Theses and Dissertations from UMD

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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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2006 - 200912020 - 20211

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Subject: search.filters.subject.Biological Control

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    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.
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    The role of relative abundance and identity in the effectiveness of generalist predators as biocontrol agents of Pieris rapae L. (Lepidoptera: Pieridae)
    (2006-12-11) Moreno, Carlo Rene; Barbosa, Pedro; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The importance of generalist arthropod predator assemblages in suppressing pests has recently received more attention. However, few studies have investigated the impacts of assemblage structure on pest mortality. This study assessed the influence of relative abundance and taxonomic identity among an assemblage of generalist predators in collards, (Brassica oleracea var. acephala), on the mortality of Pieris rapae. In field surveys and laboratory assays, I determined that Coleomegilla maculata was the numerically dominant while Coccinella septempunctata and Podisus maculiventris were numerically subdominant predators of P. rapae larvae. Experimental mesocosms were used to determine whether numerically dominant predators alone, regardless of taxonomic identity, imposed greater P. rapae larval mortality than when in an assemblage. As numerically dominant species, only C. septempunctata imposed greater P. rapae larval mortality alone than when in an assemblage. This research highlights the importance of considering both relative abundance and identity in studies involving predator assemblages and biocontrol.