Thesis (M.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 102-115). Also available in electronic format on the Internet.

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Experiments were conducted to evaluate efficacy of dicamba, glufosinate, and glyphosate on Palmer amaranth (Amaranthus palmeri S. Wats.). Residual control was evaluated after dicamba was applied alone and in combination with fomesafen, fluometuron, acetochlor, and prometryn. Postemergence efficacy of dicamba, glufosinate, and glyphosate on different size Palmer amaranth was also evaluated. In addition, combinations of dicamba, glufosinate, and glyphosate were evaluated for efficacy on Palmer amaranth as well as spray coverage and spray droplet size as affected by various spray nozzles. Lastly, tolerance to dicamba, glufosinate, and glyphosate of cotton cultivars containing Bollgard II® XtendFlex™ technology was examined. Dicamba exhibited preemergence activity on Palmer amaranth; however, activity was heavily dependent on rainfall. Postemergence applications of dicamba increased control of Palmer amaranth. Spray nozzle selection influenced spray coverage and droplet size. Tolerance of cultivars containing Bollgard II® XtendFlex™ technology was over 90% at the end of the year regardless of herbicide.

A study was conducted in Stoneville and Verona, MS, to evaluate control of failed stands of corn and soybean with different herbicide treatments and application timings, as well as control of failed stand of corn with soybean planted 1 and 7 DAT (days after treatment). Clethodim plus glyphosate proved most effective across all growth stages of corn with > 90% control 7, 14, and 21 DAT. Paraquat plus metribuzin provided the greatest control of a simulated failed corn stand 3 DAT compared with all other treatments. Pooled across all herbicide treatments, 49% control was achieved when replant occurred 7 DAT compared with 46% following replant 1 DAT. These studies demonstrated clethodim plus glyphosate was most effective in control of failed stands of corn as well as the benefits of not replanting immediately after herbicide treatment. Paraquat and paraquat plus metribuzin both provided > 90% control 3, 7, and 14 DAT.

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.

Made available in DSpace on 2014-06-11T19:22:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-08-21Bitstream added on 2014-06-13T18:48:44Z : No. of bitstreams: 1 godoy_mc_me_botfca.pdf: 760148 bytes, checksum: 5c2947cf4ff7e088c2dab98861eb1ab9 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / O fósforo é um elemento essencial para todos os organismos vivos como um componente estrutural dos ácidos nucléicos e fosfolipídios. Além disso, nas plantas o fósforo é de fundamental importância na fotossíntese. A mobilização do fosfato dentro da planta é um processo complexo que requer numerosos transportadores para a sua absorção e translocação. A deficiência de fósforo é um dos maiores estresses abióticos que afetam o crescimento das plantas, especialmente em solos tropicais. O Glyphosate (N-phosphonomethyl-glycine) é o único composto comercialmente disponível que atua na enzima EPSPS. Tal composto é um herbicida sistêmico, não-seletivo, de amplo uso, com translocação via simplasto. Denis e Delrot (1993) e Morin et al. (1997) demonstraram que proteínas transportadoras de grupos fosfatos, que estão presentes na membrana plasmática de Vicia faba e Catharanthus roseus, facilitaram a absorção de glyphosate. O objetivo deste trabalho foi avaliar o efeito de subdoses de glyphosate na absorção e translocação de fósforo nas cultivares de soja, BRS 232 e BRS 243 RR. O experimento foi conduzido em casa de vegetação, e as cultivares semeadas em vasos de 8 litros. Os tratamentos foram constituídos de adubação de plantio com duas doses de 2 fósforo (50 e 150 mg L-1) e dez doses de glyphosate (0, 1,8, 3,6, 7,2, 18, 36, 72, 180, 360 e 720 g i.a. ha-1). As plantas receberam a aplicação do herbicida quando apresentaram o terceiro trifólio expandido. Após a aplicação, estas foram conduzidas por trinta dias, e então colhidas e analisadas. As análises realizadas foram: matéria seca de folha, caule e raiz, teores de fósforo e conteúdo total de fósforo das mesmas. Para a soja convencional BRS 232 (não resistente ao glyphosate) houve estímulos ao crescimento das plantas para doses entre 3,6 e 36g e.a./ha. Para esta variedade... / Phosphorous is an essential element for all living organisms acting as a structural component of nucleic acids as well as phospholipids. Besides it is of fundamental importance in photosynthesis. The maintenance of phosphate within the plant is a complex process which requires numerous transporters for its absorption and translocation. Phosphorous deficiency is one of the major abiotic stresses affecting plant growth in tropical regions. Glyphosate (N-phosphonomethyl-glycine) is the only compound commercially available which acts upon EPSPS enzyme. It is a systemic, non-selective, broad-spectrum herbicide with translocation via symplast. Transporter proteins of phosphate groups which are present at plasma membrane facilitated glyphosate absorption. This paper aims at evaluating the effects of low doses of glyphosate in phosphorous absorption and translocation in soybean crops BRS 232 e BRS 243 RR. The experiment was carried out under greenhouse conditions and plants were cultivated in 8-liter pots. The treatments were disposed in a factorial scheme combining two doses of phosphorus (50 and 150 mg L-1) and ten doses of glyphosate (0; 1.8; 3.6; 7.2; 18; 36; 72; 180; 360 and 20 g i.a. ha-1). Glyphosate was applied to plants at the third expanded three-leaf. After thirty days plants were harvested and dry matter, stems, root, phosphorous levels and the total content of phosphorous were measured. Glyphosate aplied at rates ranging from 3,6 to 36 g a.e/ha stimulated the growth and phosphorus absorption by the conventional soybean variety BRS 232 (not resistant to glyphosate) and the stronger effects were observed for the lower level of phosphorus in the soil. In this condition, glyphosate applied at 18 g a.e./ha increased in 2,61 times the phosphorus concentration in leaves. Glyphosate didn t stimulate the growth 4 but increased the absorption of phosphorus... (Complete abstract click electronic access below)

Pre-harvest glyphosate is often applied to cereal crops, such as oats, to insure uniform grain ripeness at harvest. However, some buyers have claimed that this practice negatively affects oat end product quality. Oat samples were grown in two different growing locations for each of two crop years, and glyphosate was applied at the soft dough, physiological maturity, or not applied. Groat quality and starch quality parameters were analyzed, and rolled oats were produced to analyze end product quality. Groat hardness, groat percentage, and percent plump groats were significantly (P<0.05) affected by glyphosate application at the soft dough stage. However, application of glyphosate at physiological maturity did not appear to detrimentally affect groat starch or end product quality. Therefore, pre-harvest glyphosate application isappropriate for oats providing it occurs after plants reach physiological maturity.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

As the acreage of glyphosate-resistant (GR) cropping systems increases, so does the occurrence of herbicide-resistant weeds in the landscape. Biotypes of GR Conyza canadensis were first observed in Delaware, USA, in 2000. Since the first documentation of GR C. canadensis, there have been many instances of independent evolution of GR C. canadensis biotypes. The ecology of GR C. canadensis and any potential fitness consequences of GR trait are still unknown. If there is no fitness cost or a fitness increase associated with the GR trait, GR C. canadensis may increase in prevalence in the landscape even in the absence of glyphosate application. With the consideration that fitness is a difficult parameter to measure, other variables may be used as surrogate measures of fitness, such as reproduction, growth rate, phenology, survivorship, etc. This research seeks to determine if differences exist in surrogate measures of fitness - patterns of growth, reproductive allocation, and competitive ability - and if so, how differences may apply to future population changes, for glyphosate-resistant and -susceptible C. canadensis. The first two experiments presented test two populations of GR plants and two populations of GS plants, first in a greenhouse study of shading effects and intraspecific competition (Chapter 2), and second in a field survivorship study within two habitat types (Chapter 3). The third study tests for the prevalence of GR C. canadensis in field margins of GR cropping systems and seeks correlations in the occurrence of resistance and factors related to geography and field management (Chapter 4). The greenhouse study (Experiment 1, Chapter 2) of surrogate measures of fitness (growth, reproduction) in response to intraspecific competitive ability and shading showed that, while all populations had the same response to shading, there were differences between populations in growth and reproduction. While all measures were greater for individual plants with no competition, plants competing with individuals from one of the GR populations (R2) often had measures that were not different from the no competition treatment or were greater than the other competition treatments (R1, S1, and S2). The field survivorship study compared growth, survival, and reproduction of the previously studied four populations of C. canadensis is two habitats, a old-field in the second year of succession (ruderal) and a soybean field planted with a GR cultivar (agrestal) (Experiment 2, Chapter 3). One of the GR populations (R1) had the highest survivorship of the four populations in the ruderal habitat, while there was no difference in survivorship of the four populations in the agrestal habitat. While there was little difference in growth between ruderal populations, in the agrestal habitat, one GS population (S1) consistently had the smallest diameter, height, and leaf number. One of the agrestal GR populations (R2) was larger than the others, though not always different from R1. R1 was the first population to senesce regardless of habitat. Both agrestal GR populations produced more capitulae (seed heads) than the GS populations, and R1 also showed high reproductive success in the ruderal habitat. A test for the occurrence of GR C. canadensis in field margins of GR cropping systems (Experiment 3, Chapter 4) utilized a discriminating spray test on seed collected from the margins of 17 agricultural fields in 2008 from Illinois, Indiana, and Nebraska. The relationships between the occurrence of GR C. canadensis in 2008 field margins and 1) geography, 2) field management practices, 3) herbicide diversity, 4) weed community diversity, 5) field-interior changes in C. canadensis populations (λ), and 6) knowledge or suspicion of difficult-to-control C. canadensis populations, were tested. Geography was the clearest relationship in these data and was related to geography, with greater, more variable occurrence of GR C. canadensis in 2008 field margins in the southern and eastern sites than the northern and western sites. Management practices in field-interiors from year 2006 to 2008 had little relationship to occurrence of GR C. canadensis in 2008 field margins, except for the increased use of tillage and the increased use of non-glyphosate herbicide modes of action in 2007 field-interiors of fields with the highest occurrence of GR C. canadensis in the field margins in 2008. Additionally, the greatest occurrence of GR C. canadensis was associated with high diversity in the weed community in 2007 field-interiors. These results suggest that GR C. canadensis persisted in 2008 field margins even though there was a perceivable increase in management intensity the previous year. In conclusion, although there were no differences in fitness clearly associated with the GR trait in C. canadensis, GR populations may possess equal or greater vigor in growth, reproduction, and competition as GS populations. Based on these results, GR C. canadensis may persist in agricultural field-margins or other ruderal, unmanaged habitats and act as a seed source for future field-interior infestations. Depending on the characteristics of the GR biotype, GR C. canadensis may increase in frequency in the landscape.