Italian ryegrass (Lolium perenne spp. multiflorum) is a common weed management problem in turfgrasses, cereals and non-crop areas in the United States. In Oregon, the number of populations with multiple-resistance continues to increase. To manage these resistant populations, the resistance patterns must be determined. In this study, five Italian ryegrass populations (CT, R1, R2, R3 and R4) from two cropping systems were studied for resistance patterns and mechanisms. The CT population is from a Christmas tree plantation and was resistant to at least six herbicides with four different mechanisms of action: atrazine, diuron (2.4-fold), glyphosate (7.4-fold), hexazinone (3.1-fold), imazapyr (1.8-fold), and sulfometuron. The resistant indices (RI) for sulfometuron and atrazine could not be calculated because 50% growth reduction for the CT population was not reached even with the highest rates applied, 17.6 kg ai ha⁻¹and 16 kg ai ha⁻¹, respectively, which are 16 times the recommended field application rates for this two herbicides. The CT population accumulated less shikimate than the S population. There were two mutations in the CT population, Trp591 to Leu in the ALS gene and Ser264 to Gly in the psbA gene, which explain the ALS and PII cross resistance, respectively. R1, R2, R3 and R4 were collected from annual cropping systems. All four populations were resistant to flufenacet. RIs for two populations, R2 and R4, were 8.4 and 5.9, respectively. R2 and R4 also were resistant to mesosulfuron-methyl, pinoxaden, quizalofop and clethodim. R4 was resistant to diuron, but R2 was not. An Asp-2078-Gly substitution in the ACCase gene was found in both R2 and R4 populations, while another Ile-2041-Asn substitution in the ACCase gene was found in the R4 population. These mutations explain the ACCase cross resistance in the R2 and R4 populations. The mechanisms for the glyphosate resistance in the CT population and the flufenacet resistance in R1, R2, R3 and R4 populations were not identified in this study. None of the five populations were resistant to the herbicide pyroxasulfone. / Graduation date: 2013

Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Ripgut brome (Bromus diandrus Roth.) is a weed that causes great problems in the most wheat and grain producing areas and also in livestock practices. Until recently (1995) there were no registered chemicals for the management of ripgut brome in wheat, in South Africa. After the registration of sulfosulfuron and iodosulfuron + mesosulfuron for the management of ripgut brome in wheat, these two herbicides were widely used and in the case of wheat monocultures, it was used repeatedly. During the last few years, reports of ripgut brome that were suspected to be resistant to these chemicals, increased. With the development of herbicide resistance it is of great importance to investigate methods to confirm resistance and also to control it. The goal of this study was firstly, to confirm resistance in ripgut brome and secondly to compare growth and development of resistant ripgut brome popualtions to that of susceptible ripgut brome populations. The dormancy of Bromus seed was also investigated as were effective methods to break seed dormancy. Lastly, quicker methods to confirm resistance were investigated. A short summary of the experiments follows. In the first experiment the degree of resistance of three different ripgut brome populations were determined, by using the pot spray method. One population each of B. pectinatus and B. rigidus were also included in the study. The seed of the Bromus populations were germinated after which it was planted in plastic pots and were placed in the glasshouse until the three to four leaf stage. Subsequently the plants were treated with the following four herbicides: sulfosulfuron, iodosulfuron + mesosulfuron, imazamox and haloxyfop-R methyl ester, at seven concentrations namely, the recommended dosage, one quarter, one half, twice, four times and eight times the recommended dosage. After six weeks the percentage survival and the dry mass of the plants were determined. Results showed that the three ripgut brome populations had different degrees of resistance to sulfosulfuron and iodosulfuron + mesosulfuron, varying from no resistance to moderate resistance to strong resistance. There was no resistance to imazamox and haloxyfop-R methyl ester. The B. rigidus population exhibited strong resistance or tolerance (natural resistance) to the two sulfonylureum herbicides. In the second experiment the seed of the same Bromus populations were germinated and planted in plastic pots that were filled with three litres of river sand to determine the growth, development and seed production of the plants. The number of leaves for each plant as well as the plant height were measured weekly, until the plants became reproductive. The two resistant populations grew much faster than the susceptible population and they also produced taller plants. The susceptible population produced more leaves, but seed production was delayed considerably. This probably relates more to the plant’s adaptation to their enviroment, than to adaptation due to resistance. The susceptible population was collected from a natural environment, while the others were collected from wheat fields. In the third experiment the seed dormancy of the Bromus populations was investigated. The effect of different treatments on the dormancy of the seed was also investigated. The treatments that were applied were gibberrellic acid, fumigation with ammonia gas and an ammonia treatment combined with a cold treatment. Seed dormancy in all populations was short-lived and the cold treatment was an effective way of stimulating fresh seed to germinate. The last experiment was performed to develop a quicker method for the evaluation of resistance in Bromus spp. In this experiment the petridish method was investigated. Only sulfosulfuron and iodosulfuron + mesosulfuron were used, because resistance to them was proven earlier. Different concentrations of the herbicides were applied to the dishes with the seed and were exposed to a cold treatment before being placed in a germination chamber. The seed in al the treatments germinated and it was decided to let the seed grow for two weeks in the petri dishes to observe whether the herbicides may have a detrimental effect on the growth of the small seedlings. After two weeks there were no differences between treatments and the experiment was terminated. The study showed that resistance is present in some of the Bromus populations and that there are biological differences between populations with different degrees of resistance. However, the fact that the susceptible population comes from a completely different environment than the other populations, complicate matters and further studies are required to obtain a clearer picture. / AFRIKAANSE OPSOMMING: Predikantsluis (Bromus diandrus Roth.) is ‘n onkruid wat in die meeste koringen garsproduserende gebiede, asook in sommige vee praktyke, probleme veroorsaak. Tot redelik onlangs (ongeveer 1995) was daar in Suid-Afrika geen middels geregistreer wat predikantsluis in koring kon beheer nie. Nadat sulfosulfuron en iodosulfuron + mesosulfuron vir predikantsluisbeheer in koring geregistreer is, is die twee middels op groot skaal, en in die geval van koring monokultuurstelsels, aanhoudend toegedien. Gedurende die afgelope paar jaar is berigte ontvang dat beheer van predikantsluis met die middels nie meer so doeltreffend is nie, moontlik as gevolg van onkruiddoderweerstand wat ontwikkel het. Met die ontstaan van onkruiddoderweerstand is dit belangrik om praktyke en maniere te vind om weerstand vinniger te bevestig en doeltreffend te bestuur. Die doel van hierdie studie was eerstens om weerstand in predikantsluis te bevestig en tweedens om die groei en ontwikkeling van plante afkomstig van vermoedelike weerstandbiedende predikantsluis populasies te vergelyk met plante uit ‘n vatbare populasie. Die saadproduksie en dormansie van die saad is ook ondersoek asook effektiewe metodes om dormansie te breek. Laastens is ondersoek ingestel na ‘n vinniger manier (petribakkie metode) om weerstand te bevestig. Hieronder volg ‘n oorsig oor die vier eksperimente wat uitgevoer is. In die eerste proef is die mate van weerstand van drie verskillende predikantsluis populasies bepaal, deur van die gewone potspuit metode gebruik te maak. Daar is ook een populasie elk van Bromus pectinatus en vermoedelik Bromus rigidus ingesluit in die studie. Die sade van die verskillende populasies is toegelaat om te ontkiem en daarna is dit in plastiese potjies geplant en in ‘n glashuis geplaas totdat die drie tot vier blaarstadium bereik is. Die plante is daarna gespuit met die volgende vier middels: haloksifop-R-metielester (Gallant Super), imasamoks (Cysure), iodosulfuron + mesosulfuron (Cossack) en sulfosulfuron (Monitor), teen sewe konsentrasies elk, nl. teen die aanbevole dosis, asook teen een kwart van, een helfte van, twee keer, vier keer en agt keer die aanbevole dosis. Na ses weke is die persentasie oorlewendes en die droëmassa van die plante bepaal. Resultate het getoon dat die drie predikantsluis populasies verskillende grade van weerstand teen die twee sulfonielureums (sulfosulfuron en iodosulfuron + mesosulfuron) toon, dit wil sê van geen tot matig tot sterk weerstandbiedend. Daar is egter geen weerstand teen haloksifop-R-metielester (Gallant Super) en imasamoks (Cysure) waargeneem nie. Die B. rigidus populasie het sterk weerstand of toleransie (natuurlike weerstand) teen die sulfonielureum middels getoon. In die tweede proef is saad van dieselfde Bromus populasies ontkiem en oorgeplant in plastiese potte gevul met 3 liter riviersand om die groei en ontwikkeling en saadproduksie van die plante te evalueer. Die aantal blare per plant en hoogte van die plante is weekliks bepaal totdat die plante reproduktief geraak het. Hierna is die metings gestaak om te voorkom dat die saadproduksie van die plante benadeel word. Die resultate het getoon dat die twee weerstandbiedende predikantsluis populasies vinniger groei as die vatbare populasie en ook langer plante vorm, terwyl die vatbare populasie vinniger en meer blare vorm, maar langer neem om saad te vorm. Hierdie waarnemings hou egter waarskynlik meer verband met die oorsprong van die populasies as met die graad van weerstandbiedendheid. Die vatbare populasie is versamel in natuurlike veld vêr van enige landerye terwyl die ander populasies almal uit graanlande afkomstig is. In die derde proef is saaddormansie van die Bromus populasies ondersoek. Daar is ook ondersoek ingestel na verskillende behandelings om dormansie te breek. Die behandelings wat toegepas is, is ‘n gibberelienesuur behandeling teen verskillende konsentrasies, beroking met ammoniak vir verskillende tye en ‘n ammoniak behandeling tesame met ‘n koue behandeling. Die resultate het getoon dat saaddormansie van die Bromus populasies van korte duur is, maar dat kouebehandeling effektief is om ontkieming van vars saad te stimuleer. Die vierde proef is uitgevoer om vas te stel of daar vinniger evaluasiemetodes is vir die evaluasie van weerstand in Bromus spp., deur van die petribakkie metode gebruik te maak. In hierdie proef is slegs die middels iodosulfuron + mesosulfuron (Cossack) en sulfosulfuron (Monitor) gebruik, omdat daar ‘n mate van weerstand teen hulle waargeneem is in die eerste proef. Die middels is teen verskillende konsentrasies in petribakkies gevoeg, tesame met die sade en toe blootgestel aan ‘n kouebehandeling voordat dit in ‘n ontkiemingskabinet geplaas is vir ontkieming. Die sade in al die behandelings het ontkiem en daar is besluit om die saailinge uit die ontkiemingskabinet te haal en vir twee weke te laat groei sodat daar bepaal kon word of die middels ‘n effek op die groei van die plantjies het. Na twee weke kon geen verskil in die groei van die plantjies waargeneem word nie en die proef is beëindig. Die studie het getoon dat daar wel weerstand in sommige van die Bromus populasies voorkom, en dat biologiese verskille voorkom tussen predikantsluis populasies met verskillende grade van weerstand. Die feit dat die vatbare populasie uit ‘n heeltemaal verskillende omgewing kom as die ander populasies, maak definitiewe afleidings moeilik. Daar sal opvolgstudies uitgevoer moet word om van die onduidelikhede op te klaar.

Doctor of Philosophy / Department of Agronomy / Mithila Jugulam / Palmer amaranth (Amaranthus palmeri) is one of the most aggressive, troublesome and damaging broadleaf weeds in many cropping systems including corn, soybean, cotton, and grain sorghum causing huge yield losses across the USA. As a result of extensive and intensive selection of pre- and -post emergence herbicides, Palmer amaranth has evolved resistance to multiple herbicide modes of action, microtubule-, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS)-, acetolactate synthase (ALS)-, photosystem II (PS II)-, hydroxyphenylpyruvate dioxygenase (HPPD)- and more recently to protoporphyrinogen oxidase (PPO)-inhibitors. A Palmer amaranth population from Kansas was found resistant to HPPD-, PS II-, and ALS-inhibitors. The overall objective of this research was to investigate the target-site and/or non-target-site resistance mechanisms in Palmer amaranth from KS (KSR) to mesotrione (HPPD-inhibitor), atrazine (PS II-inhibitor), and chlorsulfuron (ALS-inhibitor) relative to known susceptible Palmer amaranth from Mississippi (MSS) and KS (KSS). Whole plant dose-response assays showed high level of resistance in KSR to mesotrione, atrazine and chlorsulfuron. KSR was 10-18, 178-237 and >275 fold more resistant to mesotrione, atrazine, and chlorsulfuron, respectively, compared to MSS and KSS. Metabolism studies using [¹⁴C] labeled mesotrione and atrazine demonstrated non-target-site resistance to both herbicides, particularly, enhanced metabolism of [¹⁴C] mesotrione likely mediated by cytochrome P450 monooxygenases and rapid degradation of [¹⁴C] atrazine by glutathione S-transferases (GSTs). In addition, molecular and biochemical basis of mesotrione resistance was characterized by quantitative PCR (qPCR) and immunoblotting. These results showed 4-12 fold increased levels of the HPPD transcript and positively correlated with the increased HPPD protein. Sequencing of atrazine and chlorsulfuron target genes, psbA and ALS, respectively, showed interesting results. The most common mutation (serine264glycine) associated with atrazine resistance in weeds was not found in KSR. On the other hand, a well-known mutation (proline197serine) associated with chlorsulfuron resistance was found in 30% of KSR, suggesting ~70% of plants might have a non-target-site, possibly P450 mediated metabolism based resistance. Over all, KSR evolved both non-target-site and target-site based mechanisms to mesotrione and chlorsulfuron with only non-target-site based mechanism of resistance to atrazine leaving fewer options for weed control, especially in no-till crop production systems. Such multiple herbicide resistant Palmer amaranth populations are a serious threat to sustainable weed management because metabolism-based resistance may confer resistance to other herbicides and even those that are yet to be discovered. The findings of this research are novel and valuable to recommend appropriate weed management strategies in the region and should include diversified tactics to prevent evolution and spread of multiple herbicide resistance in Palmer amaranth.

Orientador: Sandra Helena Unêda Trevisoli / Coorientador: Antonio Orlando Di Mauro / Banca: Dilermando Perecin / Banca: João Antônio da Costa Andrade / Resumo: O melhoramento genético de plantas é considerado um processo complexo que gera múltiplas informações e, em muitos casos, de difícil compreensão. O objetivo deste trabalho foi selecionar progênies com caracteres superiores provenientes de cruzamentos bi-parentais de soja com fonte de resistência ao glifosato (RR), além de identificar cruzamentos e genitores mais eficientes, por meio de abordagens multivariadas. Além disso, objetivou-se ainda testar a eficiência dos métodos no processo seletivo para múltiplos caracteres de interesse. O experimento foi conduzido no delineamento experimental do tipo famílias com testemunhas intercalares, no ano agrícola 2010/2011 e 2011/2012 em Jaboticabal-SP sendo que, nas populações F3 foram selecionadas seis plantas fenotipicamente superiores e avaliadas para os caracteres: número de dias para o florescimento (NDF), número de dias para a maturidade (NDM), altura de inserção da primeira vagem (AIV), altura de planta na maturidade (APM), acamamento (Ac), valor agronômico (VA), número de ramos (NR), número de vagens por planta (NV), peso de cem sementes (PCS), número de sementes por planta (NS) e produção de grãos (PG). Os dados foram analisados utilizando-se o software Statistica 7.0. Os resultados obtidos possibilitaram a seleção de 77 progênies superiores através da Análise de Componentes Principais. A análise de Agrupamentos, pelo do método de K-means, agregou as progênies em seis grupos de acordo com os caracteres de maior importância em cada um e, através do método de Ward, identificou por meio do dendrograma a estrutura de similaridade e divergência entre as progênies selecionadas. Por fim, comparou-se os métodos de agrupamentos e verificou-se que houve concordância entre ambos quanto aos resultados obtidos / Abstract: The plant breeding is considered to be a complex process that generates multiple information sources and in many cases, difficult to understand. The aim of this work was to select progenies with superior characters from bi-parental crosses with soy source of resistance to glyphosate (RR), and identify intersections and parents more efficient through multivariate approaches. Furthermore, aimed to further test the efficiency of the methods in the selection process for multiple traits of interest. The experiment was conducted in the experimental design of type families to witness progress in the agricultural year 2010/2011 and 2011/2012 in Jaboticabal being that in F3 populations selected six plants were phenotypically superior and evaluated for the traits: number of days to flowering (NDF), number of days to maturity (NDM), height of the first pod (AIV), plant height at maturity (APM), lodging (Ac), agronomic value (VA), number of branches (NR), number of pods per plant (NV), one hundred seed weight (PCS), number of seeds per plant (NS) and grain yield (GY). Data were analyzed using the software Statistica 7.0. The results allowed the selection of 77 superior progenies by Principal Component Analysis. Cluster analysis by the K-means method, all progenies added into six groups according to the characters in each of utmost importance, and by the method of Ward identified by the dendrogram structure similarity and divergence between the progenies. Finally, we compared the clustering methods and found that there was an agreement between them as to the results obtained / Mestre

Orientador: Robinson Antonio Pitelli / Banca: Janete Apparecida Desidério Sena / Banca: Ricardo Victoria Filho / Resumo: Estudos laboratoriais foram realizados com o objetivo de estudar a caracterização genética de plantas de Euphorbia heterophylla, provenientes de áreas em que a resistência aos herbicidas inibidores da ALS (Acetolactase) estava caracterizada (Santo Ângelo, RS), em processo de desenvolvimento (Sonora, MS) e onde nunca havia sido aplicado herbicida com este mecanismo de ação (Jaboticabal, SP). Testes preliminares comprovaram elevada resistência para as plantas provenientes de Santo Ângelo, moderada resistência para plantas de Sonora e elevada susceptibilidade para plantas provenientes de Jaboticabal. A análise dos resultados através das isoenzimas revelou que existem pequenas diferenças entre as três populações estudadas. A análise do DNA dos indivíduos das diferentes populações através de marcadores moleculares RAPD, permitiu a construção do Dendrograma de Cluster, que mostra uma similaridade mínima de 88% e máxima de 99% entre os diferentes indivíduos, quer pertencentes à mesma população, quer pertencentes às diferentes populações. Tal análise permitiu inferir que, apesar dos indivíduos analisados mostrarem grande similaridade entre si, apresentam variabilidade genética entre os indivíduos e as populações estudadas, de acordo com a conclusão obtida quando da utilização das isoenzimas. Crescendo em condições similares, o biótipo da Santo Ângelo apresentou maior absorção de fósforo em comparação com os demais, e maior absorção de potássio em relação ao biótipo de Jaboticabal. Comparando a densidade estomática, houve diferença estatística entre os três biótipos, sendo maior para o biótipo mais tolerante ao herbicida e menor para o susceptível. Não foi possível estabelecer qualquer relação confiável entre as características morfológicas e de crescimento das plantas e a resistência ao imazethapyr. / Abstract: Laboratory studies were carried out aim to characterize genetically Euphorbia heterophylla plants were collect in three regions. At Santo Ângelo (RS) region this plant is highly resistant to ALS inhibitors herbicides, but moderately at Sonora (MS) and susceptible at Jaboticabal region. Greenhouse tests confirmed the plants reaction in face of imazethapyr spraying. The isoenzymes studies showed small differences between the three populations. The DNA analysis using molecular markers make feasible the Cluster dendrogram showing 88-99% of similarity comparing plants, regardless the plant origin. Besides the high similarity index between the plants, it was possible to determine lower genetic variation in Jaboticabal and Santo Ângelo populations using isoenzymes technique. The nitrogen and potassium contents in the plants shoot was higher in the Santo Ângelo byotipe, although there was no difference between the K contents when the Jaboticabal and Sonora byotipes were compared. The stomata and trichomes densities decreased in the same order of the plant tolerance to herbicide: Santo Ângelo > Sonora > Jaboticabal. None correlation between biotype resistance to imazethapyr and the plant morphology features for the three biotypes studied. The differences in the plant feature may be attributable to the adaptative mechanism of the plant to the regional characteristics they were collected. / Mestre

Orientador: Carlos Gilberto Raetano / Coorientador: Caio Antonio Carbonari / Banca: Edivaldo Domingues Velini / Banca: Marcelo da Costa Ferreira / Banca: Pedro Jacob Christoffoleti / Banca: Rubem Silvério de Oliveira Junior / Resumo: O conhecimento da resistência das plantas daninhas a herbicidas, em especial do capim-amargoso (Digitaria insularis L.) e a tecnologia de aplicação são aspectos fundamentais para recomendações de manejo da espécie daninha, e melhoria da performance do uso dos herbicidas. A pesquisa teve por objetivos estudar: (i) a sensibilidade de populações de capim-amargoso (D. insularis L.) aos herbicidas glyphosate e chethodim (ii); os processos pelos quais à tecnologia de aplicação, em particular as formulações de herbicida e os adjuvantes podem contribuir para a otimização do controle de D. insularis e, (iii) a influência destes fatores na absorção e metabolismo de D. insularis suscetível e resistente ao herbicida. Para isso, 62 populações de capim-amargoso foram coletadas nos estados do Paraná e São Paulo, sendo a maior parte delas provenientes de lavouras de soja transgênica, tolerante ao glyphosate. Ensaios screening foram conduzidos para determinar a sensibilidade das populações de capim-amargoso aos herbicidas por meio de estudos de curvas de frequência de respostas. Com esses dados foram selecionadas populações de capim-amargoso resistentes e suscetíveis aos herbicidas para determinação do nível de resistência por meio de estudos de curva dose-resposta, em diferentes estádios da planta. Posteriormente realizaram-se ensaios para comparar formulações de glyphosate e adjuvantes sobre variáveis de tecnologia de aplicação. Nestes ensaios, duas formulações de glyphosate (WG e SL) e cin... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The knowledge about weed resistance to herbicides, especially of sourgrass weed (Digitaria insularis L.) and application technology are fundamental aspects for weed management recommendations and performance improvement for herbicide use. Thus, the present research had as objectives to study: (i) the sensitivity of sourgrass populations (D. insularis L.) to glyphosate and chethodim herbicides; (ii) to study the processes by which the application technology and in particular glyphosate formulations and adjuvants may to contribute for control optimization of D. insularis; (iii) the influence of these factors on the absorption and metabolism of susceptible and resistant D. insularis to herbicide. In order, 62 sourgrass populations were collected in Paraná and São Paulo states, most them coming from of transgenic soybeans crops, tolerant to glyphosate. Screening tests were conducted to determine the sourgrass populations sensitivity to herbicides by means of frequency response curves studies. With this data, resistant and susceptible sourgrass populations to glyphosate were selected for resistance level determination through dose-response curve studies at different growth stages of plant. Subsequently, assays were performed to compare glyphosate formulations and adjuvants on application technology variables. In these assays, two glyphosate formulations (WG and SL) and five combinations (without adjuvant, mineral oil, methylated vegetable oil, ethoxylated alkyl ester, polyoxyethylene alkylphenol ether) plus a control treatment (no application) were compared by evaluating the droplets spectrum, deposition, surface tension, contact angle, absorption, shikimic acid and control.Studies have also been performed to compare the foliar anatomy of D. insularis and the effects of treatments on leaf surface and internal tissues by scanning electron microscopy and light microscopy. In the last step of study, two ... / Doutor

Due to the growing recognition of the social and ecological consequences of the global decline in pollinator species, the need for more effective policies for the conservation of pollinator habitat is now more than ever. These trends call for research that provides a deeper understanding of farmers' decision-making processes. In this regard, this study tested a modified version of the Theory of Planned Behavior as a conceptual model for explaining farmers' perceptions and behavior regarding the adoption of pollinator conservation programs and practices. Specifically, the study tested how farmers' perceived behavioral control, attitudes, subjective norms, concern about herbicide resistance issues, and sociodemographic variables influence their intentions and actual adoption of pollinator conservation programs and practices. Quantitative survey data were gathered from 41 principal farm operators in the state of Illinois through the administration of a web-based survey. The resulting data were first explored using descriptive statistics and correlation analysis, following which multiple regression analysis was used to test four hypotheses on the predictors of farmers' intentions to adopt, as well as their adoption of pollinator conservation practices and programs. The results from the regression analysis showed that farmers' attitudes and their subjective norms had statistically significant positive effects on their adoption of pollinator conservation practices on their farms, as well as their intentions to adopt those practices in the near future. Perceived behavioral control also had a statistically significant positive effect on farmers' adoption of federal pollinator conservation programs, as well as their intentions to enroll in these programs in the future. Overall, these findings call for comprehensive pollinator conservation policies that facilitate the provision of information and incentives for farmers to voluntarily adopt pollinator conservation practices on their farms, as well as the provision of appropriate resources and opportunities for farmers to enroll in pollinator conservation programs over which they have minimal control.

Graduation date: 2004

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 96-107).

Giant ragweed is an extremely competitive weed and poor control in soybean could lead to significant yield losses for Ontario producers. In 2008, a giant ragweed biotype near Windsor, ON was not controlled with glyphosate and further testing confirmed it as the first glyphosate-resistant (GR) weed in Canada. Giant ragweed seed was collected from 102 locations in Essex (70), Kent (21), Lambton (10) and Waterloo (1) counties to document the occurrence and distribution of GR giant ragweed in Ontario. Giant ragweed seedlings were sprayed with glyphosate at 1800 g a.e. ha-1, and evaluated 1, 7, 14 and 28 days after application (DAA). Results from the survey concluded that there are 47 additional locations in southwestern Ontario with GR giant ragweed. The majority of the sites were found in Essex county, but there was one location in both Chatham-Kent and Lambton counties. Field trials were established at six sites with GR giant ragweed during the 2010 and 2011 growing seasons. The objectives were to determine the level of giant ragweed control with increasing doses of glyphosate, and glyphosate tank mixes applied either preplant or postemergence. Control of giant ragweed increased with higher doses of glyphosate, but only at doses that are not economical for producers. The most effective glyphosate tank mixes were 2, 4-D ester, saflufenacil, linuron, and cloransulam-methyl providing up to 98, 94, 99 and 97% control 4 weeks after application (WAA), respectively. Glyphosate plus dicamba in dicamba-tolerant soybean provided up to 100% giant ragweed control, 4 WAA at the three confined field trial locations. / Monsanto Canada Inc.; Canadian Agricultural Adaptation Program; Grain Farmers of Ontario