Acceptable Turfgrass Quality Research Articles

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.

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.

Stress coefficients for hybrid bermudagrass in the transition zone

AbstractThe use of drought tolerant turfgrass cultivars is desirable due to greater water use efficiency and sustained acceptable turfgrass quality during times of drought stress. Crop coefficients (Kc) have traditionally been utilized to assist in reducing irrigation by comparing reference evapotranspiration (ETo) to actual evapotranspiration (ETa) of specific crops. However, Kc values are most relevant during times of nonlimiting conditions and do not quantify the amount turfgrasses restrict evapotranspiration (ET) under moderate drought stress. Stress coefficients (Ks) estimate water needs while maintaining minimally acceptable turfgrass quality. The objective of this study was to derive Ks values for four bermudagrass (Cynodon spp.) cultivars managed in the transition zone. Direct measurements of actual evapotranspiration were made through weighing lysimetry during a 2‐year field study. Experimental units were allowed to naturally dry down near wilting point and maintained at a steady level of soil moisture to calculate Ks for each cultivar. A lower Ks value indicates increased turfgrass tolerance to water stress; whereas a Ks value ≥1 suggests higher soil moisture levels are required to sustain turfgrass quality. ‘TifTuf’, ‘Latitude 36’ and ‘Tifway’ were the best performing cultivars with mean Ks values of 0.747, 0.766, and 0.796, respectively. ‘Celebration’ had the highest Ks value of 0.944. The results indicate certain bermudagrass cultivars can maintain quality with less soil water, and the reduced water requirements may be used to schedule efficient irrigation applications.

Evaluation of irrigation scheduling approaches within sand‐capped turfgrass systems

AbstractIn an effort to improve performance of turfgrass irrigated with poor‐quality water, the practice of sand capping is increasing. Given current strains on water supplies, evaluation of various methods of irrigation scheduling approaches for these systems is needed. The objectives of this 2‐yr field study were to evaluate turfgrass performance, temporal and spatial soil moisture and salinity dynamics, and comparative water use among four irrigation scheduling approaches including (a) wireless soil moisture sensor (SMS), (b) on‐site reference evapotranspiration (ETo), (c) National Oceanic and Atmospheric Administration forecasted reference evapotranspiration, and (d) visual‐wilt‐based treatment. The turfgrass used was ‘Latitude 36’ hybrid bermudagrass [Cynodon dactylon (L.) Pers. ×C. transvaalensis Burtt‐Davy] planted atop a 17.8‐cm medium‐coarse textured sand cap. Results demonstrated that all approaches produced similar levels of acceptable turfgrass quality and percentage green cover with no apparent differences in root development. Forecasted reference evapotranspiration was found to be a good predictor of on‐site ETo (R2 = .97) when comparing daily values across two growing seasons. Under wilt‐based irrigation, the volumetric water content (7.6 cm sand‐cap depth) at which wilt occurred was highest mid‐summer (4.1–4.7%) but declined during early and late summer months (1.8–2.2%), suggesting different thresholds may be needed throughout the season when using SMS‐based scheduling. Finally, seasonal water use was 23% lower for the on‐site ETo–based approach compared with SMS‐based scheduling, although this did not result in elevated electrical conductivity within the sand cap. The results provide important information to guide adoption of data‐driven approaches to irrigation scheduling.

Effect of topdressing of compost, compost tea, and various fertilizers on soil and lawn characteristics

AbstractMany cities in the United States collect and compost yard waste but need more effective and efficient ways to utilize the finished product. Home lawns represent a sizeable area that could benefit from land application of yard waste compost, but little research has been conducted regarding topdressing lawns with compost. The objectives of this study were to compare the impact of topdressing yard waste compost relative to organic and inorganic fertilizers in a mature, predominantly Kentucky bluegrass (Poa pratensis L.) lawn in Wisconsin. Three different composts (two from yard waste and one from food waste), two organic fertilizers, and a compost–compost tea combination were compared against a traditional synthetic fertilization program and a nontreated control. Treatments receiving compost (1.3 cm depth per year, in two equally sized applications) maintained acceptable turf quality over the 3.5‐yr study period and resulted in significant improvements in several important physical properties of the soil. Fertilizers were also able to maintain acceptable turfgrass quality but had no impact on the physical properties of soil over the study period relative to the control. Organic and synthetic fertilizers reduced weed populations compared with the control, though the compost treatments did not. Compost and one of the organic fertilizers significantly increased the levels of soil test P but did not reach levels of environmental concern.

Plant‐available soil nitrogen fluxes and turfgrass quality of Kentucky bluegrass fertilized with humic substances

AbstractHigh quality turfgrass requires adequate amounts of nitrogen (N) fertilizer. However, excess N application can increase N losses via leaching and gaseous emissions. Enhanced efficiency fertilizers (EEF) and humic substances have been used to decrease N losses to the environment. A two‐year field experiment was conducted on a native soil with Kentucky bluegrass (Poa pratensis L.) to investigate if the addition of humic substances to fertilizers could be classified as an enhanced efficiency fertilizer. To determine this, the objectives were: a) to determine if incorporating humic substances will increase the plant‐available N collected on ion exchange membranes (IEM) over a growing season and b) to determine the N release (NR) curves of the fertilizer treatments using the mesh bag technique. Fertilizer treatments included humic‐coated urea (HCU), poly‐coated humic‐coated urea (PCHCU), urea + humic dispersing granules (HDG), poly‐coated sulfur‐coated urea (PCSCU), stabilized N, urea, and a nontreated control. Overall, the addition of humic substance to fertilizers did not improve turfgrass quality compared with fertilizers alone. Additionally, all fertilizer treatments had improved turfgrass quality relative to the nontreated control and provided acceptable turfgrass quality for almost all of the growing season. Over the growing season, PCHCU had 25% greater inorganic N captured on IEM compared with all other treatments. Both PCHCU and PCSCU show extended NR curves with PCHCU having a greater release period. In conclusion, PCHCU increased plant‐available N concentrations, released it slowly, and should be classified as an EEF.

Long-term Performance of Warm-season Turfgrass Species under Municipal Irrigation Frequency Restrictions

Landscape irrigation frequency restrictions are commonly imposed by water purveyors and municipalities to curtail domestic water use and to ensure adequate water supplies for growing populations during times of drought. Currently, published data are lacking concerning irrigation frequency requirements necessary for sustaining acceptable levels of turfgrass quality of commonly used warm-season turfgrass species. The objective of this 3-year field study was to determine comparative turfgrass quality of drought-resistant cultivars of four warm-season lawn species in the south–central United States under irrigation frequency regimes of 0, 1, 2, 4, and 8× monthly. Turfgrasses used in the study were based on previously reported drought resistance and included ‘Riley’s Super Sport’ (Celebration®) bermudagrass [Cynodon dactylon (L.) Pers.], ‘Palisades’ zoysiagrass (Zoysia japonica Steud.), ‘Floratam’ st. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and ‘SeaStar’ seashore paspalum (Paspalum vaginatum Swartz). During each growing season, slightly reduced irrigation volumes and bypassed events resulted from the 8× monthly treatment (34.95 cm, 38.13 cm, and 27.33 cm) compared with the 4× monthly treatment (35.36 cm, 40.84 cm, and 28.70 cm) in years 1, 2, and 3, respectively. For the once weekly treatment, the average fraction of reference evapotranspiration (ETo) supplied by effective rainfall and irrigation during the summer months was 1.22, 0.67, and 0.83 in years 1, 2, and 3, respectively, and was generally adequate to support acceptable turfgrass quality of all warm-season turfgrasses evaluated. Under the less than weekly irrigation frequency, st. augustinegrass and seashore paspalum generally fell to below acceptable quality levels because the average fraction of ETo supplied by effective rainfall and irrigation during the summer months of years 2 and 3 was 0.51, 0.39, and 0.26 for the 2× monthly, 1× monthly, and unirrigated treatments, respectively. Bermudagrass generally outperformed all other species under the most restrictive irrigation frequencies and also did not differ statistically from zoysiagrass. These results show that as irrigation frequency is restricted to less than once per week, species selection becomes an important consideration.

A New Method to Measure Bermudagrass (Cynodon spp.) Golf Course Putting Green Ball Roll Uniformity

Abstract The golf industry has a $170 billion economic impact in the United States, and a vital aspect of the sport is golf course putting green performance. The goal of putting green management is to provide a surface on which a golf ball is rolled uniformly while maintaining acceptable yearlong turfgrass quality. Several devices have been developed to quantify golf ball roll dynamics on putting greens; however, there are limited methods to measure putting green ball roll uniformity. The objective of this research was to assess putting green ball roll uniformity by measuring the dispersion of golf balls released from a modified Perfect Putter device. The Perfect Putter is a lightweight and portable ramped device that was modified to include a fixed hinge to minimize human error associated with golf ball release and a wider base for increased stability. Our method for quantifying ball roll uniformity was as follows: 20 golf balls were released from the device and marked individually. Dispersion length was quantified by measuring the maximum linear distance between two marks parallel to the roll line, whereas dispersion width was quantified by measuring the maximum linear distance between two marks perpendicular to the roll line. These two values were multiplied together to calculate the area of golf ball dispersion. This method measured a range of dispersion areas among geographic locations, turfgrass cultivars, and turfgrass canopy heights. This rapid test of putting surface ball roll uniformity has potential to aid bermudagrass turfgrass managers in maximizing putting green playability.

Comparing rates of mineral oil, sulfur, and phosphorous acid on Microdochium patch suppression and turfgrass quality

AbstractMicrodochium patch is a turfgrass disease caused by the fungal pathogen Microdochium nivale (Fr.) Samuels and I.C. Hallett that occurs in climates similar to the cool, humid regions of North America's Pacific Northwest. Mineral oil, S, and phosphorous acid (H3PO3) have been shown to suppress Microdochium patch on annual bluegrass (Poa annua L.) putting greens in western Oregon. Previous research using rates of 19.9 kg mineral oil ha–1 applied every 2 wk alone or as a tank mixture with 12.2 kg S ha–1, 3.7 kg H3PO3 ha–1, or both resulted in unacceptable turfgrass thinning. The objective of this field experiment was to evaluate whether tank mixes of these products would suppress Microdochium patch and yield acceptable turfgrass quality when rates of mineral oil were reduced from 19.9 to 10.0 kg ha–1, S from 12.2 to 6.1 kg ha–1, or H3PO3 from 3.7 to 1.8 kg ha–1. In both years of the experiment, all treatments suppressed Microdochium patch to <2% disease compared to more than 40% disease in the non‐treated control. Mineral oil applied with S resulted in a larger loss of green cover compared to mineral oil applied with H3PO3 regardless of rate. These results suggest that tank mixing mineral oil and S should be avoided in the winter months. Further research studying the mitigation of green cover loss associated with these treatments is warranted.

Tall Fescue (Schedonorus arundinaceus (Schreb.) Dumort.) Turfgrass Cultivars Performance under Reduced N Fertilization

The identification of minimal N requirements for sustaining turfgrass quality and functionality became necessary to reduce N fertilization inputs and avoid potential environmental impacts in the European Union. A two year study was conducted at Padova University in Legnaro, northeastern Italy to investigate the performance of four tall fescue (Schedonorus arundinaceus (Schreb.) Dumort.) cultivars (‘Lexington’, ‘Rhambler SRP’, ‘Rhizing star’, and ‘Thunderstruck’) fertilized twice per year at either 75 or 150 kg N ha−1 year−1. Turfgrass was evaluated every two weeks for turfgrass visual quality, percent green cover (PGR) as well as dark green color index (DGCI) through digital image analysis and normalized difference vegetation index (NDVI). ‘Rhizing star’ was the only cultivar that showed poor adaptation to the environment, achieving acceptable turfgrass quality (6.0 or higher) only during June and July 2019. Turf fertilized at 150 kg N ha−1 year−1 generally showed higher performance than 75 kg N ha−1 year−1, however, the increase in turfgrass quality was mostly negligible and detected only during the winter months. Results suggest that well adapted tall fescue cultivars could be fertilized at 75 kg N ha−1 year−1 in Northern Italy.

Creeping bentgrass summer decline as influenced by climatic conditions and cultural practices

AbstractDespite its popularity as a putting surface in North Carolina, creeping bentgrass (Agrostsis stolonifera L.) is highly susceptible to summer bentgrass decline (SBD) during hot summer months. Cultural practices have been shown to help alleviate the pressure of SBD. The objectives of this study were to detail the impacts of N fertility, soil water content, and hollow‐ and solid‐tine cultivation on creeping bentgrass quality. Cultural treatments included four N rates (97, 195, 293, and 391 kg ha−1 yr−1), four hollow‐tine core cultivation programs (6.4 mm diam. tines two times yr−1, 9.5 mm diam. tines two and three times yr−1, and a non‐cored control), two soil water content levels (low and high), and two summer solid‐tine spiking cultivation treatments (spiked and not spiked). Visual turfgrass quality was measured. A N rate greater than 195 kg ha−1 was needed to maintain acceptable turfgrass quality. High soil water content consistently provided better summer turfgrass quality compared to low soil water content conditions. Nitrogen fertility and soil water content interacted where higher levels of both resulted in the best quality ratings. Hollow‐core cultivation reduced turfgrass quality at the lower N rates; whereas, solid‐tine spiking had no effect on turfgrass quality. Although weather plays a large role in SBD in North Carolina, results from this study show that cultural practices can influence its severity.

Turf Performance of Shaded ‘TifGrand’ and ‘TifSport’ Hybrid Bermudagrass as Affected by Mowing Height and Trinexapac-ethyl

Heavily shaded environments often limit the performance and persistence of hybrid bermudagrass (Cynodon dactylon × C. transvaalensis), therefore a field-based shade study was performed to determine whether different mowing heights (0.5 and 1.5 inch) or two trinexapac-ethyl (TE) growth regulator management treatments (control and 2 oz/acre) allow either ‘TifSport’ or ‘TifGrand’ hybrid bermudagrass to persist under 77% shade. Turfgrass quality (TQ), green cover, normalized difference vegetation index (NDVI), and dark-green color index (DGCI) were evaluated on the two cultivars under a shade structure in Tifton, GA, during 2010 and 2011. Neither of the cultivars maintained acceptable TQ throughout the entire year under 77% shade, although ‘TifGrand’ displayed adequate TQ at the higher mowing height (1.5 inch) and demonstrated more shade tolerance than ‘TifSport’, as indicated by TQ, green cover, and NDVI. The TE application did not enhance the turf performance of ‘TifSport’ under 77% shade when mowed at 0.5 inch, but it improved turf performance of ‘TifGrand’ at the same height. The effect of TE application was cultivar and mowing height dependent under this heavily shaded environment, which warrants future study to determine the best management practices of these cultivars as well as continued efforts to develop new, shade-tolerant bermudagrass hybrids.

Frequent soil surfactant applications influence anthracnose on an annual bluegrass research green

AbstractAnthracnose is a turfgrass disease caused by the fungal pathogen Colletotrichum cereale Manns and can cause severe damage to annual bluegrass putting greens. Most turfgrass managers use fungicides to manage anthracnose, although legislation in some locations are compelling managers to seek fungicide alternatives. This 2‐yr field experiment in western Oregon evaluated different rates and application intervals of a soil surfactant—either in combination or in the absence of a spring hollow‐tine aerification on anthracnose severity—on an annual bluegrass (Poa annua L. var. reptans) research green. The highest rate of the soil surfactant applied once or twice a week consistently reduced anthracnose severity in both years compared to the nontreated control, although these applications corresponded to four and eight times the monthly label rate. A quarter of the label rate applied once a week suppressed anthracnose at the peak of disease in the second year and as measured by area under disease progress curves in both years. Spring aerification had no effect on anthracnose severity. Area under volumetric water content progress curves calculated using weekly measurements at a 38‐mm depth were not correlated with area under disease progress curves. The volumetric water content percentage was normally above 25%, reducing the risk of confounding between drought stress and treatments on anthracnose suppression. The highest rate of soil surfactant applied at the most frequent interval was the only treatment to receive acceptable turfgrass quality ratings over both years.

Immediate Irrigation Improves Turfgrass Safety to Postemergence Herbicides

Summer annual grassy weeds such as goosegrass (Eleusine indica L. Gaertn.) continue to be problematic to control selectively with postemergence (POST) herbicides within turfgrass stands. In recent years, reduced performance by certain herbicides (e.g., foramsulfuron), cancellation of goosegrass-specific herbicides (e.g., diclofop-methyl), and cancellation and/or severe use reductions of other herbicides [e.g., monosodium methanearsonate (MSMA)] have limited the options for satisfactory control and maintenance of an acceptable (≤30% visual turfgrass injury) turfgrass quality. Currently available herbicides (e.g., topramezone and metribuzin) with goosegrass activity typically injure warm-season turfgrass species. The objectives of this research were to evaluate both ‘Tifway 419’ bermudagrass [Cynodon dactylon (L.) Pers. ×Cynodon transvaalensis Burtt-Davy] injury after treatment with POST herbicides, and to determine whether irrigating immediately after application reduces turfgrass injury. Treatments were control (± irrigation); topramezone (Pylex 2.8C; ± irrigation); carfentrazone + 2,4-D + dicamba + 2-(2-methyl-4-chlorophenoxy) propionic acid (MCPP) (Speedzone 2.2L; ± irrigation); carfentrazone + 2,4-D + dicamba + MCPP in combination with topramezone (± irrigation); metribuzin (Sencor 75DF; ± irrigation); mesotrione (Tenacity 4L; ± irrigation); simazine 4L (±irrigation); and mesotrione + simazine (± irrigation). Irrigated treatments were applied immediately with a hand hose precalibrated to apply 0.6 cm or 0.25 inch (≈6.3 L). Visual turfgrass injury for combined herbicide treatments for the irrigated plots was 6% 4 days after treatment (DAT), 12% 1 week after treatment (WAT), 17% 2 WAT, and 6% 4 WAT, whereas nonirrigated plots had turfgrass injury of 14% at 4 DAT, 31% 1 WAT, 35% 2 WAT, and 12% 4 WAT. Irrigated pots had normalized differences vegetative indices (NDVI) ratings of 0.769 at 4 DAT, 0.644 at 1 WAT, 0.612 at 2 WAT, and 0.621 at 4 WAT, whereas nonirrigated plots had the lowest (least green) turfgrass NDVI ratings of 0.734 at 4 DAT, 0.599 at 1 WAT, 0.528 at 2 WAT, and 0.596 at 4 WAT. These experiments suggest turfgrass injury could be alleviated by immediately incorporating herbicides through irrigation.

Seasonal Cultural Management Practices for Aging Ultradwarf Bermudagrass Greens in the Subtropics: I. Nitrogen and Potassium Fertilization

Bermudagrass cultivars [Cynodon transvaalensis (L.) Pers. × Cynodon dactylon (Burtt‐Davy)] with more decumbent growth habits referred to as “ultradwarfs” have been released for use on golf course greens and tees as an alternative to standard bermudagrass varieties that have been used for >40 yr. Little research information is available on long‐term ultradwarf management requirements in subtropical environments. Therefore, a 4‐yr experiment was conducted in South Florida on a United States Golf Association specified green to determine the effects of nitrogen (N) fertility and N to potassium (K) ratios on quality, growth, and performance of three commercially released ultradwarfs (‘Champion’, ‘TifEagle’, and ‘FloraDwarf’). For all three cultivars, fertilizing at 879 kg N ha−1 yr−1 resulted in acceptable turfgrass quality with mean tissue N and K concentrations of 31 g N kg−1 and 14 g K kg−1, respectively. Over the 4‐yr experiment, leaf tissue N and K were present approximately as a 2:1 ratio, regardless of N rate and N:K ratio applied. As the ultradwarfs aged, fertilizing with 586 kg N ha−1 yr−1 was adequate. It appears that Champion and TifEagle have different mechanisms for increasing aboveground growth and had better quality and growth characteristics than FloraDwarf. This research documented the need for adjusting fertilization as the ultradwarf bermudagrass green ages and for the ultradwarf cultivar maintained.

Comparative Performance and Daily Light Integral Requirements of Warm‐Season Turfgrasses in Different Seasons

Shade or reduced sunlight poses a major challenge for maintaining acceptable turfgrass quality. The quantification of daily light integral (DLI, mol m−2 d−1) requirement could help to identify shade‐tolerant germplasm. The objectives of this study were (i) to compare turf performance, and (ii) to determine seasonal DLI requirement of 12 warm‐season turfgrass cultivars in response to varying levels of shade. A greenhouse study that included three experiments was conducted in spring (30/20°C), summer (35/25°C), and winter (25/15°C) months. Shade levels providing 33, 61, and 92% reductions in photosynthetic photo flux were imposed. Twelve cultivars from nine species were evaluated for turfgrass quality (TQ), normalized difference vegetation index, and shoot biomass production over 8 wk. The DLI requirement was obtained through nonlinear regression between DLI and TQ. Most warm‐season turfgrass species maintained acceptable TQ up to 33% shade. ‘TifGrand’ and ‘Tifway’ bermudagrass [Cynodon dactylon (L.) Pers × C. transvaalensis Burtt‐Davy] required each relatively higher DLI ranging from 9.2 (winter) to 21.4 (summer) mol m−2 d−1. Zoysiagrass (Zoysia spp.) cultivars maintained acceptable TQ up to 61% shade, with the lowest DLI requirements ranging from 5.9 (winter) to 10.9 (summer) mol m−2 d−1. The DLI requirements for the tested grasses were lower in winter (5.9–9.9 mol m−2 d−1) than in spring (9.4–17.4 mol m−2 d−1) and summer (9.9–21.4 mol m−2 d−1). ‘Argentine’ bahiagrass (Paspalum notatum Flugge) had an increased DLI requirement relative to other entries in summer months.

Growth Responses of Hybrid Bluegrass and Tall Fescue as Influenced by Light Intensity and Trinexapac-ethyl

Interspecific hybrids between texas bluegrass (Poa arachnifera Torr.) and kentucky bluegrass (Poa pratensis L.) are known to exhibit good heat tolerance, which has aided in their adaptation to the warmer climates of the southern United States, but their tolerance to shade has not been investigated. The objectives of this study were to 1) evaluate the growth responses of interspecific bluegrass hybrids (P. arachnifera × P. pratensis) in comparison with kentucky bluegrasses and a shade-tolerant cultivar of tall fescue (Festuca arundinacea Schreb.) under full sunlight and shaded environments, 2) identify optimum times to evaluate shade tolerance using the selected growth measurements, 3) calculate the minimum daily light requirements to retain acceptable turfgrass quality, and 4) determine if trinexapac-ethyl (TE) applications enhance hybrid bluegrass quality under shade. Two 10-week greenhouse experiments (late spring and early fall) were conducted in Dallas, TX. Within each of three light environments a randomized complete block design was used to accommodate three replications of eight genotypes treated with and without TE (0 or 0.228 kg·ha−1 a.i.). Turfgrass quality, leaf elongation rates, clipping dry weights, and percent green cover were measured. Meaningful comparisons were best during the late spring when daily light integrals (DLI) were optimum for healthy plant growth. Shade-tolerant hybrid bluegrasses (DALBG 1201 and TAES 5654) were identified using turfgrass quality and leaf elongation rates. These genotypes exhibited above-acceptable turfgrass quality in all environments, and a reduced leaf elongation rate similar to the tested dwarf-type tall fescue. DLI requirements of DALBG 1201 and TAES 5654 were ≤4 to achieve acceptable quality. TE applications generally did not improve turfgrass quality of genotypes, although leaf elongation rates were significantly reduced in all environments.

Development of Turf-type Poa pratensis L. Germplasm for Seed Production without Field Burning

Open-field burning of Kentucky bluegrass (Poa pratensis L.) post-harvest residue, which maintains grass seed yield and stand longevity, has been eliminated in Washington and is restricted in Idaho and Oregon, USA. Our objective was to develop Kentucky bluegrass germplasm that has sustainable seed yield without field burning while maintaining acceptable turfgrass quality for use as an amenity grass. From the USDA/ARS Poa pratensis L. Plant Introduction (PI) collection, 228 accessions were evaluated in a field trial and a core collection was developed. This collection was then evaluated in seed production and turfgrass trials and those possessing both good seed yield without field burning and turfgrass quality were identified and planted in a space-plant nursery at Pullman, WA. The eight PI accessions and two commercial cultivars checks were evaluated over a 2-year period and individual plants were reselected within each accession, or check, with the highest seed weight, highest seeds panicle -1 , highest panicle number area -1 , and highest seed yield. Turfgrass plots were established in 2006, 2009, and 2010 at Pullman, WA, Auburn, AL, and Puyallup, WA, respectively. Seed production plots (irrigated and non-irrigated) were established at Pullman in 2007. Selection for seed yield components had a variable response and seed yield was more dependent on accession. PI 368241, selection panicles area -1 , and Kenblue, selection seeds panicle -1 , had the best sustainable (four harvests) seed yield without field burning in both non-irrigated and irrigated seed production. Both had fair turfgrass quality. PI 371775, selection seeds panicle -1 , had good turfgrass quality while maintaining good seed yield with irrigation. These selections have been harvested for seed increase (2012-2014) and germplasm should be released by 2015.