Managing Stress Tolerance on Warm-Season Putting Greens in the Transition Zone

The use of warm-season putting greens in the transition zone has increased in recent years. Ultradwarf bermudagrass (Cynodon dactylon (L.) Pers x C. transvaalensis Burtt-Davy) is the most prevalent warm-season putting green selection in the transition zone, however, newly developed greens-type zoysiagrass (Zoysia spp.) cultivars represent another potential selection for golf courses. The two major limitations of warm-season grasses in the transition zone are a general lack of cold- and shade-tolerance. Protective covers are essential to protect ultradwarf bermudagrass putting greens in the winter months. Unfortunately, golf courses can still experience winterkill underneath protective covers. Two field trials were conducted with a goal of improving upon management strategies to improve the performance and survival of golf course putting greens under stress. Both trials were conducted on sand-based rootzones and were managed with cultural practices consistent with golf course putting greens found in the region. The first trial was conducted during the winters of 2019-20 and 2020-21 on a putting green consisting of four replicated whole plots of the three most prevalent ultradwarf bermudagrass cultivars. The goal of the trial was to improve upon cover strategies by supplementing protective covers with three air gap materials to provide additional insulation. Although materials such as straw and batting fabric provided moderate soil temperature gains compared to the cover alone, protective covers alone provided sufficient protection from winterkill during adverse weather conditions. Because of the high purchasing cost and labor requirement associated, wall to wall coverage of air gaps is not likely feasible. Where air gaps could be valuable is spot coverage of portions of putting greens that are especially vulnerable to winterkill (shade, north slopes, high traffic) and historically receive winterkill. The second trial was conducted during the growing seasons (June to October) of 2020 and 2021 on a putting green consisting of three replicated whole plots of ‘Lazer’ zoysiagrass (Zoysia matrella (L.) Merrill x Z. minima (Colenso) Zotov). Shade is a significant problem for golf course putting greens, so it is important to identify the precise amount of light is needed to maintain an acceptable putting green. Zoysiagrass is generally more shade tolerant than bermudagrass, however, ‘Lazer’ zoysiagrass has not been studied. The goal of this trial was to compare ‘Lazer’ zoysiagrass to an industry-standard putting green selection, ‘TifEagle’ bermudagrass, under varying levels of shade and management practices. Management practices included two mowing heights (2.5- and 3.2-mm) and with or without the treatment of the plant growth regulator, trinexapac-ethyl. The minimum daily light integral (DLI) was determined for both species and surface characteristics, including ball roll distance and surface firmness, were monitored. ‘Lazer’ zoysiagrass demonstrated superior shade-tolerance and had a minimum DLI requirement about 10 mol m-2 d-1 less than ‘TifEagle’. Surface firmness was greater for ‘Lazer’, while ‘TifEagle’ produced greater ball roll distance for most rating dates. However, both species consistently produced industry-standard ball roll distance. Results from this trial suggest that ‘Lazer’ zoysia can produce acceptable putting green conditions and is better adapted than ‘TifEagle’ to moderate shade conditions

Evaluation of Ultradwarf Bermudagrass Cultural Management Practices and Identification, Characterization, and Pathogenicity of Ectotrophic Root-Infecting Fungi Associated with Summer Decline of Ultradwarf Bermudagrass Putting Greens

This research addressed the effects of cultural management practices, cultivar selection, and applications of seasonal fungicides on ultradwarf bermudagrass health and playability and occurrence of foliar diseases. Additionally, novel ectotrophic root-infecting fungi were isolated from ultradwarf bermudagrass roots exhibiting symptoms of summer decline, identified via multilocus phylogenetic analyses, and characterized by morphological assessments and pathogenicity evaluations

Using Covers and Wetting Agents to Prevent Winter Injury of Ultradwarf Bermudagrass

As ultradwarf bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy) putting green use in the United States moves further north, there is risk of sustaining winter injury from low-temperature exposure and tissue desiccation. Protective covers reduce low-temperature exposure on ultradwarf bermudagrass greens. Desiccation of turf can be caused by hydrophobic soils. Wetting agents are applied to actively growing ultradwarf bermudagrass greens to relieve symptoms of hydrophobic soils. Less is known about the effects late-fall wetting agent applications on dormant bermudagrass putting greens. This research aims to define a predicted low-temperature threshold for covering ultradwarf bermudagrass greens and to quantify the effects of a late-fall wetting agent application on winter survival of ultradwarf bermudagrass. A protective cover and wetting agent trial was conducted on a sand-based putting green with plots of ‘Champion’, ‘MiniVerde’, and ‘TifEagle’ ultradwarf bermudagrass during the winters if 2015-2016 and 2016-2017. Cover treatments were placed at forecasted low-temperature thresholds of -9.4, -7.8, -5.6, and -4.0 °C and were compared to an uncovered control. A single late-fall wetting agent application was applied to each cultivar x cover treatment. An additional wetting agent trial was conducted by comparing a single application of various wetting agent treatments to an untreated control on a sand-based ultradwarf bermudagrass putting green. Spring green-up was monitored by quantifying green turfgrass coverage through digital image analysis. Soil volumetric water content was monitored at a depth of 3.8 cm using time-domain reflectometry. The wetting agent trial included two water drop penetration tests during each season. In both seasons, reducing the cover temperature threshold resulted in significant differences in green turfgrass coverage between treatments, but lower cover temperatures did not delay green-up of turf. ‘MiniVerde’ and ‘TifEagle’ greened up significantly faster compared to ‘Champion’. In 2016, wetting agent treatments greened up significantly faster than the untreated control. Multiple wetting agent treatments significantly reduced water drop penetration times in the top three cm of the soil profile. Our research demonstrates the potential to reduce the forecasted low-temperature for covering ultradwarf bermudagrass without negatively impacting turf health, potentially reducing golf course winter labor costs

Evaluation of Ultradwarf Bermudagrass Cultural Management Practices and Identification, Characterization, and Pathogenicity of Ectotrophic Root-Infecting Fungi Associated with Summer Decline of Ultradwarf Bermudagrass Putting Greens

This research addressed the effects of cultural management practices, cultivar selection, and applications of seasonal fungicides on ultradwarf bermudagrass health and playability and occurrence of foliar diseases. Additionally, novel ectotrophic root-infecting fungi were isolated from ultradwarf bermudagrass roots exhibiting symptoms of summer decline, identified via multilocus phylogenetic analyses, and characterized by morphological assessments and pathogenicity evaluations

Etiology and Epidemiology of Mini-ring in Ultradwarf Bermudagrass Putting Greens

Mini-ring is a disease in ultradwarf bermudagrass (UDBG) [Cynodon dactylon (L.) Pers. × C. transvaalensis (Burtt-Davy)] putting greens caused by Waitea zeae (Voorhees) J.A. Crouch & Cubeta, (formerly Rhizoctonia zeae). Symptoms typically resemble frog-eye patches that are 10 to 40 cm in diameter with a bronze to orange outer ring and green center. In the southeastern United States, mini-ring symptoms appear in late-summer and generally persist until UDBG dormancy in late-fall. Mini-ring is often problematic in UDBG when nitrogen (N) fertility is reduced to manage organic matter production and improve putting green performance and perceived green speed. While W. zeae is most frequently reported as the causal agent, other species of Waitea have been isolated from UDBG exhibiting mini-ring symptoms. Waitea zeae causes visible leaf lesions and basal sheath rot in other turfgrasses; however, in UDBG, dieback of leaf tissue occurs in the absence of leaf lesions and sheath rot. Although W. zeae has been isolated from UDBG leaf tissue throughout the growing season, it is unclear if other plant tissues—e.g., root, rhizomes, and stolons—may be possible infection courts and when W. zeae infection most likely occurs. The objectives of these studies were to: I) investigate the impact of N source and N rate on mini-ring disease development and severity in UDBG; II) determine what plant tissues W. zeae can infect and when infection is most likely to occur; and III) collect and characterize isolates of Waitea spp. recovered from symptomatic UDBG putting greens. To study the impact of N on mini-ring disease severity, ammonium sulfate (AMS) [(NH4)2SO4] and urea (CH4N2O) were applied weekly to ‘P18’ (MiniVerde) and ‘TifEagle’ UDBG at rates of 4.9, 9.8, and 14.7 kg N ha-1. Mini-ring severity increased with increasing rates of AMS whereas disease symptoms in plots treated with urea remained relatively low. Cores from a UDBG putting green located in Florence, SC were collected monthly from June to October in 2016 and 2017. Isolation of W. zeae occurred in all months, isolation frequencies were greatest in August and September. In a growth chamber bioassay, UDBG roots, stolons, and leaves were infected by W. oryzae or W. zeae when inoculum when growing medium was infested with representative isolates. Nineteen Waitea species isolates were recovered from UDBG putting greens expressing mini-ring symptoms in North Carolina and South Carolina. Isolates of W. prodiga, W. oryzae, and W. zeae represented 5, 16, 79% of isolates collected. Isolates were characterized by sequencing the rDNA-internal transcribed spacer region, and these sequences clustered with Waitea species isolate sequences deposited in GenBank and previously described. These studies demonstrate the primary causal agent of mini-ring in UDBG is W. zeae, while other species of Waitea are likely involved to a lesser extent. An effective mini-ring management strategy should include regular N applications using N sources other than AMS, such as urea, to promote UDBG growth and recuperative potential and applications of fungicides mid-summer before symptom development. Fungicides should be applied in a manner that encourages movement of active ingredients into the putting green rootzone to reduce W. zeae infection of UDBG roots and stolons

Investigating Cold Hardiness and Management Practices of Warm-season Putting Green Species in the Transition Zone

Warm-season turf species are becoming increasingly popular for putting green use in the transition zone. Ultradwarf bermudagrass (Cynodon dactylon (L.) C. transvaalensis Burtt-Davy) is the prevalent warm-season putting green species, but seashore paspalum (Paspalum vaginatum Swartz) and ‘Diamond’ zoysiagrass [Zoysia matrella (L.) Merr.] may also be grown in the transition zone. Warm-season species are susceptible to winter injury and may require different management regimes than cool-season species. Therefore, the objectives of this research were to assess the impacts of various management practices on warm-season putting green species and characterize the physiological basis for differences in freeze tolerance of various warm-season putting green species. Field studies determined sampling procedures form thatch-mat depth and soil organic matter content of warm-season putting greens and assessed the impact of various management practices on different warm-season putting green species/varieties. The relative freeze tolerance of ‘Champion’ and ‘TifEagle’ ultradwarf bermudagrass cultivars, ‘SeaDwarf’ seashore paspalum, and Diamond zoysiagrass were determined, along with the accumulation of proline and polyamines during cold acclimation, in growth chamber studies. All species/varieties required different sampling numbers for determination of thatch-mat depth and soil organic matter. More sand was incorporated into the turf canopy and surface hardness was increased with brushing and vibratory rolling TifEagle putting greens after sand topdressing application than either treatment alone. Putting green management programs with lower mowing heights and increased mowing frequencies increased ball roll distance on a MiniVerde putting green without negatively affecting turf quality. Weekly vertical mowing + daily grooming on TifEagle reduced thatch depth and turfgrass quality, while increasing topdressing incorporation over either treatment alone. Diamond was the most freeze tolerant species/variety, followed by TifEagle, Champion, then SeaDwarf. Cold acclimation increased proline concentration for all species/varieties except SeaDwarf, but had inconsistent effects on polyamines. Spermidine and putrescine concentrations differed with species/variety, but were not correlated to freeze tolerance

Identification and distribution of ectotrophic root-infecting fungi within an ultradwarf bermudagrass putting green and fungicide efficacy associated with these fungi

This research addressed the identification and distribution of selected ERI fungi within two greens at Mississippi State University Golf Institute using novel molecular methods, spatial relationships of fungal distribution and turf health assessments, and fungal sensitivity to selected fungicides. A complex of ERI fungi was identified in both greens. Gaeumannomyces graminis, Gaeumannomyces sp., and Candidacolonium cynodontis were randomly distributed based on spatial autocorrelation in both green samplings, while Magnaporthiopsis cynodontis clustered in Green 2 for both samplings and in Green 12 of the 2018 sampling. Clustering of turf health values was variable by month in each green, and no spatial relationship was determined between turf health values and fungal presence. Five ERI fungal isolates were exposed to four fungicide classes with relative growth present at 100 ppm. The EC50 values for the selected fungi ranged from 2.33 to \u3e100 ppm and suggests a lack of sensitivity to the selected fungicides

Evaluation of Off-Type Grasses in Interspecific Hybrid Bermudagrass [\u3ci\u3eCynodon dactylon\u3c/i\u3e (L.) Pers. x \u3ci\u3eC. transvaalensis\u3c/i\u3e Burtt-Davy] Putting Greens

The economic impact of the golf industry in the United States (U.S.) in 2011 was estimated to be $176.8 billion. Interspecific hybrid bermudagrasses [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy] are some of the most widely utilized grasses on golf courses throughout tropical, subtropical, and temperate climates. In 2007, bermudagrass was grown on 80% of putting green acreage in the southern U.S. ‘Tifgreen’ and ‘Tifdwarf’ were two of the first widely established cultivars on putting greens, but their genetic instability led to the occurrence of phenotypically different off-type (OT) grasses. Several OT grasses were selected and released as cultivars such as ‘Champion’, ‘MiniVerde’, and ‘TifEagle’. These cultivars can also be genetically unstable and OT grasses can occur in putting greens. The objectives of this research were to genetically and phenotypically characterize OT grasses and evaluate their responses to nitrogen (N) and trinexapac-ethyl (TE) applications. Off-type and desirable bermudagrass samples were collected from Champion, MiniVerde, and TifEagle golf course putting greens in 2013 and 2014. Grasses were genetically evaluated using genotyping-by-sequencing (GBS), which determined that 11% were genetically divergent from standard cultivars. Off-types were phenotypically characterized using morphology and samples clustered into three distinct morphological groups that varied in internode length and leaf length. The response of OT grasses and cultivars to six N and eight TE treatments was evaluated by measuring clippings 7, 14, 21, and 28 days after initial treatment (DAIT). The least three N rates decreased weekly clipping production 18 to 29% [percent], whereas the greatest three rates sustained growth. We observed that peak growth regulation occurred 21 DAIT for the majority of TE rates tested where clipping weights decreased 18 to 35% from 7 to 21 DAIT. We also observed a period of increased clipping production 18 to 47% from 21 to 28 DAIT for all grasses tested. It is important to maintain consistent growth among phenotypically different grasses in order to minimize any competitive growth advantage an OT grass may possess over a desirable cultivar in a golf course putting green

Methods to Hasten Zoysiagrass Establishment from Sprigs

Zoysiagrasses (Zoysia spp. Willd.) are commonly used on golf course fairways and tees in addition to residential and commercial lawns due to lower input requirements relative to bermudagrass (Cynodon spp.). This has led to increased interest in using zoysiagrass for golf course putting greens; however, zoysiagrass establishment from sprigs is prolonged compared to bermudagrass. A series of experiments were conducted in glasshouses in Knoxville, TN in 2022 to evaluate the effects of environmental conditions and management practices on the establishment of Prizm zoysiagrass from sprigs. To determine the optimal soil temperature for Prizm zoysiagrass establishment, sprigs were exposed to high, medium, and low 5 cm soil temperature treatments, which were imposed via water bath. Over the 49-day study period, the high, medium, and low treatments averaged ~36 °C, ~32 °C, and ~28 °C, respectively. The medium and low treatments averaged 92% turfgrass coverage 49 days after planting (DAP) in run A, which was significantly greater than the high-soil-temperature treatment (70%). In run B, the medium soil temperature achieved 92% turfgrass coverage 44 DAP, which was significantly greater than the low (78%) and high (74%) treatments. Independent of other environmental variables, results from this study imply that an average daily 5 cm soil temperature of approximately 32 °C would likely result in the most rapid establishment of Prizm from sprigs. Another study was conducted to evaluate the effect of irrigation frequency on the establishment of Prizm sprigs. Prizm zoysiagrass was irrigated daily (3 mm) applied via four or 192 events from 06:00 a.m. to 10:00 p.m. In both experimental runs, establishment was unaffected by irrigation frequency and averaged 40% turfgrass coverage after 21.6 and 27.3 days in run A and run B, respectively. Air vapor pressure deficit during the irrigation period averaged 1.05 kPa in run A and 1.57 kPa in run B, respectively, suggesting zoysiagrass sprigs have limited sensitivity to elevated vapor pressure deficit, granted sufficient rootzone moisture is available. These conclusions indicate soil temperature is likely a prominent factor influencing zoysiagrass establishment from sprigs

Water-Use Characteristics of Warm-Season Putting Green Cultivars and Management Practices Associated with New Putting Green Genetics

Bermudagrass (Cynodon spp.) is the most common turfgrass used on golf course putting greens in the southeastern United States (Lyman et al., 2007). In 2013, the National Turfgrass Evaluation Program (NTEP) started a 5-year trial of warm-season putting green cultivars. One of the bermudagrass cultivars in the study is MSB-285 (experimental cultivar). MSB-285 is a sister plant of MSB-264 (Philley and Munshaw, 2011) and is a distinct cultivar of C. dactylon × C. transvaalensis. MSB-285 has a more extensive root system and upright growth habit than traditional bermudagrass putting green cultivars (Philley and Munshaw, 2011). Due to MSB-285’s unique genetic makeup and growth habit, the objectives of this research were to determine if best management practices used to maintain ultradwarf bermudagrasses would be suitable for MSB-285 and to determine the water-use characteristics of MSB-285 compared to industry standard cultivars