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.

Harvest weed seed control (HWSC) methods concentrate, remove, or destroy weed seeds captured by the combine during harvest. Furthermore, chaff lining uses a chute fitted on the back of a combine to concentrate chaff and weed seed therein into a narrow line. Since chaff amount increases with crop yield, studies aimed to determine how varying crop yield and the associated chaff amount will affect chaff lining control of select weed species, while also examining subsequent crop performance. Objective 1 of this work focused on wheat chaff lining (WCL), and objective 2 studied soybean chaff lining (SCL). Weed species of interest included wild mustard (Sinapis arvensis L.) and Italian ryegrass (Lolium perenne ssp. multiflorum L. Husnot) in WCL and Palmer amaranth (Amaranthus palmeri S.) and common ragweed (Ambrosia artemisiifolia L.) subject to SCL. Each weed species was evaluated in separate experiments, and the SCL experiment included an additional factor of with and without a cereal rye cover crop treatment. Chaff lines mimicked harvest across a range of wheat and soybean yields, with equal weed seed additions (based on existing fecundity and seed shatter phenology data) to each chaff line. A conventional harvest (control) and an outside-the-chaff-line treatment were included, where total fecundity or weed seed rain occurring prior to harvest based on weed species were broadcast respectively. Inhibition of crop and weed emergence as a function of yield and the associated chaff amount was also investigated in the greenhouse. Crop yield across treatments at the field scale (accounts for both chaff lines and outside-the-chaff-line), was not affected in double-crop soybean following WCL and full-season soybean following SCL. Field scale wheat yield in WCL compared to conventional harvest was not different, increased, or decreased in 8, 3, and 1 site-years, respectively. WCL reduced total weed emergence over the combined double-crop soybean and winter wheat growing seasons by 43-54% at the field scale. SCL reduced common ragweed emergence in cereal rye by 64% and 85% in 2 of 3 locations across the soybean growing season. The cover crop did not reduce common ragweed emergence while it was growing, but residual mulch in soybean reduced emergence by 39%. No differences were observed in Palmer amaranth emergence during cereal rye growth, however cereal rye decreased total emergence by 41%. In 6 of 7 Palmer amaranth location-years, SCL decreased field scale weed emergence in soybean by 81%. These results indicate chaff may create an unfavorable environment for weed seed emergence. In both WCL and SCL, greater amounts of chaff caused larger reductions in weed emergence. Objective 3 focused on quantifying the above-ground biomass breakdown of soybean plants into chaff, straw, and seed fractions as they are processed and dispensed by various harvesters. Depending on HWSC system, chaff and straw residues may also be destroyed, removed, or concentrated. Therefore, chaff and straw nutrient composition was analyzed to evaluate the nutrient and economic consequences of HWSC. Our results show average soybean harvest index is 0.57:1. Furthermore, chaff and straw residues equal 13.4% and 68.5% of the seed weight, respectively. Using 5-year average fertilizer prices (2017 – 2021), replacement of N, P, K and S in chaff, straw, and the combination of both residues costs USD 1.58, USD 5.88, and USD 7.46, respectively. / Master of Science in Life Sciences / In conventional wheat and soybean production, the primary means of weed control is herbicides. If herbicide use is not diversified, a repeated selection pressure drives weeds to evolve resistance to such chemistries. Producers and researchers alike are constantly looking for new ways to combat weeds and herbicide-resistant issues. Originally developed to control nuisance weeds in Australia, harvest weed seed control (HWSC) offers promise in aiding our current herbicide resistance crisis. To further explain HWSC, it is important to know the harvesting mechanism. Many of the row crops including corn, soybean and wheat are harvested using a combine. Combines cut below or tear off plant material to capture the grain or seed which is processed via a threshing system and separated into three fractions: the seed, chaff, and straw. The grain is allocated to a storage bin and eventually removed from the field. In conventional harvest, the remaining crop residue is spread evenly behind the combine across the field to ensure a balanced distribution of organic matter, nutrients, and residue across the field. There is however more than chaff and straw being dispersed. Weeds present in the field at harvest whose seed is retained at crop maturity and at an elevation above the combine header height will inherently end up inside the combine. HWSC are methods intended to capitalize on the combine capturing weed seeds during harvest. Many HWSC approaches to managing weed seed exist, including destruction, removal and concentration of weed seed. Most of this research focuses on only one method of HWSC, chaff lining. Chaff lining utilizes a chute fitted onto the back of the combine and concentrates weed seed and the chaff fraction only into a narrow line behind the combine. Although not directly known, chaff may inhibit future weed emergence within the line due to a mulching effect, intraspecific competition, a greater degree of rotting and increased seed predators. The chute is inexpensive to construct, and there are no additional labor requirements at harvest making it an appealing HWSC option. There is a limited amount of research on chaff lining in North American cropping systems making it a prime HWSC candidate for this thesis. We were curious if chaff lining could benefit wheat and soybean farmers and if crop yield and the associated chaff amount deposited in chaff lines would have any impact on crops planted and weeds placed in lines. Our results indicate chaff lining does not cause field scale yield consequence in double-crop and full-season soybean following wheat and soybean chaff lining, respectively. The effect of wheat chaff lining on wheat field scale yield was variable, but only caused a yield decrease in 1 of 12 experimental locations. Reductions in weed emergence in chaff lining systems compared to conventional indicate chaff may alter the environment to be unfavorable for weed seed emergence. The final objective of this thesis investigates the economic cost of nutrient loss among HWSC systems. Using average fertilizer prices, the cost to apply N, P, K and S concentrated or lost during HWSC in chaff, straw, and the combination of both residues is USD 1.58, USD 5.88, and USD 7.46, respectively.

Dans le cadre de l’évaluation multicritère des systèmes en protection intégrée contre les adventices (PIC-Adventices), cette étude a eu pour objectif d’étudier l’impact de la combinaison de pratiques alternatives à l’usage d’herbicides sur les émissions de N2O par les sols. L’étude a été conduite sur quatre systèmes de culture, un système de référence en agriculture raisonnée (S1) et trois systèmes PIC-Adventices (S2, S3, S5), sur le site expérimental Dijon-Epoisses (47°20'N, 5°2'E). La mise en place de dispositifs de mesure à haute résolution, alliant la méthode des chambres d’accumulation de gaz en surface du sol aux analyses de gaz par infrarouge, a permis d’estimer l’intensité des émissions de N2O pour les sols argilo-calcaires caractéristiques de la plaine dijonnaise, avec des flux moyens compris entre -6 et 257 g N-N2O ha-1 jour-1. Cette intensité s’est avérée étroitement liée à certains paramètres environnementaux (température, part de porosité occupée par l’eau, teneur en azote), et certaines pratiques agricoles, induisant des différences significatives entre les systèmes. Les émissions de N2O ont notamment été affectées par le mode de gestion des sols et la nature des cultures constituant la succession de chaque système. L’absence de travail du sol depuis 2008 dans le système S2 s’est traduite par une amplification des émissions de N2O d’un facteur multiplicatif d’au moins six par rapport aux autres systèmes pour l’année 2012. Par ailleurs, ces émissions équivalentes à 0.7 t C-CO2 ha-1 pourraient avoir compensé la séquestration de carbone additionnelle induite par le travail réduit du sol pendant la période de mesure. De la même manière, la dégradation des résidus de culture légumineuse, dans les systèmes S3 et S5 ont respectivement stimulé les émissions de N2O en 2011 et en 2012, en comparaison avec le système de référence S1. Par ailleurs, le suivi mensuel de la taille des communautés microbiennes du sol a également permis de mettre en évidence une variabilité temporelle liée aux pratiques culturales (travail du sol, récolte), en plus de la variabilité saisonnière. En revanche, dans cette étude les variations de taille des communautés microbiennes nitrifiantes et dénitrifiantes ne sont pas apparues comme un facteur d’explication de la variabilité des émissions de N2O, quel que soit le système. Enfin, l’approche par la modélisation des émissions de N2O sur les quatre systèmes, à l’aide des modèles NOE et DNDC, a permis d’identifier les principaux facteurs de régulation de ces émissions. De surcroît, le modèle NOE a bien identifié le système de culture S2, sans travail du sol, comme étant le système le plus émetteur de N2O, conformément aux observations de terrain. Cette étude renforce donc la pertinence de la modélisation pour estimer et analyser les émissions de N2O dans différents systèmes de culture. / In the context of the multicriteria evaluation of Integrated Weed Management (IWM) cropping systems, our study highlights the impacts of the combination of alternative agricultural practices to herbicide reliance on N2O emissions from soils. The study was located at the INRA experimental site of Dijon-Epoisses (47 ° 20'N, 5 ° 2'E) and considered 4 cropping systems, a reference system designed to maximize financial returns (S1) and three IWM systems (S2, S3, S5). The setup of high resolution measuring devices, combining the non-steady state chamber method with infrared gas analysis, allowed to estimate the intensity of N2O emissions from the calcareous clay soil, which is specific of Dijon plain, with average fluxes laying between -6 and 257 g N2O-N ha-1 day-1. The intensity of fluxes was closely related to environmental parameters (temperature, water filled pore space, inorganic N amount) and particular agricultural practices, leading to significant differences between systems. N2O emissions were notably affected by soil management and nature of crops. The conversion of S2 system to no-till in 2008 increased the N2O emissions, fluxes being at least 6 times more important than those emitted by the other cropping systems, during the year 2012. Moreover, these emissions, equivalent to 0.7 ha-1 C-CO2 ha-1, could have offset the soil additional carbon sequestration induced by reduced tillage during the studying period. Similarly, the degradation of legume crop residues in the S3 and S5 systems respectively enhanced N2O emissions in 2011 and 2012, by comparison with the S1 reference system. Elsewhere, the monthly monitoring of the soil microbial communities sizes has also helped to highlight temporal variability induced by the agricultural practices (tillage, harvest) as well as the seasonal variability. However, in this study the fluctuations of nitrifying and denitrifying communities sizes observed did not explain the variability of N2O emissions, whatever the considered cropping system. Finally, the modeling of N2O emitted from the 4 cropping systems, using NOE and DNDC models, allowed to identify the mains factors regulating the emissions. In addition, the NOE model accurately identified the S2 system, without tillage, as the most N2O emitter, in accordance with field observations. Thus, our study reinforces the relevance of modeling to estimate and explain N2O emissions in different cropping systems.

<p>Acetolactate synthase (ALS) inhibitors are a widely used class of selective herbicides used to control grass and broadleaf weeds. The repeated use of ALS-inhibiting herbicides has selected for biotypes of weeds resistant to ALS inhibitors, especially in the weeds most problematic to growers in the Midwest. While ALS inhibitor use seems futile, new mechanisms of herbicide action are not predicted to be commercialized in the near future to solve this problem. This leads to the main objective of this research, determining what value ALS inhibitors provide in controlling populations of weeds with resistance to ALS inhibitors. </p> <p>Field experiments with soil-applied (PRE) applications of ALS inhibitors on horseweed (<i>Erigeron canadensis</i>) and tall waterhemp (<i>Amaranthus tuberculatus </i>var. <i>rudis</i>) exhibited higher efficacy than would be expected given the frequency of the ALS resistance trait in the population. Whereas control of these species with POST-applied applications was similar or less than the proportion of the population characterized as susceptible using molecular techniques. Soil-applied applications, therefore, resulted in relatively greater control than POST applications in populations with known ALS-inhibitor-resistance mechanisms.</p> <p>Greenhouse experiments showed that overall resistance ratios were higher for PRE applications of ALS inhibitors in horseweed, tall waterhemp, and Palmer amaranth (<i>Amaranthus palmeri</i>). However, GR₅₀ values decreased for both susceptible and resistant biotypes for the PRE applications compared to POST, suggesting the biologically effective dose of these herbicides is lower in soil residual applications. This research found that PRE applications of ALS inhibitors resulted in some level of control on horseweed and tall waterhemp classified as resistant to ALS inhibitors due to the higher efficacy of PRE herbicide applications.</p> <p>Genetic analysis assessing the amino acid substitutions that confer resistance to ALS inhibitors in tall waterhemp confirmed a difference in selection pressure between PRE and POST applications and between ALS active ingredients in tall waterhemp. Applications of chlorimuron PRE at 11 g ai ha^-1selected for 35% homozygous W574L genotypes and at 44 g ha^-1 selected for 70% homozygous W574L genotypes. An increase of homozygous W574L individuals along with a decrease in heterozygous individuals from 65 (11 g ha^-1) to 29% (44 g ha^-1) suggests that W574L is semi-dominant in tall waterhemp and that high labeled rates of chlorimuron applied PRE can partially overcome the heterozygous W574L-resistance mechanism. In horseweed, no difference in selection pressure was observed between application timing or between chlorimuron or cloransulam. A new mutation conferring ALS-inhibitor resistance in horseweed was discovered, a Pro197Leu amino acid substitution, with resistance ratios of 21X to chlorimuron and 8.6X to cloransulam. These resistance ratios are slightly less than those reported for the Pro197Ala and Pro197Ser amino acid substitutions in conferring ALS-inhibitor resistance in horseweed. </p> <p>Finally, a survey of 42 populations of tall waterhemp in Indiana counties with confirmed ALS-inhibitor resistant populations of tall waterhemp found that all populations contained at least 16% individuals with the W574L amino acid substitution, 35 populations contained at least 1% individuals with the S653N substitution, and 9 populations contained at least 1% individuals with the S653T substitution. Taking into consideration the three mutations tested, 8 of the 42 populations tested contained <50% ALS-inhibitor resistant individuals within the population. Using the same tall waterhemp populations as collected in the survey, Next-Generation Sequencing was used to determine if other amino acid substitutions conferring resistance to ALS inhibitors existed. Results from WideSeq revealed that 10 other amino acid substitutions in the ALS protein may be conferring resistance in tall waterhemp in Indiana: A122T, A122N, A122S, P197T, P197L, P197H, D376E, and G654F. Further research from this survey also suggests that metabolic resistance to ALS inhibitors is likely a contributor to resistance in tall waterhemp in Indiana.</p> <p>This research suggests that ALS-inhibiting herbicides, more specifically chlorimuron, would provide the greatest contribution to management of tall waterhemp. Chlorimuron would perform best when used in soil residual applications and in populations of tall waterhemp containing either individuals susceptible to chlorimuron or individuals heterozygous for ALS inhibitor resistance conferred by the W574L mutation. This research also demonstrates the specificity of the amino acid substitutions in the ALS protein and by weed species to realize the benefit of these herbicides for management of weeds resistant to ALS inhibitors. Molecular characterization of target site resistance to ALS inhibitors has traditionally been considered relatively simple. However, we found 11 new amino acid substitutions that confer resistance to ALS inhibitors in horseweed and tall waterhemp. The complexity of ALS inhibitor resistance calls for the use of methods such as NGS to detect all potential resistance mutations in a timely manner and for the use of tests detecting metabolic resistance. Overall, this research demonstrates that ALS inhibitors still provide some utility for management of weed populations classified as resistant to ALS inhibitors and that the resistance mechanisms in horseweed and tall waterhemp are more numerous than previously reported. </p>

Além dos aspectos relacionados à proteção do solo, as coberturas vegetais, vivas ou mortas, também contribuem para a redução da infestação de plantas daninhas no período da entressafra. Com o objetivo de analisar o potencial de espécies utilizadas como coberturas vegetais de inverno no manejo de plantas daninhas, conduziram-se dois ensaios em áreas pertencentes ao Departamento de produção Vegetal da ESALQ/USP, em Piracicaba SP, durante o ano de 2008. As espécies usadas como culturas de cobertura foram: Raphanus sativus L. (nabo forrageiro), Helianthus annuus L. (girassol), Avena strigosa Schreb (aveia preta), Avena bysantina L. (aveia amarela), Vicia sativa L. (ervilhaca) e Sorghum bicolor L. Moench (sorgo forrageiro), sendo que esta última espécie não foi utilizada em um dos ensaios. Realizaram-se nos dois ensaios estudos fitossociológicos, avaliações referentes à quantificação de massa seca produzida pelas coberturas, identificação e levantamento de plantas daninhas e avaliação da taxa de decomposição das coberturas. As comunidades de plantas daninhas apresentaram modificações em sua composição florística de acordo com o tipo de cobertura utilizado. D. horizontalis foi a principal espécie no primeiro ensaio, com os maiores valores de importância relativa acumulada, enquanto que G.parviflora se destacou no segundo ensaio. Verifica-se que o cultivo de culturas de cobertura durante a entressafra pode contribuir para a redução de infestação de plantas daninhas na cultura subseqüente. O girassol apresentou o melhor potencial de produção e quantidade de massa seca por hectare, no entanto as aveias, amarela e preta, demonstraram ser as coberturas com maior potencial de supressão de plantas daninhas. E estas mesmas espécies foram as que demoraram mais tempo para se decompor, apresentando tempo de meia vida superior ao das demais coberturas, ou seja, foram necessários, em média, 144 e 119 dias para a decomposição de metade da quantidade da fitomassa da aveia amarela e preta respectivamente. As coberturas de ervilhaca e nabo foram as cobeturas que apresentaram decomposição mais acelerada. / Besides contributing to aspects related to soil protection, the cover crops also contribute to the weeds suppression during the counter season. Aiming to analyze the potential of species used as winter cover crops in winter management, two experiments were set up in areas located at the Vegetal Production Departament at ESALQ/USP, in Piracicaba SP, during 2008. The cover crops used were: Raphanus sativus L. (oilseed radish), Helianthus annuus L. (sunflower) Avena strigosa Schreb (sand oat), Avena bysantina L. (red oat), Vicia sativa L. (common vetch) and Sorghum bicolor L. Moench (sorghum). The last cover crop mentioned was not used in the second area. A phytosociological study of weeds was made in both experimental areas. An evaluation of mass yield, weeds identification and collection and a decomposition rate evaluation were also performed. The weeds communities showed changes in their floristic composition according to the cover crop used. D. horizontalis was the most important species in the first area, showing high values of relative importance, whereas G.parviflora was the most important in the second one. The use of cover crops during counter season can contribute to reduce weed infestation in the subsequent crop. Sunflower was the cover crop wich produced the greatest amount of dry mass per hectare, however, the oat varieties showed the best ability to suppress weeds. Those were the species that took more time to decompose, showing a longer half life compared to the other cover crops, it is, It was required, on average, 144 and 119 days for the decomposition of half of sand oat and red oat mass, respectively. Common vetch and oilseed radish were the cover crops that showed the fastest decomposition.

Além dos aspectos relacionados à proteção do solo, as coberturas vegetais, vivas ou mortas, também contribuem para a redução da infestação de plantas daninhas no período da entressafra. Com o objetivo de analisar o potencial de espécies utilizadas como coberturas vegetais de inverno no manejo de plantas daninhas, conduziram-se dois ensaios em áreas pertencentes ao Departamento de produção Vegetal da ESALQ/USP, em Piracicaba SP, durante o ano de 2008. As espécies usadas como culturas de cobertura foram: Raphanus sativus L. (nabo forrageiro), Helianthus annuus L. (girassol), Avena strigosa Schreb (aveia preta), Avena bysantina L. (aveia amarela), Vicia sativa L. (ervilhaca) e Sorghum bicolor L. Moench (sorgo forrageiro), sendo que esta última espécie não foi utilizada em um dos ensaios. Realizaram-se nos dois ensaios estudos fitossociológicos, avaliações referentes à quantificação de massa seca produzida pelas coberturas, identificação e levantamento de plantas daninhas e avaliação da taxa de decomposição das coberturas. As comunidades de plantas daninhas apresentaram modificações em sua composição florística de acordo com o tipo de cobertura utilizado. D. horizontalis foi a principal espécie no primeiro ensaio, com os maiores valores de importância relativa acumulada, enquanto que G.parviflora se destacou no segundo ensaio. Verifica-se que o cultivo de culturas de cobertura durante a entressafra pode contribuir para a redução de infestação de plantas daninhas na cultura subseqüente. O girassol apresentou o melhor potencial de produção e quantidade de massa seca por hectare, no entanto as aveias, amarela e preta, demonstraram ser as coberturas com maior potencial de supressão de plantas daninhas. E estas mesmas espécies foram as que demoraram mais tempo para se decompor, apresentando tempo de meia vida superior ao das demais coberturas, ou seja, foram necessários, em média, 144 e 119 dias para a decomposição de metade da quantidade da fitomassa da aveia amarela e preta respectivamente. As coberturas de ervilhaca e nabo foram as cobeturas que apresentaram decomposição mais acelerada. / Besides contributing to aspects related to soil protection, the cover crops also contribute to the weeds suppression during the counter season. Aiming to analyze the potential of species used as winter cover crops in winter management, two experiments were set up in areas located at the Vegetal Production Departament at ESALQ/USP, in Piracicaba SP, during 2008. The cover crops used were: Raphanus sativus L. (oilseed radish), Helianthus annuus L. (sunflower) Avena strigosa Schreb (sand oat), Avena bysantina L. (red oat), Vicia sativa L. (common vetch) and Sorghum bicolor L. Moench (sorghum). The last cover crop mentioned was not used in the second area. A phytosociological study of weeds was made in both experimental areas. An evaluation of mass yield, weeds identification and collection and a decomposition rate evaluation were also performed. The weeds communities showed changes in their floristic composition according to the cover crop used. D. horizontalis was the most important species in the first area, showing high values of relative importance, whereas G.parviflora was the most important in the second one. The use of cover crops during counter season can contribute to reduce weed infestation in the subsequent crop. Sunflower was the cover crop wich produced the greatest amount of dry mass per hectare, however, the oat varieties showed the best ability to suppress weeds. Those were the species that took more time to decompose, showing a longer half life compared to the other cover crops, it is, It was required, on average, 144 and 119 days for the decomposition of half of sand oat and red oat mass, respectively. Common vetch and oilseed radish were the cover crops that showed the fastest decomposition.

Abstract The negative impact of invasive plant species on biodiversity and ecosystem functions, such as productivity and nutrient cycling has been deemed a global epidemic. To address this worldwide concern, information is needed on how the invasion process happens and how to control an existing invasion. The main aim of the research presented in this thesis was to develop a better understanding of the interacting role different mechanisms play in facilitating invasion and then link this understanding to the design of more effective control strategies. This aim is significant because traditional weed control strategies are not working. The estimated cost of controlling weeds in Australia is $1.4 billion per year in agricultural landscapes. Despite this substantial investment, invasive weed species are estimated to continue to cost the agricultural industry $2.2 billion per year in loss of yield. Current control strategies tend to focus on killing or removing an invasive plant species directly with the application of herbicides and/or mechanical removal. These strategies have proven ineffectual because the plant communities that assemble after management often remain dominated by the same invader or another. In this thesis, I use a combination of empirical and modelling techniques to investigate how disturbance regimes and competitive interactions between invasive plants and native plants can be manipulated to improve the efficacy of restoration efforts. To do this, I use the model scenario of the invasion of Eragrostis curvula (African lovegrass), an invasive grass species introduced into Australia in the early 1900s from South Africa. This species has now spread into every Australian state and territory (chapter 2). I specifically focus on two mechanisms: (1) disturbance, i.e. cattle grazing, and (2) competitive interactions. In chapter 3, I examine connections between dominance and competitive differences among African lovegrass and several functionally similar native grass species in a pasture community. To test the displacement hypothesis, I used a glasshouse competition trial to investigate interactions between African lovegrass and two non-persisting native grass species (Themeda australis and Bothriochloa decipiens) with manipulations of resources, neighbour density, and establishment order. To test the partitioning hypothesis, I compared in situ water use patterns among African lovegrass and two coexisting native grass species (Aristida calycina and Aristida personata) based on the assumption that water is the most limiting resource in this system. The key finding of this chapter is that competition can have important, but contingent, impacts on dominance. Competitive differences appear to partially contribute to abundance patterns after establishment, but may be relatively unimportant during the establishment phase where disturbance appears more critical. In chapter 4, I provide evidence that the identification of mechanisms that led to an invasion, while crucial for the development of effective preventative measures and understanding the invasion process, may not be necessary for the design of more effective control strategies. To examine the effects of different control strategies on African lovegrass and the resultant community, I established a large factorial field-trial with a split-plot design. I manipulated grazing, soil nutrient levels and the presence of the invader. The most common control strategy (removing the causal disturbance and killing the invasive grass), based implicitly on traditional equilibrium models, was not an effective option for restoring a desirable native community. Instead, this strategy led to the dominance of a secondary invader. The most effective control strategy was based on alternative stable states models and involved maintaining grazing, and increasing the palatability of the invader with fertilizers. The key finding of this chapter is that novel approaches for control, which consider the dynamics of the invader-dominated system, are needed. In chapter 5, I investigate the benefits of explicitly incorporating actions that manipulate disturbance (natural or imposed) into control efforts. To do this, I first developed a process model that described the dynamics of an invader whose establishment is preferentially favoured by disturbance. I then couched this model in a decision theory framework, a stochastic dynamic program, and applied a case-study of another invasive plant species, Mimosa pigra (a perennial legume shrub and pan-tropical weed). The key finding of this chapter is that strategies should not only focus on existing invader-dominated sites, but should also protect sites occupied by native species from disturbances that facilitate invasion. The research discussed in this thesis makes three key contributions to a better understanding of the invasion process and the design of more effective control strategies: 1) the search for one key mechanism is not sufficient because multiple mechanisms can interact or shift in importance to facilitate different stages of invasion, 2) a novel approach is needed to restore a more desirable native community because the dynamics of the invader-dominated system can differ from the historical native community, and 3) control efforts should be broadened in focus to include protection of the integrity of native communities from disturbances that facilitate invasion.

Folha de aprova??o ausente no trabalho. / Submitted by Jos? Henrique Henrique (jose.neves@ufvjm.edu.br) on 2016-12-15T16:26:43Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) danilo_cesar_de_abreu_costa.pdf: 2169605 bytes, checksum: 5ec8ad603683a6fdfbcbbb5e0eb92f2a (MD5) / Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2016-12-19T13:54:21Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) danilo_cesar_de_abreu_costa.pdf: 2169605 bytes, checksum: 5ec8ad603683a6fdfbcbbb5e0eb92f2a (MD5) / Made available in DSpace on 2016-12-19T13:54:21Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) danilo_cesar_de_abreu_costa.pdf: 2169605 bytes, checksum: 5ec8ad603683a6fdfbcbbb5e0eb92f2a (MD5) Previous issue date: 2016 / Companhia Energ?tica de Minas Gerais (Cemig) / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / A Reserva Particular do Patrim?nio Natural (RPPN) Fartura possui ?rea de 1,5 mil ha, dos quais aproximadamente 40 se encontram dominados por Pteridium aquilinum (samambaia). Esta esp?cie est? oferecendo grande risco a biodiversidade do local, visto que a mesma apresenta elevado potencial invasor e capacidade de competi??o, podendo inibir a regenera??o natural e atrasar a sucess?o por s?culos. Diante disso, objetivou-se com este trabalho definir t?cnicas de controle populacional de Pteridium aquilinum e induzir a regenera??o natural, assim como avaliar a resposta de algumas esp?cies de r?pido crescimento submetidas a doses crescentes de calc?rio, com potencial para serem utilizadas na restaura??o desta ?rea. O primeiro estudo foi desenvolvido em uma ?rea dominada por samambaia, utilizando delineamento em blocos casualizados arranjado em esquema fatorial 3 x 2, consistindo em tr?s t?cnicas de controle (ro?ada mecanizada, glyphosate e paraquat), removendo ou n?o a serrapilheira das parcelas. Foram alocadas parcelas de 10 x 10 m distribu?das em 3 blocos. Ap?s seis meses, foram avaliados a porcentagem de cobertura de samambaia e de radia??o fotossinteticamente ativa (RFA) incidente sobre o solo, assim como o n?mero de indiv?duos regenerantes e a diversidade para cada tratamento. Os resultados indicaram que o controle qu?mico, tanto por glyphosate quanto por paraquat, promoveu maior redu??o de samambaia e que a remo??o da serrapilheira favoreceu o ingresso de indiv?duos e o aumento da diversidade. O segundo estudo foi realizado em casa de vegeta??o, na Universidade Federal dos Vales do Jequitinhonha e Mucuri - UFVJM, em delineamento em blocos casualizados com 3 repeti??es. Os tratamentos consistiram em elevar a satura??o por bases do substrato a 50, 70 e 90%, al?m do tratamento controle (sem corre??o). O substrato utilizado foi coletado na ?rea do primeiro estudo com o m?ximo de ra?zes de samambaia, corrigido com a quantidade de calc?rio determinada para cada tratamento e distribu?do em vasos de 10 dm?, onde as mudas de quatro esp?cies arb?reas foram plantadas. As esp?cies utilizadas foram: Anadenanthera colubrina (angico), Enterolobium contortisiliquum (orelha de macaco), Inga sessilis (ing?) e platycyamus regnelii (pau pereira). As vari?veis avaliadas foram di?metro e altura das mudas e a massa seca de samambaia. As esp?cies angico e orelha de macaco se mostraram sens?veis ? acidez do solo, sendo responsivas ao aumento da satura??o por bases. J? as esp?cies ing? e pau pereira s?o mais tolerantes ?s condi??es de acidez do solo, por?m, tamb?m obtiveram melhor desenvolvimento com a calagem. A samambaia apresentou aumento da massa seca com a eleva??o da satura??o por bases, mostrando que a calagem n?o ? uma pr?tica adequada para o controle dessa esp?cie. / Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Ci?ncia Florestal, Universidade Federal dos Vales do Jequitinhonha e Mucuri, [2016]. / The Private Reserve of Natural Heritage (RPPN) Fartura has 1500 ha area of which approximately 40 are dominated by Pteridium aquilinum (bracken). This specie is offering great risk to the biodiversity of the site, since it has a high invasive potential and competitive ability and can inhibit natural regeneration and delay the succession for centuries. Therefore the aim of this study was to define techniques for promoting Pteridium aquilinum population control and induce natural regeneration, as well as to evaluate the response of some fast growing species exposed to increasing doses of limestone with potential to be used in the restoration of this area. The first study was conducted in an area dominated by bracken, using a randomized block design arranged in a factorial 3 x 2. It consisted of three control techniques (mechanized mowing, glyphosate and paraquat), removing or not litter from the plots. They were allocated 10 x 10 m plots into 3 blocks. After six months the bracken coverage percentage and photosynthetically active radiation (PAR) incident on the ground were evaluated,, as well as the number of regenerating individuals and diversity for each treatment. The results indicated that the chemical control both glyphosate as paraquat promoted greater reduction of bracken and the removal of litter favored the entry of individuals and increased diversity. The second study was conducted in a greenhouse at Federal University of Vales do Jequitinhonha and Mucuri - UFVJM under a randomized block design with three replications. The treatments consisted of raising the base saturation of the substrate 50, 70 and 90% beyond the control treatment (no correction). The substrate used was collected in the first study area with maximum bracken roots, corrected by the amount of certain limestone for each treatment and distributed in pots of 10 dm?, where the seedlings of four tree species were planted: Anadenanthera colubrina (angico), Enterolobium contortisiliquum (orelha de macaco), Inga sessilis (ing?) Platycyamus regnelii (pau pereira). The variables were diameter and seedling height and dry mass of bracken. The angico species and orelha de macaco were sensitive to soil acidity, being responsive to the increase in base saturation. The species ing? and pau pereira are more tolerant to soil acidity conditions, but they also had better development with liming. Bracken showed an increase in dry matter with increasing base saturation, showing that liming is not an appropriate practice for controlling these species.

In the Central Coast of California, USA, wine grape growers are making efforts to identify weed control practices that promote biodiversity in their vineyards while maintaining yields. A field study was conducted in Paso Robles, CA in 2006 and 2007 evaluating the effect on Zinfandel grape-vine growth and production, groundcover plant, and ground dwelling arthropod communities of five weed control practices: 1) flumioxazin, 2) simazine, 3) cultivation, 4) cover crop, and 5) untreated control. The herbicide treatments had the lowest weed biomass followed by the cultivation, being approximately 10 and 2 times lower than the weed biomass of either the cover crop or untreated control treatments respectively. However, the differences in grape yield were not as evident. In 2006, a rainy year, the herbicides and cultivation treatments did not differ in grape yield, but the cover crop and untreated control had a reduction of approximately 20% compared with the other treatments. In 2007, a dry year, in comparison to the herbicide treatments, the grape yield reductions of cultivation were around 22%, and of the cover crop and untreated control around 48%. Although the cover crop reduced grape yield, it suppressed weed species considered important such as horseweed, panicle willowherb, scarlet pimpernel, and sowthistle. The cover crop, cultivation and untreated control had 4 to 50 times higher plant density and more than 15 times higher plant diversity compared to the herbicide treatments. The arthropod abundance differed among treatments only in 2007 being higher in the cover crop and untreated control. Also, there was a positive relationship between plant and arthropod diversity (r2 = 0.42, P = 0.02 in 2006; r2 = 0.64, P < 0.001 in 2007). Laboratory seed predation tests of the two most frequently captured carabid beetles, Calathus ruficollis and Tanystoma maculicolle, indicated their preferences for Brassica nigra and Capsella bursa-pastoris, which are considered common weed species in the region. Under field conditions, treatments with higher plant diversity and biomass favoured arthropod seed predation of these weeds, which was 20-40% in the cover crop and untreated control, doubling the predation observed in the herbicide treatments. The cultivation treatment balanced the benefits of promoting diversity while minimizing yield reductions due to weed competition. Our data indicated that the critical period of weed competition for Zinfandel grape vines occurred during budbreak-bloom period. Also, it was concluded that vines can tolerate a certain amount of weed competition, and that properly timing one pass post-emergence control tactics (e.g. cultivation or POST herbicides) could provide the necessary level of control to obtain the desired yields. However, under limited soil moisture conditions, the use of PRE herbicides could prove important to maintain vine yield and vigor. The results also illustrate how weed management practices that promote higher plant diversity and density have the potential to yield ecological services within vineyards by favoring the diversity and activity of other organisms.

No description available.