Hybrid Bermudagrass Research Articles

Optimizing fungicide application timing for spring dead spot based on soil temperature and season

AbstractSpring dead spot (SDS) (Ophiosphaerella spp.) is the most detrimental disease to warm‐season turfgrasses in areas with cold‐induced dormancy. Fungicide applications do not provide consistent SDS suppression. One reason for this inconsistency is the use of solely calendar‐based fungicide applications instead of considering both calendar date and soil temperature. A field study was conducted at three separate hybrid bermudagrass (Cynodon dactylon (L.) Pers. × transvaalensis Burtt Davy) locations in Virginia to determine the optimal soil temperature and timing for SDS suppression with tebuconazole and isofetamid. Tebuconazole (1.5 kg a.i. ha−1) and isofetamid (4.1 kg a.i. ha−1) were applied at 11 different timings throughout the year based on soil temperatures at a 0‐ to 10‐cm depth. Plots were assessed for SDS severity in the spring and early summer of 2021 and 2022. Two in vitro studies were also conducted with Ophiosphaerella herpotricha and Ophiosphaerella korrae isolates to (1) determine the optimal temperature for growth on potato dextrose agar (PDA) placed on a thermogradient table (13–33°C) and (2) compare the daily growth rate of O. herpotricha and O. korrae isolates at 11, 19, and 27.5°C on PDA. In the field study, isofetamid suppressed SDS more than tebuconazole. Fall applications when soil temperatures were 13°C consistently provided the best SDS suppression. For the in vitro studies, both species grew optimally between 24 and 25°C, yet O. korrae and O. herpotricha growth rates differed at 11°C.

Performance of Different Cool-Season Species and Cultivars Overseeded on Bermudagrass and Managed with Autonomous Mower

With global warming, the cultivation area of bermudagrass is moving northwards in the Mediterranean area despite its winter dormancy and loss of green color. The most common solution is overseeding with perennial ryegrass, which can be complicated to remove in spring. DLF breeders have released a new cultivar of annual ryegrass that is stress tolerant and easy to transition in spring. A trial was carried out on a sod farm in Pisa, Italy. Twenty-nine varieties of cool-season grasses, encompassing both forage and turf species, were overseeded on a hybrid bermudagrass variety ‘Tifway’ (Cynodon dactylon x transvaalensis). The aim of this trial was to compare the overseeding potential of various cool-season turfgrass species and cultivars and to identify which ones perform best in terms of cleanness of cut when overseeded on hybrid bermudagrass in autumn and maintained at a mowing height of 25 mm. Moreover, the following parameters were also assessed: actual turf height (cm); cumulated height (cm); turf visual color and quality (1–9 scale); and visual ground cover (%). Plots were managed with an autonomous mower, which adopted a daily mowing frequency and was set to work with systematic trajectories. The results showed differences between cultivars, and the annual ryegrass showed the best spring transition (scoring a mean value of 96% green cover in July 2023) compared to the other entries. The best result of CoC was measured for rough-stalked meadow grass ‘Sabrena 1’ and tall fescue ‘Turfway’ with 0.9 mm.

Evaluation of segmentation and semi‐supervised learning for spotted spurge recognition in bermudagrass turf

AbstractDiverse datasets are crucial for training machine learning‐based weed recognition models. However, annotating (i.e., labeling) images can be laborious and time‐consuming. Choice of annotation method and training approach not only affects the overall model effectiveness but also its minimum training data requirements and development pace. Segmentation and semi‐supervised learning (SSL) may offer performance or training enhancements. This study evaluated (1) segmentation against object detection in spotted spurge [Chamaesyce maculata (L.) Small] recognition in Latitude 36 hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt‐Davy] maintained as a golf course fairway and (2) the potential of two‐step SSL‐based training procedure using data labeled both manually and automatically with a pre‐trained model to expedite the model development. The architecture used across this research was You Only Look Once version 8 (YOLOv8) employing nano, small, and medium variants. All models were trained with a dataset restricted to 1200 training and 300 validation images. Both annotation methods resulted in adequate spotted spurge identification, as evidenced with >0.60 (>0.50 acceptability threshold) medium average precision at intersection over union threshold of 0.50 (mAP@50). Although the difference was minimal, object detection performed superior to segmentation. The two‐step training effectively accelerated image annotation while preserving or improving (with 8:4 and 6:6 splits between manually and auto‐labeled data) object detection performance. Segmentation tolerated only 10:2 split and exhibited increased sensitivity to declining dataset quality proportionally to the increase in auto‐labeled images in the final training dataset. Findings show a two‐step SSL‐based training procedure expedites annotation, enhancing model development efficiency.

Improving winter survival of interspecific hybrid bermudagrass in the Mid‐Atlantic region through cultural practices

Improving winter survival of interspecific hybrid bermudagrass in the Mid‐Atlantic region through cultural practices

Urea Cocrystals as a Potential Fertilizer for Turfgrass: Responses of ‘Tifway’ Hybrid Bermudagrass and Nitrogen Release Behavior

Urea cocrystal materials are a potential fertilizer source that has shown to decrease environmental nitrogen losses. Novel nitrogen (N)-containing urea cocrystal fertilizers, CaSO4·4urea (UC1) and Ca(H2PO4)2·4urea (UC2), were synthesized using the mechanochemical method to form stable urea cocrystals to be tested as a fertilizer source for turfgrass. The objectives of this study were to 1) evaluate the response of ‘Tifway’ hybrid bermudagrass (Cynodon dactylon × C. traansvalensis Burt Davy) to N fertilization by urea cocrystals and traditional coated urea products (MU·PCU, methylene urea, urea, polymer-coated urea; PCU, polymer-coated urea, urea) supplied at two rates at the beginning of two, 10-week study periods conducted under a greenhouse setting and 2) investigate N release behavior of urea and two cocrystal products using a rapid water release test. In the turfgrass response study conducted in the greenhouse, improved turfgrass quality above the minimum quality threshold was observed when averaging across all products. For normalized difference vegetation index (NDVI), cocrystal outperformed all other products in the summer study and both cocrystal products outperformed the traditional product (MU·PCU) in the winter study. Further, both cocrystal products showed favorable growth responses compared with the commercial products provided by positive clipping production and vertical extension rates. In the nitrogen release experiment, a rapid water release test revealed the N release peak of urea was significantly higher than both UC1 and UC2. Furthermore, significantly higher N was leached from urea (15% loss) compared with both UC1 and UC2 (≈8% loss). Results from both studies provide evidence supporting suitability of urea cocrystal application on bermudagrass and potential as a slow-release fertilizer source through sustained turfgrass vigor, growth, decreased N release peak, and decreased leaching losses.

Poa annua control in golf course putting green collars via fraise mowing

AbstractPoa annua L. control on golf courses is challenging, particularly in collars adjacent to putting greens where herbicide options are limited. Field research was conducted in Knoxville, TN from 2022 to 2024 to evaluate P. annua control efficacy following summer fraise mowing of putting green collars. Plots were arranged in a hybrid bermudagrass [C. dactylon (L.) Pers. × C. transvaalensis Burtt‐Davy, cv. ‘Tifway’] collar adjacent to a creeping bentgrass (Agrostis stolonifera L.) putting green. A walk‐behind fraise mower (RR600 HDX; SISIS) was used to fraise mow plots (0.6 × 3 m) to depths of 8 or 15 mm. A non‐fraise‐mowed check (0 mm) was included for comparison. Plots were fraise mowed on June 20, 2022 and July 10, 2023 with recovery visually assessed thereafter relative to non‐fraise‐mowed check plots in each replication. Poa annua control was visually assessed 133 and 233 days after treatment relative to non‐fraise‐mowed check plots as well. In the absence of herbicide, summer fraise mowing of hybrid bermudagrass collars provided effective control (>89%) of P. annua for 133 days. Hybrid bermudagrass recovery from this mechanical control method was swift, which suggests that it could be incorporated into a weed management program with pre‐ and postemergence herbicides similar to harvest weed seed control methods used in crop production.

Is there a relationship between clipping weight and volume on golf course fairways?

AbstractPlant growth regulators (PGRs) are regularly used on golf courses to reduce mowing requirements. PGR efficacy is commonly assessed via measurements of clipping weight; however, this process is time consuming and requires specialized equipment. Golf course superintendents have started to evaluate PGR efficacy via measurements of clipping volume. Field research was conducted in Knoxville, TN, during June 2022 and 2023 to evaluate the relationship between clipping weight and volume following trinexapac‐ethyl applications to hybrid bermudagrass (C. dactylon × C. transvaalensis Burtt‐Davy, cv. ‘Latitude 36’) and manilagrass (Zoysia matrella, cv. ‘Trinity’ and ‘Zorro’) golf course fairways. Four experimental formulations of trinexapac‐ethyl [97 g ha−1 (11.4 fl oz/A)] were applied to plots 16 ft2 (1.5 m2) organized in a randomized complete block design with four replications. Clippings were collected twice weekly with volume assessed via a graduated cylinder; weight was quantified after drying clippings in a forced‐air oven for 48 hours. For hybrid bermudagrass, clipping weight and volume measurements returned similar conclusions regarding trinexapac‐ethyl efficacy for growth regulation. On dates where both metrics resulted in treatment differences, a linear relationship was present between clipping weight and volume data (R2 = 0.84). Similar responses were observed on manilagrass; however, clipping weight and volume were less closely associated (R2 = 0.78). This difference could be related to growth rate, as well as clipping size and mass differences between species. Overall, results indicate that either metric could be used to study efficacy of trinexapac‐ethyl for regulating growth of these species maintained as golf course fairways.

Estimating the soil water retention curve by the HYPROP-WP4C system, HYPROP-based PCNN-PTF and inverse modeling using HYDRUS-1D

Due to the difficulty of direct field measurement, soil hydraulic properties are often obtained in laboratory settings using small undisturbed soil samples or estimated indirectly through pedotransfer functions (PTFs). The pseudo-continuous pedotransfer function (PCNN-PTF) is a neural network-based approach for estimating soil hydraulic properties. The main objective of this study was to use field soil moisture and tension data to assess soil water retention curves obtained from the HYPROP-WP4C system and the HYPROP-based PCNN-PTF. The in-situ soil water retention data were simultaneously acquired using Acclima TDT and MeterGroup MPS-6 sensors (every 30 min, May to September 2020) from 11 hybrid bermudagrass plots under different irrigation treatments in Riverside, California. We utilized extended evaporation and dewpoint methods using HYPROP-WP4C (Meter Group Inc., USA) devices to obtain lab-measured SWRCs. In addition, SWRCs were estimated from Rosetta (Schaap et al., 2001) and by inverse modeling in HYDRUS-1D utilizing in-situ moisture retention data. Although the hysteresis impacted field data, overall, there was a good agreement between the in-situ and lab water retention data for most samples, especially within the pF range of 2–3.5. The PCNN-PTF outperformed Rosetta in estimating laboratory (RMSE=0.034 cm3 cm−3 vs 0.063 cm3 cm−3) and in-situ soil moisture data (RMSE=0.048 cm3 cm−3 vs 0.082 cm3 cm−3). Inverse modeling of in-situ data also performed well in estimating the SWRC (RMSE=0.043 cm3 cm−3); however, further attention is required in dry and saturated soil conditions. We developed a simple, free, and easy-to-access tool called PC-PTF for estimating the SWRC using the PCNN-PTF model evaluated in this study. The PC-PTF can be accessed from the Verdi Water Management Group website: http://www.ucrwater.com/software-and-tools.html.

Challenges in bermudagrass production in the southeastern USA

AbstractBermudagrass (Cynodon dactylon (L.) Pers.) is one of the primary perennial forages in the southeastern USA. Newer hybrid cultivars have superior production and nutritive value compared to common ecotypes. However, there are many challenges facing bermudagrass production in the region. First, the bermudagrass stem maggot (BSM; Atherigona reversura Villeneuve) has severely damaged bermudagrass throughout the region. Strategically timed pyrethroid applications significantly reduce adult BSM populations, but efforts are needed to develop integrated pest management plans. Second, an increasing number of producers are noting challenges with green‐up following winter dormancy. This may be attributed to disease, unbalanced soil fertility, and weed pressure. Perhaps one of the most limiting factors for continued production is the deficit of sprigs and trained personnel to sprig hybrid bermudagrasses. This research is critically important as the need for cold‐tolerant bermudagrass is increasing as tall fescue (Lolium arundinaceum (Schreb.) S. J. Darbyshire) is declining due to changes in temperature and precipitation throughout the northern parts of the region. Plant breeders are investigating hybrid bermudagrass at latitudes >35° with respect to freeze or cold tolerance. Despite the many challenges facing hybrid bermudagrass in the southeastern USA, researchers are working to ensure its persistence, productivity, and availability for the future.

Using a soil moisture sensor-based smart controller for autonomous irrigation management of hybrid bermudagrass with recycled water in coastal Southern California

There is a lack of information on the reliability of smart soil moisture sensor-based irrigation controllers for autonomous urban landscape irrigation management using recycled water where water conservation is required, which is the main objective of this study. A three-year turfgrass irrigation research trial (2019–2021) using tertiary-treated recycled water (mean EC = 1.18 dS/m, pH = 7.5) was conducted in Irvine, California, USA. A total of 12 irrigation treatments were designed, including six soil moisture-based thresholds (for triggering and terminating irrigation events) × two irrigation frequency treatments (restricted versus on-demand). Weekly NDVI and canopy temperature data were collected during the summer irrigation season to assess the impact of irrigation treatments on the overall health and quality of 'Tifgreen 328' hybrid bermudagrass. Soil salinity and sodium adsorption ratio (SAR) were measured before and after the summer irrigation seasons. Findings revealed statistically significant effects of irrigation levels and irrigation frequency restrictions on NDVI over the three years. The temperature difference (dT) between turfgrass and air (Tc - Ta) was significantly affected by irrigation levels throughout the three years, while irrigation frequency restrictions showed a significant effect in the years 2021 and 2022. On-demand irrigation resulted in a 10% reduction in temperature difference values during the study period compared to restricted irrigation. Variations in soil salinity levels were observed during the experimental periods; however, both salinity and SAR increased as the study progressed. Results indicate that fully autonomous hybrid bermudagrass irrigation with recycled water, based on recommended soil moisture thresholds of 75% of field capacity over an extended period in a semiarid climate, may lead to unacceptable turfgrass quality.

Application of fertilizer and insecticide can reduce Antonina graminis (Hemiptera: Pseudococcidae) and improve the quality of golf course putting greens.

Rhodesgrass mealybug, Antonina graminis, is a serious pest of ultradwarf hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) on golf course putting greens. A. graminis feeding damage appears as extensive yellowing of turfgrass blades and heavy thinning from mid-to-late summer into fall. Putting greens are intensively managed areas of the golf course where fertilizers are routinely applied to maintain and enhance turfgrass quality, playability and aesthetics. We hypothesize that A. graminis populations can be minimized by reducing nitrogen (N) fertilizer and then effectively managed using systemic insecticides. The objective of this study was to determine the effects of various levels of N fertilizer and flupyradifurone on the A. graminis population and turfgrass quality on the golf course putting green. The treatments were low, medium, and high N fertilizer rates with and without insecticide (flupyradifurone). Applying a high dose of N fertilizer improved turfgrass quality without increasing A. graminis densities on the golf course green. Although flupyradifurone application reduced A. graminis densities regardless of N fertilizer treatments, suppression of A. graminis densities improved at the high fertilizer dose with flupyradifurone. Additionally, the turfgrass quality on the putting green improved with high N fertilizer alone, regardless of flupyradifurone application. A. graminis populations can be managed using moderate to high levels of N fertilizer and applying a systemic insecticide. The low nitrogen fertilizer did not effectively reduce the A. graminis densities on the putting green. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Unveiling Dominant Fungal Pathogens Associated with Root Rot of Hybrid Bermudagrass Based on Culture Dependent and Independent Methods.

Hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) is widely used as turf in southern and transition zones of China. From June to September in 2022, an unknown disease was consistently observed on hybrid bermudagrass in different regions of Nanjing, China, that exhibited distinct symptoms of leaf necrosis, severe root rot, and circular or irregular necrotic patches with 20- to 300-cm diameters. In this study, culture-independent and -dependent methods were used to elucidate the dominant fungal pathogens associated with the disease. Basidiomycota and Marasmiellus were shown to be the dominant phyla (51.96 to 70.60%) and genera (50.09 to 69.84%) in the symptomatic samples. A total of 128 fungal strains were isolated from symptomatic root tissues, and 40 strains representing the largest proportion (31.25%) were identified as Marasmiellus mesosporus based on the morphological characteristics, phylogenetic analysis of the ITS and LSU rDNA region, and pathogenicity testing. Temperature sensitivity tests revealed that M. mesosporus grew well at high temperatures (growth rate of 13.74 mm/day at 36°C). To our knowledge, this is the first report of M. mesosporus causing root rot disease on hybrid bermudagrass during hot summer months. The study will have important implications for the management of the disease.

Growth and metabolic differences in the potential of phytoremediation between two hybrid bermudagrasses in roots, stems, and leaves under cadmium stress

Bermudagrass (Cynodon) species has been identified as a dominant plant species in cadmium (Cd)-contaminated soils. Objectives of current study were to evaluate Cd tolerance of two hybrid bermudagrass (Cynodon transvaalensis × Cynodon dactylon) cultivars Tifdwarf and Chuannong-3 for urban greening and slope ecological restoration and further to explore the difference in Cd tolerance associated with changes in ion absorption and distribution, antioxidant metabolism, and accumulations of phytochelatins (PCs) and metallothioneins (MTs) in roots, stems, and leaves. After exposure to equal concentration and duration of Cd stress, growth, chlorophyll content, and photochemical efficiency of both cultivars reduced significantly, but Cd-induced these inhibitory effects were more pronounced in Chuannong-3. As compared to Chuannong-3, Tifdwarf maintained significantly higher Cd concentration in roots and lower Cd concentration, bioconcentration factor, and translocation factor in aboveground parts in response to Cd stress. Each plant of Tifdwarf also accumulated more Cd in leaves, stems, and roots than each plant of Chuannong-3 due to larger biomass under Cd stress. Cd stress also significantly inhibited uptake and partitioning of iron, sodium, and potassium in two cultivars. In addition, Tifdwarf exhibited better antioxidant defense for reactive oxygen species (ROS) scavenging than Chuannong-3 under Cd stress, as reflected by higher antioxidant enzyme activities and antioxidant metabolites involved in ascorbic acid (ASA)-glutathione (GSH) cycle. Tifdwarf also accumulated more PCs in leaves, stems, and roots and more MTs in leaves and stems than Chuannong-3, which could help to chelate Cd to reduce cytotoxicity of Cd. Moreover, strong antioxidant property of MTs was beneficial for maintaining ROS homeostasis in plants. Therefore, better Cd tolerance of Tifdwarf could be mainly due to the inhibition of Cd uptake and partitioning, enhanced ASA-GSH cycle, and more accumulations of PCs and MTs. Tifdwarf showed better potential for Cd remediation or urban greening in Cd-polluted soils.

Characterization of genetic diversity of greens‐type hybrid bermudagrass selections through SSR markers and morphological analysis

AbstractThe development of Tifgreen bermudagrass, and the subsequent mutations of this cultivar, has revolutionized the game of golf in the southern United States as superintendents have access to high‐quality putting surface capable of withstanding hot summers. However, the lack of genetic diversity may make them vulnerable to various pests and the low tolerance to freeze temperatures may make them susceptible to winterkill. In recent years, Oklahoma State University and other universities have begun to create new interspecific F1 hybrids between common (Cynodon dactylon) and African bermudagrasses (C. transvaalensis) for putting greens. The objectives of this study were to investigate the genetic diversity and variation among 14 experimental genotypes and two standard cultivars (TifEagle and Tifdwarf). Simple sequence repeat (SSR) markers and morphological characteristics were used to evaluate the genetic relationships and variation among the 16 genotypes. Results showed significant variation for 11 vegetative traits and two reproductive traits. The phenotypic coefficient of variation was greatest for the third internode length and the least for the first leaf angle for both the field and greenhouse trials. The morphological cluster analysis also showed variation between the two trial environments. The SSR marker cluster analysis showed the 16 genotypes were grouped into four major groups, with a similarity coefficient ranging from 0.44 to 1. The highest similarity was found among the two commercial standards and an experimental ultradwarf from Florida. Several new genotypes (OKC3920, 5 × 23, 11 × 2, 19 × 19, and 34 × 20) were also grouped with the ultradwarf genotypes in the morphological cluster analysis, showing the possibility of achieving similar morphological traits with new genetics. Further field evaluations are needed to determine the performance of these genotypes under low mowing heights.

Dissipation of spring-applied methiozolin in turfgrass systems

AbstractMethiozolin is applied five or more times per year to control annual bluegrass (Poa annua L.) in cool, temperate areas, but high market demand in the southern United States and recent registration in Australia has expanded the product’s use in variable climates. To better design weed control programs for variable turf types, more information is needed to characterize methiozolin dissipation in different turf systems. Methiozolin was applied biweekly three times to a Kentucky bluegrass (Poa pratensis L.) lawn and adjacent bare soil in New Jersey and on 12 hybrid bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt Davy] putting greens in Virginia. Soil samples were collected immediately following each application and biweekly for 12 additional weeks. Methiozolin was extracted from each soil sample and analyzed using liquid chromatography with tandem mass spectrometry. Methiozolin was detected only within the top 2 cm of the soil (including verdure), but not below 2 cm, demonstrating its limited vertical mobility. Dissipation was significantly faster in turf-covered soil compared with bare soil. The time required for 50% methiozolin dissipation was 13 and 3.5 d in bare soil and turf-covered soil, respectively. In Virginia, methiozolin dissipation in the 1-m span of three sequential applications differed between years. Methiozolin concentration immediately following the third biweekly application to C. dactylon ×transvaalensis greens was approximately 105% and 180% of the concentration immediately following the initial application, in 2021 and 2022, respectively. This difference in methiozolin accumulation following three applications was attributed to differential C. dactylon ×transvaalensis green up during methiozolin treatments each year. Despite differences in posttreatment methiozolin concentration between years, the temporal dissipation rate later into the summer was consistent. Following the final application on C. dactylon ×transvaalensis greens, methiozolin dissipated 50% and 90% in 14 and 46 d, respectively. These data suggest that methiozolin dissipates more rapidly in turfgrass systems than in bare soil.

Growth Suppression of Hybrid Bermudagrass with Imazapic

Imazapic is an acetolactate synthase-inhibiting herbicide labeled for weed control in pastures, rangeland, and noncrop areas. Field research was conducted in Knoxville, TN, USA, during 2020 and 2021 to evaluate the tolerance of four hybrid bermudagrass (Cynodon dactylon × Cynodon transvaalensis Burtt Davy) cultivars to applications of imazapic for growth suppression. Separate experiments were conducted on ‘TifTuf’, ‘Tifway’, ‘Tahoma 31’, and ‘Latitude 36’ hybrid bermudagrass. Experiments included plots (1.5 m2) arranged in a randomized complete block design with four replications and were repeated. Treatments were applied 14 Aug 2020 and 6 Aug 2021, and were mixed with methylated seed oil. Imazapic rates were 0, 35, 52.5, 70, or 105 g⋅ha–1. Cultivar tolerance was assessed via visual ratings of turfgrass injury relative to untreated check plots. Normalized differential vegetation index data were collected on each date turfgrass injury was evaluated. Growth suppression was quantified via reductions in dry clipping weight after mowing. Hybrid bermudagrass injury increased with imazapic rate for all cultivars, and peak injury (> 30%) following all imazapic treatments occurred within 14 days. At the lowest imazapic rate (35 g⋅ha–1), injury was transient, with all hybrid bermudagrass cultivars fully recovered by 28 days. All rates of imazapic reduced hybrid bermudagrass dry clipping weight for 21 days for all cultivars. Further research is warranted to explore lower application rates than those tested in our study, in addition to determining tolerance and growth suppression of other turfgrass species commonly managed on golf courses.

Assessing the Impact of Water Conservation on Cooling Potential of Two Turfgrass Species

Highlights Empirical CWSI was developed for 'Westcoaster' tall fescue and ‘Tifgreen’ hybrid bermudagrass. The canopy temperature of both species was monitored under multiple irrigation scenarios. Deficit irrigation might reduce the cooling benefits of irrigated urban lawns. Abstract. Canopy temperature provides valuable information for efficient irrigation management and for detecting drought injury in a fast and non-destructive way. It also helps quantify the trade-offs between water conservation and the cooling benefit of the irrigated urban landscape, a critical issue in semiarid inland southern California with limited available water resources. Two adjacent hybrid bermudagrass and tall fescue irrigation trials were conducted to determine canopy temperature changes under a wide range of irrigation treatments from 2017 to 2019 in Riverside, California, USA. The canopy temperature data were also used to develop an empirical crop water stress index (CWSI) for each species. The CWSI values ranged from -0.15 to 0.71 for tall fescue and from -0.28 to 0.54 for hybrid bermudagrass. We observed a moderate correlation between visual rating scores (VR) and CWSI values for tall fescue (r = -0.68) and hybrid bermudagrass (r = -0.61). The fitted linear regression between VR and CWSI data suggested CWSI thresholds close to zero for both species to maintain their acceptable visual quality. The irrigation level consistently showed a significant effect on canopy temperature for both species. On average, a 10% decrease in irrigation application increased the canopy temperature of tall fescue and hybrid bermudagrass by 1.3°C and 0.9°C, respectively. Therefore, deficit irrigation might reduce the cooling benefits of irrigated urban lawns in the semiarid climate of inland southern California. Keywords: Canopy temperature, Evapotranspiration, Smart irrigation controller, Urban heat island, Urban irrigation, Water conservation.

Methiozolin rate and application frequency influence goosegrass (Eleusine indica) and smooth crabgrass (Digitaria ischaemum) control in turf

Abstract Methiozolin is labeled for goosegrass and smooth crabgrass control in golf course putting greens, but no peer-reviewed literature exists regarding this use. Greenhouse experiments were conducted evaluating goosegrass and smooth crabgrass response to increasing rates of methiozolin as affected by weed growth stage. In general, as weed growth stage increased, the methiozolin rate required to reduce weed biomass 90% (WR90) increased. Goosegrass was more sensitive to preemergence-applied methiozolin than smooth crabgrass, and the WR90 was 30.4 and 118 g ai ha–1 for goosegrass and smooth crabgrass, respectively. However, smooth crabgrass was generally more sensitive to postemergence-applied methiozolin than goosegrass. Subsequent field studies were conducted to evaluate goosegrass and smooth crabgrass control with methiozolin applied singularly or sequentially at standard preemergence timings. Results indicated methiozolin applied singularly or sequentially at the label-recommended rate (500 g ha–1) is not persistent enough to provide season-long control of goosegrass and smooth crabgrass. Ten field studies were conducted in Alabama, California, Florida, and Virginia to evaluate frequent methiozolin application programs with the objective of providing selective, season-long goosegrass and smooth crabgrass control. Results from these studies indicate methiozolin can be safely applied to hybrid bermudagrass and creeping bentgrass putting greens despite exceeding the yearly maximum use rate for putting greens (2,500 g ha–1) with some treatments. Methiozolin effectively controlled smooth crabgrass throughout the growing season in California and Virginia when 10 biweekly applications were applied at 250 g ha–1 or higher. In Florida, methiozolin did not acceptably (80%) control goosegrass regardless of application rate. In Virginia, methiozolin acceptably controlled goosegrass only when applied at rates and frequencies that exceeded the maximum yearly methiozolin usage rate. These data indicate that methiozolin has the potential to control smooth crabgrass preemergence when applied frequently, but does not provide acceptable goosegrass control at labeled rates.

Genetic Variability of Traffic Tolerance and Surface Playability of Bermudagrass (Cynodon spp.) under Fall Simulated Traffic Stress

Bermudagrasses (Cynodon spp.) are the most preferred turfgrass species for athletic fields in the southern and transition zones of the United States. Developing and using bermudagrasses with superior traffic tolerance and surface playability under trafficked conditions benefits turfgrass managers, athletes, and sport organizations. A 2-year field study was conducted in Stillwater, OK, to quantify the genetic variability of traffic tolerance and surface playability from a population composed of two commercially available and 87 experimental interspecific hybrid bermudagrasses under fall simulated traffic stress. The experiment design was a randomized complete block design with three replications. Plots were subjected to 60 simulated cleat traffic events for 6 weeks in the fall of 2019 and 2020 using a Baldree traffic simulator. Bermudagrasses were evaluated for turfgrass quality (TQ), normalized difference vegetation index (NDVI), fall percent green cover (FPGC), shear strength (SS), and surface hardness (SH) after 3 and 6 weeks of traffic. Spring green-up percent green cover (SGPGC) was evaluated in the spring of 2020 and 2021. Except for SH, significant entry effects were found for all parameters and reliability estimates were moderate to high (i2 = 0.49 to 0.68) under simulated trafficked conditions. Experimental entries 17-4200-19X13, 17-4200-19X9, 17-4200-36X19, 17-5200-4X11, 18-7-2, 18-7-6, 18-8-2, 18-8-3, 18-8-7, 18-9-2, OSU1101, and OSU1664, and TifTuf® had excellent traffic tolerance. Entries 18-8-7, OSU1101, OSU1675, TifTuf®, and Tahoma 31® demonstrated high SS. There was a large group of entries that had consistent early spring green-up across both years, including Tilin#5, 18-9-8, OKC1221, OSU1257, OSU1318, OSU1337, OSU1406, OSU1439, OSU1651, OSU1675, Tahoma 31®, and TifTuf®. OSU1101 was the entry ranking in the top statistical grouping most often throughout the study. Findings illustrated the possibility of improving traffic tolerance and SS through breeding and using phenotypic selection could reliably select bermudagrass genotypes with improved traffic tolerance and SS in the transition zone.

Response of goosegrass, smooth crabgrass, and newly sprigged hybrid bermudagrass to postemergence herbicides

Response of goosegrass, smooth crabgrass, and newly sprigged hybrid bermudagrass to postemergence herbicides