Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / 2,4-Diamin (2,4-D), or 2,4 dichlorophenoxyacetic acid is a systemic herbicide widely used in the world to control of broadleaf weeds. Agrochemicals of various classes are considered essential to agricultural development, but owing to toxic effects some of them can affect ecosystems through environmental contamination of soil and water. The presence of herbicides in aquatic system can contaminate fish and consequently, others animals, which feed on fish, causing indirectly contamination. Thus, the objective of this study was to investigate the effects of commercial formulation of herbicide 2,4-D concentrations of 400, 600 and 700 mg L−1, on metabolic parameters, acetylcholinesterase (AChE) activity and liver histological evaluation of silver catfish (Rhamdia quelen) exposed for 96 h. AChE activity increased in brain (600 and 700 mg L−1) and decreased in all concentrations tested in muscle tissue. Hepatic glycogen was reduced after 2,4-D exposure ranging from 47.7% (400 mg L−1) and 59.3% (700 mg L−1). Hepatic tissue showed lactate reduction at all 2,4-D concentrations tested and glucose was reduced only at 700 mg L−1. In the highest concentration tested hepatic glycogen, glucose reduced and plasma glucose levels increased. White muscle tissue showed glycogen reduction in fingerlings exposed to all herbicide concentrations and glucose reduction at 700 mg L−1. Muscle lactate levels increase at all 2,4-D concentrations tested. Vacuolation of hepatocytes and changes in their arrangement cords were observed by histologic al analysis in the group treated with 700 mg L−1 2,4-D. These results suggest that silver catfish exposed to 2,4-D concentrations near CL50 showed metabolic and histological responses to compensate some stress caused by herbicide exposure. Taken together parameters measured can be used as biomarkers to monitor fish contaminating by 2,4-D. / 2,4-diamin (2,4-D), ou ácido 2,4 diclorofenoxiacético é um herbicida sistêmico amplamente utilizado no mundo para controle de plantas daninhas broadleaf. Agroquímicos de diversas classes são considerados essenciais para o desenvolvimento agrícola, mas podem afetar os ecossistemas através da contaminação ambiental do solo e da água, devido. A presença de herbicidas no sistema aquático pode contaminar os peixes e, consequentemente, outros animais, que se alimentam de peixes, causando indiretamente uma maior contaminação contaminação. Assim, o objetivo deste estudo foi investigar os efeitos da formulação comercial do herbicida 2,4-D nas concentrações de 400, 600 e 700 mg L-1 sobre parâmetros metabólicos, atividade da enzima acetilcolinesterase (AChE) e avaliação histológica do fígado de jundiás (Rhamdia quelen) expostos por um período de 96 h. Como resultados observamos que a atividade da AChE mostrou-se aumentada no cérebro (600 e 700 mg L-1) e diminuída no tecido muscular em todas as concentrações testadas. O glicogênio hepático foi reduzido, após exposição ao 2,4- D variando entre 47,7% (400 mg L-1) e 59,3% (700 mg L-1). Já no tecido hepático houve reduções do lactato em todas as concentrações testadas e da glicose apenas na concentração de 700 mg L-1 2,4-D. Na maior concentração testada o glicogênio hepático e a glicose apareceram reduzidos, ao contrário da glicose plasmática que estava com níveis aumentados. O glicogênio do tecido muscular mostrou-se reduzido nos alevinos expostos a todas as concentrações testadas do herbicida e na concentração de 700 mg L-1 houve redução da glicose. O lactato muscular aumentou em todas as concentrações de 2,4-D testadas. Foi observada vacuolização de hepatócitos e alterações no arranjo dos cordões hepáticos através da analise histológica no grupo tratado com 700 mg L-1 2,4-D. Estes resultados sugerem que os jundiás expostos a concentrações de 2,4-D perto da CL50 mostraram resposta metabólica e histológica compensatória ao estresse causado pelo herbicida. Assim, este conjunto de parâmetros medidos pode ser utilizado como biomarcador para acompanhar a possível contaminação dos peixes pelo herbicida 2,4-D.

Le rôle de la méiofaune sur le fonctionnement des biofilms lotiques a été examiné par l'étude de son effet potentiel sur la capacité de consommation de l'azote des biofilms, au cours de quatre expérimentations. Les deux premières (Chapitres 2 et 3) concernent les biofilms épilithiques (phototrophes) tandis que les deux autres ont porté sur les biofilms (hétérotrophes) de la zone hyporhéique. Les biofilms sont soumis (1) à différents niveaux de densités (méiofaune) et à un enrichissement en nutriments ou (2) à différents niveaux de diversité (biofilm/méiofaune/macrofaune). Une partie des microcosmes présentant chaque niveau de diversité a été exposée à l'effet d'un herbicide, le diuron. Dans l'ensemble, la méiofaune associée aux biofilms des microcosmes était largement dominée par les rotifères. Les résultats basés sur les biofilms phototrophes montrent que les rotifères peuvent répondre à court terme, à un enrichissement en N-NO3 par une augmentation significative de leur densité et biomasse. De plus, le taux de consommation de N-NO3 est apparu significativement plus élevé dans les microcosmes dont les densités de méiofaune étaient les plus élevées. Cet effet positif de la méiofaune sur la consommation de N- NO3 par les biofilms a été retrouvé dans l'étude basée sur le biofilm hyporhéique pour les microcosmes non soumis aux effets du diuron. Dans l'ensemble, ce travail met donc en évidence le rôle significatif que peut avoir la méiofaune dans les processus de consommation de l'azote par les biofilms lotiques. De plus, les résultats suggèrent fortement que les invertébrés interagissent avec les micro-organismes impliqués dans les processus de réduction des concentrations en azote, dans le biofilm phototrophe comme dans le biofilm hyporhéique. Enfin, l'exposition à l'herbicide a engendré une modification significative du taux de consommation de N-NO3 dans les microcosmes hyporhéiques. Cependant, la comparaison du taux de consommation moyen de N-NO3 entre les traitements exposés à l'herbicide et ceux non exposés, a montré que la présence des invertébrés (méiofaune + macrobenthos) a significativement réduit l'effet du diuron sur ces processus. Cette étude met en exergue le rôle potentiellement important des interactions micro- organismes - invertébrés dans (1) le cycle de l'azote des biofilms et donc, dans les fonctions relatives à leur contribution aux processus " d'auto-épuration " des cours d'eau, et (2), dans la capacité de résistance des écosystèmes hyporhéiques face aux perturbations chimiques. / The role of meiofauna on the functioning of riverine biofilms was examined by studying their potential effect on nitrogen consumption capacity of biofilms in four experiments (Chapters 2 and 3: epilithic phototrophic biofilms; Chapters 4 and 5: heterotrophic biofilms of hyporheic zone). Biofilms are subjected to (1) different levels of densities (meiofauna) and nutrient enrichment or (2) different levels of diversity (biofilm/meiofauna/macrofauna). A part of the microcosms of each level of diversity was exposed to the effect of an herbicide, diuron. Overall, biofilm-associated meiofauna in microcosms was dominated by rotifers. Results in phototrophic biofilms showed that the response of rotifers to short-term nutrient enrichment was significant increases in their density and biomass. In addition, N-NO3 uptake rates appeared significantly higher in microcosms with highest meiofauna densities. This positive effect of meiofauna on biofilm N-NO3 uptake was also found in hyporheic biofilm microcosms, but not under the effect of diuron. Therefore, this thesis highlights that meiofauna can have a significant role in nitrogen consumption processes by lotic biofilms. In addition, the results strongly suggest that invertebrates interact with microorganisms involved in the reduction processes of nitrogen concentrations in the phototrophic biofilm as well as the hyporheic biofilm. Finally, the herbicide exposure resulted in a significant modification of N-NO3 uptake rate in hyporheic microcosms. However, the comparison of the average N- NO3 uptake rate between treatments exposed to herbicide and those unexposed, showed that the presence of invertebrates (meiofauna + macrofauna) significantly reduced the effect of diuron on these processes. This study highlights the potentially important role of microorganism-invertebrate interactions (1) in the nitrogen cycle of biofilms and thus functions related to their contribution to the "self-purification" process in streams, and (2) in resilient capacity of the hyporheic ecosystem to chemical perturbations.

Amphibians develop in aquatic environments where they are very susceptible to the effects of pesticides and other environmental contaminants. Glyphosate-based herbicides are widely used and have been shown to affect survival and development of tadpoles under laboratory conditions. The goal my thesis is to determine if agriculturally relevant exposure to Roundup WeatherMax®, a herbicide formulation containing the potassium salt of glyphosate and an undisclosed surfactant, influences the survival and development of wood frogs tadpoles (Lithobates sylvaticus) under both laboratory and field conditions. In the field, experimental wetlands were divided in half using an impermeable curtain so that each wetland contained a treatment and control side. Tadpoles were exposed to two pulses of this herbicide at environmentally realistic concentration (ERC, 0.21 mg acid equivalent (a.e.)/L) and predicted environmental concentrations (PEC, 2.89 mg a.e./L), after which survival, growth, development, and expression of genes involved in metamorphosis were measured. Results indicate that exposure to the PEC is extremely toxic to tadpoles under laboratory conditions but not under field conditions. Results from both experimental conditions show sublethal effects on growth and development, and demonstrate that ERC of glyphosate-based herbicides have the potential to alter hormonal responses during metamorphosis. My secondary objectives were to compare the effects of Roundup WeatherMax® to the well-studied Vision® formulation (containing the isopropylamine (IPA) salt of glyphosate and POEA), and to determine which ingredient(s) are responsible for the sublethal effects on development. Survival, growth and gene expression results indicate that Roundup WeatherMax® has greater toxicity than Vision® formulation. Contrary to my prediction, results suggest that, under realistic exposure scenarios, POEA is not the sole ingredient responsible for the observed developmental effects. However, my results demonstrate that chronic exposure to the POEA surfactant at the PEC (1.43 mg/L) is extremely toxic to wood frog tadpoles in laboratory. As part of the Long-term Experimental Wetlands Area (LEWA) project, this research contributes to overall knowledge of the impacts of glyphosate-based herbicides on aquatic communities.

L’usage répété d’isoproturon (IPU) en agriculture pour contrôler développement de plantes adventices dans les cultures céréalières a non seulement abouti à la contamination du sol et des ressources en eaux mais également à l’adaptation de la microflore du sol à la dégradation accélérée de cet herbicide appartenant à la famille des phénylurées. A l’heure actuelle, les mécanismes microbiens impliqués dans cette adaptation ne sont pas encore parfaitement élucidés. Dans ce contexte, l’objectif de cette étude était d’explorer les processus et les facteurs impliqués dans la biodégradation de l’isoproturon, et ce, depuis l’échelle agricole de la parcelle jusqu’à celle des gènes codant cette fonction dans des populations microbienne dégradantes.L’étude réalisée à partir d’une parcelle expérimentale du domaine d’Epoisses, cultivée selon une rotation blé d’hiver/ orge / colza, a montré que, suite à l’usage répété d’IPU, la microflore du sol s’était adaptée à sa minéralisation. Des analyses réalisées à l’aide d’outils statistiques et géostatistiques ont révélé l’existence d’une variabilité spatiale de la minéralisation de l’IPU au sein de la parcelle agricole. Celle-ci s’est révélée être non seulement corrélée avec différents caractéristiques physicochimiques du sol (C/N, CEC, …) mais également avec le plan d’épandage des pesticides au cours de la rotation culturale.Afin de mieux étudier les mécanismes moléculaires responsables de la minéralisation de l’IPU, une culture bactérienne ainsi qu’une souche (Sphingomonas sp. SH) minéralisant l’IPU ont été isolées par enrichissement à partir de deux sols différents, tous deux adaptés à la biodégradation accélérée de l’IPU. La culture bactérienne et la souche pure ont toutes deux montré un métabolisme spécifique pour la dégradation de l’IPU, étant capables de dégrader l’IPU et ses principaux métabolites mais aucun des autres herbicides de la famille des phénylurées. La culture bactérienne et la souche présentaient une activité dégradante optimale à pH7,5 et étaient affectées par des pH inférieurs et supérieurs à cette valeur optimale. Sur la base des métabolites accumulés lors de la dégradation de l’IPU, nous avons proposé que l’IPU serait dégradé par deux déméthylations successives, suivi par la coupure de la chaine urée aboutissant à l’accumulation de 4-isopropylaniline, et finalement la minéralisation du cycle phényl.Afin d’identifier les gènes impliqués dans la minéralisation de l’IPU, une banque de clones BAC a été réalisée à partir de l’ADN génomique purifié de la culture bactérienne. Bien que le crible fonctionnel réalisé n’a pas permis d’identifier de BAC capable de dégrader l’IPU ou l’un de ses métabolites, un criblage moléculaire par PCR ciblant la séquence catA codant la catéchol 1,2-dioxygénase, nous a permis d’identifier trois BACs. Le pyroséquençage des ces 3 BACs et l’agrégation des séquences correspondantes ont permis d’identifier un fragment génomique de 33 kb présentant notamment l’opéron cat impliqué dans le clivage ortho du cycle phényl du catéchol. De ce fait nous avons émis l’hypothèse selon laquelle la 4-isopropylaniline formée lors de la dégradation de l’IPU pourrait être minéralisée par le clivage ortho du catéchol, un intermédiaire clef de la voie des beta-kétoadipates. Ceci nous a donc permis de proposer une voie métabolique pour la voie basse de la dégradation de l’IPU qui, jusqu’alors, n’avait pas encore été décrite. / Frequent use of phenylurea herbicide isoproturon (IPU) in agricultural fields has resulted not only in the contamination of the natural resources including soil and water but also in the adaptation of the soil microflora to its rapid degradation. However, up to now, the mechanisms underlying this microbial adaptation are not well elucidated. The aim of this study was to explore the processes and factors implicated in IPU degradation from the agricultural field to the genes coding for catabolic genes. The study carried out at the experimental field of Epoisses cropped with a winter wheat / barley / rape seed crop rotation indicated that as a result of its periodically repeated use, the soil microflora adapted to IPU mineralization activity. Further analysis using exploratory and geostatistical tools demonstrated the existence of spatial variability in IPU mineralization activity at the field scale which was correlated not only with several soil physico-chemical parameters like organic matter content, CEC and C/N ratio but also with the pesticide application plan over a three year crop rotation. In order to get further insight into underlying mechanisms, an IPU mineralizing bacterial culture and strain Sphingomonas sp. SH were isolated through enrichment cultures performed from two different adapted soils. Both had the catabolic activities highly specific for the mineralization of IPU and its metabolites but none of other structurally related phenylurea herbicides. IPU metabolic activity of both the mixed culture and the strain SH was found to be affected by pH with optimal activity taking place at pH 7.5. Based on the accumulation of different known metabolites during mineralization kinetics, IPU metabolic pathway was proposed to be initiated by two successive demethylations, followed by cleavage of the urea side chain resulting in the accumulation of 4-isopropylaniline, and ultimately the mineralization of the phenyl ring. In order to identify the genes involved in IPU degradation, BAC clone library was established from the genomic DNA of the bacterial culture. Although, the functional screening did not yield in identifying any BAC clone able to degrade IPU or its known metabolites, the PCR based screening led us to identify a cat gene cluster involved in ortho-cleavage of the phenyl ring of catechol through beta-ketoadipate pathway. Based on this finding, it was hypothesized that phenyl ring of 4-isopropylaniline formed during IPU transformation might be mineralized through ortho-cleavage of catechol. This finding allowed us to propose the lower IPU metabolic pathway which was not yet described.

No description available.

Tesis por compendio / [ES] En la producción de cultivos, el frecuente uso de pesticidas y en particular de los herbicidas se encuentra bajo el foco de la atención pública. En los últimos años, muchos herbicidas han sido retirados del mercado, debido a que se buscan productos menos tóxicos. Esto ha provocado un aumento en la inversión para la investigación y el desarrollo de productos herbicidas más sostenibles. Sin embargo, hoy en día, hay pocas opciones comerciales que puedan reemplazar eficazmente a los herbicidas tradicionales. La comunidad agrícola ha posicionado al ácido pelargónico (PA) como una buena alternativa a los herbicidas de contacto convencionales, e incluso al glifosato en ciertas situaciones. El PA es un herbicida no selectivo de contacto, que presenta un buen control de las malezas sin dañar el medio ambiente. Sin embargo, su uso en la agricultura se encuentra limitado debido a algunos inconvenientes, como los problemas de su formulación, el olor rancio y desagradable después de su aplicación y principalmente las altas dosis de pulverización a las que debe ser aplicado para que sea efectivo. Por estas razones, el objetivo de esta tesis fue primero desarrollar un nuevo compuesto no toxico con actividad herbicida, que pudiera ser una alternativa a los herbicidas convencionales. A continuación, se estudiaron las condiciones óptimas de aplicación de la nueva sustancia: dosis de aplicación, ajustes de las barras de pulverización y condiciones climáticas fueron definidas para un mayor rendimiento de la nueva sustancia. Igualmente, se usaron coadyuvantes en el caldo, para incrementar la actividad del nuevo herbicida. Los resultados de esta tesis doctoral reportan la actividad herbicida de trece compuestos a base de ésteres de ácidos grasos, que podrían ser alternativas sostenibles para el control de malas hierbas. Su efectivad herbicida fue evaluada sobre Digitaria sanguinalis (L.) Scop. y Solanum nigrum L. Todos los componentes mostraron una interesante actividad herbicida de contacto que no está relacionada con el ácido libre de los ácidos grasos, además de buenas propiedades fisicoquímicas. La mayor eficacia se obtuvo con el éster de ácido pelargónico de polietilenglicol metilado (PA-MPEG), con seis óxidos de etileno. El PA-MPEG es un compuesto líquido, soluble en agua y sin olor rancio, debido a su nula volatilidad, a diferencia del PA. También tiene unas excelente propiedades mojantes, pudiéndose diluir directamente en agua y aplicar sin la necesidad de una formulación, en contraste con el PA. PA-MPEG fue pulverizado a diferentes caudales, proporcionando un control de las malas hierbas estudiadas igual o mejor que el obtenido por los herbicidas comerciales a base de PA. La aplicación de PA-MPEG a una tasa de 12.8 kg de ácido equivalente de PA por hectárea con un caudal de 500 L por hectárea, fue la dosis más adecuada para lograr un excelente control (90 %) de las malas hierbas con un tamaño medio (18-20 cm; BBCH 16-22). Esta dosis de producto y el volumen de caldo son relativamente más bajos que los recomendados en la etiqueta del herbicida comercial a base de PA, formulado con una concentración de 273.4 g L-1. Como PA-MPEG y PA tienen actividad de contacto y su eficacia depende de la cobertura de rociado, en el estudio se reportó y se confirmó que las pulverizaciones realizadas con caudales inferiores a 200 litros por hectárea presentaron un control deficiente sobre D. sanguinalis y S. nigrum, al ser la cobertura de rociado y la penetración en el follaje insuficiente. La eficacia de PA-MPEG a una dosis subóptima fue mejorada cuando la aplicación se realizó con la barra de pulverización a una altura menor, lo que redujo la distancia al follaje de las malas hierbas. Condiciones climáticas cálidas (T: 33 °C; 30 % r.h.) durante la aplicación y los siguientes días también favorecieron el control de malas hierbas. Ambos aspectos de la aplicación podrían ser útiles para reducir las dosis de pulverización, manteniendo su eficacia. El uso de / [CA] En la producció de cultius, el freqüent ús de pesticides i en particular dels herbicides es troba sota el focus de l'atenció pública. En els últims anys, molts herbicides han estat retirats del mercat, pel fet que es busquen productes menys tòxics. Això ha provocat un augment en la inversió per a la investigació i el desenvolupament de productes herbicides més sostenibles. No obstant això, hui dia, hi ha poques opcions comercials que puguen reemplaçar eficaçment als herbicides tradicionals. La comunitat agrícola ha posicionat a l'àcid pelargònic (PA) com una bona alternativa als herbicides de contacte convencionals, i fins i tot al glifosato en unes certes situacions. El PA és un herbicida no selectiu de contacte, que presenta un bon control de les males herbes sense danyar el medi ambient. No obstant això, el seu ús en l'agricultura es troba limitat a causa d'alguns inconvenients, com els problemes de la seua formulació, l'olor rància i desagradable després de la seua aplicació i principalment les altes dosis de polvorització a les quals ha de ser aplicat perquè siga efectiu. Per aquestes raons, l'objectiu d'aquesta tesi va ser primer desenvolupar un nou compost no toxic amb activitat herbicida, que poguera ser una alternativa als herbicides convencionals. A continuació, es van estudiar les condicions òptimes d'aplicació de la nova substància: dosi d'aplicació, ajustos de les barres de polvorització i condicions climàtiques van ser definides per a un major rendiment de la nova substància. Igualment, es van usar coadjuvants en el caldo, per a incrementar l'activitat del nou herbicida. Els resultats d'aquesta tesi doctoral reporten l'activitat herbicida de tretze compostos a base d'èsters d'àcids grassos, que podrien ser alternatives sostenibles per al control de males herbes. La seua efectivitat herbicida va ser avaluada sobre Digitaria sanguinalis (L.) Scop. i Solanum nigrum L. Tots els components van mostrar una interessant activitat herbicida de contacte que no està relacionada amb l'àcid lliure dels àcids grassos, a més de bones propietats fisicoquímiques. L'eficàcia més gran es va obtenir amb l'èster d'àcid pelargònic de polietilenglicol metilado (PA-MPEG), amb sis òxids d'etilé. El PA-MPEG és un compost líquid, soluble en aigua i sense olor rància, a causa de la seua nul·la volatilitat, a diferència del PA. També té unes excel·lents propietats mojantes, podent-se diluir directament en aigua i aplicar sense la necessitat d'una formulació, en contrast amb el PA. PA-MPEG va ser polvoritzat a diferents cabals, proporcionant un control de les males herbes estudiades igual o millor que l'aconseguit ingut pels herbicides comercials a base de PA. L'aplicació de PA-MPEG a una taxa de 12.8 kg d'àcid equivalent de PA per hectàrea amb un cabal de 500 L per hectàrea, va ser la dosi més adequada per a aconseguir un excel·lent control (90%) de les males herbes amb una grandària mitjana (BBCH 16-22). Aquesta dosi de producte i el volum de caldo són relativament més baixos que els recomanats en l'etiqueta de l'herbicida comercial a base de PA, formulat amb una concentració de 273.4 g L-1. Com a PA-MPEG te activitat de contacte i la seua eficàcia depèn de la cobertura de ruixat, en l'estudi es va reportar i es va confirmar que les polvoritzacions realitzades amb cabals inferiors a 200 litres per hectàrea van presentar un control deficient sobre D. sanguinalis i S. nigrum, a l'ésser la cobertura de ruixat i la penetració en el fullatge insuficient. L'eficàcia de PA-MPEG a una dosi subòptima va ser millorada quan l'aplicació es va realitzar amb la barra de polvorització a una altura menor, la qual cosa va reduir la distància al fullatge de les males herbes. Condicions climàtiques càlides (T: 33 °C; 30% r.h.) durant l'aplicació i els següents dies també van afavorir el control de males herbes. Tots dos aspectes de l'aplicació podrien ser útils per a reduir les dosis de polvorització, mantenint la seua eficàcia. L'ús d'additius en el tanc de / [EN] In crop production, a particular focus is given to the extensive use of pesticides and, in particular herbicides. In the last years, many herbicides have been withdrawn from the market due to the search for less toxic products for the environment, human health, and non-target organisms, and with lower persistence, increasing the investment for research and development of more sustainable herbicide products. However, today, there are few commercial options that can effectively replace traditional herbicides. The agricultural community has positioned pelargonic acid (PA) as a good alternative to conventional contact herbicides and even for glyphosate in specific situations. PA is a non-selective contact herbicide that achieves good weed control efficacy without harming the environment. However, its use is limited in agriculture due to some drawbacks, such as its formulation problems, the rancid and unpleasant odour after its application and mainly the high spray doses at which it must be applied to be effective, having a high cost, compared to other herbicides available on the market. Therefore, the objectives of this thesis were first to develop a non-toxic compound with herbicidal activity, which could be an alternative to conventional herbicides. Next, the optimal application conditions of the new substance were studied: application rates, spray bar settings and climatic conditions were defined for a higher performance of the new substance. Similarly, adjuvants were used to enhance the activity of the new herbicide. The results of this doctoral thesis report the herbicidal activity of thirteen sustainable alternative compounds based on fatty acid (FA) esters, which could be sustainable alternatives for weed control. Its herbicidal effectiveness in weed control was evaluated on Digitaria sanguinalis (L.) Scop. and Solanum nigrum L. All the components showed an interesting contact herbicidal activity that is not related to the free acid of fatty acids, in addition to good physicochemical properties. The highest efficacy was obtained with methylated polyethylene glycol pelargonic acid ester (PA-MPEG), with six ethylene oxides. PA-MPEG is a liquid compound, soluble in water, non-volatile and consequently without rancid smell, unlike PA. Furthermore, it has excellent wetting properties, being able to be diluted directly in water and applied without further formulation efforts in contrast to PA. Additionally, it was suggested that PA-MPEG and other FA herbicides could cause desiccation symptoms due to the break of the water continuum at the site of evaporation in the intercellular spaces. PA-MPEG applied at different spray volumes provided equal or better weed control than commercial PA herbicides. The application of PA-MPEG at a rate of 12.8 kg of PA acid equivalent per hectare in a spray volume of 500 L per hectare was the most suitable rate for achieving excellent weed control (above 90 %) on medium-sized weeds (18-22 cm height; BBCH 18-22). These product doses and spray volume are relatively lower than those recommended on the label of a commercial PA formulation (273.4 g L-1). Since PA-MPEG and PA have contact herbicidal activity and their weed control efficacy depends on the spray coverage, the study reported and confirmed that application performed with spray volumes below 200 L ha-1 resulted in poor D. sanguinalis and S. nigrum control due to insufficient weed coverage and spray penetration into the weed canopy. The efficacy of PA-MPEG at a suboptimal use rate was improved when the application was performed at a lower boom height, which reduced the distance to the weed canopy. Warm weather conditions (T: 33 °C; 30 % r.h.) during the application and the following days also increased weed control efficacy with PA-MPEG. Both application aspects could reduce PA-MPEG use rates while keeping its effectiveness. The use of adjuvants added into the spray tank also caused an enhancement of PA-MPEG performance. Although several tank / Campos Cuevas, J. (2023). Discovery and Development of a Novel Sustainable Contact Herbicide Based on Natural Fatty Acids [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/193471 / Compendio

Weed control is an integral part of a successful overall production strategy in row- cropping systems and has the potential to reduce or eliminate yield losses that negatively affect profitability. Timely and correctly selected herbicide applications are the major keys for effective weed control in a majority of instances. However, there are negative factors that contribute to ineffectiveness and weed escape issues that currently lack viable options for management. Sparsely populated late-season weeds that emerge after lay-by herbicide applications and weeds that have become tolerant and resistant to traditional herbicide chemistries are of greatest concern. Historically, these weeds would have been pulled or chopped by hand or removed by cultivation, but with current production strategies built around conservation tillage and herbicide management practices, blanket disturbance of the soil through plowing is not a viable option. There is an immediate need for site-specific weed management to address these weed escapes while minimizing soil disturbance that reduces residual herbicide efficacy and lessens moisture losses that negatively effects the growing crop

The endemic eelgrass (Zostera marina) community of Morro Bay Estuary, located on the central coast of California, has experienced an estimated decline of 95% in occupied area (reduction of 344 acres to 20 acres) from 2008 to 2017 for reasons that are not yet definitively clear. One possible driver of degradation that has yet to be investigated is the role of herbicides from agricultural fields in the watershed that feeds into the estuary. Thus, the primary research goal of this project was to better understand temporal and spatial trends of herbicide use within the context of San Luis Obispo (SLO) County and Morro Bay Watershed by analyzing data of application by mass, area, and intensity to identify herbicides with the highest potential for local environmental pollution. California Pesticide Use Annual Summary Reports (PUASR) from the years 2000 to 2017 were used to obtain data for conducting a meta-analysis to estimate total herbicide application by weight within every township, range, and section for each of the eight selected herbicides: oxyfluorfen, glyphosate, diuron, chlorthal-dimethyl, simazine, napropamide, trifluralin, and oryzalin. A second goal was to select an analytical laboratory that would be best suited for herbicide analysis of estuary sediments to determine the presence, or lack thereof, of the eight selected herbicides. Criteria of consideration in laboratory selection included herbicides detection capabilities, detection/reporting limits, testing prices, chain of custody protocols, turnaround times, and laboratory site locations. The meta-analysis yielded results showing high herbicide application rates in SLO County with glyphosate, oxyfluorfen, and chlorthal-dimethyl being identified as three herbicides of elevated risk for local environmental contamination due high rates of use by mass, by area, and/or intensity during the study timeframe. Additionally, Morro Bay Watershed exhibited moderate rates of herbicide application with chlorthal-dimethyl and glyphosate being of highest risk for contamination and accumulation within the estuary because of high application rates by mass, by area, and/or intensity. Finally, Environmental Micro Analysis (EMA) and Primus Group, Inc. (PrimusLabs) were identified as the top candidates for analytical laboratory testing of Morro Bay Estuary sediment samples to be obtained and tested for the selected herbicides. These laboratories provide superior analytical capabilities of the eight herbicides, impressive reporting limits or lower detection limits, competitive testing prices for detecting multiple constituents in multiple samples, robust chain of custody protocols, options for quick turnaround times, and laboratory site locations within California.

<p dir="ltr">Palmer amaranth (Amaranthus palmeri S. Watts) and waterhemp [Amaranthus tuberculatus (Moq.) J. D. Sauer] are two of the most troublesome weeds in U.S. soybean production and the auxin herbicides dicamba and 2,4-D, are currently used extensively for postemergence control of these species. In some cases, complete control of weeds at the time of auxin application is not achieved due to adverse environmental conditions, plant factors or misapplications. In these instances, a subsequent postemergence herbicide may be required to control any plant that survived the initial auxin herbicide application. This research was conducted to determine the efficacy and optimal successive time interval between applications of viable postemergence herbicides in soybean on Palmer amaranth and waterhemp plants surviving a previous application of 2,4-D or dicamba. Results from this research indicated that respraying a failed auxin herbicide application with a subsequent auxin herbicide, especially dicamba, was less effective than respraying with glufosinate or fomesafen to control waterhemp in addition to being a less desirable approach for resistance management. Additionally, respray herbicide applications should target 7 to 14 d after the initial failed herbicide application on waterhemp for optimal overall efficacy. When dicamba was the initial herbicide sprayed on Palmer amaranth, 94% or greater control was achieved with glufosinate in 2019 on a 7- and 14-d respray interval, which was greater than the efficacy observed with either dicamba or 2,4-D (< 82%). In 2020, these differences in herbicide efficacy were not evident within these time intervals. These general trends in treatment differences were also manifested in the data for plant height, biomass and viable apical meristems. When 2,4-D was the initial herbicide sprayed on Palmer amaranth, fomesafen and glufosinate applications on a 7-d respray interval and glufosinate on a 14-d respray interval resulted in greater control than 2,4-D in 2019. All other trends in herbicide treatments and time intervals were consistent with dicamba applied as the initial herbicide. Another part of his research was conducted with the objective of quantifying herbicide spray solution deposition and herbicide efficacy on waterhemp growing in different densities plant densities: low, high-thinned and high densities. In both field and greenhouse experiments, spray deposition (µl cm-2) on waterhemp leaves was up to 53% less on plants grown in high density compared to the other density treatments. Even though no differences in herbicide deposition between low and the high-thinned densities were observed, there were differences in herbicide efficacy. When applied to plants growing in low density, applications of glufosinate, fomesafen and topramezone reduced weed biomass to a greater extent than plants growing in the high-thinned density. Following herbicide damage to the apical meristem, plants growing in high-density produced new branches from axillary buds that were previously dormant, whereas plants growing in the low density already had axillary branches initiated from these buds and did not provide an opportunity for new shoot growth. In general, no differences in herbicide efficacy were observed across weed densities following dicamba applications. Source-to-sink translocation of dicamba to previously active meristems, or axillary buds that broke dormancy after the herbicide application, may have compensated for less spray solution interception on plants growing in high density. Lower levels of postemergence herbicide efficacy in high density weed populations are not only influenced by spray deposition differences, but also by changes in plant growth and apical dominance. This research provides further evidence that justifies the need for weed managers to reduce weed densities as much as possible, via non-chemical or soil residual herbicides (preemergence), as much as possible to optimize the efficacy of foliar herbicide applications.</p>

Appropriate management of mid-rotation pine plantations can improve habitat for early successional and pine-grassland adapted avian species. I tested effects of Imazapyr selective herbicide and prescribed fire on plant and avian communities in thinned, mid-rotation pine stands contracted under the Conservation Reserve Program. Within 12 replicate sites, 2 8.1-ha plots were assigned either herbicide and prescribed fire treatment or control. I described components of vegetation structure and composition in 2006. I tested effects of herbicide and prescribed fire treatment on avian relative abundance, species richness, total avian conservation value, and density of select species during 2003 - 2006. Hardwood midstory decreased and abundances of grasses and forbs increased following treatment. A shift occurred in the bird community from closed-canopy forest species to early successional and pine-grassland species. Treatment stands benefited many avian species exhibiting negative population trends.