Stenotaphrum Secundatum Research Articles

Deficit Irrigation and Fertility Effects on NO3-N Exports from St. Augustinegrass.

Proper management of turfgrass systems is critical for reducing the risk of nutrient loss and protecting urban surface waters. In the southern United States, irrigation can be the most significant management practice regulating the biogeochemical and hydrological cycles of turfgrass systems. A turfgrass runoff research facility was used to assess the effects of deficit irrigation and fertilizer applications on turfgrass canopy cover and nitrate-N (NO-N) exports in runoff from St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] turf over a 2-yr period. Treatments were arranged as a randomized complete block design having eight combinations of irrigation (100, 75, or 50% of estimated turfgrass water requirements) and fertility level (0, 88, and 176 kg N ha yr). Runoff from 31 rainfall events and one irrigation excess event were used to estimate annual and seasonal NO-N exports. The majority of annual NO-N exports occurred during the late winter and spring. Deficit irrigation reduced summer and early autumn runoff volumes. Lower summer and autumn runoff volumes (from deficit irrigation) coincided with reduced NO-N exports from runoff during Year 1. Deficit irrigation combined with fertilizer applications increased runoff [NO-N] in Year 2, suggesting that the previous year's export reduction contributed to higher N accumulation in the system and thus a higher N loss potential. These findings suggest that deficit irrigation can be a tool for reducing seasonal nutrient exports from St. Augustinegrass lawns so long as fertilizer inputs are moderate.

Complete nucleotide sequences and virion particle association of two satellite RNAs of panicum mosaic virus

Over six decades ago, panicum mosaic virus (PMV) was identified as the first viral pathogen of cultivated switchgrass (Panicum virgatum). Subsequently, PMV was demonstrated to support the replication of both a satellite RNA virus (SPMV) and satellite RNA (satRNA) agents during natural infections of host grasses. In this study, we report the isolation and full-length sequences of two PMV satRNAs identified in 1988 from St. Augustinegrass (Stenotaphrum secundatum) and centipedegrass (Eremochloa ophiuroides) hosts. Each of these satellites have sequence relatedness at their 5′- and 3′-ends. In addition, satC has a region of ∼100 nt complementary to the 3′-end of the PMV genome. These agents are associated with purified virions of SPMV infections. Additionally, satS and satC RNAs contain conserved in-frame open reading frames in the complementary-sense sequences that could potentially generate 6.6- and 7.9-kDa proteins, respectively. In protoplasts and plants satS is infectious, when co-inoculated with the PMV RNA alone or PMV+SPMV RNAs, and negatively affects their accumulation.

Interspecific Hybrids between Pembagrass and St. Augustinegrass

St. Augustinegrass [Stenotaphrum secundatum (Walt) Kuntze] is an important turfgrass throughout many of the warm, humid regions of the world, including the southeastern United States. Unfortunately, the grass is susceptible to a number of insects, pathogens, and nematodes that adversely reduce its desirability as a turfgrass. Another Stenotaphrum species, pembagrass [S. dimidiatum (L.) Brongn.], offers a source of resistance to some of these pests. Crosses were made between pembagrass and St. Augustinegrass in an attempt to transfer desirable resistance genes into St. Augustinegrass. Two pembagrass accessions (PI 289729 and PI 365031) were used as the maternal parents, and different St. Augustinegrass cultivars and breeding lines were used as the paternal parents. Seed from these crosses were small, shriveled, lacking fully developed endosperm, and unable to germinate. A total of 218 embryos were cultured on a growth medium using embryo rescue techniques, and 127 seedlings were recovered. Paternal‐specific expressed sequence tag‐simple sequence repeat markers were used to identify the hybrids, and all 127 seedlings were determined to be F1 hybrids. These are the first reported hybrids between pembagrass and St. Augustinegrass. The crossability between the two species ranged from 0 to 67.1%, depending on the genotypes used, and the overall mean crossability was 30.8%. Crossability was greatly influenced by which pembagrass genotype was used as the maternal parent. This is an initial step toward introgressing desired genes for insect, nematode, and pathogen resistance from pembagrass into St. Augustinegrass.

Historical ETo-based irrigation scheduling for St. Augustinegrass Lawns in the South-Central United States

Irrigation of residential and commercial lawns in excess of plant water requirements can result in waste of potable water supply and negative public perception regarding turf landscapes. A 3-year field study was conducted to evaluate simple historical ETo-based irrigation scheduling for maintenance of St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze ‘Raleigh’] lawns in College Station, TX, USA. Whole main plots were assigned crop coefficients of 1.00, 0.60, 0.36, or 0.24 (K100, K60, K36, and K24) used to adjust historical ETo (47-year average). Sub-plots received N rates of either 0.0, 0.4, or 0.8 kg ha−1 month−1 during the experimental period each year. Irrigation treatments were applied 3 days per week from July through September each year. Acceptable turf quality was maintained when irrigation depths were ≥47% of actual ETo. The K60 treatment provided adequate irrigation for turf performance but caused 31% overwatering in the wettest year. The K36 treatment resulted in acceptable turf quality not only in the wettest year, but also showed complete recovery of the turf sward by the end of fall in each year. This research has outlined a simple and effective method for conserving water used to irrigate St. Augustinegrass lawns.

Assessing freeze-tolerance in St. Augustinegrass: temperature response and evaluation methods

Winter hardiness is a major-limiting factor for St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] grown in the transitional climatic region of the United States. Lab-based freeze tests that mimic the range of field winter survivability in St. Augustinegrass can contribute to the selection of cold hardy genotypes. This study used a whole container method, four freezing temperatures, and two data collection systems to evaluate the freezing response of nine St. Augustinegrass genotypes ranging in their winter hardiness. Results indicated −3 and −4 °C with average regrowth ratings of 33.6 and 17.8% respectively, were more suitable temperatures for evaluating freeze survival in St. Augustinegrass than −5 and −6 °C with average regrowth ratings of 0.4 and 0%, respectively. Visual ratings of surviving green tissue and regrowth were generally well correlated when evaluated over a six week period post-freeze with Pearson correlation coefficients ranging of 0.17–0.62 for −3 °C freeze tests and 0.79–0.93 for −4 °C freeze tests. Additionally, measurement of percent green cover using digital imaging techniques commonly utilized in turfgrass field studies were significantly correlated (0.66) with visual ratings averaged across weekly post-freeze evaluation measurements for both −3 and −4 °C freezing temperatures. These results provide evidence that digital imaging analyses are useful in estimating surviving green tissue and regrowth in lab-based freeze tests. This study provides additional information regarding freezing temperatures, genotype responses, and data collection methods in St. Augustinegrass, which should aid breeders in the improvement of freeze tolerance in the species.

Performance of Three Warm Season Turfgrasses under Linear Gradient Irrigation

The appropriate level of irrigation for turfgrasses is vital to the performance of the turfgrass as well as conservation of water. Linear gradient irrigation system (LGIS) facilitates long-term study of turf performance under continuous irrigation gradients at extreme ends of the irrigation scale. The objectives of this study were to: a) determine the minimum irrigation requirements and relative drought resistance in three warm season turfgrasses; and b) evaluate the medium to long-term effects of irrigation levels on turf persistence, weed invasion, and susceptibility to diseases. Results suggest that grasses differed in drought resistance and persistence under variable irrigation regimes. Irrigation (Ep) required for consistent acceptable turf quality for respective grasses was Cynodon dactylon x C. transvaalensis (61%), Zoysia matrella L. Merr (73%), and Stenotaphrum secundatum 'Palmetto' (86%). Brown patch infection was most prevalent in Stenotaphrum secundatum 'Palmetto' at 12 and 125% Ep irrigation. Cynodon dactylon x C. transvaalensis and Zoysia matrella L. Merr were better able to adapt to the various irrigation regimes, and this ability allowed these species to resist drought, and maintain turf coverage which in turn, kept weeds and the occurrence of diseases at bay. Ranking these grasses for their drought tolerance abilities showed that Cynodon dactylon x C. transvaalensis had the most outstanding resistance against drought, followed by Zoysia matrella L. Merr, and lastly, Stenotaphrum secundatum 'Palmetto'. Despite having the highest irrigation requirement, Stenotaphrum secundatum 'Palmetto' was still not able to maintain persistence at high irrigation regimes. Likewise, this grass also lost turf coverage at low irrigation levels.

Comparative Performance of Three Tropical Turfgrasses Digitaria longiflora, Axonopus compressus and St. Augustinegrass under Simulated Shade Conditions

Shade affects turf quality by reducing light for photosynthesis. The shade tolerance of the tropical grasses, Digitaria longiflora and Axonopus compressus were evaluated against Stenotaphrum secundatum (St. Augustinegrass). The grasses were established under shade structures that provide 0%, 50%, 75% or 90% shade level for 30 days. A suite of leaf traits, recorded from similar leaf developmental stage, displayed distinct responses to shade conditions. Leaf length, relative to control, increased in all three species as shade level increased. The mean leaf extension rate was lowest in St. Augustinegrass (80.42%) followed by A. compressus (84.62%) and D. longiflora (90.78%). The higher leaf extension rate in D. longiflora implied its poor shade tolerance. Specific leaf area (SLA) increased in all species with highest mean SLA increase in D. longiflora (348.55 cm2 mg−1) followed by A. compressus (286.88 cm2 mg−1) and St. Augustinegrass (276.28 cm2 mg−1). The highest SLA increase in D. longiflora suggested its lowest performance under shade. The percent green cover, as estimated by digital image analysis, was lowest in D. longiflora (53%) under 90% shade level compared to both species. The relative shade tolerance of the three turfgrasses could be ranked as St. Augustinegrass > A. compressus > D. longiflora.

Dew from Warm‐Season Turfgrasses as a Possible Route for Pollinator Exposure to Lawn‐Applied Imidacloprid

Core Ideas This is the first study to report warm‐season turfgrass dew as a potential source for pollinator contact with imidacloprid. Observed imidacloprid concentrations were similar to those reported in creeping bentgrass guttation droplets but less than those typically found in agronomic crops grown from treated seed. Foliar‐treated bermudagrass contained more than 10 times the imidacloprid residue of the isolated soil‐only treatment. Imidacloprid is a neonicotinoid insecticide used for the control of turfgrass insect pests. It can be translocated into guttation fluid, thus potentially creating an exposure avenue for beneficial insects. Our research objectives were to investigate the fate of soil‐ and foliar‐applied imidacloprid in dew forming on bermudagrass (Cynodon spp.) and St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze] turf. Imidacloprid was applied at standard use rates (443 g a.i. ha−1; 6.32 oz a.i. acre−1) to soil only via sub‐irrigation (Years 1 and 2) or by foliar treatment (Year 2), which is representative of standard home lawn application. Dew fluid, which includes guttation, was collected 48 h after treatment and was analyzed for imidacloprid. During Year 1, dew collected from the soil‐only treatment of bermudagrass and St. Augustinegrass contained 15.8 and 9.2 ng imidacloprid mL−1, respectively. During Year 2, foliar treated bermudagrass contained more than 10 times the amount of imidacloprid as found in the soil‐only treatment (59.8 versus 5.2 ng mL−1, respectively). Observed imidacloprid concentrations were similar to those reported in creeping bentgrass guttation droplets but were less than those typically found in agronomic crops grown from treated seed. Levels were less than those reported to be acutely lethal to the European honeybee. However, depending on the amount of contaminated dew or guttation transported into hives, similarly low concentrations could be associated with sublethal effects (reportedly >10 ng mL−1). This is the first study to report warm‐season turfgrass dew as a potential source for pollinator contact with imidacloprid and suggests that post‐application irrigation is perhaps the best way to avoid pollinator exposure.

Gamma‐Ray Irradiation Improves Turfgrass Characteristics of St. Augustinegrass

St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is a warm‐season turfgrass with medium to high shade tolerance, a valuable trait for use in lawns, particularly in smaller residential landscapes and other green spaces where trees are dominant. However, their long internodes and very coarse leaf and stolon texture are undesirable in home lawns and public spaces. Gamma (γ) irradiation has been used to induce useful variations for various morphological traits in turfgrass breeding. The objective of the present study was to induce dwarf and semidwarf phenotypes from two St. Augustine germplasms, S1 and S2, irradiated with 50, 100, 150, or 300 Gy and 20, 40, 80 or 120 Gy respectively, using a 60Co source. The lethal does (LD50) for S1 and S2 genotypes were 95 and 103 Gy, respectively. The linear reduction of survival rate with increasing gamma rays was highly correlated (r2 = 0.96 and 0.87). The 15 morphological mutants (0.35% of the irradiated plants) with a semidwarfed growth habits were identified among 4301 node cuttings. The mutant lines exhibited up to 40% shorter plant height and finer leaf and stolon texture than parental genotypes. Mutant lines developed in this study may offer improved St. Augustinegrass cultivars for landscaping.

Association between Blissus insularis Densities and St. Augustinegrass Lawn Parameters in Florida

Core Ideas Cultural control of southern chinch bug in St. Augustinegrass by following recommended guidelines for mowing heights based on turfgrass cultivar, and practicing thatch management may reduce insecticide use and nontarget impacts. Turf parameters (turf height and thatch thickness) were closely associated to southern chinch bug densities observed in St. Augustinegrass residential lawns. Best management practices recommended for growing St. Augustinegrass in Florida may help to maintain a balance between turf health and pest pressure. Turf characteristics in conjunction with environmental factors influence the microclimate suitability for insect pest survival in grasses. In this study, we sought to find the association between southern chinch bug (Blissus insularis) densities, St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] health characteristics (weed abundance, turf density and height, turf color, chlorophyll content, total Kjeldahl nitrogen concentration, and thatch thickness), and abiotic factors (soil pH, soil and air temperature, soil moisture, and light intensity) by sampling residential lawns in Alachua and Marion counties, Florida. A 2‐year study was conducted: approximately 90 St. Augustinegrass lawns were selected for monthly sampling in May and June 2011. This was followed by weekly sampling in 17 selected lawns in July and August 2011 and 13 lawns in June to August 2012, respectively. Results from lawn surveys indicated that light intensity (r = 0.30, P = 0.0034), and thatch thickness (r = 0.22, P = 0.0390) were positively associated with B. insularis densities. The inverse relationship between turf color and B. insularis densities indicated the impact of insect feeding damage. A significant positive association of insect abundance with grass height and thatch thickness identified the need for turf management practices (mowing at recommended cut height and verticutting/thatch removal) to reduce habitat suitability for insect pest survival.

Performance of warm-season turfgrasses under different water regimes in the Mediterranean climate conditions of Southern Italy

In Mediterranean areas, very scarce rainfalls during the summer season are a limiting factor to the sowing and managing of turfgrasses. This work evaluates the response to different irrigation regimes (50 or 75% of reference evapotranspiration) of Cynodon dactylon (L.) Pers. cv Transcontinental, Paspalum vaginatum Swartz cv Salam, Pennisetum clandestinum (Chiov.) Hochst. cv AZ1, Stenotaphrum secundatum (Walt.) Kuntze cv Palmetto and Zoysia japonica Steud. cv El Toro. Performance of turfgrasses was evaluated in term of turf quality, colour index and ground cover. Only when rainfalls were scarce, water regime restoring the 75% of the evapotranspiration (ETo) showed significant effects. Under rainy conditions, the restoration of only the 50% of ETo was able to give highly acceptable values. The best performance was observed for Z. japonica, C. dactylon and P. vaginatum, whereas P. clandestinum and S. secundatum showed lower adaptability to water stress.

Richness and community structure of sand dunes (restinga) in Santa Catarina: subsidies for ecological restoration

The coast of Balneario Piçarras city (Santa Catarina) is being onstantly degraded by human action. This study aimed to haracterize the richness and vegetation structure of two areas of herbaceous restinga (preserved and degraded) of the coastal plain of this city. The lora was mapped by using the patrolling method. Identification was done by comparative morphology and specialized bibliography. The phytosociology was based on the plot method with allocation oriented parallel to the coast line. There were 48 pecies, 44 genera and 22 families identified. Fabaceae, Asteraceae and Poaceae are the richest families. The H’ index was 3.9 in the preserved area and 2.1 in the degraded area. The community tructure was represented by eight and 16 species in the degraded and preserved areas, respectively. In degraded areas, species as Spartina ciliata, Ipomoea pes-caprae, Sphagneticola trilobata and Paspalum vaginatum have the greater importance of coverage, structuring the community. In the preserved area, the organization structure of the community is given by anavalia rosea, Remirea maritima, Stenotaphrum secundatum, Spartina ciliata and Acicarpha spathulata species. These species are considered pioneers and with a great potential of fixing dunes, which reflects their importance to the achievement of a future restoration work of thedamaged area of the restinga in question. Keywords: Coastal plain; floristic; phytosociology; recovery of degraded areas.

Nitrate Leaching from Soluble Nitrogen Applied to ‘Floratam’ St. Augustinegrass and Common Centipedegrass during Dormancy

Fertilizer bans in Florida prevent turf managers from applying nitrogen (N) fertilizers during periods of active turf growth and may encourage fertilization in fall and winter. Nutrient applications during fall or winter may pose an increased risk to nitrate N (NO3–N) leaching. A 3‐yr field lysimeter study was conducted in Jay, FL, to determine the effect of N rates on NO3–N leaching from ‘Floratam’ St. Augustinegrass (SA) [Stenotaphrum secundatum (Walter) Kuntze] and common centipedegrass (CE) [Eremochloa ophiuroides (Munro) Hack.] during turfgrass dormancy. Treatments consisted of urea applied as a foliar spray every 45 d beginning in October at rates of 0.0, 6.0, 12.5, 24.0, or 49.0 kg N ha−1. Leachate was collected weekly and analyzed for NO3–N. Elevated NO3–N levels were observed for 105 d after initiation (DAI). No differences in NO3–N leached were detected among N rates until the late winter cycle of 2008 when rainfall exceeded historic levels by 268 mm. The 49.0 kg N ha−1 treatment resulted in more NO3–N leached than untreated turf during 2008, with 12.5 and 1.3 kg NO3–N ha−1 leached, respectively. These findings suggest that N rates ≤24.0 kg ha−1 applied to dormant or semidormant warm‐season turf do not pose an increased threat of NO3–N leaching even when rainfall is excessive. Soluble N rates >24.0 kg ha−1 should be avoided during dormancy when excessive rainfall is imminent. The benefits, if any, need to be investigated further before fertilization of dormant warm‐season turf is recommended.

Effects of Mowing and Trinexapac-Ethyl on St. Augustinegrass Sod Establishment during a Simulated Water Variance Period

During water conservation periods, municipal water purveyors often limit irrigation for established lawns to once every 7 to 14 days, although a 4- to 6-week variance to these restrictions is often permitted for turfgrass establishment. Therefore, establishment practices promoting rapid development of a deep and expansive root system during this time may support long-term success of the turf once irrigation is scaled back. Sod producers and turf managers could benefit from information on the influence of mowing practices and plant growth regulator (PGR) applications on turf root development during this initial establishment period. The objectives of this greenhouse study were to 1) evaluate the effects of mowing and trinexapac-ethyl (TE) application on final turf quality and root development characteristics (weight, total length, and extension rate) of st. augustinegrass (Stenotaphrum secundatum) sod during a 35-day establishment period, and 2) compare the quality and rooting potential of ‘TamStar’, a newly released, embryo-rescue-derived cultivar possessing good drought resistance, with ‘Floratam’, the current industry standard for drought resistance. Weekly mowing reduced both total (2.5 to 90 cm) and deep (45 to 90 cm) root weight and root length in both cultivars. TE had no effect on visual quality of ‘TamStar’, but decreased turf quality in ‘Floratam’. TE reduced clipping yields of both cultivars but did not improve root development for either cultivar. Depth of maximal root extension during establishment was unaffected by cultivar, mowing, or TE treatment. At the conclusion of the 35-day establishment period, ‘TamStar’ exhibited superior turf quality and root weight relative to ‘Floratam’, but also produced higher rates of shoot growth. Results emphasize the importance of withholding mowing during st. augustinegrass establishment, particularly for improving total root length and deep root production, and also show that TE does not improve root development of st. augustinegrass during establishment.

Nitrogen Rate Required for Acceptable St. Augustinegrass and Associated Nitrate Leaching

ABSTRACTThe recommended N rates for St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze.) vary in Florida. This research, conducted in Fort Lauderdale, Citra, and Jay, FL, (2006–2008), aimed to determine the minimum N rate necessary for acceptable St. Augustinegrass and to determine the influence of N and irrigation rate on NO3–N leaching. Urea was applied in Fort Lauderdale, Citra, and Jay at 98, 196, 294, and 588; 49, 196, 343, and 490; and 49, 98, 196, and 294 kg N ha−1 yr−1, respectively, based on best management practices. Irrigation was 2.5 mm d–1 and 13.0 mm three times weekly in Fort Lauderdale; 13 mm twice weekly and 26 mm wk–1 in Citra and Jay. In Fort Lauderdale and Jay, lower than recommended N rates mostly produced acceptable turfgrass. Applications of 196 kg N ha−1 (Fort Lauderdale) and 98 kg N ha−1 (Jay) were the lowest rates producing acceptable turf. In Citra, 65% more N was required for acceptable turf than the recommended minimum . Leaching from all N rates was similar, except when N rates exceeded recommendations or when turfgrass exhibited herbicide stress. The high irrigation rate doubled NO3–N leaching compared to the low rate in Fort Lauderdale; irrigation frequency had no influence on leaching in Citra or Jay. The predicted minimum N rate for acceptable turf in Fort Lauderdale was <98 kg N ha−1 yr−1 (lower than in Citra; more than in Jay). In stressed turf, additional N conferred little benefit to quality and increased leaching.

Seasonal Variation of Carbon and Nitrogen Emissions from Turfgrass

The role of turfgrasses in C and N cycling in the southeastern U.S. has not been well documented. The objectives of this research were to determine the characterization of chemical quality, clipping decomposition rates, and C and N release from warm- and cool-season turfgrasses. The study was conducted for 46 weeks in 2012 in Auburn, AL. Four warm season turfgrasses were used included (bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy], centipedegrass (Eremochloa ophiuroides (Munro) Hack), St. Augustinegrass (Stenotaphrum secundatum (Walter) Kuntze), zoysiagrass (Zoysia japonica Steud.), and one cool season turfgrass (tall fescue (Festuca arundinacea Schreb)). Litter was placed into nylon bags at an oven dry rate of 3.6 Mg?ha?1. Litter bags were retrieved after 0, 1, 2, 4, 8, 16, 24, 32, and 46 weeks, and analyzed for total C and N. A double exponential decay model was used to describe mass, C, and N loss. Results indicated that tall fescue decomposition occurred rapidly compared to warm season turfgrasses. Litter mass loss measured after 46 weeks was determined to be 61.7%, 73.7%, 72.2%, 86.8%, and 45.4% in bermudagrass, centipedegrass, St. Augustinegrass, tall fescue, and zoysiagrass respectively. Zoysiagrass litter had a higher lignin concentration, while tall fescue had the lowest lignin. Over 46 weeks’ release of C was in the order: zoysiagrass > bermudagrass = centipedegrass = St. Augustinegrass > tall fescue, and release of N was in the order zoysiagrass > centipedegrass > bermudagrass = St. Augustinegrass > tall fescue. Our study concluded that, zosiagrass is a better choice for home lawns.

18S rRNA and COI haplotype diversity of Trichodorus obtusus from turfgrass in South Carolina

The stubby-root nematode,Trichodorus obtusus, was recently identified on zoysiagrass in South Carolina, USA. In Florida,T. obtususcauses more damage than other stubby-root nematodes encountered in turfgrass. The objective of this study was to use morphological analysis, mitochondrial DNA (COI: cytochrome oxidase 1) and nuclear (18S rRNA) sequence data to study the genetic structure and haplotype diversity of populations recovered from turfgrasses in South Carolina. Numerous morphological differences were observed among populations. Three 18S haplotypes were shared among South Carolina and Florida populations, and six mitochondrial haplotypes were identified in South Carolina samples. Of the six COI haplotypes, four haplotypes were restricted to one population from St Augustinegrass. The lowest haplotype diversity was found in samples from zoysiagrass. Sequences of the COI mtDNA gene ofT. obtususwere published in GenBank and represent the first mtDNA sequences for the genusTrichodorus.

Transpiration responses of warm-season turfgrass in relation to progressive soil drying

Developing turfgrass with good drought resistant is a major goal in breeding programs when water scarcity is one of the long-term challenges facing the turfgrass industry. It has been shown that plant transpiration does not decline until available soil water drops below a certain threshold. Studying the species and genotypic differences in this threshold may lead to turfgrass that conserve water and retain turfgrass quality during drought. The objective of this study was to characterize and compare the transpiration response of 19 warm-season turfgrass genotypes and cultivars in five species during soil drying and well-watered conditions in the greenhouse. The species included in the study were: Zoysia japonica (Steud), Zoysia matrella L., common bermudagrass (Cynodon dactylon L. Pers. var. dactylon), African bermudagrass (Cynodon transvaalensis Burtt-Davy), hybrid bermudagrass (C. dactylon L. var. dactylon×C. translvaalensis Burtt-Davy) and St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze]. They were evaluated for evapotranspiration rate (ET) and the sensitivity of transpiration to soil drying which was indicated by a break point of the fraction transpirable soil water (FTSW). The range of break point during dry down was from 0.25 to 0.41, and genotypes within species had different ET when well-watered (ETck). Break point values were not correlated with the number of days to the endpoint, where ET declined below 10% of the control. Instead, the number of days to endpoint was negatively correlated with ETck (−0.59, P≤0.01). Thus, these results found significant variability in turfgrass break point and ETck that could contribute to water conservation, and a better understanding of drought responses in warm season turfgrasses.

Comparison of the New Southern Chinch Bug-Resistant Lines with Commercial Cultivars of St. Augustinegrass

St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is a warm season turfgrass and is widely used for lawns and landscapes in the southern United States of America. The southern chinch bug (Blissusinsularis Barber) is the most damaging insect of St. Augustinegrass. Use of resistant cultivars is an environmentally sound and sustainable method to control this insect pest. Two newly identified resistant St. Augustinegrass lines (NUF3231 and NUF4872) were compared with three commercial cultivars for turfgrass quality and other important traits. The two lines had turf color and turf visual quality similar to those of Captiva and similar to or better than those of Floratam and Palmetto during the experiment. NUF4872 had higher level of resistance to gray leaf spot than Floratam and Palmetto. Stolon architectures of NUF3231 were similar to those of Captiva whereas NUF4872 had the stolons similar to those of Floratam. The results indicated that the two lines could potentially be released as commercial cultivars for use on lawns to battle against the southern chinch bug.

Nitrogen Runoff Losses during Warm-Season Turfgrass Sod Establishment.

Concern exists over the potential loss of nitrogen (N) and phosphorus (P) in runoff from newly established and fertilized lawns. Nutrient losses can be higher from turf when shoot density and surface cover are low and root systems are not fully developed. This study was conducted to evaluate fertilizer source and timing effects on nutrient losses from newly sodded lawns of St. Augustinegrass [ (Walt.) Kuntze]. For each study, 12 33.6-m plots were established on an undisturbed Alfisol having a 3.7% slope. Each plot was equipped with a runoff collection system, instrumentation for runoff flow rate measurement, and automated samplers. A 28-d establishment study was initiated on 8 Aug. 2012 and repeated on 9 Sept. 2012. Treatments included unfertilized plots, fertilized plots receiving 4.88 g N m as urea 6 d after planting, fertilized plots receiving 4.88 g N m as sulfur-coated urea 6 d after planting, and fertilized plots receiving 4.88 g N m as urea 19 d after planting. Runoff events were created by irrigating with 17 mm of water over 27 min. Runoff water samples were collected after every 37.8 L and analyzed for NO-N, NH-N, dissolved organic N (DON), and PO-P. Increases of approximately 2 to 4 mg L NO-N and 8 to 12 mg L PO-P occurred in runoff 1 d after fertilization, which returned to background levels within 7 d. Total fertilizer N lost to runoff was 0.6 to 4.2% of that applied. Delaying fertilizer application until 19 d after planting provided no reduction in nutrient loss compared with a similar application 6 d after planting. Approximately 33% of the N lost in runoff was as DON. This large amount of DON suggests significant N loss from decomposing organic matter may occur during sod establishment.