Doctor of Philosophy / Department of Agronomy / Phillip W. Stahlman / Kochia [Kochia scoparia (L.) Schrad.] is a weed of great economic importance in the Great Plains and western United States and Canada. This weed is prone to evolving resistance to herbicides. Glyphosate is the most widely used herbicide in glyphosate-resistant crops and chemical fallow, and is extremely valuable to crop production. Anecdotal reports of kochia control failure with glyphosate in western Kansas arose during the mid-2000’s. The objectives of this research were to (1) confirm and characterize glyphosate resistance in kochia and measure its impact in western Kansas, (2) gather information on grower weed management practices before and since glyphosate resistance in kochia was confirmed, and (3) determine if altered absorption and translocation of glyphosate contributes to glyphosate resistance in kochia. Dose-response studies on greenhouse and outdoor grown plants, and shikimate accumulation assays confirmed one kochia population collected in 2007 and eight populations collected in 2010 tolerated three- to eleven-times more glyphosate compared to a known glyphosate-susceptible (GS) population. Furthermore, 40 kochia populations collected in 2012 showed varied response, from slightly elevated tolerance to resistance to 0.84 kg ae ha-1 glyphosate. Further analysis suggested these populations were at different stages of resistance evolution. An online survey revealed that growers increased glyphosate use rate and application frequency, but decreased exclusive use of glyphosate and diversified weed management practices during post- compared to pre-glyphosate confirmation periods. Most survey respondents reported presence of glyphosate-resistant (GR) kochia in at least in few fields, and half reported GR kochia in a majority of fields. Thus, together with the resistance confirmation studies, it is estimated that at least one-third of western Kansas kochia populations have evolved resistance to glyphosate. Nominal differences in absorption and translocation of 14C-glyphosate observed between GS and GR kochia populations likely do not contribute to differential response of these populations to glyphosate. Glyphosate-resistant kochia has become widespread in western Kansas in a short period of time. Use of weed resistance best management practices (BMP) is imperative to sustain the utility of glyphosate in the region.

Submitted by Rafael Santana (rafael.silvasantana@ufpe.br) on 2017-04-19T19:20:06Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação completa (FINAL).pdf: 5768431 bytes, checksum: 342e336553ff7aabb5d24cb8e9437063 (MD5) / Made available in DSpace on 2017-04-19T19:20:06Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação completa (FINAL).pdf: 5768431 bytes, checksum: 342e336553ff7aabb5d24cb8e9437063 (MD5) Previous issue date: 2016-11-17 / CAPES / Nas diversas etapas processuais da indústria de petróleo – extração, recuperação, armazenamento, transporte e refino, os materiais metálicos são expostos a fluidos corrosivos e solicitações mecânicas. Na etapa de armazenamento, em tanques de petróleo, é possível evidenciar a presença de duas fases, uma oleosa e outra aquosa, que de forma isolada ou associada podem influenciar no processo corrosivo. No transporte de petróleo, apresenta-se o efeito de corrosão-erosão (C-E) gerado pela presença de sais, gases e partículas sólidas que prejudicam a integridade dos equipamentos. Este trabalho teve como objetivo avaliar o comportamento do aço ASTM 572 Gr50 exposto a óleo cru, água do mar e misturas desses fluidos em diferentes proporções; sob condições estáticas simulando tanques de armazenamento e dinâmicas, visando simular transporte dos fluidos. Foram realizados testes de imersão do aço em diferentes fluidos corrosivos (óleo cru, água do mar, misturas de óleo e água do mar nas proporções de 20 e 50 % em volume de água do mar), ao longo de 60 dias em condições estáticas e dinâmicas. O processo corrosivo do material exposto aos diferentes meios foi analisado através de ensaios de perda de massa, análises eletroquímicas de potencial de circuito aberto (PCA), polarização potenciodinâmica e espectroscopia de impedância eletroquímica (EIE). A morfologia da corrosão foi avaliada através de microscopia eletrônica de microscopia óptica (MO) e varredura (MEV). Testes de microdureza Vickers e análises microestruturais foram realizados para analisar a ocorrência de mudanças nas propriedades mecânicas dos aços. Os resultados evidenciaram a influência do teor de água do mar no processo corrosivo, onde foram observados maiores valores de taxa de corrosão para os sistemas contendo maior proporção de água do mar. O mecanismo de C-E, observado nos sistemas dinâmicos mostrou ser mais agressivo que o processo de corrosão isoladamente (sistemas estáticos) o que foi observado por meio dos maiores valores de taxa de corrosão e também pelas morfologias de processo de deterioração da superfície vista por MO e MEV, onde cavidades de maior longitude e pites internos foram observados para os sistema sujeitos ao processo de C-E. Não foram observadas mudanças significativas na microestrutura do material após exposição às condições de fluido estudadas. Os resultados de MEV mostraram a presença de corrosão localizada em todos os sistemas, inclusive para os sistemas contendo apenas óleo cru, que apresentou baixa taxa de corrosão. Os ensaios eletroquímicos de PCA, polarização e EIE realizados com os eletrólitos advindos dos ensaios de imersão (fase aquosa) mostraram que o contato entre fluidos distintos (óleo e água do mar) sob condições de agitação, promove uma intensa troca composicional entre os meios, aumentando a agressividade e modificando a interação metal/meio. O eletrólito proveniente do sistema dinâmico contendo mistura de óleo e água do mar (50%) foi o que se mostrou mais agressivo, visto que no ensaio de polarização linear apresentou o maior valor de densidade de corrente anódica. / In the various procedural stages of the oil industry - extraction, recovery, storage, transportation and refining, metal materials are exposed to corrosive fluids and mechanical stresses. In oil tanks of the storage step, it is possible to demonstrate the presence of two phases, an oily and other aqueous, which isolated or associated, can influence the corrosion process. In the oil transport the corrosion-erosion (C-E) effect is present and it is generated by the presence of salts, gases and solid particles that can influence the integrity of the equipment. This study aimed to evaluate the behavior of ASTM 572 GR50 steel exposed to crude oil, sea water and mixtures of these fluids in different proportions; under static conditions simulating storage tanks and dynamic conditions, aiming to simulate fluid transport. Immersion tests were performed in different corrosive fluids (crude oil, seawater, oil mixtures and sea water in the proportions of 20 to 50% by seawater volume) for 60 days, under static conditions and dynamics. The corrosive process of material exposed to different media was analyzed by mass loss tests and electrochemical analysis of open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The morphology of corrosion was assessed by microscopy optical (OM) and scanning electron microscopy (SEM). Vickers microhardness testing and microstructure analysis were performed to examine the changes occurring in the mechanical properties of steels. The results showed the influence of the seawater content in the corrosion process, in which were observed higher corrosion rate values for the systems containing higher proportion of seawater. The C-E mechanism, seen in dynamical systems proved to be more aggressive than corrosion process isolated (static systems) which was observed by means of higher corrosion rate values and also by the morphologies of the surface deterioration process seen by OM and SEM, where the greater length and internal cavities pits were observed for the system subject to the C-E process; There were not significant changes in the microstructure of the material after exposure to conditions fluid studied. SEM results showed the presence of localized corrosion on all systems, including systems containing only crude oil, which showed low corrosion rate. Electrochemical test OCP, polarization and EIS conducted with electrolytes arising from immersion tests (aqueous phase), showed that the contact between different fluids (oil and seawater) under agitation conditions, promotes an intense exchange compositional between the fluids, increasing the aggressiveness and modifying the metal/media interaction. The electrolyte from the dynamic system containing a mixture of oil and seawater (50%) was the more aggressive electrolyte, as can be seen in the linear polarization that showed the highest value of anodic current density.