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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    SEASONAL DEVELOPMENT OF DOLLAR SPOT EPIDEMICS IN MARYLAND AND NITROGEN EFFECTS ON FUNGICIDE PERFORMANCE IN CREEPING BENTGRASS
    (2011) Ryan, Chris Patrick; Dernoeden, Peter H; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Dollar spot (Sclerotinia homoeocarpa) is a common and destructive disease of creeping bentgrass (Agrostis stolonifera). The frequency and severity of dollar spot epidemics has not been quantified and there are no effective predictive models. High rates of nitrogen (N) reduce dollar spot injury, but low N rates applied in summer have not been assessed for disease suppression. Field studies were conducted from 2008 to 2010 with the following objectives: a) to describe the relationship among season, environmental factors and the severity of dollar spot epidemics in six creeping bentgrass cultivars; b) to evaluate six water soluble N sources applied at a low rate (7.3 kg N ha-1) in summer for their impact on dollar spot severity; and c) to assess the performance of low fungicide rates tank-mixed with N on dollar spot severity. Two epidemics were observed each year between spring and mid- autumn, with the second being most severe. A third, late autumn epidemic also was observed in each year. The first epidemic in May was effectively predicated using a degree day model having a biofix date of 1 April and a 15°C base temperature. Ammonium sulfate was most consistently effective in reducing dollar spot injury, but caused foliar injury. Tank-mixing a low chlorothalonil rate with N generally reduced fungicide efficacy.
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    DOLLAR SPOT AND GRAY LEAF SPOT SEVERITY AS INFLUENCED BY IRRIGATION PRACTICE AND PLANT PROTECTION MATERIALS
    (2005-11-23) McDonald, Steven James; Dernoeden, Peter H; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Agrostis stolonifera and Lolium perenne are widely used turfgrass species grown on golf fairways, however, they are susceptible to dollar spot (Sclerotinia homoeocarpa) and gray leaf spot (Pyricularia grisea) diseases, respectively. Two field studies were conducted to assess: 1) the influence of two irrigation regimes and seven chemical treatments on dollar spot and gray leaf spot severity; and 2) the effects of two spray volumes (468 and 1020 L water ha-1), two fungicides (chlorothalonil and propiconazole) and three application timings (dew present or displaced and dry canopy) on dollar spot control. Dollar spot was more severe in A. stolonifera subjected to infrequent irrigation; whereas, gray leaf spot was more severe in frequently irrigated L. perenne. The plant growth regulator and wetting agent evaluated suppressed dollar spot, but they had no effect on gray leaf spot. Chlorothalonil was most effective when applied to a dry canopy in 468 L water ha-1.