Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Investigating Cultural Practices to Improve the Efficacy and Reliability of Biological Control Organisms in Turfgrass Systems(2021) Doherty, Joseph; Murphy, Angus; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Biological control, or suppressing plant pathogens through natural predators or competitors, has been an area of scientific intrigue for many decades. However, inconsistent efficacy remains the chief reason for a lack of widespread adoption by growers. This dissertation was developed to address the inconsistencies of biological control through three practices. First, reducing competition from resident foliar microbial communities, or niche clearing, was explored for brown patch suppression and biological control organism establishment. Second, biological control organisms were applied to the rhizosphere and evaluated for suppression of root infecting pathogens. Finally, combinations of monthly biochar topdressing and biweekly or weekly biological control organism applications were evaluated for foliar pathogen suppression and biological control organism establishment. In each study, biological control organisms were observed to suppress pathogens and reduce disease severity. However, neither niche clearing nor biochar topdressing increased disease control compared to the biological control organism applied alone. While biochar applications did not improve the efficacy of biological control organisms, they did reduce the severity of disease unaffected by biological control organisms and increased turfgrass quality. Furthermore, biological control organisms were most successful under low to moderate levels of disease pressure, as control was lost when disease pressure peaked each year. Once again, neither niche clearing nor biochar topdressing increased populations of biological control organisms compared to the organisms applied alone. Weekly applications of biological control organisms did result in higher population levels compared to biweekly applications, and rhizosphere targeted applications appeared to have resulted in an establishment of the biological control organism into the rhizosphere community. Findings from these research projects suggest that biological control organisms should be applied weekly to increase odds of successful disease reduction. Given the lack of control under high disease pressure in all studies, successful implementation of biological controls should be targeted to the shoulders of the season when disease pressure is lower, or biological control organisms should be implemented into a season long program to supplement a traditional fungicide program.Item Novel Uses of Turfgrasses for Equine Operations(2018) Jaqueth, Aubrey; Burk, Amy O; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dry lots, or small paddocks bare of vegetation, are commonly used to manage over- conditioned equids in order to restrict the diet by offering hay lower in digestible energy and non-structural carbohydrates (NSC) compared to unrestricted pasture access. However, the lack of vegetation in dry lots often caused by overgrazing and heavy traffic has been associated with negative environmental impacts such as soil erosion. Turfgrasses may be suitable as ground cover in dry lots because they are tolerant of traffic and close mowing (e.g. grazing) and may be low to moderate in both yield and NSC. The objective of this body of work was to 1) characterize the prevalence of over-conditioned equids in MD and whether dry lots were being used for their management, and 2) to assess the relative traffic tolerance, nutritional composition, and palatability of commercially available seeded cultivars of cool- season (CS) and warm-season (WS) turfgrasses for their potential use on horse farms. An online survey of licensed stable operators revealed that ~ 40% of horses in MD were over-conditioned and feeding hay in dry lots was a preferred practice despite requiring more maintenance and management time. Two additional studies evaluating wear tolerance of 8 CS and 6 WS cultivars exposed to either no, low, or high simulated horse traffic found that soil compaction increased as treatment level increased in CS and WS traffic trials (P <0.0001). Persistence was reduced in response to traffic in CS cultivars (P = 0.0003), but not in WS cultivars. Overall, tall fescue and zoysiagrass cultivars were most traffic tolerant, but only zoysiagrass had a more ideal NSC concentration. In the final study, horses exhibited no grazing preference among CS cultivars, whereas among WS cultivars they prefered common bermudagrass and crabgrass (P < 0.02). Several cultivars, including Maestro and Regenerate tall fescue, Zenith zoysiagrass, and Riviera bermudagrass cultivars were closest to meeting desired goals of being traffic tolerant, moderate in yield, and relatively low in NSC, and are thus recommended to be evaluated in future studies for on-farm persistence in dry lots and heavy use areas and for long-term effects of grazing by equids.Item Understanding the Influence of Microbial Sources and Time on the Developing Creeping Bentgrass Microbiome(2018) Doherty, Joseph Ryan; Roberts, Joseph A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microbial communities are intimately intertwined with many processes affecting the health of plants. There is increasing interest in utilizing microbial communities to increase plant health while reducing management inputs. To that end, bacterial and fungal communities associated with creeping bentgrass were evaluated using next-generation sequencing technologies. Evaluating the impact of resident seed and soil microbial communities revealed introductions of microbes from the seed despite a strong influence from the soil. Observing long-term population dynamics revealed no shifts in fungal diversity over six months, while bacterial diversity increased from emergence to two months post-emergence. Across both studies taxonomic profiling revealed that bacterial and fungal communities were consistently dominated by just a few groups. In both studies, ordination analyses revealed clustering of samples by sampling time. These results show that changes in the microbiome are driven by rare species, and that the turfgrass microbiome is resilient to change over time.