Turfgrass Characteristics Research Articles

Using electromagnetic induction to inform precision turfgrass management strategies in sand‐capped golf course fairways

AbstractTo meet the turfgrass standards that players expect, golf course superintendents rely on intense irrigation, fertilization, and cultivation programs. However, the overapplication of irrigation water and fertilizer has been shown to have negative effects on water quality. Precision turfgrass management (PTM) is an emerging area of interest as more golf course superintendents are looking to increase input efficiency while simultaneously reducing water and fertilizer input costs, as well as environmental impacts. Our objectives were to (1) use electromagnetic induction (EMI) to determine the spatial variability of apparent electrical conductivity (EC) in sand‐capped fairways and (2) correlate EC to measured soil and turfgrass characteristics to determine the applicability of mapping EC for PTM. Soil samples and EC data were collected in spring 2021 on four sand‐capped fairways from two golf courses (one hybrid bermudagrass and one zoysiagrass) belonging to the same facility in southeast Texas. Apparent EC was found to be positively and significantly correlated with soil volumetric water content (VWC, 0.40 < r > 0.62) and turfgrass normalized difference vegetation index (NDVI; 0.21 < r > 0.46) in three of four fairways, while EC was negatively and significantly correlated with penetration resistance (PR, −0.29 < r > −0.48) in two of four fairways studied. The strengths of these relationships were corroborated by strong visual similarities when comparing spatial maps of EC with those of VWC, NDVI, and PR, indicating that EMI‐based EC data have potential for use in delineating site‐specific management zones for water and fertilizer applications, as well as targeted aeration.

Development of vegetative triploid turf-type bermudagrass [Cynodon dactylon × C. transvaalensis (C. × mangennisii Hurcombe)

Hybrid bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy) is widely used for turf throughout subtropical and tropical climates because of its superior quality and performance. Development of cultivars adapted to broad range of environments is the main goal of many breeding programs. There is large variation for turfgrass characteristics and drought resistance among native bermudagrass (C. dactylon) germplasm originating from the Mediterranean region. Hence, the aim of this study was to develop triploid turf-type bermudagrass hybrids by making use of native genetic resources. Drought resistant tetraploid C. dactylon genotypes originating from the Mediterranean coastal region of Turkey were crossed with a diploid accession of C. transvaalensis from South Africa in 2011 and 2012. The hybrids were first identified using SRAP molecular markers. Then, phenotypic pre-selection was made for leaf shape, color and density and 273 hybrids were transplanted into the field. Two SSR markers further confirmed the true hybridity of 170 (62%) of these genotypes. Establishment rates in 2013, and turfgrass characteristics in 2014 and 2015 were recorded. Transgressive segregation was evident for estabilishment rate, turfgrass quality and color, and shoot density among progenies. Correlation analysis indicated that selection for shoot density, leaf texture, and prostrate growth habit could increase turf quality. The genotypes ‘45’ and ‘150’ were identified as promising parents for future breeding efforts as they provided positive general combining ability. The best ten hybrids with acceptable turfgrass characteristics were evaluated further under replicated field trials and line T4-C3 has just been released for commercial use.

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.

Gamma-ray Irradiation Induces Useful Morphological Variation in Bermudagrass

Bermudagrass, Cynodon dactylon (L.) Pers. is a widely used warm-season turfgrass species in warmer regions of the world. Gamma (ɣ) irradiation has been used to generate useful variations in turfgrass breeding for various morphological traits. The objective of the present study was to measure and determine variations in morphology and turfgrass characteristics of a native drought resistant bermudagrass germplasm irradiated with 70, 90 or 110 Gy using a 60Co source. The stolons containing a single node were irradiated and immediately planted for regeneration in a greenhouse at the Akdeniz University, Antalya, Turkey. Selected mutants regenerated from the irradiated stolons were clonally propagated and transplanted into plastic pots for further observations of turfgrass characteristics. Survival rates of stolons exposed to 70, 90 and 110 Gy were 76%, 43% and 17% respectively, 6 weeks after treatment. Dosages of 85 and 57 Gy were determined as LD50 and LD20 for the cuttings, respectively. The linear reduction of survival rate with increasing gamma-rays was highly correlated (r2=0.99). A total of four mutant lines (0.3 % of the irradiated plants) showed a distinct dwarfed growth habit. Three of these lines were originated from 70 Gy and one from 110 Gy. These mutant lines exhibited more dwarf growth habit, higher shoot density, finer leaf texture than parental genotype. Mutant lines developed in this study can be used for the development of improved bermudagrass cultivars for landscaping and sports turf.

Morphological characterization and turf performance of Paula hard fescue and Casero colonial bentgrass selections under low maintenance conditions

Planting grasses that require low maintenance is a good option for reducing the management input required. The objective of this study was to obtain information about turfgrass characteristics based on spaced-plant characterization and turf performance in turf plots of two selections (Paula hard fescue and Casero colonial bentgrass) recently released for public distribution by the Plant Production Area of the University of Oviedo. The plants were grown under conditions of no irrigation, no fertilizer, no pesticide application and minimal mowing over a 3-year period (2012-2014). The following morphological measurements were done in a spaced-plant nursery: heading date, plant height, inflorescence length and flag leaf length and width. The turf plots were evaluated for several traits including overall turfgrass quality (turf score), leaf texture and genetic colour. In both the spaced-plant nursery and turf trials, hard fescue genotypes displayed better morphological characteristics (narrow leaves, reduced plant height) and performed better (overall high turfgrass quality, fine leaf texture, dark green colour) than bentgrass genotypes under conditions of low maintenance. For areas in which climate, soil characteristics and management conditions are similar to those encountered in this trial, the selection of Paula hard fescue is recommended for use in low-maintenance turf settings because of the good turfgrass performance and morphological characteristics of this selection.

Turfgrass Performance of Diploid Buffalograss [Buchloe dactyloides (Nutt.) Engelm.] Half-sib Populations

Hybridization and selection has been one of the methods used to generate turfgrass cultivars in buffalograss improvement. Three half-sib populations were developed by crossing three buffalograss female genotypes, NE 3296, NE 2768, and NE 2769, with NE 2871, a male genotype, to 1) investigate the pattern of genetic variability generated for turfgrass characteristics through hybridization; 2) assess the effect of parental change on the level of genetic variability generated in a buffalograss diploid population; and 3) predict the performance of a progeny generated from two heterozygous parents for turfgrass performance. The four parents and 20 random F1 progeny selected from each population were established in 2006 at the John Seaton Anderson Turfgrass Research Facility located near Mead, NE. A randomized complete block design (RCBD) was used with the progeny nested in the crosses. A visual rating scale of 1–9 was used to evaluate the population. Mean population lateral spread, genetic color, density, and turfgrass quality from early summer to fall ranged from 3.5 to 4.5, 7.1 to 7.9, 6.9 to 8.1, and 5.2 and 6.8, respectively. There were significant differences among the crosses and the parents for all the traits studied except quality in June and August. The progeny nested within crosses differed for turfgrass genetic color and quality. Best linear unbiased prediction (BLUP) indicated a high improvement potential for turfgrass lateral spread and spring density in NE 2768 × NE 2871 and for turfgrass genetic color in NE 3296 × NE 2871. From these findings, it can be concluded that hybridization breeding is a worthwhile approach for generating and identifying transgressive segregants for specific buffalograss traits.

Evaluation of Buffalograss Leaf Pubescence and Its Effect on Resistance to Mealybugs (Hemiptera: Pseudococcidae)

Considerable progress has been made in improving the turfgrass characteristics of buffalograss, Buchloe dactyloides (Nutt) Engelm, a native North American grass species with low maintenance requirements (Riordan et al., 1993). Two mealybugs, Tridiscus sporoboli (Cockerell) and Trionymus sp. (Hemiptera: Pseudococcidae) have emerged as buffalograss pests Baxendale et al., 1994). Mealybugs have been associated with buffalograss stands throughout Nebraska (Baxendale et al., 1994), as well as in Texas and Arizona. Unfortunately, the Pseudococcidae are poorly described and species identification requires extensive specimen preparation (Ferris, 1950, 1953). Buffalograss mealybugs have an oblong, pale purple-grey, membranous body, ranging in length from 0.2 to 3.0 mm. They are covered with cottony wax secretions (Baxendale et aL, 1994). The adult female is relatively immobile and is found inside or near the leaf sheath, or behind the leaf axils enclosing the female flower. Clusters of eggs are deposited within a filamentous waxy ovisac. First instars, or crawlers, migrate to new feeding sites and likely play a role in host selection (McKenzie, 1967). Mealybugs are often overlooked in the field because of their small size and hidden location on the plant (Baxendale et aL, 1994). Severe mealybug infestations result in a general decline of the buffalograss stand, which can be confused with drought or other stresses. Initially, the turf takes on a reddish-purple discoloration, followed by browning and thinning. A close examination will reveal the mealybug's white cottony secretions. Possible strategies for managing mealybugs on buffalograss include pesticides, biological control, and use of resistant buffalograsses. Developing mealybug-resistant buffalograsses is of particular importance because this grass is used primarily as a low-input turfgrass species. Fortunately, several resistant buffalograsses have been identified (Johnson-Cicalese et al., 1998). Understanding the mechanism of this resistance would be helpful for formulating optimal strategies for identifying and exploiting new sources of resistance. While considerable progress has been made in identifying germplasm resistant to insect pests, progress toward characterization of the mechanisms conferring the resistance has been limited. Resistance mechanisms identified in other turfgrass species include: increased tolerance due to greater rhizome numbers, higher stored food reserves, improved turf density and plant vigor; antibiosis factors which reduce survival or oviposition of the insect, for example, endophyte-infection (Acremonium spp.) of the host plant; and antixenosis factors such as leaf size and width, and time of flowering that affect oviposition (Reinert, 1982; Quisenberry, 1990; Johnson-Cicalese et al., 1989). In buffalograss, glabrous leaf surfaces are suspected of playing an important role in mealybug resistance (Johnson-Cicalese et al. , 1998). Two glabrous buffalograsses, '609' and 'Prairie', have been shown to be highly resistant to mealybugs, and significant positive correlations were found between leaf pubescence and mealybug infestation levels in several greenhouse screening trials (Johnson-Cicalese et al., 1998). Pubescence is widely recognized as a factor in plant resistance to insects. Noms and Kogan (1980) provided 55 examples of how pubescence affects the behavioral and physiological response of arthropods to plants. In a third of the cases cited, pubescence increased the susceptibility of the host plant by making it more suitable for oviposition, affecting feeding behavior, or providing protection from predators. Pubescence enhanced oviposition by several lepidopterous insects on a number of plant species (Lambert et al., 1992; Navasero and Ramaswamy, 1991). Pubescent wheats (Triticwn spp.) were more heavily infested by airborne wheat curl mites (Eriophyes tulipae Keifer) (Harvey and Martin, 1980). Among several

Optimal Nitrogen and Potassium Fertilization Rates for Establishment of Warm‐Season Putting Greens

Proper fertilization of golf course putting greens during grow‐in provides rapid turfgrass cover, high quality putting surfaces, and limits environmental impacts. Different levels of N and K were applied to ‘TifDwarf’ and ‘TifEagle’ bermudagrasses [Cynodon dactylon (L.) Pers. × C. transvaalensis Burt Davy], ‘SeaDwarf’ seashore paspalum (Paspalum vaginatum Swartz), and ‘PristineFlora’ zoysiagrass [Zoysia japonica Stued. by Zoysia tenuifolia (L.) Merr.], sprigged at a rate of 36.6 m3 ha−1 on a USGA‐specified green, to compare grow‐in rate and qualitative turfgrass characteristics. Fertilizer treatments included 1.2, 2.4, 3.7, or 4.9 g N m−2 wk−1, and a one‐time application of polymer‐coated urea (PCU) at 39.1 g N m−2, with each N rate coinciding with four N/K fertilization ratios: 1:1, 1:2, 1:3, or 1:4. Visual measurements of grow‐in rate were generally similar within cultivars with 2.4, 3.7, or 4.9 g N m−2 wk−1 There were no significant effects for turfgrass growth or quality among N/K treatments. The 2.4 g N m−2 wk−1 rate was considered best for rapid establishment of all cultivars. Although 1.2 g N m−2 wk−1 amended turfgrass was slower to establish, this rate provided a more desirable putting surface and further decreased the potential for nutrient leaching.

Turfgrass Characteristics of Prairie Junegrass Germplasm Accessions

ABSTRACTPrairie junegrass [Koeleria macrantha (Ledeb.) Shultes] is a perennial, short‐grass prairie species distributed throughout the Northern Hemisphere. This species demonstrates tolerance to many environmental stresses in Minnesota. Forty‐eight K. macrantha accessions from the United States National Plant Germplasm System (NPGS) were grown under low‐input conditions to evaluate turfgrass quality characteristics for use in a breeding program. A second objective was to identify key geographical locations for germplasm collection. The experiment was conducted at Becker and St. Paul, MN. Nineteen accessions at Becker and 30 accessions at St. Paul performed with an adequate turf quality rating of 5.0 or higher when averaged over the 3‐yr study, suggesting the potential for use in low‐input areas. Prairie junegrass from northern collection regions displayed the highest spring green‐up ratings, an important turf trait in northern climates. There was a negative correlation between this trait and mowing quality at Becker (r = −0.44) and at St. Paul (r = −0.34). Several accessions had acceptable mowing quality and would be candidates for integration into a native prairie junegrass turfgrass breeding program. There was no correlation between inflorescence emergence and turf quality, or between inflorescence emergence and persistent straw suggesting that flowering does not necessarily affect turf quality ratings. Rust (unknown Puccinia species) was present at both locations.

Batch Analysis of Digital Images to Evaluate Turfgrass Characteristics

Techniques using digital image analysis have been recently developed to evaluate turfgrass stands for percent green cover and average color. Manually analyzing digital images may become cumbersome and tedious if turf field trials contain many plots or if images are collected at frequent intervals for analysis. The objective of the following work was to develop a user‐friendly macro capable of automated batch analysis of an unlimited number of digital images. A macro named “Turf Analysis” was written to batch analyze images using SigmaScan Pro software. The macro, which requires less than 1 min of manual execution, performs percent cover and/or color analysis on an unlimited number of images and automatically saves the results into a spreadsheet file. The macro is freely available to download.

Heritability Estimates for Turfgrass Characteristics in Bermudagrass1

No genetic estimates for turfgrass characteristics in bermudagrass, Cynodon dactylon (L.) Pers., are currently available in the literature. Therefore, the objectives of this investigation were to evaluate genetic variation among bermudagrass clones and their polycross progenies and to estimate heritability values for several turfgrass characteristics. Parental clones and polycross progenies were established in a randomized complete block design with four replications in 1981. The parental clones differed (P < 0.01) for all characteristics evaluated during 1981 and 1982. Polycross families differed (P < 0.05) for 13 of the 18 characters evaluated. Broad‐sense heritability estimates for a single year ranged from 0.83 to 0.99. Narrow‐sense heritability estimates based on the polycross family analyses ranged from 0.06 to 0.94. Heritability estimates from the parent‐offspring covariance analyses ranged from 0.00 to 1.22. For a number of characters, additive genetic variation accounted for a significant portion of the total genetic variation. Data over a 2‐year period were combined for leaf length and leaf width. Broad‐sense heritability estimates were moderately high with values of 0.94 and 0.83 for leaf length and leaf width, respectively. Narrow‐sense heritability values for leaf length and leaf width were 0.83 and 0.62 from the progeny analysis and 0.57 and 0.43 based on parent‐offspring covariance, respectively. For characteristics which had moderate‐to‐high narrow‐sense heritability values, breeding methods which involve no progeny testing should be suitable for genetic gain to be realized.

Fusarium Blight and Physical, Chemical, and Microbial Properties of Kentucky Bluegrass Sod

SMILEY, R. W., M. M. CRAVEN, and J. A. BRUHN. 1980. Fusarium blight and physical, chemical, and microbial properties of Kentucky bluegrass sod. Plant Disease 64:60-62. Kentucky bluegrass (Poa pratensis) may become severely damaged by Fusarium blight. When the disease occurred on a well-established plot, its dependence on the environment, a relationship that is not well understood, was studied. Factor analysis was performed to identify associations between Fusarium blight and the other variables. The disease was positively correlated with the thatch decomposition rate, negatively correlated with the plant growth variables, and not correlated with any microbial group including all species, sections, and composite numbers of Fusarium. Sod pH and Fusarium numbers were associated with thatch decomposition rates. Fusarium blight was least severe when the percentage of Fusarium-infected plant crowns was highest. These results are considered in relation to the possible role of phytotoxic substances that are produced during thatch decomposition and act as incitants of Fusarium blight of Kentucky bluegrass. Fusarium blight of Kentucky bluegrass (Poa pratensis L.), reportedly caused by Fusarium roseum (Lk.) emend. Snyd. & Hans. f. sp. cerealis and by F. tricinctum (Cda.) emend. Snyd. & Hans. f. sp.poae (4), destroys bluegrass stands in several regions of the United States. The disease occurs on seeded bluegrass stands that are usually older than 4 yr but may occur earlier on stands established from sod. Occurrence of Fusarium blight on mature turfgrasses is very dependent upon the environmental conditions (3,20), but these conditions remain poorly defined due to the unpredictable nature of the disease in well-controlled experiments. We investigated the longterm (3 yr) effects of fungicide applications on nontarget microbial activities and soil processes in closely monitored Kentucky bluegrass sod (14-16). Fusarium blight occurred on the plot in 1977 (18), and the disease was unexpectedly controlled by several fungicides that have been ineffective in all 1-yr studies. Several properties of sod also appeared to be associated with the incidence of Fusarium blight. An understanding of the relationships between this disease and certain characteristics of host growth and of sod and microbial numbers may allow more complete characterization of the conditions favoring or causing disease. This is especially important because several fungicides that control the disease in the field are not fungitoxic to the alleged pathogens in vitro (12,17). This investigation was conducted as part of Hatch Project NY(C)153434. Accepted for publication 21 March 1979. 00191-2917/80/000010$03.00/0 01980 American Phytopathological Society This report presents the results of correlative and multivariate analyses performed to identify associations between Fusarium blight of Kentucky bluegrass and certain turfgrass characteristics. Because a significant level of multicollinearity existed among variables, simple correlation coefficients could not be interpreted. Factor analysis was used to identify a set of independent patterns of association among the variables. The results of the factor analysis allowed estimation of partial correlation coefficients that provided a statistical measure of the degree of linear association between Fusarium blight and each of