Abstract
There is a growing trend of cultivating hybrid bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy] on golf course putting greens in the transition zone because of its excellent quality in the summer months, coupled with less pesticide input than creeping bentgrass (Agrostis stolonifera L.). However, the long-term success of bermudagrass putting greens is hindered by low temperatures in winter months, particularly in the transition zone. To address this issue, in addition to genetic improvement for cold hardiness through the development of new cultivars, effective management approaches are necessary to enhance the winter survival of putting green–type bermudagrass. The objective of this study was to investigate the relative freeze tolerance of four bermudagrasses and the effects of raising mowing height on the freeze tolerance of putting green–type bermudagrasses. In this study, two experimental putting green–type bermudagrasses (11X2 and OKC0805) along with cultivars TifEagle and OKC3920 were tested at two mowing heights (3.2 vs. 6.4 mm) at freeze temperatures that ranged between –4 and –11 °C. The lethal temperature to kill 50% of the population (LT50) as well as regrowth vigor during recovery were evaluated. Variety ‘OKC3920’ demonstrated enhanced freeze tolerance compared with ‘TifEagle’ at both mowing heights. Increasing the mowing height from 3.2 mm to 6.4 mm improved freeze tolerance for most genotypes tested in this study. After exposing the grasses to –8 °C for 1 hour, genotypes such as 11X2 exhibited better regrowth vigor and demonstrated a faster recovery. This study suggests that golf course managers can enhance winter resilience of bermudagrass putting greens by selecting genotypes strategically with superior freeze tolerance and raising mowing heights in the fall acclimation process.
Bermudagrass (Cynodon spp.) is a perennial warm-season grass that features a C4 photosynthetic pathway and is known for its drought, high-temperature, humidity, wear, and traffic tolerance (Beard 1973; Fry and Huang 2004). Ultradwarf bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy] and hybrid bermudagrasses have been used for putting greens because of their tolerance to low mowing heights and qualities for a superior putting surface. They have fewer diseases and their performance in summer golf season is better than creeping bentgrass (Agrostis stolonifera L.) (O’Brien and Hartwiger 2014). In addition, the peak growth of the ultradwarf bermudagrass aligns with peak golf rounds in the United States (Wurth et al. 2020). Creeping bentgrass, a cool-season turfgrass, is the most commonly used turfgrass species for putting greens in the transition zone. However, managing these greens during hot and humid summers requires costly inputs while the playing conditions decline (Miller and Brotherton 2020). In response to these challenges, there has been a notable shift toward planting more bermudagrass on putting greens since the late 1990s (Hanna and Elsner 1999). This transition has resulted in substantial cost savings in terms of chemical inputs and associated labor expenses (O’Brien and Hartwiger 2014). One of the challenges to the survival and long-term success of bermudagrass on putting greens is the low winter temperatures experienced in the transition zone. Popular ultradwarf bermudagrasses lack suitable winterhardiness and are subject to severe loss by winterkill when grown in the transition zone (DeBoer et al. 2019). Addressing this issue by improving winter survivability of bermudagrass putting greens is crucial for ensuring its viability and sustainability in the long term.
Previous research conducted at Oklahoma State University (OSU) demonstrated significant variation in freeze tolerance among bermudagrass cultivars (Anderson et al. 1993, 2002, 2007; Gopinath et al. 2021a, 2021b). This variation underscores the potential for developing improved freeze-tolerant bermudagrass, which would contribute to more sustainable turfgrass management practices (Yu et al. 2022). At OSU, bermudagrass breeding efforts have been ongoing since the mid 1980s, with a primary focus on developing freeze-tolerant bermudagrass varieties (Taliaferro et al. 2004). One of the recent advancements in this area is the introduction of ‘OKC1131’ (Tahoma 31®, hereafter referred to as Tahoma 31) hybrid bermudagrass (Wu et al. 2020). It has demonstrated exceptional freeze tolerance with a lethal temperature to kill 50% of the population (LT50) at least 3.4 °C lower than ‘Champion Dwarf’ (Gopinath et al. 2021b). In addition, a recently released putting green–type bermudagrass ‘OKC3920’ exhibited similar freeze tolerance to Tahoma 31 (Gopinath et al. 2021b; Wu et al. 2022). As the breeding efforts continued, additional experimental selections of green-type bermudagrass have shown improved freeze tolerance beyond industry standards (Gopinath et al. 2021b). Considering the warm-season characteristics of bermudagrass and the low winter temperatures experienced in the transition zone, it is imperative to explore alternative approaches, including appropriate management practices, to enhance freeze tolerance alongside genotype selection.
Mowing height has long been recognized as a critical factor influencing the freeze tolerance of turfgrass (Beard 1969, 1973; Beard and Rieke 1966). A study conducted by Beard (1973) noted that reducing the mowing height in Kentucky bluegrass (Poa pratensis) from 5.0 to 3.8, 2.5, and 1.3 cm reduced cold tolerance. Similarly, Kvalbein and Aamlid (2012) observed improved spring performance on cool-season golf greens with increased mowing height in Nordic countries. This improvement is likely a result of the increased carbohydrate content during the acclimation process by raising mowing height (Qian and Fu 2005). The positive impact of increased carbohydrate levels on freeze tolerance has been reported in various other species. Shahba et al. (2003) reported an increase in carbohydrates in freeze-tolerant saltgrass [Distichlis spicata (L.) Greene] compared with its freeze-sensitive counterpart. Ball et al. (2002) discovered a greater quantity of soluble carbohydrates in freeze-tolerant buffalograss [Buchloë dactyloides (Nutt.) Engelm.] compared with a freeze-sensitive variety. Similarly, Patton et al. (2007) emphasized the importance of specific carbohydrate components, such as glucose, total reducing sugars, and total soluble sugar-to-starch ratios, in enhancing the freeze tolerance of zoysiagrass (Zoysia spp.). However, limited research exists on quantifying the impacts of mowing heights on freeze tolerance in putting green–type bermudagrass. Therefore, the objective of this study was to investigate the relative freeze tolerance of four bermudagrass genotypes and the effects of raising mowing height on the freeze tolerance of selected putting green–type bermudagrasses. By examining this relationship, this study aimed to contribute valuable insights into enhancing the winter survival and performance of bermudagrass in putting green settings.
Materials and Methods
The study was conducted at the Controlled Environment Research Laboratory at OSU located in Stillwater, OK, USA. The experiment included two elite experimental putting green–type bermudagrasses 11X2 and OKC0805, which were developed by the OSU bermudagrass breeding program. In addition, a newly released cold-hardy putting green–type bermudagrass cultivar, OKC3920, was included as the freeze-tolerant standard for comparison. ‘TifEagle’ was selected as a commercial standard because it showed improved freeze tolerance than most commercial cultivars, such as ‘Champion’, ‘Floradwarf’, ‘MS-Supreme’, and ‘MiniVerde’, in a previous controlled environment study (Anderson et al. 2002).
The grasses tested in our study were propagated clonally using a single phytomer consisting of a root, crown, and shoot. This propagation was done in a mixture of sand (Lightle Sand & Construction LLC, Hennessey, OK, USA) and peat (Berger Professional Peat Moss BP-P; Saint-Modeste, QC, Canada) at a ratio of 80:20. The grasses were planted in “cone-tainers” (RayLeach Cone-tainer Nursery, Canby, OR, USA) measuring 210 mm in depth and 38 mm in diameter. Two sets of grasses were established in a plant growth chamber (PGC Flex growth chamber; Conviron, Winnipeg, Canada) on 15 Feb and 3 Mar 2022, respectively. During the establishment phase, the growth chamber was programmed to maintain a day/night temperature of 32/28 °C, with a 14-h photoperiod (0600–2000 HR) providing a photosynthetically active radiation (PAR) of 900 μmol⋅m–2⋅s–1. Weekly fertilization was carried out using a 20–10–20 N–P–K fertilizer (J.R. Peters, Allentown, PA, USA) at a rate of 24 kg N⋅ha–1. Fertilizer was applied to each cone-tainer using a syringe, with 7 mL of the fertilizer solution containing 2 g of the product per liter.
Each grass was maintained at two different heights: 3.2 and 6.4 mm. The grasses were watered twice a day during establishment to promote their growth, followed by daily irrigation thereafter. In addition, the cone-tainers were top-dressed weekly with sand and peat at an 80:20 ratio, followed by light watering. To prevent insect pests, bifenthrin (Talstar; FMC Corp., Philadelphia, PA, USA) and surfactant (Aduro; Winfield Solutions, LLC, St. Paul, MN, USA) were rotated with abamectin (Avid 0.15EC; Syngenta, Greensboro, NC, USA), all at the label rates in a biweekly schedule.
After the grasses were fully established, the temperature in the growth chamber was adjusted to 24/20 °C day/night, with a 14-h photoperiod (0700–2100 HR) at a PAR of 900 μmol⋅m–2⋅s–1 for 1 week. After preacclimating, the grasses underwent a cold acclimation period of 4 weeks at 8/2 °C day/night, with a photoperiod of 10 h (0700–1700 HR) and a PAR of 400 μmol⋅m–2⋅s–1. To minimize temperature fluctuations caused by watering during the acclimation process, a bucket of water was placed inside the growth chamber to serve as a stable water source. During the last week of the cold acclimation period, each cone-tainer was hand-watered individually with the same amount of water using a beaker to maintain consistent soil moisture levels. Irrigation was then ended 2 d before the freeze tests, and then plants were transferred subsequently to the freeze chamber (E8 plant growth chamber; Conviron, Winnipeg, Canada) for freeze tests. The cone-tainers were randomized within the mowing height treatments inside the freeze chamber (Patton and Reicher 2007). Ten additional cone-tainers with grasses were placed randomly in the freeze chamber, with thermocouple sensors inserted at the center of each cone-tainer, 2.5 cm into the potting media, to monitor soil temperature. Data from the thermocouple sensors were logged into the control panel of the freeze chamber and displayed on the screen. The same freeze test was repeated one more time with another set of grasses.
The freeze chamber was programmed to maintain an air temperature of 2 °C for 1 h, cooling linearly by 1 °C/h. When the air temperature reached 0 °C, crushed ice was sprinkled over the grass canopy to prevent super cooling (Anderson et al. 1993). When the air temperature dropped to –3 °C, it was held for 18 h to dissipate latent heat from the potting media, followed by a gradual linear decline of 1 °C/h (Gopinath et al. 2021a, 2021b). The target temperatures ranged from –4 to –11 °C, with 1 °C intervals covering the predicted temperature range associated with complete survival to complete mortality for bermudagrass. When the average soil temperature reached each target temperature, four cone-tainers of each treatment were taken out of the chamber.
After being removed from the freeze chamber, the cone-tainers were thawed overnight at 2 °C in the plant growth chamber before being transferred to a controlled-temperature greenhouse for recovery. The greenhouse was set to a day/night temperature of 30 °C/25 °C, respectively, with an average PAR of 650 μmol⋅m–2⋅s–1 supplemented with high-pressure sodium lamps. During the recovery period, the regrowth vigor of the grasses was assessed visually weekly for 5 weeks based on the percent coverage on a 0% to 100% scale. In addition, on the fifth week of recovery, the survivability of each grass was evaluated using binary values, where 1 represented an alive plant and 0 represented a dead plant.
The statistical analysis for determining the LT50 values and the percent green coverage was performed using SAS (ver. 9.4; SAS Institute, Cary, NC, USA). The PROC PROBIT procedure was used for logistic regression analysis to estimate the LT50 values for each genotype at each mowing height. This procedure generated a table of predicted percentage survival for each genotype at different temperatures and mowing heights, and LT50 was estimated for each variety at two mowing heights (Anderson et al. 1993, 2002; Dunne et al. 2019; Kimball et al. 2017; Patton and Reicher 2007; Shahba et al. 2003). For analyzing LT50 and percent green coverage, the PROC MIXED procedure was used. The appropriate error term was used to determine significant differences between genotypes across the various treatments, and means separation was conducted using Fisher’s protected least significant difference values at a significance level of α = 0.05.
Results
The LT50 values of each genotype for the first and second sets of experiments at different mowing heights are presented in Tables 1 and 2, respectively. In the first experiment, the LT50 values ranged from –7.3 to –9.1 °C at 3.2 mm. The freeze-tolerant standard, ‘OKC3920’ had the lowest LT50 value of –9.1 °C, which was significantly lower than ‘TifEagle’, 11X2, and OKC0805. At a mowing height of 6.4 mm, LT50 values ranged from –8.1 to –10.1 °C. ‘TifEagle’ had the highest LT50 value of –8.1 °C, which was significantly greater than ‘OKC3920’ and OKC0805. Raising the mowing height from 3.2 mm to 6.4 mm improved the freeze tolerance for OKC0805 significantly, with an LT50 value decreased from –8.3 to –10.1 °C. For the remaining genotypes, increasing the mowing height resulted in a numerical decrease in LT50 by 0.4 to 1 °C, although these reductions were not statistically significant.
Mean lethal temperatures resulted in 50% survival of bermudagrass genotypes at two mowing heights in the first experiment when exposed to soil temperatures ranging from –4 to –11 °C under controlled environment conditions.
Mean lethal temperatures resulted in 50% survival of bermudagrass genotypes at two mowing heights in the second experiment when exposed to soil temperatures ranging from –4 to –11 °C under controlled environment conditions.
In the second experiment, at a mowing height of 3.2 mm, the LT50 values ranged from –7.1 to –8.9 °C. ‘TifEagle’ had the greatest LT50 value of –7.1 °C, which was significantly higher than the other genotypes. At a mowing height of 6.4 mm, the LT50 values ranged from –8.9 to –10.5 °C. TifEagle had an LT50 value of –8.9 °C, which was higher than 11X2 and ‘OKC3920’. Raising the mowing height from 3.2 mm to 6.4 mm resulted in a notable decrease in the LT50 value for ‘TifEagle’, 11X2, and ‘OKC3920’. Although no statistically significant differences were observed for OKC0805, there was a recorded numerical LT50 decrease of 1 °C with the increase in mowing height. The LT50 values reported in our study were similar to findings reported by Gopinath et al. (2021b), in which ‘OKC3920’ had a lower LT50 value than commercial ultradwarf bermudagrass ‘Champion Dwarf’. However, the LT50 values reported in our study were lower than those in the study by Gopinath et al. (2021b), which may be a result of differences in the growth media used, and moisture levels during the acclimation period and freeze treatment.
The regrowth vigor was assessed over a 5-week period for each genotype. Considering that the LT50 values for the least freeze-tolerant genotypes were just less than –7°C, regrowth under the freeze treatment at –8°C was reported (Figs. 1 and 2). In the first experiment, at a mowing height of 3.2 mm, ‘OKC3920’ had 31% coverage 1 week after recovery, which was greater than the rest of the genotypes (Fig. 1). ‘TifEagle’ and OKC0805 showed a similar but slower regrowth vigor. Despite 11X2 exhibiting the same LT50 value as ‘TifEagle’ and OKC0805, it demonstrated a significantly faster regrowth rate than ‘TifEagle’ after 4 weeks, and its recovery surpassed OKC0805 after 5 weeks. At the 6.4-mm mowing height, the regrowth vigor was similar among all the nonultradwarf bermudagrass genotypes (‘OKC3920’, OKC0805, and 11X2), with minor differences. These genotypes had a greater percent coverage in comparison with ‘TifEagle’ throughout the entire recovery period (Fig. 1). At the 2-week recovery mark, OKC0805 displayed a greater percent coverage compared with 11X2 and ‘OKC3920’. Despite OKC0805 having a lower LT50 than 11X2 in the first experiment (Table 1), 11X2 showed similar growth vigor in most cases during the recovery period at 6.4 mm.
Percentage of coverage (regrowth) of four bermudagrass genotypes over 5 weeks after being exposed to a soil temperature of –8 °C for 1 h at two mowing heights in the first experiment. For each rating date, similar letters above each genotype indicate that means are not significantly different (P < 0.05). WAT = weeks after treatment.
Citation: HortScience 58, 11; 10.21273/HORTSCI17351-23
Percentage of coverage (regrowth) of four bermudagrass genotypes over 5 weeks after being exposed to a soil temperature of –8 °C for 1 h at two mowing heights in the first experiment. For each rating date, similar letters above each genotype indicate that means are not significantly different (P < 0.05). WAT = weeks after treatment.
Citation: HortScience 58, 11; 10.21273/HORTSCI17351-23
Percentage of coverage (regrowth) of four bermudagrass genotypes over 5 weeks after being exposed to a soil temperature of –8 °C for 1 h at two mowing heights in the first experiment. For each rating date, similar letters above each genotype indicate that means are not significantly different (P < 0.05). WAT = weeks after treatment.
Citation: HortScience 58, 11; 10.21273/HORTSCI17351-23
Percentage of coverage (regrowth) of four bermudagrass genotypes over 5 weeks after being exposed to a soil temperature at –8 °C for 1 h at two mowing heights in the second experiment. For each rating date, similar letters above each genotype indicate that means are not significantly different (P < 0.05). WAT = weeks after treatment.
Citation: HortScience 58, 11; 10.21273/HORTSCI17351-23
Percentage of coverage (regrowth) of four bermudagrass genotypes over 5 weeks after being exposed to a soil temperature at –8 °C for 1 h at two mowing heights in the second experiment. For each rating date, similar letters above each genotype indicate that means are not significantly different (P < 0.05). WAT = weeks after treatment.
Citation: HortScience 58, 11; 10.21273/HORTSCI17351-23
Percentage of coverage (regrowth) of four bermudagrass genotypes over 5 weeks after being exposed to a soil temperature at –8 °C for 1 h at two mowing heights in the second experiment. For each rating date, similar letters above each genotype indicate that means are not significantly different (P < 0.05). WAT = weeks after treatment.
Citation: HortScience 58, 11; 10.21273/HORTSCI17351-23
In the second experiment, when the mowing height was set at 3.2 mm, ‘TifEagle’ exhibited a recovery rate near 0% (Fig. 2). This can be attributed to its LT50 value of –7.1 °C, indicating that the majority of the plants were killed when exposed to temperatures as low as –8 °C. On the other hand, 11X2 showed high regrowth vigor throughout the 5-week period, followed by ‘OKC3920’ and OKC0805. The results indicate that 11X2 demonstrated favorable regrowth performance whereas ‘TifEagle’ exhibited poor recovery. This outcome can be attributed to the low freeze tolerance of ‘TifEagle’ and the potentially slower lateral growth rate. At 6.4 mm, 11X2 and ‘OKC3920’ showed similar overall regrowth vigor throughout the experiment and reached 100% coverage by week 5 (Fig. 2). In addition, OKC0805 initially had better recovery than ‘TifEagle’ in week 1, but their coverages were comparable thereafter. This can be attributed to the fact that ‘TifEagle’ exhibited a lower LT50 value (–8.9 °C) (Table 2) in the second experiment compared with the first experiment (–8.1 °C) (Table 1), resulting in greater survivability. Among the genotypes, 11X2 displayed greater regrowth vigor than OKC0805 in most cases, despite their LT50 values being similar (Table 2).
Discussion
‘TifEagle’ is a popular ultradwarf variety commonly used for putting greens (Guertal and Evans 2006). Similar to other commercially available ultradwarf bermudagrasses such as ‘Champion’, ‘Mini Verde’, and ‘Tifdwarf’, they were likely derived from a mutation of the ‘Tifgreen’ bermudagrass (Harris-Shultz et al. 2010). There is a high genetic similarity among them, as indicated by a coefficient of 1.00 using simple sequence repeat molecular markers (Fang et al. 2017; Wang et al. 2010). In contrast to ‘TifEagle’, the rest of the genotypes tested in our study were nonultradwarf types, but were tolerant to a mowing height of 3.2 mm or greater (Earp 2023). Using these improved freeze-tolerant putting green–type bermudagrasses could potentially lower the current recommended threshold for covering putting greens during winter. The reduction in covering events would result in cost savings in terms of labor required for the installation and removal of the protective covers (O’Brien and Hartwiger 2013). Incorporating these improved cold-hardy putting green bermudagrasses could also increase the revenue of golf courses by extending the number of playable days during the winter months, leading to potential economic benefits for the facility.
Raising mowing height has been a commonly recommended practice in golf course management for enhancing carbohydrate accumulation by increasing leaf area for photosynthate production (Beard 1973; Lowe 2012; O’Brien and Hartwiger 2007). Maintaining crowns with sufficient stored carbohydrates is essential for the continuous production of new roots and shoots, which helps replace damaged organs. Furthermore, the extra foliage produced by raising mowing height creates a protective buffer zone that acts as a barrier against various detrimental factors, including traffic and extreme temperature fluctuations that could affect the crown adversely (Vincelli et al. 2017). However, to the best of our knowledge, this study is the first to quantify the impact of mowing height on the freeze tolerance of putting green–type bermudagrasses.
Conclusion
The relationships among mowing height, freeze tolerance, and regrowth vigor after freezing injury is a crucial aspect of turfgrass management. The results obtained from our study demonstrate the potential improvements that can be made to enhance the winter survival of bermudagrass putting greens. One of the findings of this research is the superior freeze tolerance exhibited by nonultradwarf genotypes, with particular emphasis on ‘OKC3920’ outperforming the widely used ‘TifEagle’ variety. This discovery opens up new possibilities for maintaining the longevity of bermudagrass putting greens in the transition zone. By incorporating more freeze-tolerant genotypes into golf course management strategies, golf course managers can ensure that turfgrass can better withstand freezing conditions, leading to improved playability in the spring. Furthermore, our study highlights the prominent regrowth vigor observed in the recovery process of the 11X2 genotype. This characteristic suggests that this particular bermudagrass genotype has a remarkable ability to bounce back and restore its vigor after experiencing freezing conditions. By integrating these resilient genotypes into turfgrass management practices, recovery after injury caused by freeze stress can be expected.
In addition to genotype selection, the study highlighted the crucial role of mowing height in relation to the cold tolerance of bermudagrass. Lowering the mowing height can compromise the capacity of turfgrass to tolerate freezing conditions, making it more susceptible to damage. Raising the mowing height can promote carbohydrate accumulation within the turfgrass and shield the growing point from injury, thereby enhancing its resilience against freezing temperatures. This finding underscores the importance of raising mowing height during fall overwintering preparation as a vital management practice for improving the freeze tolerance of turfgrass. Quantifying the effect of mowing height on freeze tolerance enables golf course managers to make informed decisions when implementing turfgrass management practices. By selecting genotypes with superior freeze tolerance and by optimizing mowing heights, golf course managers can create more resilient bermudagrass putting greens during winter conditions. Future research is needed to quantify the amount of carbohydrates during cold acclimation at different mowing heights for putting green bermudagrasses.
References Cited
Anderson JA, Taliaferro CM, Martin DL. 1993. Evaluating freeze tolerance of bermudagrass in a controlled environment. HortScience. 28:955–959. https://doi.org/10.21273/HORTSCI.28.9.955.
Anderson JA, Taliaferro CM, Martin DL. 2002. Freeze tolerance of bermudagrasses: Vegetatively propagated cultivars intended for fairway and putting green use, and seed-propagated cultivars. Crop Sci. 42:975–977. https://doi.org/10.2135/cropsci2002.9750.
Anderson JA, Taliaferro CM, Wu YQ. 2007. Freeze tolerance of seed- and vegetatively-propagated bermudagrasses compared with standard cultivars. Appl Turfgrass Sci. 4:1–7. https://doi.org/10.1094/ATS-2007-0508-01-RS.
Ball S, Qian YL, Stushnoff C. 2002. Soluble carbohydrates in two buffalograss cultivars with contrasting freezing tolerance. J Am Soc Hortic Sci. 127(1):45–49. https://doi.org/10.21273/JASHS.127.1.45.
Beard JB. 1969. Winter injury of turfgrasses, p 226–234. Proc 3rd Int Turfgrass Res Conf., Sports Turf Res Inst., Bingley, Yorkshire, UK.
Beard JB. 1973. Turfgrass: Science and Culture. Prentice Hall, Englewood Cliffs, NJ, USA.
Beard JB, Rieke PE. 1966. The influence of nitrogen, potassium and cutting height on the low temperature survival of turfgrasses. Agron Abstract. 1966:34.
DeBoer EJ, Richardson MD, McCalla JH, Karcher DE. 2019. Reducing ultradwarf bermudagrass putting green winter injury with covers and wetting agents. Crop Forage Turfgrass Manag. 5(1):1–9. https://doi.org/10.2134/cftm2019.03.0019.
Dunne JC, Tuong TD, Livingston DP, Reynolds WC, Milla-Lewis SR. 2019. Field and laboratory evaluation of bermudagrass germplasm for cold hardiness and freezing tolerance. Crop Sci. 59(1):392–399. https://doi.org/10.2135/cropsci2017.11.0667.
Earp R. 2023. Evaluation of experimental greens–type hybrid bermudagrass selections by genetic profiling, morphological measurements, and field testing (MS thesis), Oklahoma State University, Stillwater, OK, USA.
Fang T, Wu YQ, Moss JQ, Walker NR, Martin DL. 2017. Genetic diversity of greens-type bermudagrass genotypes as assessed with simple sequence repeat markers. Int Turfgrass Soc Res J. 13:1–8. https://doi.org/10.2134/itsrj2016.05.0435.
Fry JD, Huang B. 2004. Applied turfgrass science and physiology. Wiley, Hoboken, NJ, USA.
Gopinath L, Moss JQ, Wu YQ. 2021a. Evaluating the freeze tolerance of bermudagrass genotypes. Agrosys Geosci Environ. 4:e20170. https://doi.org/10.1002/agg2.20170.
Gopinath L, Moss JQ, Wu YQ. 2021b. Quantifying freeze tolerance of hybrid bermudagrasses adapted for golf course putting greens. HortScience. 56:478–480. https://doi.org/10.21273/HORTSCI15606-20.
Guertal EA, Evans DL. 2006. Nitrogen rate and mowing height effects on TifEagle bermudagrass establishment. Crop Sci. 46(4):1772–1778. https://doi.org/10.2135/cropsci2006.01-0006.
Hanna WW, Elsner JE. 1999. Registration of ‘TifEagle’ bermudagrass. Crop Sci. 39(4):1258.
Harris-Shultz KR, Schwartz BM, Hanna WW, Brady JA. 2010. Development, linkage mapping and utilization of microsatellites in bermudagrass. J Am Soc Hortic Sci. 135:511–520. https://doi.org/10.21273/JASHS.135.6.511.
Kimball JA, Tuong TD, Arellano C, Livingston DP, Milla-Lewis SR. 2017. Assessing freeze-tolerance in St. Augustinegrass: Temperature response and evaluation. Euphytica. 213:110. https://doi.org/10.1007/s10681-017-1899-z.
Kvalbein A, Aamlid TS. 2012. Impact of mowing height and late autumn fertilization on winter survival and spring performance of golf greens in the Nordic countries. Acta Agric Scand. 62:122–129. https://doi.org/10.1080/09064710.2012.681059.
Lowe T. 2012. Changing times in ultradwarf bermudagrass putting green management. chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.usga.org/content/dam/usga/pdf/imported/course-care/lowe-changing-6-22-12.pdf. [accessed 30 Aug 2023].
Miller GL, Brotherton MA. 2020. Creeping bentgrass summer decline as influenced by climatic conditions and cultural practices. Agron J. 112(5):3500–3512. https://doi.org/10.1002/agj2.20362.
O’Brien P, Hartwiger C. 2007. Ultradwarfs in the off-season–a winter wonderland. USGA. Green Section Record. November/December. 45(6).
O’Brien P, Hartwiger C. 2013. Covering guidelines for ultradwarf bermudagrass putting greens. https://www.usga.org/course-care/2013/01/covering-guidelines-for-ultradwarf-bermudagrass-putting-greens-21474853349.html. [accessed 30 Aug 2023].
O’Brien P, Hartwiger C. 2014. Calculating costs confidently. Green Section Record. 52(9):1–6.
Patton AJ, Cunningham SM, Volenec JJ, Reicher ZJ. 2007. Differences in freeze tolerance of zoysiagrasses: II. Carbohydrate and proline accumulation. Crop Sci. 47(5):2170–2181. https://doi.org/10.2135/cropsci2006.12.0784.
Patton AJ, Reicher ZJ. 2007. Zoysiagrass species and genotypes differ in their winter injury and freeze tolerance. Crop Sci. 47:1619–1627. https://doi.org/10.2135/cropsci2006.11.0737.
Qian YL, Fu JM. 2005. Response of creeping bentgrass to salinity and mowing management: Carbohydrate availability and ion accumulation. HortScience. 40(7):2170–2174. https://doi.org/10.21273/HORTSCI.40.7.2170.
Shahba MA, Qian YL, Hughes HG, Koski AJ, Christensen D. 2003. Relationships of soluble carbohydrates and freeze tolerance in saltgrass. Crop Sci. 43(6):2148–2153. https://doi.org/10.2135/cropsci2003.2148.
Taliaferro CM, Martin DL, Anderson JA, Anderson MP, Guenzi AC. 2004. Broadening the horizons of turf bermudagrass. US Golf Assoc Turf Environ Res Online. 3(20):1–9.
Vincelli P, Clarke B, Munshaw G. 2017. Chemical control of turfgrass diseases 2017. Univ. Kentucky Coop. Ext. http://www2.ca.uky.edu/agcomm/pubs/ppa/ppa1/ppa1.pdf. [accessed 11 Apr 2017].
Wang Z, Wu Y, Martin DL, Gao H, Samuels T, Tan C. 2010. Identification of vegetatively propagated turf bermudagrass cultivars using simple sequence repeat markers. Crop Sci. 50:2103–2111. https://doi.org/10.2135/cropsci2010.02.0116.
Wu YQ, Martin DL, Moss JQ, Walker NR, Fontanier CH (inventors). 2020. Bermudagrass plant named ‘OKC 1131’. The Board of Regents for Oklahoma State University (assignee). US Plant Patent PP31695. (Filed 25 May 2018, granted 21 Apr 2020).
Wu YQ, Moss JQ, Martin DL, Walker NR, Fontanier CH. 2022. ‘OKC3920’ turf bermudagrass: A new cold hardy cultivar for use on golf course putting greens. Presented at the ASA, CSSA, SSSA International annual meeting, 6–9 Nov, Baltimore, MD.
Wurth AM, Ellington EH, Gehrt SD. 2020. Golf courses as potential habitat for urban coyotes. Wildl Soc Bull. 44(2):333–341. https://doi.org/10.1002/wsb.1081.
Yu S, Schoonmaker AN, Yan L, Hulse‐Kemp AM, Fontanier CH, Martin DL, Moss JQ, Wu YQ. 2022. Genetic variability and QTL mapping of winter survivability and leaf firing in African bermudagrass. Crop Sci. 62(6):2506–2522. https://doi.org/10.1002/csc2.20849.
