Poa Arachnifera Research Articles

Relationships between Normalized Difference Vegetation Index and Visual Quality in Cool‐Season Turfgrass: I. Variation among Species and Cultivars

Canopy spectral reflectance may provide an objective means to evaluate visual quality of turfgrass, but evaluations of visual quality may be confounded by differences in reflectance among species or cultivars. In this 3‐yr study near Manhattan, KS, we examined effects of species and cultivars on relationships between normalized difference vegetation index (NDVI) and visual quality ratings in Kentucky bluegrass (Poa pratensis L., ‘Apollo’), two Kentucky bluegrass × Texas bluegrass (Poa arachnifera Torr.) hybrids (‘Thermal Blue’ and ‘Reveille’), and tall fescue (Festuca arundinacea Schreb., ‘Dynasty’). A broad range of visual quality was imposed on all four grasses through deficit irrigation and NDVI was measured using broadband spectral radiometry across this range for each grass. Distinct linear regression models of visual quality were found for each grass, and models were also distinct among years in each grass. Relationships between NDVI and visual quality were stronger in the bluegrasses (r2 = 0.41 to 0.83) because they had a greater range in quality under deficit irrigation than tall fescue. The 95% confidence intervals surrounding predictions of visual quality from NDVI ranged from ± 1.25 to 2.10 (on a 1 to 9 scale). Results indicated that the requirement to develop separate models for each grass and in each year, combined with relatively wide confidence intervals, represents a practical limitation to predicting visual quality with NDVI.

Relationships between Normalized Difference Vegetation Index and Visual Quality in Turfgrasses: Effects of Mowing Height

Canopy spectral reflectance may provide an objective means to evaluate visual quality of turfgrass, but evaluations of quality may be confounded by cultural practices that affect reflectance, such as mowing height. In this 2‐yr study near Manhattan, KS, we examined effects of mowing height on relationships between normalized difference vegetation index (NDVI) and visual quality ratings in Kentucky bluegrass (KBG; Poa pratensis L., ‘Apollo’) and in a KBG × Texas bluegrass (Poa arachnifera Torr.) hybrid (HBG; ‘Thermal Blue’). Mowing heights were 7.62 cm (high) and 3.81 cm (low). The NDVI averaged 4.5 to 7% greater in high‐ than in low‐mown plots. Distinct regression models of visual quality were found at each mowing height and in each species (r2 from 0.40 to 0.81); separate relationships between NDVI and visual quality were also found between years in the same plots. Correlations between NDVI and visual quality were stronger at high than at low mowing heights, possibly because of greater green biomass at high mowing heights. The 95% confidence intervals surrounding predictions of visual quality from NDVI ranged from ±1.34 to 2.75 (on a 1‐to‐9 scale). Thus, lack of precision is a concern when using these models for detection of differences between treatments. Results indicate that when using NDVI to evaluate turfgrass quality, evaluations should be limited to plots maintained at the same mowing height and with the same species to reduce variability in NDVI.

Low-Input Turfgrass Species for the North Central United States

Public attention is being increasingly focused on the environmental impact and management costs of turfgrass areas such as lawns for schools, parks, and homes. The objectives of this study were to: (i) identify grass species adapted to low-input environments (limited water, no fertilizer or pesticides after establishment) in the North Central Region (NCR) of the USA; and (ii) evaluate these species for turfgrass quality under mowed and non-mowed conditions. Low-input turf trials of 12 grass species were established at eight locations and evaluated for turf quality over two years. Plots were mowed monthly at either 5.1 or 10.2 cm or not mowed. Hard fescue (Festuca brevipila Tracey), colonial bentgrass (Agrostis capillaris L.), tall fescue (Festuca arundinacea Schreb.), and sheep fescue (Festuca ovina L.) performed well at most locations at the 5.1 and 10.2-cm mowing heights. Several other species were also evaluated: tufted hairgrass [Deschampsia cespitosa (L.) P. Beauv.], hybrid bluegrass (Poa arachnifera Torr. × Poa pratensis L.), meadow fescue [Schedonorus pratensis (Huds.) P. Beauv.], prairie junegrass [Koeleria macrantha (Ledeb.) Schult], crested wheatgrass [Agropyron cristatum (L.) Gaertn.], alkaligrass [Puccinellia distans (Jacq.) Parl.], blue grama [Bouteloua gracilis (Willd. Ex Kunth) Lag. Ex Griffiths], and crested dogstail (Cynosurus cristatus L.).

Foraging by Red Imported Fire Ants,Solenopsis invicta(Hymenoptera; Formicidae) on Turfgrasses

Red imported fire ant, Solenopsis invicta Buren (Hymenoptera; Formicidae) is a major pest in urban landscapes including residential/commercial lawns, sports fields, golf courses, parks, and highway rights-of-way. Foraging preferences for various turfgrass clippings were investigated under controlled lab conditions. Among bermudagrass (Cynodon sp.) cultivars, clippings of ‘Tifway’ and ‘Baby’ were 7 times more preferred than clippings of ‘Tifton 10’ and ‘GN1’. The Texas bluegrass × Kentucky bluegrass hybrid (Poa pratensis L. × P. arachnifera Torr.), TXKY 00-34-2 had 5 times more foraging ants on it than TXKY 01-59-9. Among the zoysiagrasses (Zoysia japonica), ‘El Toro’ was only 2 times more preferred than ‘Crowne’. For St. Augustinegrass (Stenotaphrum secundatum Walt. Kuntze), ‘BitterBlue’ was 3.4 times more preferred than ‘Floratam’. On the buffalograss cultivars (Buchloe dactyloides (Nutt.) Engelm.), there were 2 and 4 times more ants foraging ‘Texoka’ than either ‘Prairie’ or ‘Bison’, respectively. After foraging for 5 h on clippings of the 5 or 6 cultivars in each replicate, the number of ants on each grass was bermudagrass (169.3) > zoysiagrass (137.5) = bluegrass hybrids (136.8) > St. Augustinegrass (127.1) > buffalograss (34.5).

Pigment Concentrations among Heat-tolerant Turfgrasses

Heat-tolerant bluegrass varieties were developed to resist dormancy and retain pigmentation during heat stress events. The objective of this study was to investigate the influence of grass species, nitrogen (N) fertilization, and seasonality on the accumulation patterns of lutein, β-carotene, and chlorophyll a and b in the leaf tissues of turfgrass. The heat-tolerant bluegrass cultivars Dura Blue and Thermal Blue (Poa pratensis L. × Poa arachnifera Torr.), Apollo kentucky bluegrass (Poa pratensis L.), and Kentucky 31 tall fescue (Festuca arundinacea Schreb.) were compared for the accumulation of plant pigments. Evaluations were conducted over 2 consecutive years (Years 4 and 5 after establishment) during two different seasons (spring and summer) and under varying N fertilization. Fertilizer applications of 5, 14, and 27 g N/m2/year resulted in a significant positive correlation for the accumulation of leaf blade lutein and chlorophyll a and b, but not for β-carotene. The accumulation of the four measured plant pigments among the grasses was significantly different with ‘Apollo’ having the largest concentration of pigments followed by ‘Dura Blue’, ‘Thermal Blue’, and finally ‘Kentucky 31’. Specifically, when comparing the cultivars Apollo and Kentucky 31, the pigment levels decreased 27%, 26%, 26%, and 23% for lutein, β-carotene, and chlorophyll a and b, respectively. The interesting observation of the analysis of the grass pigment concentrations was that the least reported heat-tolerant cultivar in our study (‘Apollo’) had the largest measured pigment concentrations.

Population dynamics of greenbug biotypes “E” and “F” on Texas bluegrass

AbstractCool‐season perennial forage grasses are known to serve as alternate hosts of the greenbug, Schizaphis graminum (Rondani) in the southern Great Plains of the USA. Texas bluegrass (Poa arachnifera Torr.) is a cool‐season perennial forage grass indigenous to this region and because of its persistence under grazing is being bred for improved forage production. An experiment was conducted to determine the population dynamics of greenbug biotype “E”, the predominant biotype found in this region and biotype “F” which is known to infest bluegrass species. Twenty‐five Texas bluegrass genotypes, three Kentucky bluegrass (Poa pratensis L.) genotypes, a Canada bluegrass (Poa compressa L.) genotype, two Texas × Kentucky bluegrass hybrids, and a Texas × Canada bluegrass hybrid were screened for their abilities to support greenbug population growth. Bluegrass species and genotypes varied significantly in their ability to support greenbug biotypes E and F. On the basis of higher aphid numbers, biotype E had a higher population growth rate as compared with biotype F on Texas bluegrass. Some Texas bluegrass genotypes were not included in both biotype trials due to lack of availability of uniform plant material for inoculation. Nine of 25 Texas bluegrass genotypes did not support biotype E greenbug population growth. Similarly, 13 of 22 Texas bluegrass genotypes did not support biotype F population growth. Both Canada and Kentucky bluegrass supported high populations of biotype F and interspecific hybrids varied in their host suitability to both biotypes.

Drought Stress Responses and Recovery of Texas × Kentucky Hybrids and Kentucky Bluegrass Genotypes in Temperate Climate Conditions

Turf quality (TQ) decline due to drought is a major concern in cool‐season turfgrass management. The study was conducted to examine whether selected Texas (TBG) × Kentucky bluegrass (KBG) hybrids (HBGs) (Poa arachnifera Torr. × P. pratensis L.) exhibit improved drought stress tolerance and recuperative ability in comparison to commonly‐used KBG (P. pratensis) genotypes. Plant material included two HBG selections (HBG568 and HBG668), two commercially‐available HBGs (‘Thermal Blue’ and ‘Bandera’), and two KBG genotypes (‘Midnight’ and ‘Baron’). The experiment was conducted in field plots covered with a rainout shelter in 2006 and 2007 in North Brunswick, NJ. Treatments consisted of (i) well‐watered controls; (ii) drought stress (withholding irrigation) from June to August; and (iii) recovery (rewatering after a period of drought stress) in September and October. The HBGs Thermal Blue and Bandera generally did not show significant difference in turf growth from the two KBG genotypes in both years. HBG568 maintained significantly higher TQ, relative water content (RWC), cell membrane stability, and canopy density estimated as the reflectance ratio of infrared to red (IR/R, leaf area index) and normalized difference vegetation index (NDVI), compared with the two KBG genotypes and other HBGs following a prolonged period of drought stress (after 20 d of treatment) on most sampling dates in both years. HBG568 exhibited more rapid recovery of TQ, IR/R (IR935/R661), NDVI, and sod tensile strength than the other genotypes in both years, while HBG668 also had better recovery in 2007. The results demonstrate genetic variation in drought stress tolerance and recovery among HBGs and KBGs and the potential for the development of HBGs with improved tolerance to drought stress and performance during recovery.

Frequency of androgenesis in Poa arachnifera interspecific hybridizations

AbstractAndrogenic dihaploids represent a unique form of dihaploids that have historically been utilized for cytoplasmic transfer, the generation of inbred lines and polyploid genome manipulations. Due to the apomictic nature of many Poa species, breeding improvements can be slow and difficult; therefore, alternative approaches that can capitalize on sampling the genetic diversity of near obligate Poa could be advantageous. This study investigates the frequency and potential use of androgenic derived dihaploids generated from a series of Poa arachnifera (Texas bluegrass) × Poa secunda (Sandberg bluegrass), Poa pratensis (Kentucky bluegrass) and Poa ligularis (Argentine bluegrass) interspecific hybrids. The examination of 2041 F1 hybrids generated from three interspecific hybridizations, confirmed the generation of 31 dihaploid individuals. Though low in occurrence, the generation of androgenic dihaploids derived through P. arachnifera interspecific hybridizations offers a non‐traditional breeding approach for sampling genetic variability of Poa species and the development of new breeding resources.

Membrane Lipid Composition and Heat Tolerance in Cool-season Turfgrasses, including a Hybrid Bluegrass

Cool-season turfgrasses may experience heat stress during summer. Hybrid bluegrasses (HBGs), crosses between kentucky bluegrass [KBG (Poa pratensis L.)] and native texas bluegrass (Poa arachnifera Torr.), have improved heat tolerance but the mechanisms of heat tolerance are poorly understood. Our objectives were to quantitatively profile membrane lipid molecular species in three cool-season turfgrasses exposed to optimal (22/15 °C, 14/10 h light/dark) and supra-optimal temperatures (35/25 °C and 40/30 °C, 14/10 h light/dark). Grasses included a low heat-tolerant tall fescue [TF (Festuca arundinacea Schreb. ‘Dynasty’)], a mid-heat–tolerant KBG (‘Apollo’), and a heat-tolerant HBG (‘Thermal Blue’). At high temperature, glycolipid digalactosyldiacylglycerol (DGDG) in HBG was 12% and 16% greater than in KBG and TF, respectively, and the ratio DGDG to monogalactosyldiacylglycerol was 19% and 44% greater in HBG than in KBG and TF, respectively. Greater heat tolerance in HBG and KBG was associated with higher contents of phosphatidylethanolamine and phosphatidylglycerol, and with reduced overall unsaturation compared with TF. Overall, 20 lipid molecular species were present in greater amounts and another 20 species in lesser amounts in HBG and KBG than in TF. Results suggest 40 membrane lipid molecules are potential biomarkers for heat tolerance and that compositional changes in membrane lipids in response to heat contribute to differences in heat tolerance among cool-season grasses.

Water-use patterns of tall fescue and hybrid bluegrass cultivars subjected to ET-based irrigation scheduling

In turf industry, the ability of a cultivar to use less water is an important consideration, especially where rainfall and irrigation water are insufficient. Knowledge of turf grass water-use patterns is therefore important for developing efficient water management practices and also for selection of drought-resistant cultivars. We evaluated the soil water‐use patterns of tall fescue and hybrid bluegrasses cultivars irrigated at different rates. Field experiments were conducted at the Turfgrass Research Facility, Auburn University, AL, in 2005 and 2006. Two tall fescue (Festuca arundinacea Schreb.) cultivars (‘Kentucky 31’ and ‘Green Keeper’) and four hybrid bluegrass (Poa pratensis L. × Poa arachnifera Torr.) cultivars, viz., HB 129 [‘Thermal Blue’], HB 130 (Experimental line), HB 328 (Experimental line) and HB 329 [‘Dura Blue’] were included in this study. Plots were irrigated based on the potential evapotranspiration, viz., 100% ET, 80% ET and 60% ET replacements. Tensiometers were installed at 0.075, 0.15 and 0.30 m depths, and their readings used to calculate the matric head, water content and water-use values. Turf color quality was determined from turf canopy digital images. Analysis of variance (ANOVA) for a random complete block design (RCBD) was conducted for available water, water-use and turf color quality values. Hybrid bluegrasses revealed significantly (P = 0.05) higher turf color indices compared to the tall fescue cultivars, but there was no indication of differential responses to irrigation among cultivars. Based on water-use data, hybrid bluegrass cultivars revealed significantly (P = 0.05) lower water-use compared to tall fescue cultivars.

Differential Responses of Hybrid Bluegrass and Kentucky Bluegrass to Drought and Heat Stress

This study was designed to investigate differential responses of hybrids from Texas bluegrass (Poa arachnifera Torr.) × Kentucky bluegrass (Poa pratensis L.) (KBG) and KBG genotypes to drought and heat stress. Plants of two hybrids, ‘845’ and ‘BDF’, and two KBG genotypes (‘Midnight’ and ‘C-74’) were grown under optimal temperature (22/18 °C) and well-watered (control) or unwatered (drought) or superoptimal temperatures (35/30 °C; heat stress) conditions for 35 days in growth chambers. Under optimal conditions, the two hybrids and two KBG genotypes were not significantly different in turf quality, leaf photochemical efficiency expressed as chlorophyll fluorescence ratio (Fv/Fm), leaf net photosynthetic rate (Pn), transpiration rate, water use efficiency (WUE), root dry matter, or root viability. The results suggest that the interspecific hybridization resulted in similar growth and physiological traits in the hybrid bluegrass as in a turf-type species under optimal temperature and irrigation regimes. Under drought stress, all these parameters were comparable to those for KBG ‘Midnight’, but significantly higher than the corresponding parameters for KBG ‘C-74’. Under heat stress, both hybrids had significantly higher turf quality, Fv/Fm, Pn, transpiration rate, WUE, root dry weight in deeper soil depth (40 to 60 cm), and root viability in the upper 40-cm layer compared with both KBG genotypes. These results suggested that hybrid bluegrass exhibited improvement in drought and heat tolerance, particularly in comparison with KBG ‘C-74’, but to a great extent for heat tolerance. The maintenance of higher transpiration and photosynthesis, WUE, and root viability was associated with the improvement in heat tolerance in hybrid bluegrass.

The use of ISSR markers to identify Texas bluegrass interspecific hybrids

AbstractSeventeen ISSR primers were screened on Texas bluegrass (Poa arachnifera), Kentucky bluegrass (P. pratensis), Canadian bluegrass (P. compressa), Argentine bluegrass (P. ligularis), cv. ‘Sherman’ (P. secunda), putative Texas × Kentucky (TK) (P. arachnifera ×P. pratensis) hybrids and hybrids involving Texas, Canadian, and Sherman bluegrass [(P. arachnifera × P. compressa) × (P. arachnifera ×P. secunda)], to determine whether they could be used to produce robust and reproducible DNA fingerprints and identify interspecific hybrids. Nine of the 17 primers consistently produced robust fingerprints and nine 2‐way primer combinations were also selected. DNA fingerprints were highly reproducible and the majority of the selected primers (16/18) amplified hybrid profiles using two putative TK full‐sib hybrids. Combined with a rapid DNA extraction protocol, the ISSR technique enabled a fast and practical way to detect F1 interspecific hybrids early in the breeding programme and could also be useful for other applications that require DNA‐based markers.

Rooting Characteristics and Canopy Responses to Drought of Turfgrasses Including Hybrid Bluegrasses

Drought stress is common among cool‐season turfgrasses during summer in the U.S. transition zone. A 2‐yr field study was conducted near Manhattan, KS, to evaluate rooting characteristics and effects of drought on canopy physiology and appearance of ‘Apollo’ Kentucky bluegrass (Poa pratensis L.) (KBG), ‘Dynasty’ tall fescue (Festuca arundincea Schreb.) (TF), and two hybrid bluegrasses (HBG) ‘Reveille’ and ‘Thermal Blue’; HBG are genetic crosses between native Texas bluegrass (P. arachnifera Torr.) and KBG. Rooting characteristics were measured in the field and greenhouse under well‐watered conditions to evaluate root contributions to drought avoidance. Two irrigation treatments in the field included: (i) 60% (water‐deficit); and (ii) 100% (well‐watered) evapotranspiration (ET) replacement. Ninety to 96% of all root length (0–80 cm) in the field and 74 to 80% of all root length (0–120 cm) in the greenhouse were in the upper 30 cm among Thermal Blue, Reveille, and KBG while in TF, only 86 and 70% of all root length in the field and greenhouse, respectively, were in the top 30 cm. In the field, tall fescue had 3 to 12 times greater root length in the lower profile (60–80 cm) among turfgrasses. Visual quality and gross photosynthesis (Pg) were greatest in TF among turfgrasses in both irrigation treatments. Reveille used more water from the 0 to 50 cm profile and performed better than Thermal Blue during water‐deficit, but both HBG recovered from water‐deficit slightly faster than KBG. Performances in visual quality and Pg generally ranked: TF > Reveille ≥ Thermal Blue = KBG.

Hybrid Kentucky Bluegrass Tolerance to Preemergence and Postemergence Herbicides

Field studies were conducted near Knoxville, TN, from 2003 to 2005 to evaluate the response of ‘Thermal Blue’, a new interspecific hybrid Kentucky bluegrass to commonly applied PRE and POST herbicides for weed management. Dithiopyr, oryzalin, oxadiazon, pendimethalin, prodiamine, quinclorac, and trifluralin applied at seeding injured hybrid bluegrass greater than 81% and reduced hybrid bluegrass cover greater than 57%. In a second study, established hybrid bluegrass was treated POST with acetolactate synthase–inhibiting herbicides including bispyribac-sodium, chlorosulfuron, foramsulfuron, halosulfuron, imazapic, imazaquin, metsulfuron, rimsulfuron, sulfosulfuron, and trifloxysulfuron at low and high rates (one and two times the suggested use rates in Kentucky bluegrass or other turfgrasses). By 5 wk after treatment (WAT), foramsulfuron at 88 g ai/ha and trifloxysulfuron at 35 g ai/ha injured hybrid bluegrass greater than 26% and reduced visually estimated quality and chlorophyll meter indices. However, hybrid bluegrass injury was no longer evident at 10 WAT. In a third study, established hybrid bluegrass was treated with clethodim, diclofop-methyl, fluazifop-p-butyl, and sethoxydim applied at low, medium, and high rates (0.5, 1, and 2 times the registered Kentucky bluegrass or other turfgrass use rates). Clethodim applied at 280 and 560 g ai/ha, fluazifop at 420 g ai/ha, and sethoxydim at 630 g ai/ha injured hybrid bluegrass 5 WAT. These treatments also reduced quality (to less than 5 on a scale of 1 to 9) and chlorophyll meter indices (24 to 37%) when compared to the untreated control. By 10 WAT, only clethodim at 560 g ai/ha caused injury (14%). By 10 WAT, hybrid bluegrass had recovered and injury was only observed in plots treated with clethodim at 560 g ai/ha. No differences in chlorophyll indices or quality were observed at 10 WAT for any POST graminicides.Nomenclature: Bispyribac-sodium, chlorosulfuron, clethodim, diclofop-methyl, dithiopyr, fluazifop-p-butyl, foramsulfuron, halosulfuron, imazapic, imazaquin, metsulfuron, oryzalin, oxadiazon, pendimethalin, prodiamine, quinclorac, rimsulfuron, sethoxydim, sulfosulfuron, trifloxysulfuron, trifluralin, Kentucky bluegrass, Poa arachnifera Torr. × P. pratensis L. ‘Thermal Blue’

Fall Armyworm (Lepidoptera: Noctuidae) Resistance in Texas Bluegrass, Kentucky Bluegrass, and Their Hybrids (Poa spp)

The fall armyworm Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is a destructive pest of many species of both C3 and C4 (cool- and warm-season) turfgrass. No-choice experiments were conducted to evaluate 13 turfgrass genotypes of various Poa spp. for susceptibility or resistance to the fall armyworm. All 13 genotypes, including 8 Texas bluegrass (Poa arachnifera Torr.), 2 Kentucky bluegrass (P. pratensis L.) and 3 Kentucky bluegrass × Texas bluegrass interspecies hybrids, were antibiotic and produced an accumulated >80% mortality of neonate larvae before they pupated. ‘Reveille’ (a hybrid) provided 100% antibiosis of larvae within 4 d of feeding. When 4-d-old fall armyworm larvae that had first fed on a susceptible Poa host were confined on the same 13 Poa genotypes as in the neonate test, a much higher survival rate was recorded. ‘Reveille’ produced 94.4% mortality after 3 d of feeding and 100% mortality after 8 d of feeding, while TXKY90-13-16 (another hybrid) provided 100% mortality of larvae within 13 d of feeding. A third hybrid, TXKY90-13-8 was one of the more susceptible genotypes. For the 4-d-old larvae, ‘Baron’ and ‘Delwood Fine’ Kentucky bluegrass provided only 50 and 22.2%, respectively, mortality after 8 d of larval feeding and did not produce 100% mortality until pupation. Also, mortality of larvae on the 8 Texas bluegrass genotypes produced ≤45% maximum accumulated mortality by pupation or adult emergence. ‘Laser’ rough bluegrass (P. trivialis L.) is an excellent host with ≤5.6% larval mortality.

Effects of High Temperature and Drought on a Hybrid Bluegrass Compared with Kentucky Bluegrass and Tall Fescue

High temperature and drought stresses may reduce quality in cool‐season turfgrasses during summer months in the transition zone. This growth chamber study was conducted to evaluate effects of high temperature and drought on physiology and growth of ‘Apollo’ Kentucky bluegrass (Poa pratensis L.) (KBG), ‘Dynasty’ tall fescue (Festuca arundincea Schreb.) (TF), and ‘Thermal Blue’, a hybrid (HBG) between KBG and Texas bluegrass (Poa arachnifera Torr.). Turfgrasses were exposed for 48 d to supra‐optimal (high temperature; 35/25°C, 14‐h day/10‐h night) and optimal (control; 22/15°C, 14‐h day/10‐h night) temperatures under well‐watered (100% evapotranspiration [ET] replacement) and deficit (60% ET replacement) irrigation. Heat resistance was greater in HBG, which had greater visual quality, gross photosynthesis (Pĝ), dry matter production, and lower electrolyte leakage and soil surface temperatures than KBG and TF under high temperature. Cumulative Pĝ during the study was 16 and 24% greater in HBG than in KBG and TF, respectively. Green leaf area index (LAI) in HBG was not affected by high temperature, but LAI was reduced by 29% in KBG and 38% in TF. Differences in drought resistance were negligible among species. The combination of high temperature and drought caused rapid declines in visual quality and dry matter production, but HBG generally performed better. Results indicated greater heat resistance, but not drought resistance, in HBG than in KBG or TF.

Hybrid Bluegrass Tolerance to Postemergence Applications of Mesotrione and Quinclorac

New hybrid bluegrass cultivars have been bred for increased heat and drought tolerance compared with traditional Kentucky bluegrass cultivars. Research was conducted to evaluate hybrid bluegrass tolerance and smooth crabgrass and goosegrass control with mesotrione and quinclorac during seeded establishment. Mesotrione applied as a single application 14, 28, or 42 d after emergence (DAE) injured hybrid bluegrass acceptably from 1 to 11% 7 d after treatment (DAT). A sequential mesotrione application at 0.14 kg/ha 28 DAE did not injure hybrid bluegrass greater than the initial 14 DAE application; however, a sequential application at 0.28 kg/ha 28 DAE injured hybrid bluegrass greater than the initial 14 DAE application. Three sequential mesotrione applications did not reduce hybrid bluegrass ground cover 63 DAE. Quinclorac applied singly at 1.68 kg/ha 14 DAE and sequentially at 0.84 kg/ha 14 and 28 DAE injured hybrid bluegrass that continued throughout the rating period resulting in decreased ground cover at 63 DAE. Quinclorac at 0.84 kg/ha plus mesotrione at 0.28 kg/ha injured hybrid bluegrass < 20% throughout the rating period but reduced ground cover 63 DAE. All quinclorac-containing treatments controlled smooth crabgrass ≥ 92%. All mesotrione sequential-application treatments controlled smooth crabgrass and goosegrass ≥ 87%. These data indicate that sequential mesotrione applications can be used for smooth crabgrass and goosegrass control during seeded hybrid bluegrass establishment. Quinclorac should be applied according to label recommendations at 0.84 kg/ha no earlier than 28 DAE.Nomenclature: Mesotrione, quinclorac, goosegrass, Eleusine indica (L.) Gaertn. ELEIN, smooth crabgrass, Digitaria ischaemum (Schreb.) Schreb. ex Muhl. DIGIS, hybrid bluegrass, Poa pratensis L. × Poa arachnifera Torr. ‘Solar Green’, ‘Durablue’, and ‘Thermal Blue’, Kentucky bluegrass, Poa pratensis L. POAPR

Texas Bluegrass Responses to Seeding Rate and Fertilization

ABSTRACT Texas bluegrass has potential as a cool-season perennial pasture grass for the south-central USA. Slow stand establishment in competitive environments is a limitation. Forage production of this grass increases with nitrogen (N), and rhizome growth increases with phosphorus (P). Stand responses by Texas bluegrass from three seed sources to seeding rate and a complete mixed fertilizer were assessed from 1997 through 2005 on a Louisiana Coastal Plain site. A linear response (R2 = 0.39, P ≤ 0.0001) to seeding rate in March 1998 persisted through 2005, even though stands at all seeding rates improved over time. Stands did not differ (P > 0.05) among seed sources. At only the higher seeding rates, rhizome mass increased with fertilization. Soil pH decreased with fertilization, and pH was positively correlated with the final stand rating in 2005. Direct stand responses to fertilization were not detected. Lack of competitive advantage, despite growth responses, and soil acidification with fertilization indicate that increased seeding rates and delayed fertilization may enhance initial establishment of Texas bluegrass in humid environments.

Moderate Salinity Does Not Affect Germination of Several Cool- and Warm-Season Turfgrasses

Germination of warm- and cool-season turfgrasses was assessed at salinity levels commonly found in recycled irrigation water. Cool-season grass seeds included in the study were Thermal Blue hybrid bluegrass [Poa arachnifera (Torr.) x pratensis (L.)]; Barlexas II, Southeast, and Tar Heel II tall fescue [Festuca arundinacea (Schreb.)]; Brightstar SLT and Catalina perennial ryegrass [Lolium perenne (L.)]; Salty and Fults alkaligrass [Puccinellia distans (Jacq.)]; and Dawson red fescue [Festuca rubra trichophylla (L.)]. Warm-season grass seeds used in the study were bermudagrass Numex Sahara, Princess 77, and Transcontinental [Cynodon dactylon (L.)]; Companion zoysiagrass [Zoysia japonica (Steud)]; and Seaspray seashore paspalum [Paspalum vaginatum (Swartz)]. Each grass was incubated at salinity levels from 0.6 to3.0 dS/m. Germination was considered successful upon radicle emergence and the first leaf growing past the coleoptile. Despite species and cultivar variation in germination success, germination was not inhibited in any of the tested cultivars at the salinity levels used in this study, suggesting that germination may not be the most salt-sensitive stage in turfgrass development.

Performance in the Transition Zone of Two Hybrid Bluegrasses Compared with Kentucky Bluegrass and Tall Fescue

Hybrid bluegrasses (HBG) are crosses between Kentucky bluegrass (Poa pratensis L.) (KBG) and Texas bluegrass (Poa arachnifera Torr.), which may exhibit better heat tolerance and drought resistance than other cool-season turfgrasses. Two HBG cultivars (‘Thermal Blue’ [HBG1] and ‘Dura Blue’ [HBG2]), one KBG (‘Apollo’), and one tall fescue (Festuca arundinacea Schreb.; ‘Dynasty’ [TF]) were evaluated for two years in northeastern Kansas for establishment rates after seeding, visual quality and growth characteristics, and drought resistance. Irrigation treatments included 60% and 100% evapotranspiration (ET) replacement and a control receiving only natural precipitation. Tall fescue reached full cover 37, 52, and >73 days faster than HBG1, KBG, and HBG2, respectively. In both years, average quality over the growing season ranked: TF > KBG > HBG1 > HBG2; an infestation of bluegrass billbugs (Sphenophorus parvulus Gyllenhal) in 2003 reduced quality among bluegrasses but not TF. Canopy density was lower in HBG2 and higher in TF among treatments. Clipping biomass of TF was 42 to 73% higher than that of the bluegrasses. Vertical growth rates were highest in HBG1 and TF and lowest in KBG. Drought generally reduced quality among bluegrasses, but effects on TF were negligible. Results indicate that TF is better adapted than HBG where soils are deep in the transition zone. Further research is needed using new cultivars of HBG and in areas with different soils.