Dissertations / Theses on the topic 'Weed control methods'

Master of Science
Department of Horticulture, Forestry, and Recreation Resources
Steven Keeley
Common dandelion (Taraxacum officinale Weber) is an important perennial weed in turfgrass. Fall is considered the optimal time for postemergence herbicidal control of dandelions; however, applications in spring, when volatility damage to surrounding plants is an additional concern, are often needed. Therefore, we conducted research to determine the volatility of common broadleaf herbicides, and their efficacy when applied at spring and fall application timings. Volatility was determined by applying herbicides to turfgrass and using potted tomatoes as indicator plants. Tomatoes exposed to turfgrass treated with Trimec Classic, Confront, Surge, Escalade 2, and Imprelis exhibited little or no volatility damage, while exposure to Speedzone, 4 Speed XT, and Cool Power caused significant damage. In general, herbicides causing little or no damage were amine formulations. Two field studies determined the effect of spring and fall application timing on dandelion control with several herbicides. Herbicide applications in the spring coincided with dandelion anthesis stages: pre-bloom, peak bloom, and post-bloom. Results were dependent on dandelion pressure in the studies. In 2010, with lower pressure, there were no differences among herbicides at any spring timing when dandelion control was evaluated after one year; all herbicides gave ≥ 80% control. In 2011, with higher dandelion pressure, Imprelis SL and 4 Speed XT provided ≥ 96% dandelion control at the spring pre- and post-bloom timings, which was better than Surge, Escalade 2, Cool Power, and Confront. The best choices for spring efficacy combined with minimal to no volatility were Escalade 2 and Trimec Classic. Finally, because interest in organic dandelion control is increasing, we compared several organic weed control tactics with a conventional herbicide. In a two-year field study, the conventional herbicide gave much better control (> 96%) than any organic method. Horticultural vinegar corn gluten meal, and fertilizer-only gave < 25% control, while hand-weeding gave 58 to 71% control. While hand-weeding was the best of the organic tactics, the time required was considered prohibitive for turfgrass managers, unless initial weed levels were very low.

Field experiments were conducted in Virginia to evaluate the efficacy of AEF-130060 03 plus AEF-107892 applied postemergence (POST) for the control of Italian ryegrass [Lolium multiflorum (Lam)] in barley [Hordeum vulgare (L.)] in comparison to other herbicides currently registered for use in wheat [Triticum aestivum (L.)] and barley. Laboratory experiments were also conducted to evaluate absorption, translocation and metabolism of AEF-130060 03 plus AEF-107892 in wheat, barley, and Italian ryegrass with or without the addition of dicamba. AEF-130060 03 plus AEF-107892 was applied alone at three POST timings. All of these applications were effective in controlling Italian ryegrass. The third application timing of AEF-130060 03 plus AEF-107892 commonly resulted in lower yields than the first or second application timing, due to increased duration of Italian ryegrass competition, increased barley injury and insufficient time for barley recovery from this injury. In the field experiment, significantly greater barley injury was observed when AEF-130060 03 plus AEF-107892 was combined with 2,4-D and dicamba. Early postemergence (EP) treatments of AEF-130060 03 plus AEF-107892 provided control of Italian ryegrass equivalent to that of delayed preemergence (DPRE) applications of flufenacet plus metribuzin when rainfall was received. However, when rainfall was not received AEF-130060 03 plus AEF-107892 provided superior control. Because the efficacy of AEF-130060 03 plus AEF-107892 is not dependant on rainfall, it should provide more consistent control of Italian ryegrass than DP treatments. Laboratory experiments indicated that Italian ryegrass absorbed greater than 2.5, 2.0, and 1.5 times the amount of applied radioactivity at 24, 48, and 96 hours after treatment (HAT), respectively, than wheat or barley. Metabolism experiments indicated that quantity of parent compound in the three species was greatest in Italian ryegrass, followed by barley and then wheat. However, the sum total of metabolites was not different between species. A higher rate of metabolism of AEF-130060 03 plus AEF-107892 was also observed in wheat and barley than in Italian ryegrass. Thus, lower absorption of herbicide by wheat and barley, coupled with a more rapid rate of metabolism, most likely accounts for differential selectivity between these plant species. No differences in absorption, translocation or metabolism were observed within the three plant species due to the addition of dicamba. An additional experiment was conducted in 2000 and 2001 to evaluate the efficacy of preemergence (PRE) and EP applications of DPX-R6447 for the control of Italian ryegrass in wheat and barley in comparison to other herbicides currently registered for use in these crops. Barley and wheat injury and yield were similar with treatments of DPX-R6447 at rates below 176 g ai/ha and treatments of flufenacet plus metribuzin applied alone in both years. Consistent Italian ryegrass control with DPX-R6447 occurred only with rates of 176 g ai/ha or greater in both years. However, these rates resulted in variable injury in both wheat and barley between years. Rates higher than 176 g ai/ha of DPX-R6447 resulted in unacceptable barley and wheat injury. The lack of consistency with regard to barley and wheat injury could limit the utility of this compound in these crops. Field trials were conducted in Virginia to evaluate herbicide programs for control of Italian ryegrass in no-till corn [Zea mays (L.)] establishment. Herbicide programs using transgenic corn hybrids were compared to standard programs that utilize non-selective herbicides in combination with high rates of triazine herbicides. Italian ryegrass control and corn yields similar to those provided by standard programs could be attained through the use of paraquat plus atrazine, and glyphosate applied in combination with atrazine or rimsulfuron plus thifensulfuron-methyl. In glyphosate-tolerant corn, EP applications of glyphosate controlled Italian ryegrass, but yield did not differ from yields of corn treated with standard PRE applications of glyphosate plus atrazine. The use of glufosinate, imazethapyr plus imazapyr, or sethoxydim with appropriate herbicide-tolerant hybrids did not demonstrate potential for improved control of Italian ryegrass. Field experiments were also conducted to investigate the incidence and severity of maize chlorotic dwarf virus (MCDV) and maize dwarf mosaic virus (MDMV) in response to POST johnsongrass control in two corn hybrids. Recent observations have indicated a lack of virus-tolerance in glyphosate-tolerant corn hybrids in Virginia. The rapidity of virus disease development in corn resulting from application of glyphosate or nicosulfuron was also investigated. The virus-susceptible glyphosate-tolerant hybrid developed significantly higher levels of virus incidence three weeks after treatment than the virus-tolerant, non-transgenic hybrid, and virus incidence and severity increased throughout the duration of the growing season. Little or no disease incidence occurred in the virus-tolerant hybrid. The virus-susceptible hybrid exhibited significant increases in disease incidence in response to any herbicide treatment applied to johnsongrass-containing plots relative to the same treatment applied to weed free plots. Johnsongrass control with nicosulfuron or glyphosate caused similar disease incidence and severity in the virus-susceptible hybrid, regardless of application method. Results of these experiments indicated that growers' choice of hybrid should focus primarily on disease resistance rather than herbicide resistance.
Ph. D.

Riparian zones lie at the interface between aquatic and terrestrial ecosystems and usually have fertile soils, which play a crucial role in maintaining ecosystem productivity and biodiversity. Riparian zones are currently subject to vegetation loss and degradation due to human activities, intensification of agricultural practices, weed invasion, and global climate change. Therefore, there is an urgent need to revegetate and/or maintain the current vegetation of riparian zones. Soil nitrogen (N) is one of the most important growth-limiting nutrients and plays a crucial role in plant growth and productivity. Various management practices such as revegetation establishment, weed control methods, fertiliser applications, and/or organic amendments are practiced to sustain vegetation in riparian zones. However, management practices can alter soil N cycling. It is essential to understand the effect of different land management practices on soil N transformations, to maintain the long-term functional stability of riparian zones ecosystems. Revegetation of degraded riparian zones is considered one of the most effective measures in riparian management, which may influence soil N cycling. To date, no systematic literature review (meta-analysis) exists to assess the effects of different vegetation types and age on soil N pools regarding the revegetation of riparian zones (Chapter 2). Vegetation types along the riparian zones can be both native tree species and/or horticultural trees. The success of riparian revegetation projects with tree species currently depends on weed control to reduce the non-target vegetation competing over nutrients. I, hence, investigated the effects of chemical weed control on N cycling using glyphosate (commonly used herbicide) and organic-based herbicides including the registered products BioWeedTM, Pelargonic acid (Slasher®), and horticultural vinegar (acetic acid) compared with mulching. Additionally, there is a lack of information on how different herbicides could affect soil N dynamics and microbial community structure even after the application was ceased for at least one year (Chapter 3). Horticultural crops established within riparian zones are also one of the major land-use practices requiring large quantities of fertiliser, particularly N, and herbicide inputs. Glyphosate is commonly applied in horticultural lands and glyphosate interactions with organic amendments (e.g., biochar) remain uncertain. I explored the long-term interactions between biochar-amended soil and repeated application of glyphosate even after the application has ceased for over two years on soil microbial communities and soil N transformations are not well understood (Chapter 4). Glyphosate application is likely to be resumed even after stopping for a period of time and usually, very short-term N pools in response to glyphosate application in the presence of soil organic amendments like biochar are overlooked. Short-term N pools may have implications for long-term N management and hence it is important to understand short-term N pools with respect to treatments (Chapter 5). Therefore, my thesis specifically aimed to: (1) Examine the influence of riparian zone revegetation with different revegetation types and age on soil N pools by conducting a quantitative literature review (meta-analysis) (Chapter 2). (2) Assess and compare the effects of different organic-based herbicides (BioWeedTM, Slasher®, and acetic acid) and the commonly used herbicide glyphosate with mulch, on soil N dynamics and microbial community structure at two riparian revegetation sites up to two years repeated application of herbicides followed by one year after stopping herbicides applications (in total three years since the revegetation establishment) (Chapter 3). (3) Investigate the impacts of long-term repeated application of glyphosate (12 years) interacted with biochar (for three years) on soil N cycling, more specifically abundance of nitrifying populations such as the ammonia-oxidizing bacteria and archaea (AOB and AOA) as well as the overall soil microbial diversity and community structure (both fungi and bacteria) after two years following the cessation of herbicide applications (Chapter 4). (4) Explore how the interaction of biochar and glyphosate would immediately affect soil N transformations in short-term (in a 5-day laboratory incubation) using the 15N pool dilution techniques (Chapter 5) In Chapter 2: A meta-analysis was undertaken using a categorical mixed effect model to synthesise the results from 52 published articles. This study aimed to explore how different revegetation types (woodland, shrubland, and grassland) and revegetation age (< 3 years, 3-10 years, 10-20 years, 20-40 years, or > 40 years) would affect soil N pools. This meta-analysis revealed that revegetation of riparian zones significantly increased soil total nitrogen (TN) particularly in woodlands, which was associated with the presence of N fixing species and high litter inputs. Soil TN increased in revegetation ages between 10 and 40 years following revegetation, which might be associated with the increased soil organic carbon (SOC) inputs within those ages following establishment. Of the revegetation types considered in this study, NO3--N concentration in soil followed the order of grassland < shrubland < woodland, suggesting that woodland might be more efficient in soil NO3--N retention than grassland. However, revegetation significantly decreased soil moisture by 7.6% compared with the corresponding control, which might be associated with the selection of exotic species as dominant vegetation in riparian zone revegetation. This study provides insight into the influence of different revegetation types and age on soil N pools and soil moisture. This study also highlights the importance of revegetating riparian zones to increase soil TN, particularly in woodlands. Therefore, in Chapter 3, I used two newly established revegetation sites at (Kandanga and Pinbarren sites), planted with native wood species to investigate how different weed control methods including organic-based herbicides (BioWeedTM, Slasher®, and acetic acid) and the commonly used herbicide, glyphosate with mulch would affect soil N dynamics and microbial community structure over three years following revegetation establishment(two years repeated application of herbicides followed by one year after stopping herbicides applications). Soil samples were collected three times following revegetation establishment at months 2, 14, and 26 at the Kandanga site and at months 10, 22, and 34 at the Pinbarren site. The last sampling at the Pinbarren site (at month 34) occurred one year after the last herbicide was applied. In this study, I found that soil microbial biomass carbon (MBC) was significantly higher in response to mulch compared with glyphosate and organic-based herbicide treatments at months 26 at the Kandanga site and months 10 at the Pinbarren site following the revegetation establishment. However, soil MBC at month 34 at the Pinbarren site was only significantly higher in the mulch treatment than glyphosate and BioWeedTM. The level of MBC in glyphosate and BioWeedTM was also lower than the acceptable threshold at month 34 at the Pinbarren site. I also found that soil nitrate (NO3--N) was significantly higher in the soil treated with mulch than only glyphosate treatment at months 22 and 34 after revegetation at the Pinbarren site. Higher soil NO3--N in mulch compared with that of glyphosate could be partly explained by decreased denitrifying bacteria (Candidatus solibacter and Candidatus koribacter). However, there were no significant differences in soil NO3--N between mulch and other organic-based herbicides despite the fact that C. solibacter and C. koribacter were still lower under mulch than those of other herbicides. My study suggested that the application of mulch in the riparian revegetation projects would be beneficial for soil microbial functionality, particularly soil MBC as compared with [glyphosate and other organic-based herbicides. Additionally, this study suggested that some herbicides like glyphosate and BioWeedTM may have long-lasting effects on soil 125 microbial biomass even if they do not necessarily change microbial diversity. Hence, the long-term use of glyphosate and BioWeedTM needs to be considered with caution. Some woodlands within riparian zones are also horticultural sites where intensive weed control management practices are applied (Chapter 4). Therefore, an established horticultural site (Macadamia orchard) located in a riparian zone, with a history of repeated application of glyphosate (up to four times per annum for 12 years) was chosen to understand the impacts of repeated application of glyphosate interacted with biochar on soil N cycling. Wood-based biochar was first applied at this site in 2012 (64 months before my sampling time) at two different rates of 10 dry t ha-1 (B10) and 30 dry t ha-1 (B30) and the glyphosate had not been applied for two years before my sampling. Therefore, biochar and glyphosate applications coincided for three years before glyphosate was ceased. The results showed that soil TN was significantly higher in the glyphosate applied areas compared with those of no glyphosate, which may suggest that glyphosate may have stimulated N transformations in this study through increasing soil carbon (C) substrate resulting from the degradation of glyphosate and dieback of weeds. Similarly, no effect of glyphosate on soil microbial diversity and community structure was observed two years after glyphosate application had been ceased. However, glyphosate-treated soil had significantly higher AOB abundance than no glyphosate areas, which might be potentially associated with increased total carbon (TC). Conversely, biochar did not affect soil TN in this study, potentially due to the low TN content of the biochar used in this study (wood-based biochar), but had also significantly higher AOB abundance than those of no biochar plots, potentially through stimulated N cycling. In summary, neither glyphosate nor biochar impacted soil microbial diversity or community structure, but both increased AOB abundance with possible long-term implications on soil N cycling even after two years since the last glyphosate was applied. In Chapter 5, I then investigated the short-term N pools in response to the immediate interaction of glyphosate in an amended soil with biochar. I conducted an incubation study (5-day) to understand the short-term and immediate effects of glyphosate interacted with biochar on soil N transformations (ammonification, nitrification, and N mineralisation) using the 15N pool dilution techniques. Soil samples were collected from the same horticultural site used in Chapter 4. My 5-day incubation study showed that δ15N of NO3--N was not affected by any of the factors assessed including glyphosate, biochar, nd moisture content, nor were their interactions significant. However, this study showed that both nitrification and N mineralisation were stimulated by biochar. My results also showed that application of glyphosate significantly decreased δ15N of NH4+-N in soil following 3- and 5-day incubation, indicating that N mineralisation occurred, which could be related to stimulation of soil microbes due to the addition of C as a source for soil microbes resulting from the decomposition of glyphosate. In summary, my work highlighted the importance of revegetating riparian zones to increase soil N retention particularly using woodland species and showed that glyphosate and organic-based herbicides may not necessarily alter soil microbial diversity but there were long-lasting effects on soil microbial biomass observed about one year after the application being terminated. In the horticultural site, there was also an indication of both glyphosate and biochar having affected soil microbial abundance. This long-lasting effect of herbicides on soil N cycling may have implications for the long-term sustainability of riparian zones. Therefore, my work suggested that the application of mulch should be an alternative for chemical weed control when possible.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
Full Text

The methods currently used to evaluate cultivator weed control are imprecise and often biased. A new method was tested. An experiment was carried out at two sites in 1993 and again in 1994, using a split-plot design with four repetitions. Cultivation was carried out on weed populations simulated with rye grass (Lolium spp L.) and mustard (Sinapis alba L.) in 1993 and on both simulated and natural weed population in 1994 with Rabe Werk, Hiniker and Kongskilde cultivators. Weed control was assessed by the effective weed kill and the percentage of the area of the simulated weed population which was affected, and by counts and visual observations on the natural weed population. The new method provided an objective assessment of the cultivation treatments, especially by the effective weed kill index. The area affected approach was not suitable for all cultivation treatments. There was agreement between the proposed method and the conventional methods. This validated the proposed new method. Overall, the Hiniker with ridgers performed the best. The Hiniker without ridgers, and the Kongskilde with or without ridgers performed similarly. The Rabe Werk without goosefoot attachment resulted in the poorest weed control. The degree of weed displacement varied among the cultivators and was associated with weed density. The degree of weed displacement onto the crop row from the inter-row area was low ($<$1% in 1993 and up to 3.4 in 1994). The weed displacement distance was related to weed density and the degree of weed uprooting produced by cultivation.

Aquatic weeds transform and degrade the ecosystems which they invade, impacting various aspects of their surroundings ranging from the community level to disrupting important processes affecting ecosystem services. All of the major aquatic weeds of South Africa are found in the Cape Town Metropolitan Area. Landowners, whether private or public, are legally obliged to manage the listed invasive species through applying environmentally acceptable methodologies. This thesis provides an overview of the strategic management options, prevention, early detection, rapid response and eradication of new invasions, and containment and control species of established species. It discusses the different control methods available for managing aquatic weeds, namely mechanical, manual, chemical and biological, and the integration of different methods to improve their effectiveness. Although various studies have shown that biological control is the most cost–effective, environmentally-friendly and sustainable method, it is not yet fully integrated into weed management programmes in South Africa. In addition, the successes achieved in other parts of the world with the control of water hyacinth through biological control have not been repeated in the urban environment, despite the fact that South Africa has the highest number of biological control agents available for the weed. Urbanisation puts pressure on the natural environment and ecosystem functioning. Nutrient-enriched waters support aquatic weed growth and pose a challenge to the management thereof, in particular with regard to integrating biological control into management programmes. The aims of this study were to determine the reasons for the lack of integration of biological control into weed management programmes in South Africa, to determine the feasibility of integrating biological control in aquatic weed management programmes in a complex urban environmental and socio-political landscape by means of three case studies in the Cape Town Metropolitan Area, which showed that biological control is feasible in urban environments and should be considered. Two surveys were conducted to determine the reasons for the lack of integration of biological control into weed management programmes. The surveys showed that there is a gap between research and implementation as a result of poor communication, non-supporting institutional arrangements and a lack of appropriate capacity and skills at the implementation level. Recommendations were offered to address these issues.

A series of experiments were conducted to determine the potential of a new method of steam treatment for the control of soil-borne diseases, insects and weeds in sustainable crop production.  The new method involved rapidly heating a bed of prepared soil on a porous base by passing an upward flow of steam through it.  The aim was to determine whether the new method would be suitable for use in a field machine, making large-scale field steaming practically and economically viable. In the first experiments, the feasibility of the new method was tested.  It was shown that it was an effective and rapid way in which a soil bed could be steamed.  However, for some soils at, or near, permanent wilting point, the entrainment of aggregates in the steam flow was shown to be a problem.  The second series of experiments showed that the key factor determining the flow rate at which aggregate entrainment occurred was the mean aggregate diameter of the soil being treated.  The third series of experiments examined the rate at which heated soil would cool when placed in the field.  It was shown that where there was contact with unheated field soil, cooling was very rapid.  The final series of experiments investigated the effects of the new steaming method on the soil.  A three minute steaming time was used to account for the short time it had been shown some of the heated soil would remain at steam temperature when replaced in the field.  The effects of the new method, including the effectiveness of disinfection, were shown to be similar to those of a conventional steam treatment. It was concluded that the new steaming method was an effective way to steam treat soil and should be suitable for use in a field machine.

Cette étude s’inscrit dans le cadre de l’inspection en service des soudures des réacteurs nucléaires de génération IV, en vue de contribuer à la démonstration de sûreté. La structure anisotrope et hétérogène des soudures multipasses en acier inoxydable austénitique rend leur contrôle ultrasonore difficile. Ainsi, afin d'interpréter correctement les signaux mesurés et de caractériser les défauts potentiels, une description de la soudure est utilisée. Elle constitue la connaissance a priori introduite dans la méthode de l'Energie Topologique. L’étude réalisée se décline en deux temps : le développement de la méthode en milieu borné et sa comparaison avec le Matched Field Processing, puis son application au cas de soudures réelles. L'extension de la méthode de l'Energie Topologique aux milieux bornés isotropes et homogènes vise à tirer parti des réflexions multiples. Plusieurs solutions du problème numérique de propagation, obtenues pour différentes conditions aux frontières, sont judicieusement associées afin de sélectionner les échos de diffraction porteurs d'information. Selon le type de défaut à imager des énergies topologiques spécifiques sont définies. La technique est introduite analytiquement avant d'être validée numériquement puis expérimentalement.Dans un second temps, la méthode est appliquée au milieu complexe de la soudure. La procédure est testée expérimentalement sur des soudures réelles afin d'évaluer les performances en localisation. Cependant, en raison de la variabilité de la structure, la qualité de l'image peut se dégrader selon les cas d'étude. La possibilité de générer des sources arbitraires permet de pallier en grande partie cette difficulté
The present study has been done as part of the in-service inspection of weld structure belonging to generation IV nuclear reactors. It aims at checking both the safety and integrity of these components. The anisotropic and heterogeneous structure of austenitic stainless steel welds disturbs the ultrasonic non destructive testing. Thus, a weld description model is necessary to properly analyze the ultrasonic measured signals and to characterize potential flaws. The weld model makes a priori knowledge up in the Topological Energy method. The study is divided into two parts: development of the method in a bounded medium and comparison with the Matched Field Processing method, and then its application to real weld structures.The work firstly focuses on expanding the Topological Energy method to isotropic and homogeneous bounded medium to take advantage of multiple reflections between the flaw and edges. For that, different conditions are numerically applied to boundaries. By adding up these conditions it becomes possible to select the appropriate scattering signal. Modified topological energies are defined according to the type of analyzed flaws. The approach is analytically demonstrated before being validated firstly from synthetical data and then from experimental data.The second part deals with the application of the method to the complex weld structure. The process is experimentally tested on welds in order to evaluate efficiency of flaws localization. However, the image's quality can be deteriorated because of variability of the structure. By generating arbitrary ultrasonic source this difficulty is mostly overcame

Le travail presente dans ce memoire concerne une etude du devenir d'un herbicide du mais, l'atrazine en condition de plein-champ: bilan et modes de dissipation. Des experimentations de laboratoire mettant en jeu des methodes diverses (suivi de l'atrazine #1#4c, couches minces et colonnes de terre, lysimetre non remanie) permettent d'etayer les resultats obtenus sur la parcelle experimentale du site observatoire des pollutions diffuses du lycee agricole de la cote saint andre (isere, france) ou a ete suivie pendant 3 ans la composition en herbicide et metabolites du sol sur 1 metre de profondeur et celle de l'eau interstitielle prelevee par bougies filtrantes. La matiere active (1 kg/ha) apportee annuellement fin avril se dissipe selon cinq voies d'importances tres inegales: volatilisation (15%), absorption par la culture (10%), adsorption sur le complexe argilo-humique et metabolisation (40-50%), entrainement vers les eaux profondes (30-40%). Dans la situation etudiee, les deux voies principales sont la metabolisation par la microflore du sol et l'entrainement lors des episodes pluvieux precoces. Apres un an de culture, la teneur en atrazine et derives au sein du premier metre de sol est voisine de 400 g/ha ce qui indique que l'evacuation de la matiere active n'est pas complete. Notre etude de terrain completee par une experimentation de laboratoire, conduit a mettre en evidence la possibilite de pertes precoces importantes de matiere active durant les deux premiers mois de culture. Trois concepts importants relatifs a l'efficacite d'un herbicide de prelevee emergent de notre etude: la concentration critique dans l'eau du sol, la duree critique durant laquelle cette concentration doit etre maintenue pour assurer l'effet herbicide, la profondeur critique qui represente la couche de sol dans laquelle doit jouer l'effet herbicide. Pour l'atrazine en culture de mais, dans nos conditions, ces criteres ont ete mesures: concentration critique: entre 50 et 200 micromoles ; duree critique: deux mois ; profondeur critique: 10 cm. Avec 1 kg/ha d'atrazine sous forme de suspension concentree, les trois criteres d'efficacite sont remplis malgre d'importantes pertes par drainage lors des episodes pluvieux precoces. Des modifications de formulation ayant pour consequence un relargage progressif devrait permettre l'economie d'une part importante de matiere active. La derniere partie de ce travail concerne une approche de mise en place de solutions alternatives de traitements herbicides en culture de mais

Thesis (M. S.)--Michigan State University, Dept. of Crop and Soil Science, 2006.
Title from PDF t.p. (viewed on November 12, 2007). Available through UMI ProQuest Digital Dissertations. Includes bibliographical references (leaves 88-93).

Thesis (M.A.) (Agriculture) --University of Limpopo, 2008.
Striga control through agronomic practices is the key to maize production predominantly in small holder farmers who cannot afford chemical weed control. Striga has affected maize yield in many areas in Limpopo Province, South Africa. Field experiments were carried out over one season at three sites to determine the effect of weed control method on striga on maize. The experiment was done at Mafarana village (Mopani District) near Tzaneen where striga is a serious problem. It was conducted on three fields, belonging to Mrs. Shingwenyana, Mr. Nyathi and Mr. Mushwana. A randomized complete block design experiment was laid out consisting of two factors; (i) two maize cultivars i.e. Zm 1421 and Zm 423 (ii) three agronomic practices: hand hoeing alone (as the control factor), hand hoeing plus inorganic fertilization using lime ammonium nitrate (LAN-28%N) at the rate of 56kg/ha, and hand hoeing plus inter-row intercropping of maize with cowpea. Cowpea cultivar Bechuana White was used for the experiment. The results indicated that the effect of the method of weed control on the number of striga plants was significant at the 5% level of significance at all locations except at Mushwana’s where at 105 days after planting (DAP) there was no significant effect. Striga numbers were lower in hand hoed plus inorganic fertilizer plots compared to hand hoed alone and hand hoed plus intercropping. At Shingwenyana’s field the results indicated that effect of weed control methods on grain yield was significant and this is where the striga numbers were the highest than at Mushwana and Nyathi’s fields. The effect of weed control methods on grain yield was significant only at Shingwenyana’s field ranging from 2219kg/ha (hand hoeing), 2248kg/ha (hand hoeing plus inorganic fertilizer) to 3928kg/ha (hand hoeing plus intercropping). The effect of weed control method on shelling %, hundred seed weight, number of cobs per plant and lodging % was not significant. The effect of weed control method on number of plants per plot was significant at Mushwana’s field only. There was significant difference of striga numbers among maize varieties at Nyathi’s field at 105 DAP. In hand hoed, striga numbers were 0.075 for Zm 1421 and 0.489 for Zm 423. Plots that were hand hoed plus inorganic fertilizer application striga numbers were 0.075 for Zm 1421 and 0.270 for Zm 423 and finally hand hoed plus intercropped plots with maize and cowpeas had striga numbers of 0.739 for 1421 and 0.850 for ZM 423. It is recommended that farmers improve the fertility status of their soils in order to control striga problem.
Limpopo Department of Agriculture

Maize (Zea mays L) is a staple food crop grown in South Africa by both large scale commercial and smallholder farmers. During the 2013/14 cropping season maize occupied about 2.6 million hectares of the total 3.9 million hectares of arable land that was under field crops in South Africa. Maize accounted for about 12.4 million tonnes of the 14.4 million tonnes of all field crops produced. Excessive competition from weeds is a major constraint, reducing maize yield and farmer income. Resource poor and inexperienced emerging farmers who have acquired land through the government land redistribution programmes are particularly affected. To date about 5.7 million hectares of land have been transferred to about 4.2 million black (previously disadvantaged) emerging farmers. Although emerging farmers have several options available for weed control, these still need to be appraised with regards to benefits, in the form of grain yield measured against the cost of weed management. An on-farm study was carried out at two sites in the North West province of South Africa during the 2011/12 and 2013/14 cropping seasons. The objectives were:- ? To determine the effect of different weed control methods on maize yields of emerging farmers at two localities in the North West province. ? To identify the most competitive or problematic weed species at two localities in the North West province. ? To compare the economic benefit of different weed control methods at the two localities. The experiment was laid out in a split-plot randomised block design. A stacked gene (stalk borer and herbicides resistance) and a conventional maize cultivar were planted in strips. Eight weed control methods that included hand-weeding, mechanical, chemical (herbicides) and combinations of these methods were randomly allocated across the strips. Weed species were counted and crop heights were recorded at three and eight weeks after crop emergence (WACE). Weed dry biomass was also determined. Grain yield and the yield components of ear mass and 100 kernels mass were recorded. A cost-benefit analysis of these weed control methods was carried out in the context of total production costs. The highest maize grain yields were obtained, where weed competitive effects were satisfactorily suppressed. The clean field and pre- and post-emergence herbicides methods produced the highest grain yields in the two seasons. In the first season the highest grain yields obtained were 73% higher than the lowest yield in no-weeding method for both cultivars. The second season was characterized by below average and erratic rainfall. The stacked gene cultivar outperformed the conventional cultivar by 63% where weeds were effectively controlled. Weed competition seemed to cancel the superiority of the stacked gene cultivar over the conventional cultivar in a drier season. The cost-benefit analysis revealed that a single cultivation operation at six WACE was the cheapest method, costing only R 495 ha-1 irrespective of the cultivar used. Keeping a clean field throughout the season was the most costly endeavour, at R 2 528 ha-1 and R 2 174 ha-1 for the conventional and the stacked gene cultivar respectively. The use of both pre- and post-emergence herbicides on stacked gene cultivars can provide farmers with a return of up to R 2.60 for every R 1 invested. Controlling weeds in a conventional maize cultivar, using tractor-drawn cultivator at six WACE, can give a return of up to R 1.64 for every R 1 invested. The weed control methods that provide the highest grain yields are not necessarily the most cost effective. It is preliminarily recommended that chemical weed control methods be considered if stacked gene cultivars are to be planted. However, mechanical weed control methods must be considered when planting conventional cultivars. The present study needs to be intensified, covering a wider geographical extent, to cater for variation that can be expected as a result of differences in climate, soil type and weed spectra.
Dissertation (MSc Agric)--University of Pretoria, 2016.
tm2016
Plant Production and Soil Science
MSc Agric
Unrestricted

This thesis deals with the occurrence, biology and control of dangerous weeds on arable land. The thesis aims to process the selected weeds in stands of cultivated crops overview of the biology, extension and suggest regulatory measures for especially dangerous weeds on arable land as for example Elytrigia repens L., Cirsium arvense L. and other. For selected species were assayed determination germination of seeds and detection weight thousands of seeds.

Weeds currently represent a constant risk to the crop plants. They are able to either suppress the development of a crop plant in the initial period of its growth or to hinder and even make the harvest impossible due to its stand density at the end of the vegetative phase before the harvest. Perennial weeds rank among very noxious weeds. They are highly resistant and able to adapt to the used control measures. The character of the crop plants itself and the applied agronomic practices determine the occurrence of different weed species. For this reason, the question of how to deal with weeds still remains crucial. The diploma thesis is focused on the occurrence and the harmful effects of selected weeds in two Maize hybrids (Zea mays). The incidence of weeds and the effect of herbicides on those weeds were monitored within an experiment conducted on a small plot of land. The following weed plants occurred: Couch-grass (Elytrigia repens L.), Creeping thistle (Cirsium arvense L.), Barnyard grass (Echinochloa crus-galli L.), Scentless mayweed (Tripleurospermum inodorum L.), Goosegrass (Galium aparine L.) etc. The aim of the thesis is to expand knowledge of the use of different weed control methods in Maize. Recommendations on the use of those methods in agriculture shall be suggested.

The thesis contains various methods of regulating dangerous weeds occurring on arable land in the cover of oilseed. It also contains a brief description of how the actual oilseed (Brassica spp.), as well as various weeds that are widespread in oilseed covers. The actual work took place at the at the School Farm the Agricultural Technical School in Tábor. A small-plot experiment was conducted here. The evaluation of the frequency of weed occurrence n the selected experimental plots was conducted in two varieties of oilseed and two hybrid varieties of oilseed. The findings of different varieties were compared. At the conclusion of the actual work, the thesis includes economic evaluation and the proposed measures.

In spite of the relative simple vegetation structure, the Grassland biome has surprisingly high species diversity. The Grassland biome is also the most transformed biome in South Africa, with cultivation having the largest impact. When croplands are abandoned, secondary succession leads to low diversity Hyparrhenia hirta dominated grassland. A combination of two seed mixtures, two seeding densities and two establishment methods was established in plots on a recently abandoned cropland at Suikerbosrand Nature Reserve to evaluate their effect on secondary succession. The rip plots, where more resources were available between the rip lines, have shown higher densities of relic weeds as well as local perennials, showing some progressive successional movement. However, Hyparrhenia hirta was one of the non-sown perennials increasing in the rip plots. Hyparrhenia invasion and relic weeds were best controlled in the plough plots. Although Hyparrhenia was successfully controlled in plough plots, no secondary succession occurred in these treatments.
Agriculture, Animal Health & Human Ecology
M. Tech. (Nature Conservation)

Thesis (M.S.)--University of Wisconsin--Madison, 1990.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 77-81).

Thesis (M.S.)--University of Wisconsin--Madison, 1991.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 92-98).

Eucalyptus grandis was introduced into South Africa in the 19th century, and has since become the most important of the hardwood plantation tree species grown for pulp. Until the late 1980's E. grandis was virtually the only eucalypt species grown. In order to meet the increasing demand for pulpwood in South Africa, forestry companies need to increase their timber output from an existing land base (Brown and Hillis, 1984; Kimmins, 1994 and Little and Gardner, 2003), or alternatively extend the planting of favourable alternative tree species into areas previously considered unsuitable for forestry due to unfavourable climatic conditions. From 1984 the major timber companies expanded their plantation forestry into the colder, frost-prone highland areas of western KwaZulu-Natal, the northeastern Cape and southeastern Mpumalanga Highveld. As E. grandis was not tolerant to severe frost, E. macarthurii amd E. nitens were planted in these areas as alternatives (Schonau and Gardner, 1991). As much of the earlier research had been centered around the development of silvicultural standards for E. grandis, it became necessary to test these for the different eucalypt species. Two trials were therefore established to E. marcarthurii and E. nitens with the following objectives: - to extend current recommendations to include different species, - to determine the degree of interaction between different silvicultural standards (genetic improvement, fertilisation and weed control), - to determine the effects of weeds, fertilisation, genotype and regeneration method (seedling vs coppicing) on the initial and long term growth, uniformity, tree straightness and survival of cold tolerant eucalypts, - cost effectiveness of various methods for re-establishing E. nitens and E. macarthurii. Genetic improvement played an important role in the establishment and initial growth of E. macarthurii and E. nitens. The improved treatments outperformed the unimproved treatments in terms of tree growth until canopy closure. At the last measured date when the trees were six years of age, the E. nitens improved seedlings were still significantly better in terms of basal area when compared to unimproved seedlings. The initial positive effect of genetic improvement of E. macarthurii seedling however, was not sustained. Genetic improvement of E. macarthurii and E. nitens also had a positive effect on tree straightness and survival when the trees were assessed at five years of age. The genetic improvement of both species also showed to be a viable option to produce an optimum timber output at a lower cost when regeneration is carried out by means of replanting with seedlings. Fertilisation also showed positive effects in terms of the establishment and initial growth of E. macarthurii and E. nitens. At six years after planting, the basal area of E. macarthurii seedlings without fertiliser was still significantly lower than any one of the other treatments. However, the initial positive effect fertiliser had on the growth of E. nitens seedlings decreased to a non-significant level at six years after planting. Fertilisation of E. macarthurii and E. nitens had a positive effect on tree straightness and survival when the trees were assessed at five years of age. The fertilisation of E. macarthurii seedlings also produced an adequate amount of timber at a relatively low cost. The controlling of weeds did not have an impact on tree performance initially or after canopy closure for either E. macarthurii or E. nitens. This is due to the lack of weed growth at these high altitudes at which the sites were planted. Little and Schumann (1996) found that eucalypts could tolerate an aboveground weed biomass of up to 2000 kg ha (-1) before there were any severe losses in growth due to competition. At both these trials, the weed load did not reach these levels in order to compete with the trees. No significant interactions between any of the treatments were detected at both these sites at any stage. At the last measured date, there were no significant differences in terms of tree growth between the coppice and seedling treatments for either E. macarthurii or E. nitens. Regeneration by means of E. macarthurii and E. nitens coppice had a positive effect on tree straightness and survival when the trees were assessed at five years of age. Re-establishment by means of coppice for both E. macarthurii and E. nitens was also shown to be by far the most cost-effective way at present to produce an adequate amount of timber. Coppicing was shown to be the least costly way to produce a m2 ha(-1) of timber provided the right species are coppiced, and optimum density levels are obtained.
Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

Prosopis spp. are prolific seeders with estimates of seed production reaching from 630,000 to 980,000 seeds per mature tree per annum (Felker 1979; Harding 1988). Prosopis velutina shrubs have been recorded to produce up to 5,000 seeds per year (Glendening and Paulsen

1955). The plant has the ability to establish on disturbed or bare soil and can develop into very dense infestations. The plant often grows on scalded areas devoid of other vegetation and out-competes native herbage for moisture and light.

The plant is armed with long axillary spines; it branches from the base and has long arching stems. Its leaves are not commonly eaten by sheep and bovine breeds. Consequently, it forms dense stands that restrict the movement of stock, particularly around watering points, and this interferes with mustering.

There are many options for control of mesquite with herbicide application being integral in a management suite of mesquite control initiatives. Other control methods, which limit its distribution and spread, include mechanical removal, grazing management, competitive pasture

establishment, biological control, and a burning regime where adequate fuel is available.

The thesis discusses merits of the Prosopis species. Commonly known as mesquite or prickly bush, the Australian pest plant is endemic in the southern United States. The description then turns to how the weed was introduced into Queensland at both Quilpie and Hughenden in the north of the state. Some detail is given to its distribution and the effects on primary producers and the environment, and on the cost of control initiatives conducted through the Queensland Department of Natural Resources and Mines. 

Scientific findings from the research process are considerable given the base knowledge when the mesquite research project was revived in 1989. Initially, a research review of available literature was conducted revealing a large pool of knowledge from the United States of America. Their research findings on foliar applied herbicides have resulted in a high utilization of tank mixes principally containing triclopyr + clopyralid formulations sometimes with hydrocarbon additives. A more comprehensive summary of field research findings for Queensland is compiled as part of this thesis (Chapter 8) and presents some herbicide control options and constraints that may qualify their performance. Basal stem research in North America has produced many adopted recommendations. There have been numerous experiments on controlling mesquite with herbicides with many referred to in Control of Mesquite in the USA (Chapter 1). 

Chapter 2 presents a comparative analysis conducted to determine the different effects of applied herbicides to targeted young mesquite when applied in early summer compared to application in autumn. Formulations of fluroxypyr as well as metsulfuron methyl did not prove

efficacious in this trial. For the first time glyphosate proved to be a valuable herbicide in controlling mesquite when applied in autumn. Triclopyr + picloram and triclopyr alone proved to be more effective following wet conditions when applied in the early summer compared to the autumn application. However, treated plants growing adjacent to continuous paddock ponding were able to recover. Clopyralid exhibited high efficacy in both early summer and autumn treatment applications. 

Following poor control of Prosopis velutina at Quilpie by treatments recommended for control

of Prosopis pallida, a potted plant pilot trial was conducted to determine if the two species responded similarly (Chapter 3). The results indicated that Prosopis velutina was ineffectively controlled by herbicide application, at standard rates, compared to the control of Prosopis pallida. The follow-on replicated trial detail in Chapter 4 indicates a similar response for both

species. The effects of the treatments indicated differing susceptibility between the two species,

with metsulfuron, fluroxypyr, 2,4-D + picloram and triclopyr + picloram demonstrating the most pronounced differences compared to the glyphosate formulations here negligible difference occurred. A re -application of all herbicides to the surviving plants, and to a control

group, indicated that susceptibility can decrease when a follow-up application is in autumn and the time since initial application is short. This trend was particularly noticeable for P. velutina where previous sub -lethal damage prevented effective herbicide action. 

More fieldwork was conducted following this shade -house work as a prolific growth phase occurred in Quilpie mesquite in the early summer of 1999 (Chapter 5). Four glyphosate, and four triclopyr tank mixes and a control set out in each of three habitats made up the 27 plots evaluated in this aerial herbicide experiment. The triclopyr + picloram formulations at 5 and 7 L ha -1 with the addition of paraffinic oil (582 g L-1) and non-ionic surfactants (208 g L-1) produced the most efficacious and uniform results although triclopyr treatment with the addition of 1000 g L-1 alcohol alkoxylate produced similar results. However, the long-term effect was compromised because of the lack of a residual component in this formulation. 

A more manageable result was obtained when larger older plants were foliar overall sprayed using truck -mounted high pressure equipment (Chapter 6). A total of 33 treatments were assessed after each of four assessments of various herbicide mixtures. A blocking factor was plant density. Glyphosate tank formulations were consistently more efficient than other treatments, at all densities, except in combination with metsulfuron methyl. In the low density plots flumetsulam 0.10 g L-1 + glyphosate 3.60 g L-1 tank mix performed significantly better

than other treatments between the second and third applications and the third and fourth applications. Treatments containing clopyralid also showed high efficacy.  

A further experiment using the most common method of control (basal stem application technology) was conducted using dieseline as the herbicide carrier in March 1995 (Chapter 7).

The higher strength treatments with dicamba and triclopyr formulations showed the most activity irrespective of plant size (> 1.5 m or < 1.5 m) or water availability with the higher strength of each formulation, dichloromethoxybenzoic amine @ 10 g a.i. L-1 and triclopyr butoxyethyl ester 10 g a.i. L-1, being the most efficacious and not showing significant differenc from each other. 

In conclusion a three-year cycle planner was developed incorporating best control strategies researched within this thesis (Chapter 8). Suggestions were also put forward covering grazing management to enhance the effect of control strategies.

Dengue is a mosquito-borne flavivirus and is the leading arboviral cause of mortality and morbidity in the world. The World Health Organization estimates there are ca. 50 million dengue cases yearly, with 2 billion people at risk of contracting dengue. In Australia, 27 outbreaks of dengue have occurred in North Queensland since 2000, resulting in over 2,500 notifiable cases, including two deaths in 2004 and another dengue related death in 2009. The mosquito Aedes aegypti (Linnaeus) (Diptera: Culicidae) transmits dengue in Australia. In Australia current dengue control consists of a combination of source reduction and deployment of Lethal Ovitraps (LO). With increasing numbers and spread of dengue cases a fast, cost-effective control tool was required. This need lead to the development of the Biodegradable Lethal Ovitrap (BLO), an ovitrap made from a starch-based plastic which could be set in the field and allowed to biodegrade over time. If the BLO was to be a true "set and forget" tool against Ae.aegypti (and dengue) it was important to determine what happened to the BLO after the standard four week control period. The aim of this research was to determine the effectiveness of the BLO as a dengue control tool post four weeks deployment. This research also aimed to investigate what impact, if any, the BLO might have on the non-target fauna in the immediate area around where the ovitrap was set. It was also hoped that the research could also determine public acceptability of the BLO as a personal protective tool against mosquito borne diseases. Our results suggest that the BLO is still an effective control tool against Ae.aegypti twenty-two weeks post deployment. The ability of Culex quinquefasciatus (Say) (Diptera: Culicidae) to breed in the BLOs post nine weeks deployment was an important discovery, especially if the BLOs are to be deployed in countries where Cx.quinquefasciatus act as disease vectors. The research did raise the question of chemical resistance becoming an issue with the BLOs in the field for such extended periods of time. The research also found little impact on non-target fauna populations when compared against other non-target studies. Our results suggest that numerous (<90) insect Families are attracted to the BLOs with limited impact on their numbers. Further studies on specific non-targets could be of interest, especially to a broader international audience. Due to the limited number of participants in our BLO public acceptability research, our results were inconclusive, but suggested a limited acceptability. Further research into the acceptability and understanding of mosquito control tools such as the BLOs would be beneficial to mosquito control activities in the future.