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Browsing by Author "Dayan, Franck, committee member"

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    A new paradigm in rangeland restoration: using a pre-emergent herbicide to assist in native plant establishment and release
    (Colorado State University. Libraries, 2019) Clark, Shannon Lee, author; Nissen, Scott, advisor; Dayan, Franck, committee member; Meiman, Paul, committee member; Bjostad, Lou, committee member
    Invasive winter annual grasses (IWAG), especially downy brome (Bromus tectorum L.), are a significant threat to rangeland ecosystems in the western United States. Invasions in natural ecosystems can cause severe negative impacts by reducing native plant diversity and lowering community productivity, increasing fire frequency, and displacing native vegetation that is critical wildlife and pollinator habitat. Herbicides currently used for IWAG management can provide adequate short-term control; however, results can be inconsistent and injury to desirable species can occur. Indaziflam (Esplanade®, Bayer CropScience) is a new herbicide option for long-term IWAG control in natural areas and rangeland. As a cellulose biosynthesis inhibitor, indaziflam stops root growth in newly germinated seedlings by preventing cellulose formation. Field studies were conducted to assess native plant tolerance, revegetation and broadleaf weed seedling control with indaziflam applications. At two sites, indaziflam did not impact perennial grass cover, native species richness, or the community composition of forbs and shrubs at one and two years after treatment (YAT). However, the abundance of native forbs and shrubs was reduced by treatments containing picloram and aminocyclopyrachlor. In a separate field study at two sites, a glyphosate dose response showed approximately three times more glyphosate was needed for a 50% reduction (GR50) in feral rye biomass (GR50 = 126.0 g ae ha-1) compared to downy brome biomass (GR50 = 40.4 g ae ha-1). Indaziflam treatments still resulted in reduced downy brome and feral rye biomass compared to the non-treated check 3 YAT, while imazapic and glyphosate did not provide control beyond the first year. Establishment of cool-season grasses (C3), warm-season grasses (C4) and forb/shrubs through drill seeding was only successful across all three functional groups in treatments which included indaziflam. C3 grasses had greater establishment, with an average frequency of 61 ± 1.7% (mean ± SE) at Site 1 and 46 ± 2.6% SE at Site 2 at 3 YAT. In a third field study, treatments containing indaziflam had increased Dalmatian toadflax [Linaria dalmatica (L.) P. Mill], diffuse knapweed (Centaurea diffusa Lam.), and common mullein (Verbascum thapsus L.) control 2 YAT compared to treatments without indaziflam. A laboratory assay was conducted to evaluate the impact of litter on imazapic, rimsulfuron, and indaziflam availability. Downy brome litter at 2,600 kg ha-1 intercepted 84.3 ± 1.0% SE of the applied herbicide. Simulated rainfall at 0 days (d) after application was able to recover 100% of the intercepted rimsulfuron and imazapic, while recovery decreased to 65 ± 1.7% at 1 d and 7 d. Only 54 ± 1.9% of indaziflam could be recovered at 0 d, and recovery decreased to 33 ± 1.1% when simulated rain was applied at 1d or 7 d after application. The multi-year winter annual grass control provided by indaziflam could provide a new strategy for rangeland restoration, allowing enough time for the release of the remnant native plant community or the establishment of native species through revegetation. Indaziflam could potentially be incorporated into management systems to manage the weed seed bank and extend biennial and perennial weed control.
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    Candidate gene identification for glyphosate resistance and rapid cell death in Ambrosia trifida
    (Colorado State University. Libraries, 2024) Sparks, Crystal Devona, author; Gaines, Todd, advisor; Dayan, Franck, committee member; Beffa, Roland, committee member; Nishimura, Marc, committee member; Westra, Phil, committee member
    Glyphosate is one of the most widely used herbicides worldwide due to favorable chemical characteristics and availability of compatible transgenic biotechnology in crops. Resistance to glyphosate has evolved in many weed species capable of significant yield reduction in top production systems globally. One such species is Ambrosia trifida (giant ragweed), a monoecious broadleaf with imperfect flowers native to North America where it is highly competitive in corn, soybean, and cotton production. Some glyphosate resistant populations of A. trifida also display a rapid response with cell death in the mature leaves within 24-48 hours after treatment with glyphosate. Transcriptomic analysis revealed differential expression of multiple gene families associated with known glyphosate resistance mechanisms such as ATP-binding cassette (ABC) transporters and aldo-keto reductases. Gene ontology analysis showed an enrichment of many genes related to phytohormone response to biotic and abiotic stress in the differentially expressed genes. This could be related to a novel glyphosate resistance mechanism or a signaling cascade involved in the rapid cell death response. The A. trifida genome contains two loci of the glyphosate target site gene 5-enolpyruvylshikimate-3-phosphate-synthase (EPSPS), with a previously reported Pro106Ser mutation in EPSPS2. This locus showed up-regulation by three hours after treatment. Trait mapping revealed three genomic regions associated with glyphosate resistance and a single interval associated with the rapid response. Along with phenotypic segregation ratios, this indicates that resistance and rapid response traits are genetically independent and multiple genes likely contribute to resistance.
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    Endothall behavior in five aquatic weeds
    (Colorado State University. Libraries, 2018) Ortiz, Mirella F., author; Nissen, Scott, advisor; Gray, Cody, advisor; Dayan, Franck, committee member; Meiman, Paul, committee member
    Endothall is one of the original aquatic herbicides being primarily to control submersed plants since 1960. Endothall is considered a contact herbicide, in a chemical class of its own, it is a serine/threonine protein phosphatase inhibitor, which has broad-spectrum control and is effective in controlling both monocotyledons and dicotyledons. Eurasian watermilfoil (Myriophyllum spicatum L.) (EWM), hydrilla [Hydrilla verticillata (L.f.) Royle], curlyleaf pondweed (Potamogeton crispus L.) (CLP), and sago pondweed (Potamogeton pectinatus L.) (SPW) are submersed aquatic species considered troublesome throughout the United States, which can be controlled with endothall. These species can form extensive, undesirable surface canopies, which can negatively impact water flow, water quality, economic and ecological value of water bodies. Although endothall is considered a contact herbicide, many field observations suggest that it might have systemic activity. The goals of this research were to (1) determine maximum herbicide absorption and absorption rate, (2) evaluate herbicide translocation from shoots to roots in EWM, two hydrilla biotypes, CLP, and SPW, and (3) evaluate herbicide desorption in EWM and two hydrilla biotypes. Each weed species was clonally propagated from apical shoot cutting or turions/tubers when present. For herbicide absorption and translocation, plants of each species with developed roots and 15 cm of shoot growth were transferred to test tubes containing unwashed silica sand and sealed at the top with a low melting point eicosane wax to isolate the root system from the water column. Plants were exposed to the herbicide over 192 h. At predetermined time points three plants of each species were harvested, divided into shoot and root tissue, and oxidized. Herbicide desorption was evaluated over 96 h. Endothall absorption was linear in hydrilla, while in EWM, CLP and SPW it best fit an asymptotic rise function. Translocation to EWM, CLP, and SPW roots was limited, reaching a maximum translocation of 8%, 3% and 1% of total absorbed radioactivity, respectively. Monoecious and dioecious hydrilla showed a linear increase without reaching maximum absorption or translocation 192 HAT. Endothall translocation to monoecious and dioecious hydrilla roots was 18% and 16% of total absorbed radioactivity, respectively. Herbicide desorption was less than 30% for all the three species evaluated. These data provide strong evidence that endothall behaves as a systemic herbicide in these aquatic species.
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    Integrated weed management: insights from a weed resistance survey and non-chemical weed seed control in the Central Great Plains
    (Colorado State University. Libraries, 2023) Simões Araujo, André Lucas, author; Gaines, Todd, advisor; Dayan, Franck, committee member; Fonte, Steven, committee member
    With the impending release of genetically engineered sugar beet varieties with resistance to glyphosate, dicamba, and glufosinate, significant changes are expected in weed management practices, particularly with regards to in-crop weed control. Glyphosate is used during fallow and in-crop periods, while dicamba is commonly employed in fallow applications, specifically targeting glyphosate-resistant weed species. This study provides insights into the resistance status and frequency of resistance in problematic weed species to the three active ingredients in sugar beet systems across Colorado, Nebraska, and Wyoming. While numerous studies have highlighted the widespread prevalence of glyphosate-resistant kochia and Palmer amaranth across the United States, there is limited research focusing on these species within the context of a sugar beet system. Additionally, our findings reveal the first occurrence of glyphosate-resistant and dicamba-resistant Palmer amaranth populations in Colorado, and dicamba-resistant kochia populations within a sugar beet system. Furthermore, we report that all dicamba-resistant kochia populations tested in Colorado lack a known target-site resistance mechanism, suggesting the involvement of a novel resistance mechanism. Surveys assessing glufosinate resistance in the sugar beet system have not been conducted until now, and we provide valuable baseline information on the resistance frequency for this herbicide prior to an anticipated increase in glufosinate use. To address the widespread issue of herbicide resistance in various crop systems, it is crucial to adopt alternative strategies that mitigate resistance evolution and maintain the long-term effectiveness of available herbicides. One promising approach is chaff lining, a harvest weed seed control method that has gained popularity in Australia due to its effectiveness in reducing populations of herbicide-resistant ryegrass, especially when combined with other weed control methods. However, the efficacy of chaff lining may be influenced by several factors, including crop and environmental factors, as reported in Australian literature. Scientific studies assessing the applicability and effectiveness of chaff lining in the United States are limited. Recognizing this research gap and aiming to explore the potential of chaff lining, our study investigated its applicability in field settings within the Central Great Plains region of the United States. Through our research, we provide insights into chaff lining efficacy of and highlight the potential inconsistencies that may arise in suppressing weed seeds using this method. Notably, we demonstrate that various factors, including location and environmental conditions, may be involved and impact the effectiveness of chaff lining as a weed management strategy. These findings underscore the importance of integrating chaff lining with other weed management methods to achieve effective and sustainable weed control. Chaff lining, like any other weed management strategy, should not be solely relied upon. Instead, it should be implemented as part of an integrated approach to ensure its long-term effectiveness.
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    Investigating the impact of soil type, soil moisture, and soil surface residue cover on the efficacy of Diflufenican
    (Colorado State University. Libraries, 2021) Effertz, Andrew David, author; Westra, Phil, advisor; Dayan, Franck, committee member; Khosla, Raj, committee member
    Diflufenican is a pre-emergent and early post-emergent herbicide that inhibits phytoene desaturase, an essential enzyme in the biosynthesis of carotenoids. It has been used effectively in overseas markets such as Europe and Australia, but it never has been registered for use in the United States. With the herbicide resistance issues in the United States continuing to increase each year, the necessity for developing effective options to combat herbicide-resistant weeds magnifies. Recently, Bayer CropScience has begun research into developing diflufenican as a tool to manage herbicide-resistant weeds, namely Palmer amaranth (Amaranthus palmeri), in United States' corn and soybean systems. In this thesis, research is presented on the impacts soil type, soil moisture, and soil surface residue cover have on diflufenican efficacy. Broad-spectrum weed control with diflufenican was reduced when applied to soils with higher organic matter. This is a consequence of diflufenican having higher sorption coefficients in soils with higher organic matter. Control of Palmer amaranth with diflufenican was not impacted by soil moisture when applied to sandy soils. Under increasing levels of corn residue cover, control of redroot pigweed (Amaranthus retroflexus) was not impacted in the field or the greenhouse. In the greenhouse, control of Palmer amaranth with diflufenican was reduced when applied at a lower rate to the highest corn residue coverage in comparison to treatments with no residue cover. Indications are that when robust rates of diflufenican are applied to soil surfaces with high corn residue cover, necessary control can be expected of susceptible species.
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    Turning the tide on the sagebrush sea: long-term invasive annual grass control and rangeland restoration with indaziflam
    (Colorado State University. Libraries, 2022) Courkamp, Jacob S., author; Meiman, Paul, advisor; Paschke, Mark, advisor; Dayan, Franck, committee member; Ocheltree, Troy, committee member
    The invasive winter annual grass downy brome (Bromus tectorum L.) has invaded vast expanses of sagebrush-grassland in western North America, and the fine fuel associated with invasion increases the frequency of burning such that native plants struggle to persist. Recent research suggests that B. tectorum invasion may expand across an even larger portion of the US Intermountain West in the absence of effective and proactive management. The herbicide imazapic is widely used to manage B. tectorum, but control often declines after one year and reinvasion is typical. Several trials have demonstrated that the newer herbicide, indaziflam, can selectively control annual grasses for three or more years, and past studies indicate that B. tectorum seed banks are relatively short-lived in the field (<5 years). This suggests that consecutive years of control with indaziflam may eliminate B. tectorum seed banks and increase the duration of control, but it is unclear if this will require multiple applications. In addition, existing studies evaluating the effects of treatment on native rangeland plant communities are limited by small plot sizes, and the potential for impacts to native species seed banks is unclear. The studies detailed in Chapter 1 evaluated the effectiveness of imazapic and indaziflam for reducing B. tectorum density and cover over a period of approximately 5 years (57 months after treatment; MAT) at two invaded sagebrush-grassland sites near Pinedale, Wyoming. Treatments included three different indaziflam rates (51, 73, and 102 g ai ha-1) and imazapic (123 g ai ha-1) and were reapplied to half of each plot 45 MAT to evaluate the effects of two sequential applications. Perennial grass cover was also measured because positive perennial grass responses were observed after release from B. tectorum competition in other studies, and perennial grasses may provide resistance to B. tectorum reinvasion. Intermediate and high indaziflam rates (73 and 102 g ai ha-1) resulted in significant reductions in B. tectorum cover and density 45 MAT, and perennial grass cover responded positively to some treatments early in the study. Imazapic reduced B. tectorum initially, but did not have a significant effect on density or cover at either site beyond 21 MAT. Reapplication did not substantially improve B. tectorum control 57 MAT in plots treated with intermediate and high indaziflam rates, suggesting that long-term control with a single indaziflam treatment may be possible in some cases. The studies detailed in Chapter 2 assessed the potential for non-target impacts resulting from indaziflam treatment. Modified-Whittaker multiscale vegetation plots were used to compare diversity (species accumulation) in three treatment (73 g ai ha-1 indaziflam) and three control plots in a sagebrush-grassland plant community near Pinedale, Wyoming that is invaded by B. tectorum. In addition, a seed bank assay assessed the density and richness of shallow (0-1 cm depth) and deep (1-5 cm depth) germinable seed banks in these same treatment and control plots during a 20-week greenhouse study. Vegetation data and seed bank samples were collected during the third growing season after treatment. Species diversity did not differ between treatment and control plots, but this contrasted with the results of the seed bank assay, which showed that the shallow and deep seed banks had significantly fewer germinable seeds and native species richness was significantly lower in the shallow seed bank of treated areas. While significant non-target impacts to native annual seed banks were observed, all impacted species were detected in the aboveground plant community in treatment plots after treatment occurred, suggesting that reduced native annual abundance may be temporary. The results presented herein suggest that long-term B. tectorum control is possible with a single indaziflam application, and that when indaziflam treatment without associated revegetation is a suitable management intervention (i.e., invaded perennial communities), the benefits of protecting and promoting established perennial plants likely far outweigh the potential for non-target impacts to native species and native species seed banks. The ultimate goal of any weed management program is to reduce the impacts of invasive species to the greatest degree possible with the resources available, whether that is through eradication or conciliation and containment. Our results suggest that in the case of B. tectorum invading established sagebrush-grassland plant communities, indaziflam will have a significant role to play in helping managers achieve this objective.