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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    CUCURBIT DISEASE MANAGEMENT WITH REDUCED CHLOROTHALONIL AND IMPROVED UNDERSTANDING OF PSEUDOPERONOSPORA CUBENSIS POPULATION DYNAMICS
    (2020) Jones, Jake Gardner; Everts, Kathryne L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Research has linked chlorothalonil exposure to declines in pollinator health due to an increased likelihood of Nosema ceranae infection, altered gut microbial community, and a reduction in colony fitness and survival of honey bees (Apis mellifera). Therefore, a reduction in use of chlorothalonil, a large component of cucurbit disease management, may be needed. Without chlorothalonil, a widely used, broad-spectrum fungicide, the fungal and oomycete pathogens in cucurbit cropping systems can more quickly evolve resistance to targeted fungicides due to a limited number of efficacious modes of action and frequent sprays. Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew, for example, has a short life cycle, experiences repeated applications of fungicides, and has a wide host range making it a high risk for fungicide resistance development. Our research focused on the development of an alternative fungicide spray program in melons to reduce the use of chlorothalonil, identifying the fungicide insensitivities of local P. cubensis populations and determining the efficacy of fungicides used to manage cucurbit downy mildew, and investigating the clade-host relationship and formation of oospores in regional P. cubensis samples. Efficacy on two important diseases in melon, powdery mildew and gummy stem blight, can be largely maintained without chlorothalonil but anthracnose control was not adequate without the inclusion of chlorothalonil. Currently, there are a number of highly effective targeted fungicides available to growers for management of cucurbit downy mildew including oxathiapiprolin, zoxamide + chlorothalonil, chlorothalonil, and cyazofamid. Our research shows evidence of P. cubensis clade-host associations, with clade 1 preferentially infecting acorn and summer squash (Cucurbita pepo), butternut squash (Cucurbita moschata), and watermelon (Citrullus lanatus), while clade 2 preferentially infects cucumber (Cucumis sativus). Melons (Cucumis melo) and pumpkin (Cucurbita maxima) are hosts to both clade 1 and clade 2 P. cubensis. Using these findings, producers can choose the fungicide that most appropriately targets the more virulent clade 2 or less virulent clade 1 infections.
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    Assessment of Pesticide Residues In Farmers' House Dust and Educational Intervention to Improve Pesticide Handling Practices
    (2004-12-02) Clark, Lisa M; Brown, Amy E; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This study investigated whether pesticide residues occur inside homes of vegetable and small fruit growers, identified pesticide handling practices that could contribute to home contamination, and evaluated the impact of an educational intervention in changing those handling practices. Dust samples were collected from the subjects' homes and analyzed for chlorothalonil. Residues were detected in carpet dust samples (8-277 ng/g), floor wipe samples (0.08-5.1 ug/sq m) and one washing machine sample (1.0 ug/sq m of washing machine). Each subject received an educational intervention consisting of a personalized report noting sites contaminated and providing recommendations of handling practices that would be expected to reduce any residues. Three sequential surveys of Maryland growers provided information regarding handling practices and changes over time. Lessons from this study could be incorporated into pesticide safety education to promote safer pesticide handling.