growth regulators are commercially available for regulating plant growth and production, few of them have been reported to have positive effects on improving plant heat resistance. Cytokinins and TE are two chemicals that have shown potential beneficial effects for plant heat resistance in previous reports. However, no work has been conducted to determine the interactive effects of TE and 6-benzyladenine (BA). The objectives of this study were to investigate 1) whether a TE and cytokinin combination can enhance heat resistance of creeping bentgrass and 2) the morphological and physiological effects of TE and BA in the regulation of turf summer performance and heat resistance in creeping bentgrass. Materials and Methods

Atmospheric Composition under Impermeable Winter Golf Green Protections

The utilization of impermeable winter covers on annual bluegrass [Poa annua var. reptans (Hauskn.) Timm.] golf greens as a protection against excess water and ice is increasing rapidly in Canada and elsewhere in northern climates. A study was conducted to examine the impact of these covers on the atmospheric composition over golf green turfgrass during the 1997–1998 and 1998–1999 winters in Québec City and in Montréal, Canada. Winter protective covers tested included a commercial impermeable cover on top of either curled wood shavings mat (CW‐CC), 15 cm of straw mulch (SM‐CC) or a felt material (FM‐CC), a clear polyethylene cover on top of a curled wood shavings mat (CW‐PC), and an unprotected control. Oxygen was consumed at variable rates under impermeable winter protective covers. As a result, anoxic conditions were not reached during winter at the Québec City site but high respiration rates at the Montréal site resulted in anoxic conditions that lasted for periods as long as 50 d, without apparent damage to the annual bluegrass plants. Further tests were conducted on greens experiencing recurrent damages that could not be explained by freezing temperatures, snow mold pathogens, excess water, or ice. We showed that these problem greens had higher soil respiration rates than nonproblem greens indicating that the differences in O2 consumption amongst golf greens are likely due to differences in soil biological activity rather than in plant respiration. We also established that the higher activity in soils of recurrently damaged greens was related to higher levels of soil organic C. Accordingly, sand‐based golf greens built according to the USGA specifications had lower soil organic matter and lower respiration rates than greens built on native soils. We conclude that high rates of O2 consumption by golf greens with high soil organic matter content results in potentially harmful anoxic conditions under impermeable covers during winter.

Bermudagrass Putting Green Growth, Color, and Nutrient Partitioning Influenced by Nitrogen and Trinexapac‐Ethyl

Plant growth regulators (PGRs) improve turf color by inhibiting leaf growth and may reduce fertilization requirements of bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt‐Davy] golf greens by reducing nutrients removed through clipping collection. To test this hypothesis, growth, color, and nutrient allocation of ‘TifEagle’ bermudagrass maintained at 3.2 mm were investigated in field experiments conducted in Clemson, SC, from April to August in 2003 and 2004. Ammonium nitrate was applied at 6, 12, 18, or 24 kg N ha−1 wk−1 with a PGR, trinexapac‐ethyl {[4‐(cyclopropyl‐[α]‐hydroxymethylene)‐3,5‐dioxo‐cyclohexane carboxylic acid ethyl ester]} (TE), at 0 or 0.05 kg a.i. ha−1 3 wk−1 Turf required 18 to 24 kg N ha−1 wk−1 from May to June and ≤12 kg N ha−1 wk−1 from July to August to maintain acceptable color (≥7, 1–9 scale). Trinexapac‐ethyl initially caused discoloration but bermudagrass recovered and had color enhanced 10 to 25% from nontreated. Trinexapac‐ethyl reduced clippings 67% from nontreated while clippings, percentage of lateral regrowth, and aerification recovery increased with N rate. Bermudagrass treated with TE had similar root mass to nontreated but 5% greater stolon and rhizome mass, 18% higher chlorophyll concentration, up to 67% reduced lateral regrowth, and up to 38% reduced aerification recovery. Trinexapac‐ethyl reduced leaf N, P, K, Mg, S, and Fe concentrations 10 to 25% and increased rhizome concentrations 8 to 36%. Nutrients recovered through clippings were reduced ≈70% from TE applications while TE‐treated turf had increased N, P, K, Ca, Mg, S, Mn, and Fe retention in stolons and rhizomes. Overall, TE enhanced color while reducing nutrient translocation from rhizomes to leaves, thus increasing bermudagrass nutrient retention.

Nitrogen Uptake and Leaching under Annual Bluegrass Ecotypes and Bentgrass Species: A Lysimeter Experiment

Nitrate (NO3−) can leach from golf greens, potentially causing the degradation of surface and ground water quality. A greenhouse experiment was conducted with 11 annual bluegrass (Poa annua var. reptans Hausskn.) ecotypes from eastern Canada (Quebec and Ontario) and the USA, and three bentgrass (Agrostis spp.) species to compare N uptake and potential for N leaching. Two‐month‐old grasses were established for a 6‐wk period in lysimeter columns simulating a golf‐green profile. An unplanted root zone control was included. Water‐soluble fertilizer was applied at 25 kg N ha−1 (NH4NO3) every 14 d for 57 d. Leachate samples were collected every second day and analyzed for NO3–N and ammonium N (NH4–N) content. Dry weight and N concentration were determined on clippings, shoots, and roots. Ammonium N leaching was negligible for all grasses. Less NO3–N leaching losses occurred under bentgrasses (6–11% of applied N) than under annual bluegrasses (28–71% of applied N). Differences in NO3–N leaching were also found within annual bluegrasses; Quebec P. annua > Ontario P. annua > USA P. annua Grasses with a greater aboveground biomass developed a larger and deeper root system and were associated with a greater N uptake (r = 0.94) and, therefore, a lower NO3–N leaching (r = −0.94). Breeding programs and management practices to improve turfgrass root development appear to be critical to reduce fertilizer N leaching under sand‐based putting greens.

Normal and Flush Irrigation Effects on Nitrogen Leaching from Simulated Golf Greens in the Greenhouse

Nitrogen (N) can leach in porous golf greens, especially when they are flushed with high rates of irrigation. Drain water often discharges to the surface, possibly endangering surface waters with eutrophic concentrations of nitrogen. A greenhouse study was initiated to study the effects of fertilizer source and rate and irrigation schemes on leaching of nitrate and ammonium nitrogen. Simulated golf green columns were sodded with bermudagrass. Treatments were 3 fertilizer sources (20‐20‐20, ammonium nitrate, and a sulfur‐coated urea), 3 rates (zero control, 12, and 24 kg ha−1), and 2 irrigation schemes. The first was a daily rate of 0.6 mm (N.I.), and the second was the same daily rate with several flushes of 11.5 cm each (FL). Essentially no nitrogen leached for the N.I. scheme, whereas the FL treatment resulted in significant leaching of nitrate‐N. Ammonium‐N leached to a much less extent than nitrate‐N. The nitrate‐N concentration “break through” occurred earlier, the peaks were higher, and the flushes were more prominent for 20‐20‐20 and ammonium nitrate than for the sulfur‐coated urea. The sulfur‐coated urea had a gradual nitrate‐N concentration peak that tapered off slowly. The percent N leached of that applied was higher for the flushes, and all sources were the same for flushes and the high N rate (about 20%). At the low N rate and flushes, the percent leached was highest for ammonium nitrate (10.2%), 20‐20‐20 was intermediate (4.3%), and sulfur‐coated urea was the lowest (0.14%). These data show that fertilizer sources and rates can make a difference in nitrate‐nitrogen leaching but only when significant leaching is taking place as with flushing.

Dead Spot Severity, Pseudothecia Development, and Overwintering of Ophiosphaerella agrostis in Creeping Bentgrass

ABSTRACT Dead spot (Ophiosphaerella agrostis) is a damaging disease of young </=6 years old) creeping bentgrass (Agrostis stolonifera) golf greens. The objectives of this 3-year field study were to determine the peak periods of dead spot activity based on increasing patch diameter and pseudothecia development, and to determine where O. agrostis overwinters. Patch diameter generally increased at a linear rate between mid-June and early August. Increases in pseudothecia production closely followed increasing patch diameter. Pseudothecia could be found within necrotic tissue as early as the first day of symptom expression and as many as 478 pseudothecia were found in a single patch. Periods of rapid dead spot development coincided with air and soil temperatures ranging from 22 to 26 degrees C. Increases in patch diameter and pseudothecia development were negligible after late August. Dead spot severity was highest in the year following green construction or fumigation, but then rapidly declined in severity in subsequent years. O. agrostis was capable of overwintering as pseudothecia or as hyphae within or on bentgrass leaf sheaths, crowns, roots, and especially the nodes of stolons.

Sorption, degradation and leaching of the fungicide iprodione in a golf green under Scandinavian conditions: measurements, modelling and risk assessment

In cold climates, fungicides are used on golf greens to prevent snow mould causing serious damage to the turf. However, fungicide residues have been detected in runoff from golf courses, which may lead to restrictions on use. There is therefore an urgent need to improve understanding of the processes affecting leaching of fungicides from turfgrass systems to allow identification of green construction and management practices that minimize environmental impacts. In this study we monitored the leaching of the fungicide iprodione in a putting green. Sorption and degradation of iprodione was measured in batch and incubation experiments, and the simulation model MACRO was used as a risk assessment tool. Degradation of iprodione was bi-phasic, with a rapid initial phase (half-life 17 h) caused by enhanced biodegradation. Degradation rates slowed considerably after 5 days, with half-lives of up to 38 days. Sorption of iprodione was linear, with a K(oc) value of ca 400 cm(3) g(-1). MACRO reasonably accurately matched measured drainflows and concentrations of iprodione in soil and drainflow. However, peak concentrations in drainage were underestimated, which was attributed to preferential finger flow due to water repellency. The results also showed the importance of the organic matter content in the green root zone in reducing leaching. It was concluded that, with 'reasonable worst-case' use, losses of iprodione from greens can occur at concentrations exceeding water quality limits for aquatic ecosystems. Snow mould problems should be tackled by adopting green root zone mixes that minimize leaching and 'best management practices' that would avoid the need for intensive prophylactic use of fungicides.

Dinitroaniline‐Induced Genetic Changes in Bermudagrass

Off‐type bermudagrasses (Cynodon spp.) continue to be a major concern on southern U.S. golf greens because of the disruption of surface uniformity and playability. The current study was undertaken to measure the genetic stability of six bermudagrass cultivars (Champion, Floradwarf, MS‐Supreme, Tifdwarf, TifEagle, and Tifgreen) in response to the two dinitroaniline herbicides pendimethalin {N‐(1‐ethylpropyl)‐3,4‐dimethyl‐2, 6‐dinitrobenzenamine} and oryzalin (3,5‐dinitro‐N 4N 4‐dipropylsuffanilamide), which are commonly applied for preemergent weed control in turf management. Four off‐types (Off‐Type 1, Off‐Type 2, Off‐Type 3, and Off‐Type 4) were derived from Champion treated with dinitroanilines during the experimental cycles. The amplified fragment length polymorphism (AFLP) analysis identified a total of 311 informative fragments with seven primer combinations, of which 162 (52.09%) were polymorphic. The number of polymorphisms detected per primer combination ranged from 18 to 27. The grouping of cultivars according to molecular and morphological data was made by multidimensional analyses: cluster analysis and canonical discriminant analysis (CDA). Phenetic analysis as well as CDA revealed that all bermudagrasses and off‐types were genetically diverse. Pairwise D 2 estimates ranged from 0.69 to 0.99 with Off‐Type 3 being the most genetically dissimilar. Unweighted pair‐group method arithmetic average analysis (UPGMA) produced two major clusters. The first contained the six bermudagrass cultivars and Off‐Type 1, Off‐Type 2, and Off‐Type 4, while Off‐Type 3 formed the second cluster. Total gene diversity (HT) across all bermudagrasses was estimated to be 0.15 and within Champion and derived off‐types gene diversity (Hc) was 0.18. Cytological analysis as well as AFLP comparison with African bermudagrass (C. transvaalensis Burtt Davy) supports our assertion that Off‐Type 3 (2n = 38) is derived from common bermudagrass. In general, results suggest that dinitroaniline herbicide principles may be used as a pathway to understand the evolutionary processes and the origin of off‐types in bermudagrass.

Soil CO2 Concentration Effects on Creeping Bentgrass Grown under Various Soil Moisture and Temperature Conditions

Use of creeping bentgrass [Agrostis stoloniferous L. var. palustris (Huds.)] on golf greens has expanded into the hotter, more humid regions of the United States where its quality is often low during summer months. The summer decline in bentgrass quality may be partially attributed to respiration rates exceeding photosynthesis during periods of supraoptimal temperatures and adverse soil conditions, such as excessive CO2 and inadequate O2 levels. The objectives of this study were to examine the effects of high temperature, high soil CO2, and irrigation scheduling on creeping bentgrass growth. A growth chamber study was conducted using `A-1' creeping bentgrass. Treatments included all combinations of three day/night temperature regimes (26.5/21 °C, 29.5/24 °C, and 32/26.5 °C), three irrigation schedules (field capacity daily, field capacity every two d, and half field capacity daily), and four soil CO2 injection levels (10%, 5%, 0.03%, and a noinjection control). Creeping bentgrass shoot and root dry weights and net photosynthetic rates were greater for day/night temperatures &lt;32/26.5 °C. High temperatures (32/26.5 °C) and 10% CO2 reduced bentgrass net photosynthesis by 37.5 μmol CO2/m2/s. Shoot and root total nonstructural carbohydrates also were lowest for highest temperature regime. Respiration exceeded gross photosynthesis at 32/26.5 °C when 5% and 10% CO2 injection levels were used, indicating a carbon deficit occurred for these conditions. Irrigation volume and frequency did not affect bentgrass growth. High temperatures combined with high soil CO2 levels produced poorest turf quality.

Effect of environmental characteristics onPythiumandMesocriconemaspp. in golf course greens in Alabama

The role the environment has on populations of Pythium and Mesocriconema spp. was investigated at 5 golf course locations in east central Alabama. Every 4 to 5 weeks soil samples were collected from 3 golf greens on each of the 5 golf courses. Environmental data, including air and soil temperature, pH and relative humidity, were also collected. Dilution plating and a combined sieving and sugar flotation procedure were conducted to determine the populations of Pythium and Mesocriconema spp. for each month. Isolates of Pythium from 4 months were also identified. Pythium spp. populations increased as soil temperature and ambient air temperature prior to sampling decreased (P < 0.05). Pythium spp. populations were highest in the winter and lowest in the spring. At some locations, populations of Mesocriconema spp. increased as soil acidity and populations of Pythium spp. decreased (P < 0.05) and as ambient air temperature prior to sampling increased (P < 0.05). Eight species of Pythium were isolated from 4 months, with Pythium rostratum being the most commonly isolated. Results suggest that Pythium and Mesocriconema spp. prefer different soil environments.

Normal and Flush Irrigation Effects On Phosphorus Leaching from Simulated Golf Greens in the Greenhouse

Fertilizer nutrients have the potential to leach from porous golf greens, especially when “flushing” is practiced where 8 or 10 cm of irrigation is applied. A greenhouse experiment was carried out with 52 cm columns (15 cm diameter) made to United States Golf Association green specifications and sodded to ‘Tifdwarf’ bermudagrass to determine the amounts of phosphorus leached for two fertilizer sources (20–20–20 and superphosphate) at three rates (0, 5, and 11 kg ha−1 added every other week for a total of 6 weeks) and two irrigation schemes (normal irrigation at 6.3 mm day−1 and the same irrigation with an additional four flushes of 8 cm each). Weekly leachate collections for 29 weeks were analyzed for soluble P. Flushes resulted in higher P concentrations in the leachate where as much as 40% of the added P was recovered in the leachate. In contrast, normal irrigations resulted in less than 10% of the P applied moving through the columns. The two fertilizer sources gave essentially similar results. The higher P rate caused higher concentrations of P in the leachate, but P concentrations for the low rate for normal irrigation were not different than the control. For flushes, the extractable P in the top 15 cm of the rooting media was lower than for normal irrigation and the extractable P in the columns was higher. Results indicate that low rates of P should be applied to golf greens and, if flushing is practiced, it should be done when little P is in the rooting media.

Effect of Ozonated Water on Creeping Bentgrass Growth in a Sand Medium

Irrigation of sand-based golf greens with ozonated water may affect grass growth and chemical processes in the root zone. The objective of this study was to evaluate the effects of ozonated and aerated water on bentgrass growth and root zone chemistry in sand-based greens over a 12-month period. Creeping bentgrass (Agrostis stolonifera) cores [10 cm diameter × 12 cm depth (3.9 × 4.7 inches)] were collected from a sand-based bentgrass nursery and placed in columns designed to collect leachate water. Cores were placed in a greenhouse and irrigated with 1) municipal tap water [6 to 8 mg·L-1 (ppm) dissolved oxygen (DO)], 2) aerated tap water (12 mg·L-1 DO), or 3) ozonated tap water (aerated plus 0.8 mg·L-1 ozone). Leachate was periodically collected and analyzed for pH, electrolytic conductivity (EC), and nutrients. Grass clippings were weighed and analyzed for total nitrogen (N) and phosphorus (P). Roots were periodically collected from selected cores to determine root distribution. At 40 and 90 days after initiating water treatments, bentgrass irrigated with ozonated water had a higher chlorophyll index than bentgrass irrigated with tap water. After 128 and 157 days, bentgrass clipping weights were significantly greater for the cores irrigated with ozonated water and, to a lesser extent, aerated water. At 61 and 149 days, nitrate (NO3-N) and EC levels were elevated in leachate from aerated and ozonated samples, suggesting increased mineralization of organic matter in those bentgrass cores. Ozonated water increased bentgrass crown weights, but had no effect on root mass. Ozonated water did not affect bentgrass tissue N and P concentrations. Statistically significant effects from ozonated water occurred within the first few months, but sustained benefits were negligible.

Regional Differences in the Relative Competitive Ability of Annual Bluegrass (Poa annua L.)

Annual bluegrass (Poa annua L.) and creeping bentgrass (Agrostis palustris Huds. syn. A. stolonifera L.) coexist on golf greens as a dynamic ecosystem in the temperate regions of the United States. In a two year field study, the competitive ability of different populations of annual bluegrass was investigated both in and out of their native environment. In April 2000, at both The Country Club in Cleveland, Ohio, a temperate environment, and Camargo Club in Cincinnati, Ohio, a transition zone environment, 72 plugs of annual bluegrass were removed from golf greens and inserted into polyvinyl chloride pipe measuring 10.2 cm in diameter and 15 cm in length to eliminate root competition between species. Thirty-six plugs then were reestablished into one of three greens at the same golf course, and the remaining 36 plugs were transported to the opposite location and also established into one of three preselected greens. Each plug was centered in a 20.3-cm-diameter sward of `L-93' creeping bentgrass to provide an initial point of reference. Competitive ability was measured as the rate of increase or decrease in average diameter of each plug. Measurements initially were taken on a bimonthly basis and then on a monthly basis for the remainder of the study. Significant (P &lt; 0.05) differences in the location × population interaction were seen in the first 2 months of the study and then not seen again until the last 2 months. The most frequent occurrence of significant (P &lt; 0.05) differences was in the variability between greens within a particular location. At each location the native population of annual bluegrass outperformed the imported population. Differences at the beginning of the study are attributed to an additional acclimation period required by the exported population following transportation to the opposite location. From our study, annual bluegrass performance was similar across populations, suggesting that management recommendations can be made on a regional basis.

Plant Responses and Characteristics Associated with Dollar Spot Resistance in Creeping Bentgrass

Dollar spot, incited by Sclerotinia homoeocarpa F.T. Bennett, is one of the most important diseases affecting creeping bentgrass (Agrostis stolonifera L.) golf greens, fairways, and tees. Genetic resistance to dollar spot is a promising control strategy. A study was initiated to: (i) evaluate dollar spot resistance of 265 collections of creeping bentgrass in two locations; (ii) determine bentgrass clone stability of dollar spot resistance; and (iii) evaluate 10 resistant and susceptible clones for disease, turf, and leaf traits. The field experiments were arranged in randomized complete blocks with six and five clonally propagated replicates in each of two locations evaluated across 2 yr in North Brunswick, NJ. Five isolates of S. homoeocarpa were used to inoculate the field experiments. New Jersey fairway collections had the highest percentage of stable dollar spot resistant clones compared with Illinois fairway and New Jersey and New York golf green collections in this particular study. Resistant clones maintained a significantly higher turf density and percentage green turf cover and smaller dollar spot diameter sizes compared with susceptible clones.

Identification of denitrifying rhizobacteria from bentgrass and bermudagrass golf greens.

As high rates of nitrogen fertilization are used in turfgrass management, there is a great potential for nitrogen loss. Research on identification of denitrifiers in turfgrass has been limited. Therefore, the aim was to identify denitrifier species and genes from turfgrass roots. Rhizobacteria were isolated from roots of bentgrass and bermudagrass in sand-based United States Golf Association (USGA) golf greens and used for denitrification biochemical analysis. Seventeen per cent (34 isolates) were identified as denitrifiers, 47% were classified as nitrate-reducers and 36% were nondenitrifiers. Identification of species of the denitrifiers was performed by chromatography fatty acid methyl ester (GC-FAME) and16S rDNA analyses. Bacillus and Pseudomonas were the major turfgrass denitrifiers. The two methods showed a 60% agreement at the genus level. Nitrite reductase genes nirK and nirS were detected in 74 and 15% of the denitrifiers, respectively, but not in nondenitrifiers. The nosZ gene encoding nitrous oxide reductase was detected in all the denitrifiers, but also in some nondenitrifiers. To our knowledge, this is the first report for identification of denitrifiers and denitrification-related genes associated with turfgrass roots. These results provide valuable data for future denitrification studies that seek to improve turfgrass nitrogen management for maximum efficiency.

Soil Gas, Temperature, Matric Potential, and Creeping Bentgrass Growth Response to Subsurface Air Movement on a Sand-based Golf Green

Creeping bentgrass (Agrostis palustris Huds.) is used on putting greens for its fine-leaf texture, consistent speed, smooth ball roll, and year-round color. In recent years bentgrass use has extended into the warmer climates of the southern United States. Being a C3 plant, bentgrass is not well adapted to extended hot and humid environmental conditions. Subsurface air movement systems are now commercially available that can transport air through the root zone to alter soil conditions and potentially improve bentgrass survival. This research investigated the effects of subsurface air movement on the composition of soil gases, matric potential, temperature, and growth response of a sand-based creeping bentgrass golf green. Treatments included: air movement direction (evacuate, inject, and no air) and duration of air movement (0400-0600 hr, 1000-1800 hr, and 24 hours). Treatment combinations were imposed for 13 days. Subsurface air movement reduced CO2 at the 9-cm depth to values &lt;0.0033 mol·mol-1 when evacuating or injecting air, depending upon duration. Soil matric potentials at a 9-cm depth were decreased by a maximum of 96% when evacuating air for 24-hour duration compared to no-air plots. Soil temperatures at 9 cm were decreased ≈1 to 1.5 °C when injecting air from 1000 to 1800 hr and 24-hour treatments and increased ≈0.75 °C when evacuating air from 1000 to 1800 hr. Subsurface air movement did not improve creeping bentgrass turf quality or rooting. Although not effective in improving the growth response of creeping bentgrass, subsurface air movement may be a useful tool to improve soil gas composition, reduce excess soil moisture, and potentially reduce soil temperature(s) of heat-stressed creeping bentgrass golf greens.

Ploidy variation among herbicide-resistant bermudagrass plants of cv. TifEagle transformed with the bar gene.

A protocol was developed for biolistic transformation of hybrid bermudagrass cv. TifEagle using the bar gene. TifEagle is an ultradwarf used exclusively on golf greens. Herbicide resistance should serve as a useful management tool, especially if methyl-bromide is unavailable for fumigation prior to plant establishment. Hybrid bermudagrass is completely sterile, which should limit the chance of gene escape via out-crossing. Sliced nodes were used to initiate embryogenic tissue cultures on MS medium supplemented with 1 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.01 mg/l 6-benzylaminopurine (BA). Embryogenic tissue was bombarded with the bar gene, and herbicide-resistant tissue was selected in the dark on medium supplemented with 0.75 mg/l 2,4-D, 0.01 mg/l BA and 5-15 mg/l phosphinothricin (PPT). Resistant somatic embryos were induced to germinate in the light on MS medium supplemented with 0.13 mg/l 2,4-D and 0.5 mg/l BA. Plants were transferred to the greenhouse after rooting in the presence of 10-15 mg/l PPT and testing positive in a chlorophenol red assay. A total of 89 herbicide-resistant plants were recovered from at least nine independent events from six separate bombardments, although the number of independent transformation events was not confirmed for the entire group. Flow cytometry indicated that most of the plants (82/89) were hexaploid and that the remaining seven plants were triploid. The hexaploid plants were a darker green than the triploids or TifEagle control. Other variation, present only in the hexaploids, included an increased leaf width and length. Southern blot hybridization confirmed genomic integration of the bar gene in triploid and a subset of hexaploid herbicide-resistant plants. AFLP analysis did not indicate changes in DNA profiles using [33P] and a sample of 32 hexaploid plants recovered from a single bombardment. DNA profiles were very similar to that of the TifEagle control with a semi-automated fluorescence-based AFLP.