Turfgrass Quality Research Articles

Genome Editing for Grass Improvement and Future Agriculture

Abstract Grasses, including turf and forage, cover most of the earth’s surface; predominantly important for land, water, livestock feed, soil and water conservation, as well as carbon sequestration. Improved production and quality of grasses by modern molecular breeding is gaining more research attention. Recent advances in genome-editing technologies are helping to revolutionize plant breeding and also offering smart and efficient acceleration on grass improvement. Here, we reviewed all recent researches using (CRISPR)/CRISPR-associated protein (Cas)-mediated genome editing tools to enhance the growth and quality of forage and turf grasses. Furthermore, we highlighted emerging approaches aimed at advancing grass breeding program. We assessed the CRISPR-Cas effectiveness, discussed the challenges associated with its application, and explored future perspectives primarily focusing on turf and forage grasses. Despite the promising potential of genome editing in grasses, its current efficiency remains limited due to several bottlenecks, such as the absence of comprehensive reference genomes, the lack of efficient gene delivery tools, unavailability of suitable vector and delivery for grass species, high polyploidization, multiple homoeoalleles, etc. Despite these challenges, the CRISPR-Cas system holds great potential to fully harness its benefits in grass breeding and genetics, aiming to improve and sustain the quantity and quality of turf and forage grasses.

Maximizing genetic gains across agronomic and consumer preference traits in St. Augustinegrass breeding

AbstractCombining large multi‐environment trial (MET) datasets to decide which genotypes to move forward in the breeding process can be challenging, especially when dealing with negatively correlated traits. The use of a selection index has long been identified as an effective strategy in these situations. However, the method has found limited application in turfgrass breeding. The objective of this study was to use MET data for St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] breeding lines evaluated across the southern United States to compare genetic gains achieved with the additive additive genetic index (AI) versus the turf performance index (TPI) incorporating agronomic as well as consumer preference traits. The use of either selection index produced more positive genetic gains across traits than direct selection even in the presence of negative correlations. However, the higher genetic gains obtained with AI versus TPI indicate that the use of an index that weighs traits according to their importance is a better approach for selection. Moreover, under a more stringent selection intensity, none of the best lines identified with AI would have been selected with TPI emphasizing the importance of choosing selection criteria that provide a more nuanced ranking of lines. Additionally, higher heritability values and gains from selection were obtained for turfgrass quality under stress (drought and shade) than under normal conditions indicating that selection under stress environments might be more efficient. Most of the evaluated St. Augustinegrass lines outperformed the checks, further supporting the value of cross‐institutional breeding collaborations.

Assessing Biofungicides and Host Resistance against Rhizoctonia Large Patch in Zoysiagrass.

Rhizoctonia large patch (Rhizoctonia solani AG2-2 LP) significantly reduces turfgrass quality, aesthetics, and playability. Synthetic fungicides are commonly used for managing this disease, but they present high costs, potential for fungicide resistance, and environmental concerns. We conducted in vitro assays to test the effectiveness of three biofungicides, seven synthetic fungicides, and ten combinations against R. solani. We then assessed seven spray programs that included Bacillus subtilis QST713 and propiconazole, either alone or tank-mixed, on zoysiagrass 'El Toro' in a growth chamber and in field trials. Biofungicide B. subtilis QST713 reduced pathogen growth by up to 100% in vitro. B. subtilis QST713 alone or combined with synthetic fungicides and/or in rotation was as effective as the standalone synthetic fungicide, reducing disease severity and AUDPC by 81 and 77% (growth chamber) and by 71 and 52% (field), respectively, while maintaining acceptable turfgrass quality. Additionally, we screened zoysiagrass genotypes and advanced breeding lines against three R. solani isolates in growth chamber studies. Five genotypes and two breeding lines demonstrated resistance to Rhizoctonia large patch across isolates, highlighting their potential for developing disease-resistant cultivars. Our findings suggest that integrating biofungicides, resistant cultivars with chemical controls offer sustainable and effective strategies for managing Rhizoctonia large patch.

Effects of foliar silicon and nitrogen applications on winter color retention and spring green-up of zoysia grass

Zoysia japonica Steud. (zoysia grass), with its high drought, shade, and salt tolerance, it is an excellent choice for green areas. However, in regions with subtropical climates, it goes into winter dormancy with a loss of green color and functionality, which is a main barrier to its widespread use. The application of silicon and nitrogen in fall was hypothesized to enhance winter color retention of Z. japonica. This study assessed the impact of fall (late-season) nitrogen (0, 2.5, or 5.0 g/m2 ammonium sulfate) and foliar silicon (0, 3, or 6 mL/L potassium silicate) applications on the winter color retention of Z. japonica grown in the field. The experiment was conducted over two consecutive growing seasons in Antalya, Türkiye. Turfgrass quality, color, chlorophyll content, shoot density, and winter dormancy were all improved by late-season nitrogen application. Overall, two sequential nitrogen applications at 5 g/m2 in fall provided 65% to 100% green coverage with acceptable turfgrass quality during fall and winter, indicating the possibility of maintaining the year-round green color of Z. japonica in subtropical climates. However, the silicon treatment did not affect the winter color retention of Z. japonica. The apparent lack of a beneficial response of Z. japonica to the silicon application might be due to the dose, application methods, and silicon source.

Water Conservation Practices and Nitrogen Fertility for the Reduction of Greenhouse Gas Emissions from Creeping Bentgrass Putting Greens

Irrigation practices that conserve water use have the potential to reduce greenhouse gas (GHG) emissions but may adversely affect turfgrass appearance. The purpose of this study was to identify irrigation practices and N fertilizers that will decrease carbon dioxide (CO2), methane (CH4,), and nitrous oxide (N2O) emissions while evaluating turfgrass color and quality. In both years, supplemental rainfall (SRF) soil moisture content was higher than business as usual (BAU) irrigation and syringing (SYR). Higher soil moisture led to increased fluxes in both soil CO2 and soil N2O. In 2017, the SRF fluxed lower soil CO2 as soil moisture reached levels that restricted respiration. Soil moisture was also an important predictor of soil N2O flux with BAU and SRF having higher soil N2O fluxes. SRF produced the greenest turf from May to July, whereas SRY and SRF produced the greenest turf from August to October in 2016. Both BAU and SRF had the greenest turf in 2017. BAU had the highest turfgrass quality ratings in 2016 followed by SRF and SRY, respectively, whereas in 2017 SRF and SRY had higher turfgrass quality ratings. When adopting water conservation practices to reduce GHG emissions, soil moisture content and site-specific rainfall should be closely monitored to prevent overwatering.

Machine learning-based smart irrigation controller for runoff minimization in turfgrass irrigation

Inadequate turfgrass irrigation management poses a significant challenge, resulting in considerable water loss through runoff and the transport of contaminants, ultimately jeopardizing surface and groundwater quality. This study introduces a Machine Learning (ML)-based Decision Support System (DSS) designed to optimize turfgrass irrigation, concurrently minimizing runoff and preserving turfgrass quality. A robust ML classifier, specifically the Radial Basis Function - Support Vector Machine (RBF-SVM) was trained on synthetic data generated through the Monte-Carlo (MC) technique, which was then used to specify a set of irrigation rules implemented in the irrigation controller. The synthetic data were derived from observations collected from irrigation plots at the Texas A&M University Turfgrass Laboratory in Texas, United States, with Soil Wetting Efficiency Index (SWEI) serving as the target variable. When tested against a commercially available irrigation controller, the ML-based controller significantly reduced runoff by an average of 74 % while maintaining high Green Cover (GC) in turfgrass, achieving an accuracy of 87 %. These findings highlight the potential of ML-driven irrigation systems to improve water use efficiency, reduce environmental impact, and maintain turf quality. Such systems could be beneficial for urban landscapes, sports fields, and agriculture, helping users conserve water while achieving sustainable turf management.

The Effects of Cultivation Practices and Fertilizer Use on the Mitigation of Greenhouse Gas Emissions from Kentucky Bluegrass Athletic Fields

Greenhouse gas (GHG) emissions are known to contribute to global climate change. A two-year field study on Kentucky bluegrass (Poa pratensis L.) evaluated cultivation practices and fertilizer use on GHGs. The presence of urea and hollow-tine aerification resulted in the highest soil carbon dioxide (CO2) emissions. No significant differences between soil methane (CH4) flux were observed based on fertilizer; however, in 2014 the verticutting cultivation treatment fluxed significantly more soil CH4 than the uncultivated control. Results showed no significant differences in soil nitrous oxide (N2O) in 2013; however, in 2014, both fertilizer and cultivation practices showed significant differences between treatments, with the urea and the hollow-tine treatments fluxing significantly more soil N2O. The hollow-tined plots produced the greenest turf in 2013, followed by the uncultivated control and the verticutted treatment. In 2014, both the hollow-tine and the uncultivated control produced the greenest turf, followed by the verticutted treatment. The hollow-tined and uncultivated control treatments had significantly higher turfgrass quality than the verticutted treatment. The verticutted urea treatment was above acceptable levels (>6.0) for turfgrass quality following all cultivation events. The results show cultivation practices can be identified that reduce GHG emissions while maintaining turfgrass quality and color.

Shade and Nitrogen Fertilizer Effects on Greenhouse Gas Emissions from Creeping Bentgrass Putting Greens

Climate change mitigation requires creative solutions to reduce greenhouse gases (GHG). Little research has been performed on GHG emissions from shaded turfgrass systems, resulting in a lack of best management practice (BMP) development. The aim of this research was to investigate the soil flux of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) as impacted by shade [shade (98.8%) versus sun (100%)] and differing sources (fast- versus slow-release) and rates (147 versus 294 kg ha−1 yr−1) of nitrogen (N) fertilizers on creeping bentgrass putting greens. The results show that emissions of soil CO2 and soil N2O are significantly lower in shaded plots versus sunny plots. The presence of N fertilizer significantly increased soil CO2 emissions over unfertilized plots. Quick-release N fertilizer fluxed significantly more soil N2O than the slow-release N fertilizers. Turfgrass color was significantly higher on the sunny green versus the shaded green except in late summer. Turfgrass quality was significantly higher for the shaded green versus the sunny green. Milorganite improved turfgrass quality whereas urea decreased turfgrass quality due to fertilizer burn. When N is needed to improve turfgrass color and quality, the use of slow-release N sources should be a BMP for shaded greens.

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.

Persulfate photolysis and limited irrigation of recycled wastewater for turfgrass growth: Accumulation of pharmaceutical and personal care products and physiological responses

Recycled wastewater effluent irrigation and implementing limited irrigation rates are two promising strategies for water conservation in agriculture. However, one major challenge is the accumulation and translocation of Pharmaceutical and Personal Care Products (PPCPs) from recycled water to crops. This study investigated the effects of UV persulfate (UV/PS) treatment of recycled water and limited irrigation rate on PPCPs accumulation and physiological responses of St. Augustine turfgrass via a 14-week field trial. Carbamazepine (CBZ), sulfamethoxazole (SMX), triclosan (TCS), fluoxetine (FLX) and diclofenac (DCF) were spiked at 0.1–1.5 µg/L into recycled water and two limited irrigation rates corresponding to 60 % and 80 % of reference Evapotranspiration (ETo) were applied. Results showed that UV/PS removed 60 % of CBZ and > 99 % of other PPCPs from recycled water. Irrigation with UV/PS treated recycled water resulted in approximately a 60 % reduction in CBZ accumulation and complete removal of SMX, DCF, FLX and TCS in both turfgrass leaves and roots. A more limited irrigation rate at 60 % ETo resulted in a higher accumulation of CBZ accumulation compared to 80 % ETo. Similarly, the canopy temperature increased under 60 % ETo irrigation rate compared to 80 % ETo, suggesting that turfgrass under 60 % ETo was more prone to water stress. Applying a 60 % ETo irrigation rate was not sufficient to maintain the turfgrass quality in the acceptable range. A negative correlation between the visual quality and cumulative mass of PPCPs in turfgrass leaves at different irrigation rates was observed, yet irrigation rate was the major driver of turfgrass overall quality and health. Insights from this study will help to integrate recycled water with treatment and limited irrigation, thereby enhancing agricultural water reuse practices.

Effect of turfgrass care products on soil biological health, disease suppression, and turfgrass quality

Despite the wide use of turfgrass care products such as wetting agents (WAs), plant growth regulators (PGRs), and biological products (BPs), little is known about their effect on soil biological health, turfgrass quality, and disease suppression. Studies were conducted to evaluate the effect of some commonly used turfgrass care products on soil biological health, dollar spot suppression, and turfgrass quality. The turfgrass care products were: nine WAs (Vivax, Fleet, Magnus, Cascade, Dispatch, Duplex, Pervade, Sixteen90, and Revolution); four PGRs (Anuew, Trimmit, Proxy, and Cutless) and; three BPs (Plant Helper, KaPreRemeD8-NSL, and KaPreRemeD8-NSP). Potted bentgrass (Agrotis stolonifera L.) were treated independently with the WAs, PGRs, and BPs, and deionized water was used as a control. Soil samples were collected from the pots at 7 and 14 weeks after treatment (WAT) and analyzed for soil biological health using soil respiration, urease, and phosphatase activities as indicators. Disease suppression was evaluated by inoculating potted bentgrass with an isolate of Clarireedia jacksonii, the causal agent of dollar spot of cool season grasses and the infection was visually assessed at intervals of 10 days. The WAs Dispatch, Fleet, Magnus, and Vivax stimulated rate of soil respiration at 7 WAT compared to the control. The PGRs Cutless, Trimmit, and Proxy had no effect on soil respiration whereas Anuew suppressed soil respiration. Turfgrass quality was improved by the WAs Revolution, Cascade, Pervade, Duplex, and Sixteen90 at 7 WAT, but none of the PGRs and BPs improved turf quality. Cascade stimulated phosphatase activity and was the only product to impact this indicator. None of the products had a significant effect on dollar spot suppression. These results could guide turfgrass growers and professionals in making decisions that enhance the quality of turfgrass without compromising the health of the soil that sustains it.

A One-Dimensional Light Detection and Ranging Array Scanner for Mapping Turfgrass Quality

The turfgrass industry supports golf courses, sports fields, and the landscaping and lawn care industries worldwide. Identifying the problem spots in turfgrass is crucial for targeted remediation for turfgrass treatment. There have been attempts to create vehicle- or drone-based scanners to predict turfgrass quality; however, these methods often have issues associated with high costs and/or a lack of accuracy due to using colour rather than grass height (R2 = 0.30 to 0.90). The new vehicle-mounted turfgrass scanner system developed in this study allows for faster data collection and a more accurate representation of turfgrass quality compared to currently available methods while being affordable and reliable. The Gryphon Turf Canopy Scanner (GTCS), a low-cost one-dimensional LiDAR array, was used to scan turfgrass and provide information about grass height, density, and homogeneity. Tests were carried out over three months in 2021, with ground-truthing taken during the same period. When utilizing non-linear regression, the system could predict the percent bare of a field (R2 = 0.47, root mean square error < 0.5 mm) with an increase in accuracy of 8% compared to the random forest metric. The potential environmental impact of this technology is vast, as a more targeted approach to remediation would reduce water, fertilizer, and herbicide usage.

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.

Quality and Establishment of Some Water-Conserving Turfgrass Species for Sustainable Development and Some Ecosystem Services in Arid Urban Environments

Turfgrasses are essential landscape plants with social, environmental, and aesthetic services for urban ecosystems. However, more is needed to know how to establish them so that they can benefit from their ecosystem services in urban environments. This research examined some quality and morphological and physiological factors for the establishment and social and environmental service assessment of three warm-season turfgrasses, including Kikuyu grass (Pennisetum clandestinum), bermuda grass (Cynodon dactylon), and buffalo grass (Buchloe dactyloides), compared to the cool-season grass of tall fescue (Festuca arundinacea Schreb.). The experiment was split-plot in time, based on a randomized complete block design with eight replications. The main plot was the season with four levels, and the subplot was the four turfgrass species types. The results indicated that seasons and turfgrass types and their interaction significantly impacted most measured variables (p ≤ 0.01). Some quality measurements like turf density, color, texture, coverage, and quality after clipping and establishment confirmed the superiority of Buchloe dactyloides over the other species. Also, kikuyu grass showed higher turfgrass density, more potential for weed control, and higher coverage and growth rate but also showed invasiveness features. Tall fescue had the lowest visual aesthetic compared with the other turfgrass species. Warm-season turfgrasses adaptable to the ecology of the region should be used compared to tall fescue to achieve better turfgrass quality and social and ecosystem services for the sustainable development of arid urban environments.

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.

Phenology and sampling crawlers of rhodesgrass mealybug (Hemiptera: Pseudococcidae) in Georgia golf course putting greens.

Rhodesgrass mealybug, Antonina graminis Maskell (Hemiptera: Pseudococcidae), is an emerging pest of turfgrass in Georgia golf course putting greens. Because the feeding damage of A. graminis severely affects the aesthetics of the putting surface, it is necessary to understand the phenology of A. graminis on putting greens. To develop management strategies, the temporal emergence of crawlers is determined; however, a sampling tool for A. graminis crawlers on putting greens has not been developed. Thus, the objectives were to determine (i) the phenology of A. graminis and turfgrass quality and (ii) the best trap types for sampling crawlers on the putting greens in Georgia. From 2019 to 2022, 10-20 turfgrass plugs were sampled from the putting greens at biweekly intervals from the spring to fall. The numbers of crawlers, sessile nymphs, and adults of A. graminis were quantified from these plug samples. To determine the best trap types for sampling crawlers, 6 trap types were evaluated on the putting greens in 2021 and 2022. In the spring, the A. graminis densities remained low until June or July, then all stages of A. graminis increased. In the late fall and winter, A. graminis densities declined and remained low. The turfgrass quality improved temporally from April to June but progressively declined from the mid-to-late summer to fall. Significantly greater numbers of crawlers were sampled in the paper-folded sticky card method than in the turfgrass plug method. Thus, sticky traps could be used to sample crawlers for pest management decision.

Evaluation of Two Soil Surfactants for Soil Water Management of Creeping Bentgrass on a Wettable Clay Loam Rootzone During an Imposed Dry-down Period1

Abstract The use of soil surfactants is an established practice in turfgrass management. However, a reduction in irrigation water inputs has seldom been quantified on a mineral soil. The purpose of this one-season “proof-of-concept” field study was to apply soil surfactants to creeping bentgrass (Agrostis stolonifera ‘L-93’) on a clay loam rootzone and measure the amount and frequency of irrigation water needed to maintain a daily volumetric water content (VWC) above 25% with a maximum threshold of 35% during an imposed dry-down period. OARS HS (15.9 L·ha−1; 5 fl oz·1000 ft−2) or PBS150 (15.9 L·ha−1; 5 fl oz·1000 ft−2) soil surfactants each were applied three times (30 March, 27 April, 26 May 2016; 28-day interval) prior to a 63-day dry-down period (8 June - 9 August 2016). Compared to maintaining untreated plots irrigated to 35% VWC daily or untreated plots irrigated by threshold, plots treated with OARS HS or PBS150 resulted in a mean range of 36.5 to 41.9% reduction in water applied, and a mean range of 41.6 to 69.7% reduction of irrigation events. Use of soil surfactants in this field study resulted in a statistically significant (p < 0.05) savings in both amount and frequency of irrigation water inputs while maintaining acceptable turfgrass quality. Species used in this study: creeping bentgrass (Agrostis stoloniferous L. ‘L-93’). Chemical soil surfactants used in this study: PBS150 (100% polyoxyalkylene polymers; AquaAid Solutions, Rocky Mount, NC); OARS HS (85% octahydroxy polyoxyalkyene polymers, 7.5% amine salt of alkyl substituted maleic acid, and 7.5% inert ingredient; AquaAid Solutions, Rocky Mount, NC).

Nutrition of Florida lawns when summer fertilizer blackout period is enforced

AbstractIn Florida, multiple counties restrict the application of N to turfgrass and landscapes during the summer rainy season. These summer fertilizer blackout periods could impact turfgrass quality and the functionality of warm‐season turfgrass species. A 2‐year study was conducted at the University of Florida's Fort Lauderdale Research and Education Center (FLREC) and West Florida Research and Education Center (WFREC) to assess turfgrass performance of ‘Floratam’ and ‘Classic’ St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze] as well as ‘Empire’ and ‘Palisades’ zoysiagrass (Zoysia japonica Steud.), respectively, receiving no N fertilization during summer blackout period using eight fertilization programs compared to an unfertilized control. Visual quality, normalized difference vegetation index, percentage green cover, and dark green color index were assessed biweekly. Roots were collected before and after the fertilizer blackout period to determine root dry weight. While no differences were detected in St. Augustinegrass at the FLREC and zoysiagrass at the WFREC, all fertilized treatments except urea reached and maintained an acceptable turfgrass quality (≥6) throughout the blackout period, suggesting that urea by itself was not sufficient to support an optimal turfgrass performance during a fertilizer blackout period. The addition of P to nutrition programs did not influence turfgrass quality. Results indicate that N source is the most important factor to sustain turfgrass quality year‐round in Florida.

Warm‐season turfgrass species genotype‐by‐environment interaction for turfgrass quality under drought

AbstractOne of the biggest challenges the turfgrass industry is currently facing is limitations of available water for irrigation of turfgrass areas. Efforts on breeding for drought resistance have increased over the past several years across the United States. Thus, the objectives of this study were to evaluate the performance of bermudagrass (Cynodon spp. Rich.), St. Augustinegrass (Stenotaphrum secundatum (Walter) Kuntze), seashore paspalum (Paspalum vaginatum Swartz) and zoysiagrass (Zoysia spp. Willd.) breeding lines from five different breeding programs under drought and estimate genetic parameters in order to increase selection efficiency for drought resistance improvement in these breeding programs. The germplasm sources were bermudagrass from Oklahoma State University and University of Georgia (UGA); St. Augustinegrass from North Carolina State University, Texas A&M University System (TAMUS) and University of Florida (UF); zoysiagrass from UF and TAMUS; seashore paspalum from UGA. Field trials were conducted from 2016 to 2019 at research facilities in Citra, FL and Dallas, TX. The response variables evaluated were per cent living ground cover (%GC), and turfgrass quality under normal or non‐drought (TQND) and drought conditions (TQD). The genetic variance was significant for TQND and TQD in bermudagrass, TQD in St. Augustinegrass and all traits in zoysiagrass. The heritability estimates were higher for TQD than for TQND in bermudagrass and St. Augustinegrass. Genetic correlation estimates showed that indirect selection can be effective to select drought‐resistant genotypes. Several genotypes performed better than all commercial cultivars in both St. Augustinegrass and zoysiagrass.

Minimal light requirements and performance under reduced photosynthetic photon flux of GA2ox‐transformed and conventional Kentucky bluegrass

AbstractShade stress is a common problem encountered in turfgrass management situations worldwide. Shade reduces photosynthetic photon flux (PPF), alters light quality, reduces air movement, and may introduce tree root competition. As a species, Kentucky bluegrass (Poa pratensis L.) possesses relatively poor shade tolerance, which limits its use in reduced light environments. However, genetic alteration of the gibberellic acid enzyme pathway has shown promise in some plant species for improving growth in shade. The objective of this 2‐year field study was to determine the comparative performance under reduced PPF and determine minimal daily light integral (DLIm) requirements for acceptable quality of a conventional (CONV) Kentucky bluegrass (KBG) blend and gibberellic acid 2‐oxidase (GA2ox) transformed “ProVista” (PV) KBG. A 2‐year field study was conducted under neutral density shade treatments producing monthly daily light integrals averaging from ∼5.8 (90% shade) to 48 mol m−2 day−1 (full sun) for mid‐June through October study periods. Based on nonlinear regression of mean monthly DLI during the study period versus turfgrass quality (TQ) at the end of each study period, DLIm was found to range from 7.5 to 10 mol m−2 day−1 for PV and from 22.5 to 26.2 mol m−2 day−1 for CONV KBG. Improved TQ of PV under low light intensities may be associated with reduced rates of leaf elongation, greater stand density, higher chlorophyll concentrations, and darker green color compared to CONV KBG. Although shade duration did not exceed 4 months, the results suggest that GA2ox‐transformed PV KBG possesses improved tolerance to reduced PPF compared to CONV KBG.