Advancements in cold tolerance of seeded bermudagrass and introduction of sulfonylurea herbicides have given turf managers new tools. Seedling bermudagrass response to sulfonylurea herbicides applied before or soon after seeding has not been characterized. Field observations have indicated that variability exists among sulfonylurea herbicides used for perennial ryegrass control. Objectives of the conducted research were to evaluate sulfonylurea herbicides for safety and utility while establishing seeded bermudagrass, and to elucidate variability in perennial ryegrass control with foramsulfuron. Field experiments were conducted in Blacksburg, VA to assess turfgrass and smooth crabgrass response to flazasulfuron, foramsulfuron, metsulfuron, rimsulfuron, sulfosulfuron, and trifloxysulfuron-sodium, applied 1 and 3 weeks after and before seeding. Herbicides applied 3 weeks after seeding (WAS) were generally more injurious than when applied 1 WAS. Foramsulfuron, metsulfuron, and sulfosulfuron are safe to apply 1 and 3 WAS, causing no reduction in turf cover. Herbicides applied before or after seeding injured bermudagrass in the following order from most to least injurious: flazasulfuron = trifloxysulfuron > rimsulfuron > metsulfuron = sulfosulfuron > foramsulfuron. Flazasulfuron and trifloxysulfuron-sodium are not safe to use within 3 weeks of seeding, while foramsulfuron and metsulfuron can be used anytime before or after seeding bermudagrass. Flazasulfuron, foramsulfuron, and trifloxysulfuron-sodium were evaluated for perennial ryegrass control as affected by environment. Among environmental variables collected soil temperature averaged 7 DAT correlated best with perennial ryegrass response of the three tested products. Soil temperatures below 18 C perennial ryegrass reduced control 9 WAT from 78 to 31% for foramsulfuron while flazasulfuron and trifloxysulfuron-sodium efficacy were not significantly affected. Temperature dependence on perennial ryegrass control can be ranked from most to least as follows; foramsulfuron > trifloxysulfuron-sodium > flazasulfuron. Studies were conducted to determine absorption and translocation of 14C flazasulfuron when applied to perennial ryegrass roots or foliage. Roots treated with 14C flazasulfuron absorbed 41% of recovered 14C while 25% of 14C moved from treated roots to foliage. It appears root absorption is an important component of flazasulfuron efficacy since most of the absorbed 14C remained in treated leaves and root absorbed 14C moved rapidly to foliage. / Ph. D.

Spring dead spot (Ophiosphaerella spp.) (SDS) of bermudagrass (Cynodon dactylon (L.) Pers. x transvaalensis Burtt Davy) is one of the most challenging diseases in the United States transition zone. Six projects were conducted from 2019 to 2022 to better understand the environmental, edaphic, and spatial distribution of SDS epidemics and to examine management strategies for SDS with chemical and cultural practices. A survey of 51 locations provided support of the geographic distribution of Ophiosphaerella species across the Mid-Atlantic United States. Ophiosphaerella herpotricha and O. korrae were isolated from the Mid-Atlantic region, yet O. narmari was not. Cultivars in which parent material originated from the midwestern United States had predominantly O. herpotricha and cultivars in which the parent material originated from the southeastern United States had predominantly O. korrae. In vitro and in situ fungicide efficacy screenings were conducted for O. herpotricha and O. korrae. Additionally, field studies were conducted to optimize fungicide applications and bermudagrass recovery from SDS. Results highlighted that, generally, O. korrae was less sensitive to fungicides than O. herpotricha; the fungicides isofetamid, mefentrifluconazole, penthiopyrad, and pydiflumetofen were generally the most efficacious against SDS; the different fungicide application methods deployed produced mixed results in their effect on fungicide efficacy against SDS with increased efficacy of tebuconazole against SDS with soil surfactant applications and post-application irrigation in certain scenarios; the optimal timing for fungicide applications for SDS was from 13-18°C with tebuconazole and 13-21°C with isofetamid; and nitrogen applications without cultivation practices in the late spring/early summer optimized bermudagrass recovery from SDS. Lastly, a geospatial survey study was conducted to determine the environmental and edaphic factors that influence SDS epidemics. Results were variable with numerous environmental and edaphic factors influencing SDS depending on the year and location; however, soil pH, soil potassium content, and thatch depth were among the most consistent and influential factors on SDS epidemics. Ultimately, these data improve our recommended strategies for successful SDS management. / Doctor of Philosophy / Spring dead spot is a damaging turfgrass disease that causes aesthetically displeasing symptoms and potential safety and playability concerns for pedestrians and athletes traversing turfgrass surfaces. This disease is caused by three fungal species, and the distribution of these species in the Mid-Atlantic US and the management of spring dead spot epidemics are not well understood. Studies were conducted from 2019 to 2022 to determine the geographic distribution of the species that cause spring dead spot in the Mid-Atlantic, best management strategies for spring dead spot with chemical and cultural practices, and factors in the environment and soil that influence spring dead spot epidemics. Results from the geographic distribution study showed that two of the three fungal species that cause spring dead spot were found in the Mid-Atlantic US, which has major implications on management strategies for the disease. The results from the studies focusing on best management strategies for spring dead spot with chemical and cultural practices highlight that the two fungal species found in the Mid-Atlantic US responded differently to fungicides, few fungicides suppressed the disease to an acceptable level, fungicide application methods provided variable suppression of the disease, optimal timing for fungicide applications was in the fall months when soil temperatures were between 13°C and 18°C, and nitrogen fertilization without cultivation optimized bermudagrass recovery from spring dead spot symptoms. Lastly, the study examining the environmental and soil factors that influence spring dead spot epidemics showed that many factors in the soil and environment influenced spring dead spot epidemics with soil pH, soil potassium content, and thatch depth among the most prevalent. These studies provide turfgrass managers and researchers a better understanding of spring dead spot and allow for more informed management decisions for prevention of and recovery from the disease.

Managing turf for high aesthetic value is costly. Such management usually involves mowing, disease prevention, insect control, and weed control. Mowing is the most expensive practice on golf courses and annual bluegrass (Poa annua L) is the most challenging weed problem in professional turf. The plant growth regulators trinexapac-ethyl and paclobutrazol are commonly used in VA for these two costly and challenging jobs. Prohexadione calcium (PC) is an experimental chemical that inhibits the same enzyme (3ß-hydroxyalase) as trinexapac-ethyl and may selectively suppress annual bluegrass. Experiments were conducted at the Virginia Tech Turfgrass Research Center and Glade Road Research Facility to determine the PC rate required to reduce clipping biomass of four turfgrass species as effectively as trinexapac-ethyl. Prohexadione calcium reduced clipping biomass of bermudagrass (Cynodon dactylon (L.) Pers.), Kentucky bluegrass (Poa pratenis L.), perennial ryegrass (Lolium perenne L.), and zoysiagrass (Zoysia japonica Steud.) equivalent to trinexapac-ethyl at 0.70, 0.22, 0.60, and 0.27 kg a.i./ha -1, respectively. Further experiments conducted at three locations across Virginia determined that PC was comparable to paclobutrazol for annual bluegrass suppression. Since turfgrass response to PC was different between annual bluegrass, Kentucky bluegrass, and perennial ryegrass, 14C labeled PC was used to assess absorption, translocation, and metabolism of PC between annual and Kentucky bluegrass, creeping bentgrass (Agrostis stolonifera L.), and perennial ryegrass. Annual and Kentucky bluegrass absorbed more PC than creeping bentgrass or perennial ryegrass and partially explained the selectivity between these species. Translocation and metabolism of PC did not differ between species. Our final objective launched experiments characterizing possible resistance to acetolactate synthase (ALS) inhibiting herbicides in annual bluegrass. Several selective herbicides for annual bluegrass control inhibit ALS. Since many weeds have developed resistance to ALS-inhibiting herbicides, the ALS gene in annual bluegrass was sequenced and derived amino acid sequences were at least 87% similar to other previously sequenced grass species. This sequencing data will be used in future experiments to predict the likelihood of ALS resistance in annual bluegrass. / Ph. D.

Brown patch, caused by <i>Rhizoctonia solani</i> Kuhn, is an important disease on tall fescue (TF, <i>Festuca arundinacea</i> Schreb, synonym <i>Schedonorus phoenix</i> (Scop.) Holub). <i>Rhizoctonia zeae</i> Voorhees, a related pathogen, causes similar symptoms. Confusion over which <i>Rhizoctonia</i> species is causing symptoms and subjective visual evaluations of disease severity may contribute to variability in observed BP resistance of TF cultivars at multiple locations. The objectives of this study were to develop an objective digital image analysis (DIA) method for evaluating disease and to use DIA to screen tall fescue plant introductions (PIs) for resistance to <i>R. solani</i> and <i>R. zeae</i>. There was a strong correlation (r² = 0.97) between actual disease severity, measured by applying lesioned tissue of a known area to healthy leaves, and DIA calculated disease severity using scanned images of individual leaves (DIA-IL). The accuracy and precision of visual evaluations and DIA evaluations of entire plants (DIA-WP) were evaluated using DIA-IL as a standard of accuracy. Accuracy of DIA-WP was not significantly different from visual evaluation accuracy. Precision was significantly higher for DIA-WP. Evaluation of PIs and putatively BP resistant TF cultivars for resistance to <i>R. solani</i> and <i>R. zeae</i> using DIA-WP identified clones within each PI that ranked high for resistance to <i>R. solani</i> or <i>R. zeae</i>. No clones were identified with high resistance to both <i>R. solani</i> and <i>R. zeae</i>. Improved precision of DIA evaluation methods and inclusion of <i>R. zeae</i> in BP resistance breeding may decrease variability of TF cultivar performance across locations. / Master of Science

Creeping Bentgrass (Agrostis stolonifera var. palustris (Huds.) Farw.) is the most widely used cool-season turf grass used for putting greens in North America. Frequently it becomes invaded with a persistent weed, annual bluegrass (Poa annua L.). Studies were conducted on a predominately annual bluegrass area managed as a putting green to attempt to quantify the impacts of plant growth regulator, seeding rate" and season on the success of introducing creeping bentgrass. Also, the impact of plant growth regulating substances on creeping bentgrass overall quality and seasonal rootmass production was evaluated. It was observed that creeping bentgrass does not become well established when overseeded into annual bluegrass regardless of plant growth regulator applications or season. Additionally 1I plant growth regulator application, following seedling emergence reduced creeping bentgrass seedling populations. Competition from established annual bluegrass and close frequent cutting were deemed reasons for lack of creeping bentgrass establishment success. Creeping bentgrass turf was maintained at a high level of quality with plant growth regulating substances. The use of the plant growth regulator trinexapac-ethyI reduced clipping production and was not detrimental to root production. Propiconizole application increased clippings and controlled Sclerotinia dollarspot. The application of a proprietary biostimulator material (3D) enhanced creeping bentgrass green color and generally increased rootmass over untreated turf. / Master of Science

Remote sensing techniques are important for detecting disease within the turfgrass canopy. Herein, we look at two such techniques to assess their viability in detecting and isolating turfgrass diseases. First, thermal imagery is used to detect differences in canopy temperature associated with the onset of brown patch infection in tall fescue. Sixty-four newly seeded stands of tall fescue were arranged in a randomized block design with two runs with eight blocks each containing four inoculum concentrations within a greenhouse. Daily measurements were taken of the canopy and ambient temperature with a thermal camera. After five consecutive days differences were detected in canopy – ambient temperature in both runs (p=0.0015), which continued for the remainder of the experiment. Moreover, analysis of true colour imagery during this time yielded no significant differences between groups. A field study comparing canopy temperature of adjacent symptomatic and asymptomatic tall fescue and creeping bentgrass canopies showed differences as well (p<0.0492). The second project attempted to isolate spring dead spot from aerial imagery of bermudagrass golf course fairways using a Python script. Aerial images from unmanned aerial vehicle flights were collected from four fairways at Nicklaus Course of Bay Creek Resort in Cape Charles, VA. Accuracy of the code was measured by creating buffer zones around code generated points and measuring how many disease centers measured by hand were eclipsed. Accuracies measured as high as 97% while reducing coverage of the fairway by over 30% compared to broadcast applications. Point density maps of the hand and code points also appeared similar. These data provide evidence for new opportunities in remote turfgrass disease detection. / Master of Science in Life Sciences / Turfgrasses are ubiquitous, from home lawns to sports fields, where they are used for their durability and aesthetics. Disease within the turfgrass canopy can ruin these aspects of the turfgrass reducing its overall quality. This makes detection and management of disease within the canopy an important part of maintaining turfgrass. Here we look at the effectiveness of imaging techniques in detecting and isolating disease within cool-season and warm-season turfgrasses. We test the capacity for thermal imagery to detect the infection of tall fescue (Festuca arundenacea) with Rhizoctonia solani, the causal agent of brown patch. In greenhouse experiments, differences were detected in normalized canopy temperature between differing inoculation levels at five days post inoculation, and in field conditions we were able to observe differences in canopy temperature between adjacent symptomatic and non-symptomatic stands. We also developed a Python script to automatically identify and record the location of spring dead spot damage within mosaicked images of bermudagrass golf fairways captured via unmanned aerial vehicle. The developed script primarily used Hough transform to mark the circular patches within the fairway and recorded the GPS coordinates of each disease center. When compared to disease incidence maps created manually the script was able to achieve accuracies as high as 97% while reducing coverage of the fairway by over 30% compared to broadcast applications. Point density maps created from points in the code appeared to match those created manually. Both findings have the potential to be used as tools to help turfgrass managers.

Conversion of native forests to turfgrass-dominated residential landscapes under a wide range of management practices results in dramatic changes to vegetation and soils, which may affect soil carbon storage. To better understand the effects of landscape conversion and management on soil carbon, we conducted a study on residential properties in the Valley and Ridge physiographic province of southwest Virginia to compare soil carbon storage and dynamics between turfgrass landscapes and the surrounding mixed oak forests from which they were developed. Sixty-four residential properties ranging from 5 to 52 years since site development were investigated. Soil samples were collected from lawns and adjacent forest stands to a depth of 30 cm and analyzed for carbon and nitrogen content. Additional measurements taken were soil bulk density, temperature, moisture, and total soil CO₂ efflux rate. Homeowners participating in the study completed a survey on their lawn management practices so that the effects of specific practices (e.g. fertilization) and intensity levels on carbon dynamics could be analyzed. Also included in the survey were 11 questions regarding the homeowners' commitment to the environment. Homeowners were assigned an environmental commitment score based on their responses which was compared with lawn management practices in order to identify any connection between environmental attitude and lawn management practices. Total soil carbon content to 30 cm depth of lawn (6.5 kg C/m²) and forest (7.1 kg C/m²) marginally differed (P=0.08); however, lawn soil contained significantly greater C than forest soil at the 20-30 cm depth (0.010 vs. 0.007 g C/cm³, P=.0137). There was a weak negative relationship between carbon in the lawn and time since development at the 20-30 cm depth (P=0.08), but no significant relationship between time and C content at shallower depths. We found a positive relationship between time since development and percent C of lawn at the 0-5 cm depth (P=0.04), whereas there was a negative relationship with percent C and time at the 20-30 cm depth (P=0.03). Based on the homeowner survey, we found a positive correlation between lawn fertilization frequency and both lawn nitrogen content (P=.07) and lawn carbon content (P=.0005) in the top 0-5 cm of soil. Nitrogen content was greater in lawn than forest soil at the 0-5 cm depth (0.0025 vs. 0.0018 g/cm³³, P<.0001) and the 5-10 cm depth (0.0013 vs. 0.0009 g/cm³, P <.0001). There was a positive relationship (P=0.059) between overall environmental commitment score and level of management intensity. Higher environmental commitment (EC) score corresponded with a higher level of management intensity (fertilizer and pesticide use). Our results indicate that converting unmanaged Appalachian hardwood forest into managed, turf-grass dominated residential homesites results in similar soil organic concentration and depth distribution as the previous forest within a short period of time following development. Although total soil carbon does not differ between lawn and forest, lawn may develop greater density at 20-30cm depth over time. Fertilization enhances carbon and nitrogen content in the upper 0-5cm in lawns. Homeowners who feel that they are more strongly committed to the environment are more likely to apply higher levels of fertilizer to their lawn. / Master of Science

The contribution of non-point source pollution to degrading surface water quality is considerable throughout Virginia and beyond. While research on agricultural best management practices in nutrient management and nutrient and soil stabilization has made progress in reducing agricultural contributions to nutrient and sediment loading of watersheds, little is known about how land covers of different vegetation representative of urban areas (e.g., bare soil versus turfgrass lawns versus urban forest) influence the potential for non-point source pollution. Ambient rainfall volumes were manipulated to provide 50%, 100%, and 150% of natural precipitation to plots with landscape covers of bare soil, shredded wood mulch, turfgrass, and simulated urban forest (complete pin oak canopy with shredded hardwood leaf mulch). Precipitation amounts, runoff volumes, and eroded sediment masses for ten rain events between July and December 2004 were measured. Runoff was analyzed for nitrate and orthophosphate concentrations for three rain events. Turfgrass was found to be the most effective of the land covers tested at reducing components of non-point source pollution from stormwater. Turfgrass plots produced, on average, the least runoff and sediment, and lower nitrate concentrations in runoff water as compared to the other land covers tested. Results from urban forest plots apparently reflected the disturbance of tree planting, even six months later. This study contributes to a sparse body of knowledge about the influences of urban landscapes on water quality, and will inform land use policy and urban Best Management Practices. / Master of Science

Bermudagrass (Cynodon spp.) is the most common turfgrass used on golf course putting greens in the southeastern United States (Lyman et al., 2007). In 2013, the National Turfgrass Evaluation Program (NTEP) started a 5-year trial of warm-season putting green cultivars. One of the bermudagrass cultivars in the study is MSB-285 (experimental cultivar). MSB-285 is a sister plant of MSB-264 (Philley and Munshaw, 2011) and is a distinct cultivar of C. dactylon × C. transvaalensis. MSB-285 has a more extensive root system and upright growth habit than traditional bermudagrass putting green cultivars (Philley and Munshaw, 2011). Due to MSB-285’s unique genetic makeup and growth habit, the objectives of this research were to determine if best management practices used to maintain ultradwarf bermudagrasses would be suitable for MSB-285 and to determine the water-use characteristics of MSB-285 compared to industry standard cultivars.

<p>  </p> <p>Several plant-parasitic nematode (PPN) species cause decline in the health of creeping bentgrass putting greens. PPNs target and parasitize the root systems of turfgrass which may exacerbate the impact of other biotic and abiotic stress. Turfgrass managers often apply nematicides preventatively or curatively to control PPN populations. However, the inherent chemistries of the nematicides may inhibit their ability to permeate through the thatch layer and soil, resulting in an ineffective application. This research aimed to evaluate the depth of PPN populations through the growing season to maximize the effectiveness of nematicide applications, with a primary focus on lance (<em>Hoplolaimus</em> spp.) and root-knot nematodes (<em>Meloidogyne</em> spp.). To determine the depth of genera across time, soil samples were taken with a 1.9 cm diameter soil probe to a depth of 25 cm during the months of April, June, August, and October at 7 sites across Missouri, three in eastern Kansas and ten sites in Indiana in 2021 and 2022, respectively. Significant interactions occurred between sampling depth and month in both Missouri and Indiana for some PPN genera. Additionally, individual lance and root-knot nematode species obtained from sampling were characterized with molecular methods and in the case with one lance nematode from Indiana, with scanning-electron microscopy. Results suggest an over-representation of <em>H. galeatus</em> in diagnostic literature, and a diverse collection of <em>Meloidogyne</em> spp. present in Indiana on golf course putting greens. </p>