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Browsing by Author "Norton, Andrew, committee member"

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    Chemical control of Cytospora leucostoma, a major limiting factor of peach production in western Colorado
    (Colorado State University. Libraries, 2017) Miller, Stephan, author; Stewart, Jane, advisor; Minas, Ioannis, advisor; Norton, Andrew, committee member; Uchanski, Mark, committee member
    Cytospora canker, Cytospora leucostoma, is a major limiting factor of peach production in Colorado, accounting for 15-20% of crop production loss annually. Given the unique environmental factors of the western slope region of Colorado, C. leucostoma has developed into a severe fungal disease, reducing yields annually. Chemical measures are important for Cytospora control as few options currently exist for preventing new infections. The specific objectives of the following thesis are to: (1) evaluate the efficacy of conventional and organic fungicides for C. leucostoma control, (2) test wound sealing fungicides, embedded in paint or kaolin clay, to develop preventive and containment approaches in existing orchards. Topsin, Topsin amended in 50% latex, Captan, Captan amended in 50% latex, 50% latex, lime sulfur, and lime sulfur amended in kaolin clay (Surround WP) showed evidence of efficacy from laboratory and field trials. Of these treatments, 50% latex, Topsin amended in 50% latex, and Captan amended in 50% latex, were shown to limit pathogen growth most effectively on pruning wounds during field trials in the summer season. In all field trials, however, NuCop showed absolutely no efficacy and should be avoided for C. leucostoma control in western Colorado. When various chemicals were tested on existing cankers to reduce spore inoculum loads, efficacy could not be statistically confirmed. The results of this study were compicated by variable field conditions and a large range of spore produced by each canker. Thus, larger sample sizes should be used in future studies to tease a part chemical efficacy and abiotic influences. Further, kaolin clay alone may shield fungal cankers from extreme temperatures, enhancing its growth in the field.
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    Ecosystem impacts of tamarisk (Tamarix spp.) management in the Arkansas River watershed, Colorado: effects of disturbance and herbicide residues on passive plant community restoration
    (Colorado State University. Libraries, 2013) Douglass, Cameron Hale, author; Nissen, Scott, advisor; Bauerle, Bill, committee member; Meiman, Paul, committee member; Norton, Andrew, committee member
    Tamarisk (Tamarix L.) is now one of the most common species of woody plants along waterways in arid and semi-arid areas of the western United States. Tamarisk was intentionally introduced over a century ago for ornamental purposes and erosion control projects, but its expansion since has been influenced by altered hydrologic regimes and global climate change. Approximately sixty years ago the species started to be perceived by federal scientists as noxious and was targeted for control. As the first chapter in this dissertation outlines, management of tamarisk has occurred by many methods, but primarily combinations of herbicides and mechanical tree removal. Successive chapters detail laboratory, greenhouse and field experiments that determined the ecological impacts of currently used tamarisk control strategies, with a particular emphasis on the effects of herbicide residues on plant community restoration patterns following management. First, an in vitro study and high-performance liquid chromatography (HPLC) analysis were used to quantify soil degradation rates for imazapyr and triclopyr from six sites in Colorado. A dose response study was then conducted at two of these sites to determine the relative sensitivity of important restoration plant species to the two herbicides. Exponential decay models estimated imazapyr half-lives (t50) for two soils at 51 and 76 days, and triclopyr half-lives (t50) for all soils averaged 7 days. Glycyrrhiza lepidota was the only species to demonstrate sensitivity to triclopyr. Atriplex canescens, Elymus canadensis and Sporobolus airoides were the most sensitive to typical imazapyr residues. Fecundity in S. airoides and Bouteloua curtipendula were also negatively impacted by the highest rate of both triclopyr (3.92 kg ai ha-1) and imazapyr (0.28 kg ai ha-1). Microbially-mediated degradation of triclopyr was estimated to occur 6.5 times more rapidly than imazapyr. Second, at three field sites in southeastern Colorado a study was conducted that used three dimensional artificial trees and repeated soil sampling to determine whether tamarisk tree canopies retained aerially-applied imazapyr, and if this retention affected soil residues and degradation. Tamarisk mortality was also quantified using repeated stand and individual tree measurements. The average tree canopy captured 75% of aerially-released imazapyr, resulting in significantly lower soil residues beneath the tree canopy. Although initial imazapyr soil residue levels outside the tree canopy were almost four time greater than those inside, soil degradation occurred more than twice as rapidly in outside soils and resulted in lower residue levels. Helicopter imazapyr applications resulted in 98% tamarisk mortality within two years, but the consistency of treatment effectiveness was reduced by non-linear stand boundaries and tall site obstructions. The same factors also increased variability in the actual quantity of herbicide applied to sites, increasing the probability of substantial non-target ecosystem impacts. Last, field plots were established at four sites in southeastern Colorado where tamarisk stands were treated with either an aerial imazapyr application or mechanical biomass removal followed by secondary herbicide (imazapyr and triclopyr) or biological control treatments. In the fourth chapter a study conducted at these sites is detailed in which the tamarisk control and cost effectiveness of the different treatments was quantified over a three year period. Whole plant extraction caused 20% higher tamarisk mortality than aerial imazapyr applications or biomass mulching. Of the secondary treatments evaluated, individual plant treatments (IPTs) of imazapyr caused higher mortality than either triclopyr IPTs or releases of tamarisk leaf beetles (Diorhabda carinulata). Aerial imazapyr applications alone were very cost effective, but when the subsequent removal of tree biomass was accounted for, this strategy was less cost effective than primary mechanical treatments followed by biological control releases. In the final chapter a second study carried out at the same sites is described in which the validity of ecologically based integrated pest management (EBIPM) models for tamarisk management are tested by measuring plant community and ecosystem responses to the different tamarisk control strategies. Plant community dynamics in response to the adjacent treatments were evaluated over three years. Helicopter imazapyr applications severely reduced plant community richness, diversity and abundance and appeared to facilitate invasion by resistant populations of Bassia scoparia. Plant communities did not show a strong response to integrated tamarisk management, which in itself was notable because mechanical tree removal caused soil disturbances that in theory would have promoted secondary invasions of existing ruderal species. Ultimately data suggested that plant community re-vegetation patterns following tamarisk removal were more strongly affected by drought and longer term shifts towards community assemblages dominated by upland plant species. These results provide evidence for the need to integrate state and transition models of ecosystem structure and function into the EBIPM framework in order for this tool to be valuable in managing tamarisk and other woody invaders.
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    Evolution at the edge: how hibernation, heat waves, and hybridization impact a range expansion
    (Colorado State University. Libraries, 2024) Clark, Eliza, author; Hufbauer, Ruth, advisor; Bitume, Ellyn, committee member; Norton, Andrew, committee member; Funk, Chris, committee member
    Evolutionary processes shape the diversity of life on earth. Over millennia, species diverge from one another, radiating out into the tree of life. The same processes of evolution are also acting in much shorter periods of time, selecting for traits, mixing genes across populations, and generating new mutations each generation. These rapid evolutionary processes interact with ecological processes, which are happening on similar time scales. Range expansions, or expansions of a population's geographic distribution, were once considered strictly ecological processes of populations interacting with other populations and the environment, unaffected by evolution. However, modern theory understands range expansions to be crucibles of rapid evolution. Rapid evolution shapes the process of range expansion itself, and is also integral to determining the outcomes of range expansion. During range expansions, ecological and evolutionary processes intertwine, combining to shape the dynamics of a range expansion, like where a population can establish, and how quickly the expansion moves. The study of evolution during range expansions has only just begun to make it out of the theory to be tested in wild populations in nature, so we don't yet know how common evolution during range expansion is, or how large its effects might be. Here, I explore how evolution impacts range expansions that are current and ongoing in natural systems in the wild. I focus on the tamarisk beetle (Diorhabda spp.), deliberately introduced in the United States about two decades ago for biological control of a widespread invasive weed. Through its role as a biological control agent, the tamarisk beetle has expanded its range hundreds of kilometers along rivers, colonizing new areas of the invasive weed in environments very different from its original release habitat. The range expansion of the tamarisk beetle provides a unique opportunity to study evolution during an ongoing natural range expansion across an environmental gradient. Through the following four chapters, I document evolution of dispersal ability and life history traits (Chapter 1), evolution of seasonal dormancy and genetic variation of that trait (Chapter 2), evolution of phenotypic plasticity (Chapter 3), and the impacts of hybridization (Chapter 4). Throughout, I discuss the implications for biological control and the tamarisk beetle specifically, and more generally how these results improve our understanding of how evolution is caused by, enables, and alters natural range expansions over short time periods, even in natural range expansions.
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    Management and epidemiology of Cytospora perennial canker, Cytospora plurivora, in western Colorado
    (Colorado State University. Libraries, 2021) Miller, Stephan T., author; Stewart, Jane, advisor; Ocheltree, Troy, committee member; Norton, Andrew, committee member; Minas, Ioannis, committee member; Uchanski, Mark, committee member
    Cytospora canker is a ubiquitous disease in deciduous fruit tree systems in western Colorado. The research conducted herein, explores the host-pathogen-environmental framework which has enabled Cytospora plurivora to thrive and become a threat to peach production in the region. My research also focuses on management strategies, both cultural and chemical, which can help mitigate pathogen infections. Chapter II, published in the Journal of Crop Protection, presents preventative control of C. plurivora through wound protection of pruned shoots. Several fungicides and sealants were evaluated either in vitro or in field trials, to explore antifungal activity. Fungicides which have been shown effective, were also evaluated for half maximum effective concentration rates (EC50) to better understand pathogen dose sensitivity. Chapter III explores the susceptibility of thirteen peach cultivars to C. plurivora infection under different abiotic conditions. Abiotic stressors such as water deficit and high-pH can be major limiting factors to tree fruit production and can increase tree susceptibility and pathogen severity. My research shows increased severity of C. plurivora infection and decreased plant water potentials when trees experienced increased soil pH and irrigation deficits. Chapter IV provides a detailed analysis of the epidemiology of C. plurivora in the field. This study estimates spore production rates and lesion infection rates over a 12-month period. Further, it evaluates possible dissemination mechanisms of C. plurivora, reporting detection of C. plurivora spores in aerial and on insect samples, although at low concentrations. The results presented herein help inform management strategies by elucidating field patterns of C. plurivora and identifying effective cultural and chemical control measures.
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    Plant-insect interactions and management options for Verbascum thapsus L. in Colorado
    (Colorado State University. Libraries, 2011) Wilbur, Hannah Darrough, author; Hufbauer, Ruth, advisor; Norton, Andrew, committee member; Meiman, Paul, committee member
    In the field of invasion biology, understanding the ecology of a species goes hand and hand with understanding management options. Common mullein (Verbascum thapsus L.) is a non-native plant introduced to North America from Europe in the 1700s. It has naturalized and spread throughout North America, with populations establishing after disturbance. Through a series of field experiments, I tested the effect of insect herbivory on the growth of V. thapsus in Colorado and also investigated management options for the reproductive stage of this biennial plant. Verbascum thapsus, while widespread, is rarely problematic in undisturbed habitats. This may be due to interactions with new community members, such as insect herbivores, that limit population size. Starting in 2009, I followed a population of V. thapsus plants in a disturbed landscape in Loveland, Colorado. A subset of the population was protected from herbivores with insecticides, reducing overall herbivore damage during the bolting year, for the first year, and throughout the lifecycle of the plants. Reducing herbivory in the first year increased the size that V. thapsus rosettes reached by the fall. Reducing herbivory during only the bolting year of the plant increased the height of the bolting plants. Reducing herbivory over both growing seasons increased plant height, the length of the reproductive stalk, and seed set. Plants with reduced herbivory also had higher rates of survival. Thus, insect herbivory reduced performance of V. thapsus in this study and may be one of the factors that prevents this introduced plant from dominating its recipient communities. Mechanical control of V. thapsus via digging or cutting stalks is considered the best option for management. Current practice encourages the collection of reproductive stalks from the field to limit the spread of seeds. While effective, this substantially increases the labor involved in management. I tested the viability of V. thapsus seeds collected at three sites in Colorado at various times during the growing season to see if the collection and disposal of reproductive stalks is necessary. I found that harvesting before seed capsules had turned brown reduced seed viability dramatically (mean early reproductive stage = 0.08%, 95% CI = 0.06%, 0.67%; mean mid reproductive stage = 1.52%, 95% CI = 0.49%, 3.11%). I suggest focusing mechanical control efforts during the early and mid-season if possible, as at those times plants can safely be left on site. When control efforts occur later in the season after seed capsules begin to turn brown, it is important that reproductive stalks be removed from the field.
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    Restoration impacts on understory plant species in a Colorado Front Range ponderosa pine and Douglas-fir forest
    (Colorado State University. Libraries, 2015) Ertl, Elizabeth, author; Smith, Frederick, advisor; Fornwalt, Paula, advisor; Norton, Andrew, committee member
    Land managers working in Colorado’s ponderosa pine – dominated forests are faced with many challenges concerning forest health and resiliency, such as higher tree densities, greater risk of high severity wildfire, and depauperate understory plant communities. Restoration treatments designed to move forests toward less degraded conditions that are more in line with those found prior to the settlement era are being increasingly implemented, and have been shown to decrease stand density, minimize ladder fuels, and decrease severe fire risk. However the impacts of such treatments on understory plants are less clear, especially over the long-term. To address this knowledge gap, I quantified changes in the richness, cover, and composition of understory grass, forb, and shrub species, and in the density and composition of trees regenerating in the understory, following restoration treatments at a 383-ha site located near Trumbull, Colorado. The site, which was treated in 2002, was chosen by the Upper South Platte Watershed Protection and Restoration Project (USPWPRP) as a priority area for restoration and was the first area on the Pike National Forest to receive such treatments. In 2004, 15 randomly located 1000-m² plots were established in treated stands, with five north-, five south-, and five east- or west-facing plots. Twenty randomly located plots were also established in nearby untreated stands, with slopes, aspects, and elevations comparable to treated plots. Data were collected in 2004, 2005, 2006 and 2014 (two, three, four, and 12 years post-treatment). Overstory stand structure post-treatment indicated that the goals of the restoration treatment were met, with basal areas reduced from 20.3 to 8.1 m² ha⁻¹ on north aspects, from 14.8 to 10.9 m² ha⁻¹ on east and west aspects, and from 12.7 to 5.1 m² ha⁻¹ on south aspects. Site factors such as treatment and aspect influenced tree seedling (<1.37 m tall) recruitment twelve years post-treatment. Tree regeneration in treated plots consisted of mostly ponderosa pine less than 45 cm tall, suggesting that they largely established post-treatment, while regeneration in untreated plots consisted of mostly Douglas-fir of varying sizes. Understory richness, cover, and composition also changed significantly during the 10-year period of observation. The most dramatic changes occurred on north-facing aspects, perhaps because these relatively mesic aspects are generally considered to be the most favorable for plant growth, and because the considerable reduction in basal area that they experienced ensured that ample resources were available for understory vegetation. Treated plots on north aspects saw increases in total, forb, graminoid, and native species richness in one or more years. Exotic species richness also increased on north aspects following treatment, although values were low. Plant communities further revealed changes in composition between treated and untreated plots on north and east/west aspects post-treatment. This study shows that restoration treatments can stimulate understory vegetation in the long-term, having few negative effects, which would be the increase in exotics and overly abundant tree regeneration on north aspects. Site factors can further influence understory response, with the most dramatic responses occurring on more mesic sites and/or where treatments are most aggressive.