Crop production provides the food and fiber necessary to sustain the world\'s population. Effective weed management is critical to maintaining agricultural productivity. Intensive or continuous use of herbicides that act on the same target site, or are detoxified by similar processes within crops and target weeds frequently results in the development of weeds resistant to a specific herbicide or class of herbicides. Weed resistance due to the extensive use of glyphosate in glyphosate tolerant crop systems has become one of the most serious issues facing agriculture today. Thus PPO-inhibitor herbicides are an alternative mechanism of action that have the potential to mitigate the development of resistant weeds in weed control systems where crop tolerance is sufficient to allow them to be effectively deployed. While there are few reports of weed resistance to PPO-inhibitor herbicides it has not developed to the extent that it is a commercial problem for growers. When used at recommended doses, they typically have favorable regulatory profiles. Furthermore, most of them are highly compatible with no-tillage agriculture. However, PPO-inhibitor herbicides are typically more active on dicots than monocots. This thesis provides information with regards to effectiveness of certain binary mixtures of PPO herbicides as weed control agents. The mixtures showed synergistic effects and could control monocots as Echinochloa crus-galli and volunteer corn besides control the dicots species. Regarding the compounds studied, trifludimoxazin and flumioxazin required less amount of compound to inhibit 50% of PPO2 activity in all plants species tested, while sulfentrazone and saflufenacil, one of the best mixtures in the field, showed that needed bigger concentrations to inhibit 50% of the PPO2 compared to other compounds evaluated.The absorption and translocation of these compounds individually or in mixtures, showed that as single compounds, the absorption was slower in maize than E. crus-galli and there was no difference among the herbicides except trifludimoxazin, that was significantly lower than the other compounds. Saflufenacil was the herbicide that showed the best translocation out of treated leaf point, while trifludimoxazin has not shown any translocation out of leaf treated. In mixtures, the compounds showed some differences in absorption and translocation, which it was variable according to species studied. Some traits of PPO-tolerant were also evaluated in Arabidopsis thaliana which indicates potential traits to be developed in crops of interest. / Agricultura é responsável por fornecer alimento e fibras necessárias para sustentar a população mundial. Controle de plantas daninhas é essencial para obter uma boa produtividade. O uso intensivo de herbicidas que age no mesmo sitio de ação ou são detoxificados por processos similares pelas plantas daninhas resulta geralmente no desenvolvimento de plantas daninhas resistentes a um herbicida específico ou à uma classe de herbicidas. A resistência de plantas daninhas devido ao uso de culturas tolerantes à glifosato tem se tornado um dos mais sérios problemas na agricultura. Inibidores da PPO pode ser uma ferramenta para mitigar o desenvolvimento de plantas daninhas resistentes. Há poucos relatos de plantas daninhas resistentes a este mecanismo de ação. Quando aplicados na dose recomendada, apresentam perfil toxicológico favorável e além disso, a maioria dos herbicidas deste grupo são compatíveis com plantio direto. No entanto, são mais eficientes em dicotiledôneas do que em monocotiledôneas. O objetivo dessa tese foi fornecer informações em relação a associação binária de herbicidas inibidores da PPO no controle de plantas daninhas. As associações mostraram efeito sinérgico no controle de Echinochloa crus-galli e milho voluntário, além do controle de dicotiledôneas. Avaliou-se também a atividade de alguns inibidores da PPO na inibição de 50% da enzima PPO2 e observou-se que para inibir 50% da PPO2 necessitou de menor quantidade de trifludimoxazin e flumioxazin em todas as plantas testadas, enquanto que sulfentrazone e saflufenacil, que associados apresentaram a melhor eficácia nos ensaios de campo, mostraram que precisar de maiores concentrações para inibir a PPO2 comparada aos outros produtos. A absorção e translocação destes produtos, isolados ou em mistura, mostraram que a absorção foi mais lenta em milho do que em E. crus-galli. Os herbicidas apresentaram comportamentos similares, sendo absorvidos quase 95% até 72 horas após aplicação, com exceção do trifludimoxazin, que foi significativamente mais lento que os outros. Saflufenacil foi o herbicida que apresentou melhor translocação na folha aplicada, enquanto trifludimoxazin não apresentou nenhuma translocação. Em relação às associações, os produtos mostraram diferenças na absorção e translocação, variando conforme as plantas daninhas estudadas. Alguns eventos tolerantes a inibidores da PPO foram avaliados em Arabidopsis thaliana e indicaram como potenciais eventos para ser desenvolvidos nas culturas de interesse.

Crop production provides the food and fiber necessary to sustain the world\'s population. Effective weed management is critical to maintaining agricultural productivity. Intensive or continuous use of herbicides that act on the same target site, or are detoxified by similar processes within crops and target weeds frequently results in the development of weeds resistant to a specific herbicide or class of herbicides. Weed resistance due to the extensive use of glyphosate in glyphosate tolerant crop systems has become one of the most serious issues facing agriculture today. Thus PPO-inhibitor herbicides are an alternative mechanism of action that have the potential to mitigate the development of resistant weeds in weed control systems where crop tolerance is sufficient to allow them to be effectively deployed. While there are few reports of weed resistance to PPO-inhibitor herbicides it has not developed to the extent that it is a commercial problem for growers. When used at recommended doses, they typically have favorable regulatory profiles. Furthermore, most of them are highly compatible with no-tillage agriculture. However, PPO-inhibitor herbicides are typically more active on dicots than monocots. This thesis provides information with regards to effectiveness of certain binary mixtures of PPO herbicides as weed control agents. The mixtures showed synergistic effects and could control monocots as Echinochloa crus-galli and volunteer corn besides control the dicots species. Regarding the compounds studied, trifludimoxazin and flumioxazin required less amount of compound to inhibit 50% of PPO2 activity in all plants species tested, while sulfentrazone and saflufenacil, one of the best mixtures in the field, showed that needed bigger concentrations to inhibit 50% of the PPO2 compared to other compounds evaluated.The absorption and translocation of these compounds individually or in mixtures, showed that as single compounds, the absorption was slower in maize than E. crus-galli and there was no difference among the herbicides except trifludimoxazin, that was significantly lower than the other compounds. Saflufenacil was the herbicide that showed the best translocation out of treated leaf point, while trifludimoxazin has not shown any translocation out of leaf treated. In mixtures, the compounds showed some differences in absorption and translocation, which it was variable according to species studied. Some traits of PPO-tolerant were also evaluated in Arabidopsis thaliana which indicates potential traits to be developed in crops of interest. / Agricultura é responsável por fornecer alimento e fibras necessárias para sustentar a população mundial. Controle de plantas daninhas é essencial para obter uma boa produtividade. O uso intensivo de herbicidas que age no mesmo sitio de ação ou são detoxificados por processos similares pelas plantas daninhas resulta geralmente no desenvolvimento de plantas daninhas resistentes a um herbicida específico ou à uma classe de herbicidas. A resistência de plantas daninhas devido ao uso de culturas tolerantes à glifosato tem se tornado um dos mais sérios problemas na agricultura. Inibidores da PPO pode ser uma ferramenta para mitigar o desenvolvimento de plantas daninhas resistentes. Há poucos relatos de plantas daninhas resistentes a este mecanismo de ação. Quando aplicados na dose recomendada, apresentam perfil toxicológico favorável e além disso, a maioria dos herbicidas deste grupo são compatíveis com plantio direto. No entanto, são mais eficientes em dicotiledôneas do que em monocotiledôneas. O objetivo dessa tese foi fornecer informações em relação a associação binária de herbicidas inibidores da PPO no controle de plantas daninhas. As associações mostraram efeito sinérgico no controle de Echinochloa crus-galli e milho voluntário, além do controle de dicotiledôneas. Avaliou-se também a atividade de alguns inibidores da PPO na inibição de 50% da enzima PPO2 e observou-se que para inibir 50% da PPO2 necessitou de menor quantidade de trifludimoxazin e flumioxazin em todas as plantas testadas, enquanto que sulfentrazone e saflufenacil, que associados apresentaram a melhor eficácia nos ensaios de campo, mostraram que precisar de maiores concentrações para inibir a PPO2 comparada aos outros produtos. A absorção e translocação destes produtos, isolados ou em mistura, mostraram que a absorção foi mais lenta em milho do que em E. crus-galli. Os herbicidas apresentaram comportamentos similares, sendo absorvidos quase 95% até 72 horas após aplicação, com exceção do trifludimoxazin, que foi significativamente mais lento que os outros. Saflufenacil foi o herbicida que apresentou melhor translocação na folha aplicada, enquanto trifludimoxazin não apresentou nenhuma translocação. Em relação às associações, os produtos mostraram diferenças na absorção e translocação, variando conforme as plantas daninhas estudadas. Alguns eventos tolerantes a inibidores da PPO foram avaliados em Arabidopsis thaliana e indicaram como potenciais eventos para ser desenvolvidos nas culturas de interesse.

À l’origine, les Terres Rares (TR) sont utilisées pour tracer les processus géochimiquesnaturels. Depuis quelques années, elles sont de plus en plus utilisées par l'industrie, la médecine etl'agriculture. Cette utilisation croissante entraîne de nouveaux risques et nous amène à considérerles TR comme des polluants émergents. Dans ce contexte, ce travail de thèse propose une étude dela mobilité et de la répartition des TR dans le système sol-plante, ainsi que leur effet sur lavégétation. La première partie de ce document présente l'approche de terrain employée, soit le choixde sites non pollués avec des contextes géologiques différents (calcaire, granitique et carbonatique),afin de comparer les transferts et la répartition des TR en milieu naturel. La deuxième partie de cemanuscrit est orientée vers une approche en milieu contrôlé, permettant d'étudier l'effet des TR surla germination et la croissance des plantes.Les résultats indiquent que les concentrations en TR ne reflètent pas directement lesconcentrations de la roche, dans la mesure où elles apparaissent dépendantes des processuspédologiques et des teneurs en phases minérales riches en TR. Les sols présentent tous unenrichissement en TR lourdes lié aux complexes formés à partir des TR lourdes et des oxydes defer. La végétation, quant à elle, présente systématiquement un enrichissement en TR légères,résultant en partie de cette liaison entre TR lourdes et oxydes de fer. Les TR montrent un fort lienavec le fer dans le continuum sol- végétation, indiquant que les processus pédologiques etphysiologiques à l’origine de l'absorption des TR, sont étroitement liés à ceux du Fe. Le transfertdes TR dans la plante entraîne leur accumulation dans le système racinaire, où elles seront bloquéespar la bande de Caspary. Ce phénomène limite alors le transfert vers les organes aériens via le fluxnutritif. Les concentrations en macro-éléments de ce flux nutritif pourraient être influencées par laprésence de fortes concentrations de TR dans les racines. L'application de fortes concentrations enTR influencent également la germination et la croissance racinaire des végétaux. / Background and aims Rare Earth Elements (REE) are widely used to trace naturalgeochemical processes. They are also increasingly used by man (electronics industry, medicine,agriculture) and therefore considered as emerging pollutants. The present documents studies REEmobility in non-polluted natural soil-plant systems in order to characterize their environmentalavailability for future anthropogenic pollution. The first part of this thesis is based on a fieldapproach in non-polluted natural sites with contrasting geological environments (limestone, granite,and carbonatite) and highly variable REE contents. The second part consist in an experimentalapproach under controlled conditions, in order to study REE’s effect on vegetation.REE concentrations in soils do not directly reflect bedrock concentrations, but dependlargely on pedogenetic processes and on the mineralogy of bedrock and soil. The soils of all sitesare with respect to bedrock enriched in heavy REE. The REE uptake by plants is not primarilycontrolled by the plant itself, but depends on the concentration and the speciation in the soil and theadsorbed soil water pool. REE uptake by plant roots are linked with those of Fe. Roots absorbpreferentially the light REE. Before translocation, REE are retained by the Casparian strip leadingto much lower concentrations in the aerial parts. The transport of the REE within the xylem isassociated with the general nutrient flux. This nutrient flux could be affected by the addition of highREE concentrations. Thus, the presence of high REE concentrations in the environment has anegative effect on the germination and the roots growth.

Sustainable weed control in managed agricultural systems requires the judicious use of multiple weed control tactics and prevents over-reliance on any one tactic. In this context, sustainable weed management plays a critical role in the mitigation of one of agriculture's most pressing problems- herbicide resistance. Research conducted in Virginia sought to explore the effects of integrating multiple weed management tactics in corn and cool-season turfgrass. Additionally, research was conducted to confirm nicosulfuron and glyphosate herbicide resistance in Virginia johnsongrass and elucidate the molecular mechanisms conferring those resistances. Rye and hairy vetch cover crop residues, combined with reduced rates of preemergence herbicide and postemergence glyphosate applications, were shown to provide sufficient weed control and corn yield. Cover crop type or residue level did not augment weed control in corn production systems, but the use of glyphosate was essential for late-season weed control. Rye and vetch biculture as a cover crop increased corn yield compared to rye cover crop alone. In cool-season turfgrass, the addition of reduced preemergence herbicide rates to corn gluten meal, an organic herbicide product, reduced crabgrass 25%. Moreover, control was dependent on herbicide choice. Herbicides applied at half of recommended labeled rates or less did not control crabgrass at a commercially-acceptable level, regardless of corn gluten meal addition. In field experiments, Virginia johnsongrass expressed resistance to nicosulfuron and glyphosate. Glyphosate at 0.88 kg ae ha-1 controlled johnsongrass 65%. Nicosulfuron at 0.14 kg ai ha-1 controlled the same population 10%. Greenhouse experiments confirmed differential sensitivity of putative herbicide-resistant johnsongrass seedlings to nicosulfuron and glyphosate when compared to a susceptible population. Herbicide resistance was not conferred via target-site mutation. Five ALS-gene site mutations were confirmed absent in Virginia johnsongrass, while three others were located in coding regions that could not be elucidated in johnsongrass. Further investigations showed glyphosate resistance was not conferred via reduction in herbicide absorption or translocation. The susceptible johnsongrass caused an increase in a polar metabolite at Rf = 0.17 with concomitant reduction in glyphosate over time. Although the mechanism is not clear, these data suggests that glyphosate resistance in johnsongrass may be associated with differential metabolism. / Ph. D.

Zoysiagrass (Zoysia spp.) is utilized as a warm-season turfgrass because of its density, visual quality, stress tolerance, and reduced input requirements. Turf managers often exploit winter dormancy in warm-season turfgrass to apply nonselective herbicides such as glyphosate and glufosinate to control winter annual weeds. Although this weed control strategy is common in bermudagrass (Cynodon spp.), it has been less adopted in zoysiagrass due to unexplainable turf injury. Many university extension publications recommend against applying nonselective herbicides to dormant zoysiagrass despite promotional language found in a few peer-reviewed publications and product labels. Previous researchers have used vague terminology such as "applied to dormant zoysiagrass" or "applied prior to zoysiagrass green-up" to describe herbicide application timings. These ambiguous terms have led to confusion since zoysiagrass typically has subcanopy green leaves and stems throughout the winter dormancy period. No research has sought to explain why some turfgrass managers are observing zoysiagrass injury when the literature only offers evidence that these herbicides do not injure dormant zoysiagrass. We sought to explore various herbicides, prevailing temperatures surrounding application, heat unit based application timings, and spray penetration into zoysiagrass canopies as possible contributors to zoysiagrass injury. The results indicated that a wide range of herbicides may be safely used in dormant zoysiagrass. However, as zoysiagrass begins to produce more green leaves, herbicides such as metsulfuron, glyphosate, glufosinate, flumioxazin, and diquat become too injurious. Glufosinate was consistently more injurious regardless of application timing than glyphosate and other herbicides. When temperatures were 10 °C for 7 d following treatment, a delayed effect of glyphosate and glufosinate effect on digitally-assessed green cover loss was noted on zoysiagrass sprigs. In subsequent studies on turf plugs, a 14-d incubation period at 10 °C reduced glyphosate but not glufosinate effects on turf green color reduction. Glyphosate applied at 125, and 200 GDD5C can safely be applied to zoysiagrass while glufosinate applied at the same timings caused inconsistent and often unacceptable zoysiagrass injury in field studies conducted at Blacksburg, VA, Starkville, MS, and Virginia Beach, VA. Zoysiagrass green leaf density was described as a function of accumulated heat units consistently across years and locations but variably by turf mowing height. Turf normalized difference vegetative index was primarily governed by green turf cover but reduced by herbicide treatments, especially when applied at greater than 200 GDD5C. Substantial spray deposition occurred to subcanopy tissue regardless of nozzle type, pressure and height above the zoysiagrass canopy based on spectrophotometric assessment of a colorant admixture. However, increasing nozzle height above the turf canopy and avoiding air induction type nozzles significantly reduced the percentage of green tissue exposed at lower canopy levels. Absorption of radio-labeled glyphosate and glufosinate was up to four times greater when exposed to zoysiagrass stems compared to leaves. Glyphosate translocated more than glufosinate and both herbicides moved more readily from stem to leaf than from leaf to stem / Doctor of Philosophy / Zoysiagrass (Zoysia spp.) is utilized as a warm-season turfgrass because of its density, visual quality, stress tolerance, and reduced input requirements. Being that zoysiagrass is a warm-season turfgrass, it enters a dormancy period during the winter months. During this period, zoysiagrasses' active growth is halted, and leaves lose their green color and turn a golden-brown color. The winter dormancy period presents turfgrass managers with a unique opportunity to apply nonselective herbicides such as glyphosate and glufosinate to control a broad spectrum of winter annual weeds. Although this weed control strategy is common in bermudagrass (Cynodon spp.), it has been less adopted in zoysiagrass due to turfgrass managers observing unexplainable turfgrass injury. Many university extension publications recommend against applying nonselective herbicides to dormant zoysiagrass despite language found in peer-reviewed publications and product labels suggesting they could be safely applied. Previous researchers have used vague terminology such as "applied to dormant zoysiagrass" or "applied prior to zoysiagrass green-up" to describe herbicide application timings. These terms have led to confusion about when to make these applications since zoysiagrass typically has subcanopy green leaves and stems throughout the winter dormancy period. No research has sought to explain why some turfgrass managers observe zoysiagrass injury when the literature only offers evidence that these herbicides do not injure dormant zoysiagrass. Research projects were designed to explore various herbicides, temperatures surrounding herbicide applications, application timings, and spray penetration into zoysiagrass canopies as possible contributors to zoysiagrass injury. The results indicated that a wide range of herbicides may be safely used in dormant and semidormant zoysiagrass. However, as zoysiagrass begins to produce more green leaves and stems, herbicides such as metsulfuron, glyphosate, glufosinate, flumioxazin, and diquat become too injurious and should be avoided. Across multiple research studies, glufosinate was consistently more injurious regardless of application timing than glyphosate and other herbicides. When temperatures were 10 °C for 7-d following treatment, it delayed zoysaigrass response to glyphosate and glufosinate. In a subsequent study, when temperatures were at 10 °C for a 14-d period, glyphosate and the nontreated reached 50% green cover at the same time, which suggests cold temperatures could mitigate glyphosate injury on zoysiagrass over a 14-d period. The 10 ° temperature only delayed glufosinate injury on zoysiagrass, and no safening was observed. The results also indicated that as temperatures increased, glyphosate and glufosinate rate in which injury was observed increased on the zoysiagrass. Glyphosate applied at 125, and 200 GDD5C can safely be applied to zoysiagrass while glufosinate applied at the same timings caused inconsistent and often unacceptable zoysiagrass injury in field studies conducted at Blacksburg, VA, Starkville, MS, and Virginia Beach, VA. Zoysiagrass injury increased when glyphosate and glufosinate were applied later into the spring when more green leaves were present regardless of location. Accumulated heat units and zoysiagrass green leaf density were closely related, indicating that accumulated heat units could be a useful tool for turfgrass managers to track zoysiagrass spring green-up. Substantial spray deposition was found on subcanopy zoysiagrass leaves and stems regardless of nozzle type, pressure, and height above the zoysiagrass canopy based on recovered colorant at the upper, middle and lower levels of the zoysiagrass canopy. However, avoiding air induction-type nozzles and raising spray height may slightly decrease penetration of spray droplets into a zoysiagrass subcanopy, but a large percentage of droplets still reached the middle and lower canopy layers in this research. Absorption of radio-labeled glyphosate and glufosinate was up to four times greater when applied directly to zoysiagrass stolen compared to leaves. Glyphosate translocated more than glufosinate, and both herbicides moved more readily from stem to leaf than from leaf to stem. These data suggest limiting the number of green zoysiagrass leaves at application would be an effective method to avoid injury zoysiagrass when applying nonselective herbicides