Dissertations / Theses: 'Weeds'

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Tracey, Sara A. "In the Weeds." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1195243379.

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Howatt, Stephen M. (Stephen Michael). "Control of hexazinone tolerant weeds in lowbush blueberries." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61161.

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Field experiments were conducted from 1989 to 1991 to evaluate several sulfonylurea herbicides, glyphosate and clopyralid for the control of bunchberry and other hexazinone tolerant weeds in lowbush blueberry. Broadcast applications of chlorosulfuron, metsulfuron and glyphosate reduced bunchberry densities at all application dates, though crop damage and subsequent yield reductions were unacceptable. Glyphosate was very effective in controlling a large number of plant species when applied as a spot spray treatment. Tribenuron and DPX R9674 were effective in suppressing bunchberry stem densities at all application dates, without major adverse effects on blueberry, and also controlled a large number of hexazinone tolerant weeds when applied as a spot spray treatment. Clopyralid, at rates as low as 100 g a.i. ha$ sp{-1}$, was very effective as a broadcast treatment for the control of tufted vetch, although problems with crop tolerance and yield reductions were evident in some instances. Clopyralid did not control a large number of hexazinone tolerant species when applied as a spot spray treatment.

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Minkey, David Mark. "Weed seed predation by ants in the crop growing areas of Western Australia /." Connect to this title, 2006. http://theses.library.uwa.edu.au/adt-WU2007.0089.

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McGinley, Susan. "Fighting Weeds in Lemon Orchards: Weed-Sensing Sprayer Could be the Key." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2002. http://hdl.handle.net/10150/622246.

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Mühleisen, Martin Bernd. "Chemical weed control : options in fibre flax." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0031/MQ64411.pdf.

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Sciegienka, Joanna Katarzyna. "Vegetative reproduction and the integrated management of Canada thistle." Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/sciegienka/SciegienkaJ0509.pdf.

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Canada thistle (Cirsium arvense (L.) Scop.) is an aggressive, introduced creeping perennial weed that flourishes in a wide variety of environments. Its deep, creeping root system and colony forming tendencies make it one of the most difficult weeds to control. A strategy that incorporates a better understanding of the biology of Canada thistle into the development of an integrated management plan that includes herbicides and biological control could help reduce the dispersal and impact of this species. The objectives of this work were to: 1) determine how Canada thistle emergence and growth are affected by changes in root size, biomass, burial depth, and soil moisture and 2) compare single and joint impacts of herbicides and biological control agents on Canada thistle growth. Objective 1 was carried out in a greenhouse and in field conditions. To monitor Canada thistle emergence and growth responses, a completely randomized factorial design was used in the greenhouse, and a randomized complete block design was used in the field. Models were developed to predict emergence and growth patterns based on available water, burial depth, and various root metrics. For the exception of available water, the same predictors were used in field conditions to predict Canada thistle emergence and growth. The variables that were manipulated were able to significantly predict the responses measured, and we concluded that available water, root burial depth, and root weight, length, diameter, and volume are indicators of emergence likelihood, emergence time, shoot and root growth, and shoot number. Objective 2 was carried out in greenhouses and field settings. Three herbicides were evaluated with and without insects to determine reduction in Canada thistle root and shoot biomass in the greenhouse. One herbicide was also used at a low rate and evaluated singly and in combination with a stem-boring weevil (Hadroplontus litura (F.)) and a pathogen (Pseudomonas syringae pv. tagetis) to determine effect on Canada thistle response in the greenhouse and field. We failed to reject our null hypothesis of additivity between control agents, and concluded that integrating individual control methods yields greater Canada thistle control than any singular method.

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Goudy, Heather Jayne. "Evaluation of site-specific weed management and implications for spatial biology of weeds." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0022/MQ51068.pdf.

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Shirzadifar, Alimohammad. "Identification of Weed Species and Glyphosate-Resistant Weeds Using High Resolution UAS Images." Diss., North Dakota State University, 2018. https://hdl.handle.net/10365/29304.

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Adoption of a Site-Specific Weed Management System (SSWMS) can contribute to sustainable agriculture. Weed mapping is a crucial step in SSWMS, leads to saving herbicides and protecting environment by preventing repeated chemical applications. In this study, the feasibility of visible and near infrared spectroscopy to classify three problematic weed species and to identify glyphosate-resistant weeds was evaluated. The canopy temperature was also employed to identify the glyphosate-resistant weeds. Furthermore, the ability of UAS imagery to develop accurate weed map in early growing season was evaluated. A greenhouse experiment was conducted to classify waterhemp (Amaranthus rudis), kochia (Kochia scoparia), and lambsquartes (Chenopodium album) based on spectral signature. The Soft Independent Modeling of Class Analogy (SIMCA) method on NIR (920-2500 nm) and Vis/NIR (400-2500 nm) regions classified three different weed species with accuracy greater than 90 %. The discrimination power of different wavelengths indicated that 640, 676, and 730 nm from red and red-edge region, and 1078, 1435, 1490, and 1615 nm from the NIR region was the best wavelengths for weed species discrimination. While, wave 460, 490, 520 and 670 nm from Vis range, and 760, 790 nm from NIR region were the significant discriminative features for identifying glyphosate-resistant weeds. Random Forest was able to detect glyphosate-resistant weeds based on spectral weed indices with more than 95% accuracy. Analysis of thermal images indicated that the canopy temperature of glyphosate-resistant weeds was less than susceptible ones early after herbicide application. The test set validation results showed the support vector machine method could classify resistant weed species with accuracy greater than 95 %. Based on the stepwise method the best times for discrimination of kochia, and waterhemp resistant were 46 and 95 hours after glyphosate application, respectively. In addition, a field study was proposed on soybean field to identify weed species and glyphosate-resistant weeds using multispectral and thermal imagery. Results revealed that the object-based supervised classification method could classify weed species with greater than 90% accuracy in early growing season. Furthermore, the glyphosate-resistant kochia, waterhemp and ragweed were identified based on canopy temperature with 88%, 93% and 92% accuracy, respectively.

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Zwickle, Sarah Lynn. "Weeds and Organic Weed Management: Investigating Farmer Decisions with a Mental Models Approach." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1316453516.

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McCloskey, William B., Paul B. Baker, and Will Sherman. "Survey of Cotton Weeds and Weed Control Practice in Arizona Upland Cotton Fields." College of Agriculture, University of Arizona (Tucson, AZ), 1998. http://hdl.handle.net/10150/210369.

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The distribution of weed species and the herbicides and cultural practices used to control weeds in Arizona cotton fields were surveyed in 1995 and 1996. The most common weeds were purple nutsedge, bermudagrass, annual morningglory, Palmer amarnath, Wright groundcherry, common purselane, yellow nutsedge and Johnsongrass. The average statewide cost for hand weeding in 1995 was reported as $27.87 per acre in addition to other weed control costs. Statewide, most growers used preemergence herbicides before or at planting and used pre- and post-emergence herbicides later in the season. Most of these applications were broadcast applications suggesting that many of the postemergence herbicide applications were layby applications. Preemergence herbicides (usually applied preplant incorporated) such as Treflan, Prowl, and Prometryn were more commonly used than postemergence herbicides. Statewide, few growers banded preemergence herbicides or used electro- hydraulic quick-hitch guidance systems and in-row weeding tools with their cultivators.

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St, John-Sweeting Robin. "The biology and ecology of rampion mignonette Reseda phyteuma L." Title page, contents and abstract only, 1998. http://web4.library.adelaide.edu.au/theses/09AFM/09afms152.pdf.

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Bibliography: leaves 82-89. Rampion mignonette is an annual to short-lived perennial agricultural weed from the Mediterranean region, first found in vineyards at Clare, South Australia, in 1986. The biology and ecology of rampion mignonette was studied to provide a basis for its integrated control and management. The study includes a literature review, maps of world and Australian distribution and drawings showing plant habit and details. A field survey found that rampion mignonette showed little migration and that containment and population reduction could be achieved by careful management including both chemical and cultural techniques. Common herbicides were also found to be effective in controlling the weed. An experiment established that it is unlikely to become a major weed of broadacre crops and pastures in the South Australian dryland farming system. It does however have the potential to compete with grapevines and reduce grape yields.

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Weller, Sandra. "Detection and prevention of the dispersal of the seeds of Chilean needle grass (Nassella neesiana Trin. & Rupr. (Barkworth)) in hay bales." Thesis, Federation University Australia, 2016. http://researchonline.federation.edu.au/vital/access/HandleResolver/1959.17/103000.

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Invasive and noxious weeds are well known as a pervasive problem, imposing significant economic burdens on all areas of agriculture, and thus their control and eradication are of central concern to the industry. Whilst there are multiple possible pathways of weed dispersal in this industry, of particular interest to this discussion is how the unintended dispersal of Chilean needle grass (Nassella neesiana) weed seeds, within emergency fodder, may be prevented. Periodic drought is a feature of the Australian climate, which, together with natural disasters of flood and bushfire, necessitates the urgent provision of emergency fodder for maintenance of livestock production. However, previous investigations into weed seed dispersal by this fodder type have revealed a significant risk for the dispersal of a number of noxious weeds well beyond their current range. Because preventive work, relating to detection and eradication of noxious species, is at an early stage of development, the development of faster, more reliable, and non-destructive sampling methods for seed species has become essential. In addition to prevention of weed seed dispersal in fodder, the use of appropriate methods of controlling troublesome pasture weeds in situ is of relevance for addressing established infestations. Whilst silage preservation is one such typical method that can reduce weed seed input into the soil seed bank, there is currently little data on the absolute effectiveness of this method for control of N. neesiana. To investigate whether rapid detection of seeds in bales is possible and how the numbers of seeds in a pasture are linked to the numbers of seeds that may be incorporated into hay bales made from an infested pasture, an investigation of a rapid, non-destructive technique to detect seeds in bales, together with an examination of a pasture to estimate seed density and dispersal prior to baling, were carried out. Additionally, since pastures infested with this weed are of no use for producing hay and little use for grazing, a third experiment was devised, which was an investigation of silaging for preventing inadvertent seed input into pasture soil seed banks. This thesis has shown that this approach of non-destructive core sampling of bales to detect the seeds of N. neesiana, and possibly others, which can be visually recognised, shows promise for those involved in weed control. Similarly, the simultaneous demonstration that silage fermentation is an efficient viable method for both eliminating viability of mature (germinable) seeds of this species while also reducing the probability of injury to livestock from these seeds, confirms that reducing the impact of this weed in agro-ecological systems and on livestock during emergency situations is possible.
Doctor of Philosophy

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Smith, Carey. "Studies on weed risk assessment." Title page, contents and abstract only, 1999. http://web4.library.adelaide.edu.au/theses/09AFM/09afms644.pdf.

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Bibliography: leaves 124-136. This thesis gives an overview of factors used in weed risk assessments and explores the disparity between the measured high accuracy rate of the weed risk assessment system (WRA) as implemented in Australia and the pessimistic assessments of some workers about the possibility of predicting the weed potential of plant species imported in the future. The accuracy of the WRA may not be as high as previously thought, and it varies with weed definition and taxonomic groups. Cluster analysis and comparative analysis by independent contrasts were employed to determine the value of individual biological and ecological questions on the WRA questionnaire. Results showed that some WRA questions could be deleted from the questionnaire and the scores for others weighted differently. The WRA is not a reliable predictor of weeds when it is considered in the context of the base-rate probability of an introduced plant becoming weedy in Australia. As a result a far greater number on non-weeds will be placed on the prohibited imported list than was initially expected.

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Gunderson-Izurieta, Sharlyn Elizabeth. "Pulling together in the Estes Valley, Colorado a case study of a weed management area /." Laramie, Wyo. : University of Wyoming, 2007. http://proquest.umi.com/pqdweb?did=1317326611&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.

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Maina, J. Mukami. "The effects of intercropping on weeds and weed management in maize growing in Kenya." Thesis, University of Reading, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363436.

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Mutinda, Irene. "Biological control of mignonette weeds." Thesis, University of Reading, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266625.

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McMillan, James Paul. "Rounding Up The Astrophysical Weeds." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1460398754.

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McCoy, Jan. "Treating Waste Water With Weeds." College of Agriculture, University of Arizona (Tucson, AZ), 1990. http://hdl.handle.net/10150/295662.

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19

Thomas, Dean Timothy. "Selective grazing by sheep to improve the control of weeds of crops." University of Western Australia. School of Animal Biology, 2006. http://theses.library.uwa.edu.au/adt-WU2006.0041.

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[Truncated abstract] With the rapid development of multiple herbicide resistant weeds in crops, it is likely that an important role now exists for new grazing management strategies in farming systems to provide an integrated approach to weed management. In this thesis we examined the general hypothesis that sowing a legume of low preference by sheep relative to the target weeds of crops would improve the control of those weeds in a grazed pasture. To test this general hypothesis, legumes of low preference by Merino sheep were identified and a series of experiments conducted to determine the effect on pasture composition when these less preferred legumes were incorporated into a grazed pasture. We found a learned response that altered forage preference by sheep was important in determining the effectiveness of grazing to reduce seed set by weeds of crops. Investigations on this aspect of the grazing behaviour of sheep were a key part of this thesis. The short-term relative preference of Merino hoggets among 15 pasture legumes, 4 grain legumes and annual ryegrass was determined by offering adjacent monocultures of each of the forage genotypes to the sheep. The relative preference of the hoggets for each of the 20 forages was determined at three phases of plant growth from estimates of the amount of forage consumed. Sheep showed a low selective preference for Vetch (Vicia sativa L.), chickpea (Cicer arietinum L.), biserrula (Biserrula pelecinus L.), lotus (Lotus ornithopodioides L.) and snail medic (Medicago scutellata L.) cvs. Kelson and Sava at the vegetative phase of plant growth. An indoor method was also developed to test the relative preference of sheep among forages growing in pots. Using this method chickpea and snail medic, but not biserrula, were found to have a low relative preference by sheep at the vegetative phase.

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Thomas, Dean Timothy. "Selective grazing by sheep to improve the control of weeds of crops /." Connect to this title, 2005. http://theses.library.uwa.edu.au/adt-WU2006.0041.

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Toresson, Fredrik. "Tidig Ozu / Sen Ozu : En jämförande stilanalys av A Story of Floating Weeds och Floating Weeds." Thesis, Stockholm University, Department of Cinema Studies, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-912.

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Syftet med denna uppsats är att jämföra ett av Ozus tidigare verk stumfilmen A STORY OF FLOATING WEEDS (1934) med ett senare, färg- och ljudfilmen FLOATING WEEDS (1959). Hur skiljer sig dessa åt stilistiskt, vad förenar dem, vad följer t ex av närvaron av färg och ljud i den senare och avsaknaden av desamma i den tidigare filmen.

Analysen utgår från ett neoformalistiskt perspektiv och i en teoretisk genomgång redogörs för denna inriktnings begreppsapparat. Centrala begrepp häri är t ex främmandegörning, d v s av-naturaliseringen av den vardagliga perceptionen, stil, definierat som innefattande allt i verket, stilgrepp – det enskilda uttrycket isolerat, fabel, sujett, greppets funktion och bakomliggande motiv samt idén om den parametriska formen – verket som strukturerat efter en stilmässig dominant överordnad berättelsen.

Uppsatsen inkluderar även ett inledande kapitel vari tidigare forskning kring regissören redogörs för. Donald Richie är här en centralgestalt och uppsatsen pekar på den konflikt som kan skönjas mellan Richies traditionella budskapsorienterade perspektiv och neoformalismen.

Vidare diskuteras regissörens egensinniga stil och uppmärksamhet ägnas aspekter som t ex den lågt placerade kameran, rummet som ordnat kring 360 grader, det estetiskt motiverade rummet, mellan-liggande rum, hypermarkerade objekt, sujikai, rumsliga ankare, grafisk gestaltning och pillow-shots. Även budskapsorienterade tolkningar som återkommer i diskursen kring regissören ges utrymme, som idén om Mono no Aware, förnimmelsen om alltings förgänglighet och Mu, tomhet som närvaro.

I analysdelen studeras sedan olika sekvenser i båda verken utifrån dessa stilistiska aspekter. Slutsatsen blir att även om nya teknologier såsom färg och ljud ger upphov till nya grepp så ordnas dessa nya grepp i någon mån in i den befintliga logiken – in i dominanten. Den tydligaste skillnaden mellan verken utöver dessa tillkomna stilistiska aspekter finns i sujetten som antar en än mer episodisk struktur i den senare filmen.

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Lavrador, Filipe Alexandre Casaca. "Vegetação infestante da linha ferroviária do Oeste. Controlo químico de Equisetum." Master's thesis, ISA/UTL, 2011. http://hdl.handle.net/10400.5/4066.

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Mestrado em Engenharia Agronómica - Instituto Superior de Agronomia
This study presents a characterization of vegetation composition in Oeste railway line of Portugal, owned by REFER EPE, with 196,947 kilometres between the towns of Agualva- Cacém and Figueira da Foz in Western Portugal. At 2010 Spring, inquiries were made at REFER EPE and at 2011 Spring, 109 weed surveys were made in three locations on railway track profile, plus an adjacent area. 372 taxa were recorded and distributed in 75 families, with predominance of Fabaceae, Asteraceae e Poaceae. The taxon Equisetum ramosissimum was the only with a high infestation degree, showing a relative frequency of 30,3% and a mean abundance of 20,7 plants per square metre. The bank area was, in some critical areas, colonized by perennial invasive species. Considering that the genus Equisetum was frequent and abundant, a field assay with different concentrations of flazasulfuron and triclopyr+aminopyralid was carried out. Three months after herbicide application the best efficacy was obtained with 0,30 g L-1 of flazasulfuron (90%) and 1002 g L-1 (80%) triclopyr+aminopyralid.

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Clayton, Neil, and n/a. "Weeds, people and contested places : selected themes from the history of New Zealanders and their weeds 1770-1940." University of Otago. Department of History, 2007. http://adt.otago.ac.nz./public/adt-NZDU20071129.105550.

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This study examines three basic questions. Why did so many familiar floral species with which agricultural people have more or less successfully contested places for some 10,000 years apparently become highly problematic in New Zealand? How did those in whom the developing contest aroused considerable anxiety try to solve the problems they saw emerging? And what were the outcomes of their chosen courses of action? This study is organised around three main themes, science, the law and agricultural practices. Within each theme I take into consideration the ways New Zealanders used particular aspects of these broad disciplines to try to identify, understand and solve the problems they perceived to have been caused by their weedy biota. I also consider the extent to which recourse to these means has helped or hindered the ends they sought. The methodology adopted for this study is a variation of an 'organisational approach', advocated by the German environmental historian Frank Uekoetter. It focuses on the ways responses to perceived environmental problems are organised within a society. From my use of Uekoetter�s model I conclude that, despite a number of setbacks during the mid to late 19th century, by 1939 New Zealanders had developed highly dynamic processes within their weed science, extending into the wider farming community, by which they could feel their way with some confidence into a future where they might better manage the contest with their weeds, if not actually eradicate them.

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Omami, Elizabeth Nabwile, of Western Sydney Hawkesbury University, of Agriculture Horticulture and Social Ecology Faculty, and School of Horticulture. "Amaranthus retroflexus seed dormancy and germination responses to environmental factors and chemical stimulants." THESIS_FAHSE_HOR_Omami_E.xml, 1993. http://handle.uws.edu.au:8081/1959.7/66.

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A large number of weed seeds in the soil persist because of seed dormancy, and depletion of the seed bank through manipulation of seed dormancy has been suggested as one of the goals in weed control. This study was designed to investigate some of the factors which control dormancy and germination in Amaranthus retroflexus seeds. Germination studies were conducted at different temperatures, and either in continuous white light or in the dark. Higher temperatures increased germination and, although light interacted with temperature, its effect on germination varied with the temperature. In an attempt to determine changes in dormancy during dry storage, two lots of seeds were stored dry at different temperatures. Loss in dormancy increased with an increase in storage temperature and duration, but the time required for maximum germination varied according to the seedlot. Seeds germinated to higher percentages at high temperatures, but storage at higher temperatures and for prolonged duration resulted in seeds gaining the ability to germinate at lower temperatures. Changes in dormancy under field conditions were also examined. Seeds were buried at different depths and for different durations and they all lost viability with time, but this loss was greater in surface-sown and shallowly buried seeds. Dormancy was broken during cold periods and induced as warmer periods progressed. The effects of chemical stimulants on dormancy and germination were investigated. The response of seeds to ethephon and nitrate were assessed at different temperatures either at continuous white light or in the dark. Germination increased with the concentration of the chemicals, and a greater response was observed at lower temperatures. The response to light varied depending on temperature
Master of Science (Hons)

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Stark, Jennifer Grace. "The establishment, drought tolerance, and weed suppression potential of multispecies sod." Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/stark/StarkJ0509.pdf.

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Re-seeding is a frequently used technique to revegetate disturbed areas, but often leaves bare ground prone to weed invasion. Mixtures of drought tolerant or native species in sod could be used as an alternative to seed to provide rapid establishment of desirable plant communities that may potentially reduce weed emergence, survival, and productivity. Additionally, the reinforcement material required to aid transport of multispecies sod could further contribute to weed suppression and sod establishment. The objective of this study was to evaluate the weed suppression and establishment potential of multispecies sod. Three experiments were each subject to a water regime ranging from 2.54 cm of water/week to natural precipitation, and repeated over two/three years. In the first two experiments (A and B) Brassica napus (canola) was used as a surrogate weed species and sown either below the multispecies sod to represent weed seed bank, or above the multispecies sod to represent weed seed rain. In experiment A, B. napus was sown at six densities; while in experiment B reinforcement materials (nylon netting control, coconut-straw, jute, excelsior) were added below the sod and B. napus was sown at one density. B. napus suppression by multispecies sod, with or without reinforcement material, was evaluated by recording seedling emergence, survival and above-ground biomass. Multispecies sod, especially combined with reinforcement material, suppressed a large proportion of seedling emergence. The seedlings that did establish produced less vegetative and seed biomass as water decreased. In the second season of both experiments no seedlings survived to maturity. The establishment success of the multispecies sod was evaluated through repeated measures of percent sod cover over two/three years. The results suggested that the multispecies sod was able to establish and persist under natural precipitation. The third experiment evaluated the ability of multispecies sod to suppress Cirsium arvense (Canada thistle) vegetative propagules in two different habitat types, bare ground or multispecies sod, under high and low water treatments. More C. arvense shoots emerged in the bare ground, suggesting that multispecies sod could act as a buffer zone and reduce the vegetative spread of perennial weeds if used as a revegetation strategy.

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Mirsky, Steven B. "Evaluating constraints and opportunities in managing weed populations with cover crops." Restricted access (UM), 2008. http://libraries.maine.edu/gateway/oroauth.asp?file=orono/etheses/37803141.pdf.

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These (Ph.D.)--Pennsylvania State University, 2008.
Title from PDF title page. Available through UMI ProQuest Digital Dissertations. Includes bibliographical references (leaves 164-171). Also issued in print.

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Ford, M. A. "Pollinator-mediated interactions between outbreeding annual weeds." Thesis, Swansea University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636991.

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Self-incompatible annual weed species, with similar flowers, flowering time and ecology were used to investigate the relationship between relative abundance, pollinator service and seed-set in two-species mixtures. In mixed stands of the mayweeds Anthemis cotula L. and Tripleurospermum inodorum (L.) Schultz Bip. the common capitulum-visiting insects (hoverflies and other diptera) seemed to find the two species equally attractive, frequently flying from one to the other. In a survey of wild populations of these species the number of insect visitors per capitulum was independent of the number of capitula per m². These observations suggest that where A. cotula and T. inodorum co-occur the number of insect visits to each is not affected by the presence of the other. However, when mixtures of A. cotula and T. inodorum were grown in garden plots the number of insect visitors per capitulum was lowest in the plots where the number of capitula per m² was highest. Thus it would seem that sometimes when A. cotula and T. inodorum grow together each species reduces the number of insect visits to the other. In 9:1 and 1:9 mixtures of A. cotula and T. inodorum the percentage of seeds set by each species when the minority type was sometimes significantly lower than when forming the majority in a nearby plot. It is likely that this occurred because most pollinators visited both species (ie. they were not 'constant'), and thus there were few direct flights between minority individuals, so that pollination of these plants was very ineffective. Container-grown Sinapis arvensis L. and S. alba L. were placed in an experimental garden in single-species groups (6 plants) and 1:9 and 9:1 mixtures (60 plants, a 'majority' of 54 and a 'minority' of 6). Individuals were moved between sites and their seed-set assessed when in single-species, majority and minority situations. Majority and single-species seed-sets were similar, but minority seed-sets were significantly lower (in both species). The low minority seed-sets were due to ineffective pollination which occurred because most insects visited both species whilst foraging in the mixed groups, and thus few visits to minority flowers were immediately preceded by visits to flowers on another minority plant. The incompatibility system of Sinapis arvensis was studied in plants collected from farmland in South Wales. The results obtained are consistent with there being a single locus, multiallelic, sporophytic incompatibility system in this species. In the population investigated there were at least 14 S-alleles, and probably more than 24. By labelling individuals it was shown that females of the solitary bee species Colletes daviesanus Smith returned repeatedly to forage at the same sites.

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Tickes, Barry. "Preharvest control of broadleaf weeds in wheat." College of Agriculture, University of Arizona (Tucson, AZ), 2003. http://hdl.handle.net/10150/205404.

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Nine herbicide treatments were evaluated for the control of mature nettleleaf goosefoot in durum wheat that was ten days from harvest. The only effective treatments were combinations of Glyphosate (Roundup Ultra Max and Touchdown) and Paraquat (Gramoxone). Applications of Aim, Gramoxone, and Glyphosate alone were ineffective.

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Amisi, Karen Janila. "Strategies for managing weeds in a wheat, red clover, vegetable crop rotation transitioning to organic production /." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1070933281.

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Thesis (Ph. D.)--Ohio State University, 2004.
Document formatted into pages; contains 154 p. Includes bibliographical references. Abstract available online via OhioLINK's ETD Center; full text release delayed at author's request until 2005 Dec 28.

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De, Luna Lilian Z. "Pathogenicity of the three Curvularia isolates to Cyperaceae weeds and rice, Oryza sativa L." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=35869.

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Three isolates of Curvularia belonging to Curvularia tuberculata (isolates 93-020 and 93-022) and Curvularia oryzae (isolate 93-061) were obtained from diseased Cyperus difformis, Cyperus iria, and Fimbristylis miliacea, respectively, in the Philippines in 1993. Under greenhouse conditions, these fungal isolates caused high mortality and significant plant dry weight reduction in C. difformis, C. iria, and F. miliacea when sprayed at the rate of 1 x 108 spores/m3. Cross-pathogenicity of the isolates was demonstrated in three other sedge weed species. C. difformis, C. iria, and F. miliacea were killed but C. rotundus was resistant. Most of the thirteen rice varieties tested were resistant to the fungal isolates. The order of decreasing pathogenicity to rice was C. oryzae (93-061), C. tuberculata (93-020), and C. tuberculata (93-022). The infection process of C. tuberculata and C. oryzae was similar. Spore germination was polar for C. tuberculata and bipolar for C. oryzae. Germ tube growth was random and branching. Appressoria were formed preferentially over epidermal cell wall junctions on sedge hosts and over stomatal apertures in rice. Complex infection cushions were observed only on sedge hosts. Infection hyphae developed inter- and intracellularly, causing epidermal cell walls to separate and mesophyll cells to shrink and collapse. The vascular bundles were not invaded. Colonization of susceptible weeds was rapid and conidiophores emerged from the stomatal aperture between 96 to 120 hours post inoculation (HPI). Resistance to C. tuberculata and C. oryzae in C. rotundus and rice was expressed as a delay in appressorial formation, inhibition of fungal growth after penetration, and lack of sporulation.

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Minkey, David Mark. "Weed seed predation by ants in the crop growing areas of Western Australia." University of Western Australia. Faculty of Natural and Agricultural Sciences, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0089.

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[Truncated abstract] In the crop growing areas of Western Australia, two economically important weed species, Lolium rigidum Gaud. (annual ryegrass) and Raphanus raphanistrum L. (wild radish), have evolved widespread herbicide resistance to multiple chemistry groups. Consequently, grain growers in the region have adopted an integrated approach to weed management that includes many non herbicide tools, however many more are needed as these weed species become increasingly more difficult to control. This thesis examines, in a series of field trials carried out in the Western Australian crop growing area, the potential for weed seed predation of annual ryegrass and wild radish by naturally occurring granivores as a new weed management tool for grain growers . . . The study discusses the implications of these results with the view to manipulating predation of weed seed through agricultural management practices. Ants were shown to be the dominant seed predator in this environment, especially in the centre of fields. The study has identified that the ant species Melophorus turneri (Forel), Monomorium rothsteini (Forel), Pheidole hartmeyeri (Forel) and Rhytidoponera metallica (Smith) are potential biological control agents for annual ryegrass seeds while P. hartmeyeri was identified as the only species suitable for biological control of wild radish seed pods. Ants were found to be sensitive to disturbance and some to crop residue type and these effects are discussed in relation to seed removal. This study of weed seed predation in agricultural fields is the most complete in this environment and can be used to inform further work in this area. It has identified that naturally occurring granivores can be used as a weed management tool.

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Davis, Philip Browning. "The invasion potential and competitive ability of Camelina sativa (L.) Crantz (camelina) in rangeland ecosystems." Thesis, Montana State University, 2010. http://etd.lib.montana.edu/etd/2010/davis/DavisP0510.pdf.

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Camelina sativa (L.) Crantz (large-seeded false-flax) is a recently introduced oilseed crop in Montana and has potential for large scale production for the biofuel market. However, due to weedy characteristics, the invasive potential of this species is of concern. A need exists to create a pre-entry protocol to accurately assess risk to minimize uncertainty inherent in qualitative weed risk assessment approaches. We assessed the probability of C. sativa to invade rangeland ecosystems of southwest Montana to address this concern. The objectives of this study were to 1) quantitatively assess the invasion potential of C. sativa by collecting demographic data over two years and developing a population dynamics model, 2) compare experimental results and modeling outcomes to predictions suggested by a qualitative weed risk assessment system, and 3) assess the impact of growing conditions on the relative competitiveness of C. sativa and Brassica napus (L.) (canola). Objective 1 was carried out in two contrasting rangeland ecosystems to assess the effects of disturbance and seeding season on emergence, survival, and fecundity rates of C. sativa. Population growth (lambda) was forecasted by developing a population dynamics model. Resulting lambda values from simulations using observed data never exceeded 0.03 and the maximum time to extinction was six years. The low lambda values indicate that the threat of invasion by this species in the studied ecosystems is low. Objective 2 compared quantitative results to predictions from the Australian weed risk assessment (WRA) model. In contrast to experimental results, outcomes from the WRA suggested that this species should not be allowed entry into the region. These opposing results highlight the need for a more comprehensive approach to weed risk assessment. Objective 3 was conducted over three trials in two greenhouses. A replacement series design was used to estimate the effects of soil conditions and the presence of an invasive weed, Bromus tectorum (L.) (cheatgrass, downy brome), on the competitive outcomes between C. sativa and canola. Replacement series diagrams determined that competition occurred and that canola was the superior competitor in all treatments, thus providing further evidence that the invasion potential of C. sativa is low.

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Eriksson, Anna-Mia Hansson David Huisman Mark Lundh Jan-Erik. "Metoder för vegetationsbekämpning på banvallar : en summering av resultat från UICs Vegetation Control Project och erfarenheter från Institutionen för landskaps- och trädgårdsteknik = Vegetation control methods on railway embarkment and track area/." Alnarp : Sveriges lantbruksuniversitet, Institutionen för landskaps- och trädgårdsteknik, 2004. http://publikationer.slu.se/Filer/Rjrapportslutversionskrivskyddad.pdf.

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Poliquin, Bernard. "Quackgrass [Agropyron repens (L.) Beauv.] control in potatoes with quizalofop-ethyl." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59287.

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Field trials were conducted to evaluate the effect of quizalofop-ethyl on quackgrass plants in a potato cropping sequence. Fall and summer applications were compared for their quackgrass control potential. Season-long quackgrass control was obtained with quizalofop-ethyl at 96 g/ha following summer application. An increase in the rate of quizalofop-ethyl did not further improve control. Yields with quizalofop-ethyl at 96 g/ha were similar to standard treatments sethoxydim and fluazifop-butyl at recommended rates. Quackgrass control following a summer application was not maintained through to the following season. Fall applications did not result in adequate control of quackgrass the following season at any of the quizalofop-ethyl rates tested.

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Humphries, Talia. "Initiating temperate grassland restoration by controlling the dominant weed species; a case study with Nassella trichotoma." Thesis, Federation University Australia, 2022. http://researchonline.federation.edu.au/vital/access/HandleResolver/1959.17/187267.

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Temperate grasslands are globally important biomes, in that they (i) provide habitat for a wide diversity of species, (ii) sequester large stocks of carbon, and (iii) provide forage for important pollinators (Chapter 1). These ecosystems often fall within highly fertile areas, and consequently humans have come to depend on them to provide high quality forage for grazing livestock and land for agricultural development. Temperate grasslands are considered to be critically endangered on a global scale. The grazing industry relies upon healthy and productive grasslands for the production of a substantial proportion of human food products, however, when these systems incorporate unsustainable land-management practises, such as over-grazing and continual fertilisation with inorganic matter, has resulted in a significant decline in important native grass species. This has resulted in encroachment of unpalatable, noxious plants, which decrease the quality of available forage. One such noxious weed species, Nassella trichotoma, known commonly as serrated tussock, is having a significance impact on the constitution of temperate grasslands and grazing systems, globally, due to its unpalatability and competitive growth form. In order to return temperate grasslands to a fully-functional and a high-quality forage state, human intervention in terms of ecosystem restoration is required. The control of noxious species, together with the reintroduction and establishment of native species, is a critical step for restoration efforts with the return of native plant diversity, and the re-establishment of ecosystem services, such as habitat for higher trophic levels. This thesis reviews and overlaps the scientific disciplines of ecosystem restoration (Chapter 2), weed science relating to N. trichotoma (Chapter 3), and environmental management in order to provide solutions for controlling N. trichotoma in non-native grassland communities (Chapter 4). The effect of direct herbicide application, soil tillage, grazing exclusion, fire, and broadcasting native seeds for the control of this dominant weeds in a total of 13 different combinations is investigated. The experimental plots were surveyed over a four-year period and soil cores were collected over a three-year period to survey the seedbank density. It was found that the inclusion of fire significantly increased the establishment of the native broadcast species. Also, without the integration of fire or tillage, N. trichotoma recovered, and consequently was observed to be the dominant species in the final sampling period. To support the findings of Chapter 4, research into the seed longevity and seedbank persistence of N. trichotoma was undertaken in Chapter 5. It was found that less than 10% of the seeds were observed to be viable after 12 months of burial in field. In addition to this, the longevity of the seeds was determined by rapidly ageing the seeds through exposure to high relative humidity and temperature. This process determined that N. trichotoma produces transient seedbanks, referring to those that persist for 12 months or less, and therefore the seedbank would be reliant on new seed input annually to remain a competitive threat. This implies that management control of new seed fall is essential to prevent the reestablishment of the seed bank. The seedbank persistence for N. trichotoma is complicated by disturbance events such as fire. To investigate this impact, four different collection years; 2016, 2017, 2018, and 2019 were subjected to increasing heat (80, 100, 120, or 140OC) and time of exposure (1, 3, 6 or 9 minutes) by placing them into a temperature-controlled oven for the given treatment. It was found that only the 140OC treatment was significant for killing N. trichotoma, as detailed in Chapter 6. High moisture content (95%) increased the seeds sensitivity to radiant heat, with all tested temperature effective for killing this species. The seedlings were not killed by the tested treatments. Management implications and recommendations for the control of N. trichotoma in temperate grasslands (Chapter 7) include; (i) the use of herbicide in Autumn to prevent seed set in the following summer, and (ii) in addition to initial herbicide, use, subsequent fire treatment and broadcasting native seeds appear to provide ongoing competition against N. trichotoma reestablishment in treated areas. Further, high fire intensities, where the soil is heated to 140OC or more, can kill N. trichotoma’s seedbank and prevent its recruitment. In all cases of treatment, monitoring recruitment from the seedbank is recommended for up to one year after treating a site. This thesis suggests that localised eradication of N. trichotoma is achievable in as little as three years if (i) above-ground plants are treated, (ii) seedling recruitment from the seedbank is managed intensely within the first year, (iii) high densities of native grass is established to provide competition, and (iv) the addition of new seed is prevented.
Doctor of Philosophy

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Serage, Tammam Ibrahim. "Effects of overseeded legume living mulches and tillage on weed suppression and broccoli yield." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-01102009-063231/.

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Röhrig, Manfred. "Modelling the light competition between crops and weeds." [S.l. : s.n.], 1999. http://deposit.ddb.de/cgi-bin/dokserv?idn=956719619.

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Tripp, Timothy A. "Cultural control of broadleaf weeds in turfgrass swards." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ27549.pdf.

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Lintell-Smith, Gail. "The population dynamics of weeds in winter wheat." Thesis, University of East Anglia, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297011.

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Marshall, Harriet. "Management of grass weeds in over-wintering stubbles." Thesis, University of Reading, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433468.

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Thacker, Gary W., and Wayne E. Coates. "How to Mechanically Remove Weeds from the Row." College of Agriculture, University of Arizona (Tucson, AZ), 1996. http://hdl.handle.net/10150/210862.

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Crider, Kimberly Kay. "BIOLOGICAL CONTROL: EFFECTS OF TYRIA JACOBAEAE ON THE POPULATION DYNAMICS OF SENECIO JACOBAEA IN NORTHWEST MONTANA." The University of Montana, 2010. http://etd.lib.umt.edu/theses/available/etd-03092010-140634/.

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Biological control, using introduced, specialist insects is a common strategy for controlling plant invasions. However, the efficacy of biological control agents in controlling their host plants is rarely quantified population level. I quantified the impact of a specialist biological control agent, the cinnabar moth (Tyria jacobaeae) on its host plant, tansy ragwort (Senecio jacobaea) in northwest Montana. Cinnabar moth damage and its effects on important plant vital rates were tested with and without specialist herbivores. The presence of moth larvae corresponded to a reduction in population growth rates to less than one, compared to herbivore-free controls, indicating the potential for successful biological control by this insect. However, delayed effects of cinnabar moth herbivory on tansy ragwort vital rates were realized during the year following moth herbivory, after the moths had disappeared from the system. Individual damage to flowering plants in 2005 led to increased survival of these plants in the following year compared to controls, by reverting back to a vegetative state. In addition, seed set was reduced in plants that were damaged as juvenile rosettes in 2005 that went on to flower in 2006. When these delayed effects were combined in matrix models, gains in adult survival did not outweigh the decreases in fecundity or transition rates in terms of population growth and our initial conclusions remained unchanged. However, further study revealed that moth larvae were more likely to be depredated by carpenter ants in xeric sites suggesting that moth populations may not be sustained in these areas. Cinnabar moth larvae can be effective in this system provided they consume a large number of seeds (>90%) in consecutive years, but requires that moth populations are established and sustained from year to year. While herbivores do show the ability to control an invasive plant species, this relationship is strongly contextual in this system. This work emphasizes the importance of recognizing the influence of habitat context on the outcome plant-herbivore interactions, specifically in invaded ecosystems.

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Sosnoskie, Lynn Marie. "Investigations in weed biology studies at the plant, population, and community levels /." Connect to this title online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1102976937.

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Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xx, 147 p.; also includes graphics (some col.) Includes bibliographical references (p. 137-147).

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Asquith, Ilse Bernadette. "An investigation of statistical methodologies for evaluating natural herbicides for the control of yellow nutsedge (Cyperus esculentus)." Thesis, Nelson Mandela Metropolitan University, 2007.

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The present study was undertaken with the view to evaluate methodologies based on traditional Scheffé experimental designs that study mixtures as a tool for discovery research particularly when seeking new and or improved uses of existing mixtures. For the purpose of this study, the topic of controlling the problematic weed known as Yellow Nutsedge (Cyperus esculentus L. var. esculentus) or “Geel Uintjie”, was selected on a rather ad hoc basis. Yellow Nutsedge is a troublesome perennial weed found in most agricultural countries in the world. Herbicidal control is often difficult because of the weeds’ ability to propagate via tubers, which can remain dormant for a number of years and are also resistant to most synthetic herbicide controls. As a first step the study involved the selection of a group of chemical compounds that would be used in suppressing the germination of Yellow Nutsedge tubers. Treatment with various combinations of these chemical compounds as determined by statistical experimental designs was carried out. A review of the literature, particularly literature concerned with the study of the phenomenon of allelopathy, suggested that various phenolic-D-glucopyranosides could show promise in the suppressing the germination of Yellow Nutsedge tubers. This led to the selection of this group of compounds as the target group of “active” substances for the study. Since the group of phenolic-D-glucopyranosides is quite large, and in order to keep the study to a reasonable size, only four phenolic-D-glucopyranosides were selected namely: 4-nitrophenyl-D-glucopyranoside, 4-chlorophenyl--Dglucopyranoside, arbutin and salicin. This selection was based firstly based on a particular phenolic-D-glucopyranoside being a suspected allelochemical, and secondly the ease of technical synthesis using a catalytic process. In addition to the four selected phenolic-D-glucopyranosides, their aglycones (4,nitrophenol, 4,chlorophenol, hydroquinone and salicyl alcohol) were also included as potential “active” substances in order to discern any potential activity between the phenolic-D-glucopyranosides and the aglycones. iii The selected “active substances” were combined in various combinations according to various mixture designs in such a manner that the sum of the proportions of the various actives in any one mixture was always equal to 1. The mixtures of actives were then used in various germination experiments and three experimental responses were measured namely the germination, average dry mass and length of longest shoot. From the results of these germination studies the canonical form of the polynomial equation describing the variation in each of the three germination responses was calculated and evaluated statistically. These equations were then used to estimate the presence of, and the magnitude of synergism between the various active substances. The results from these screening experiments and their detailed statistical analysis indicated that the response surface model for the germination response contains three synergistic blends (4-nitrophenyl--D-glucopyranoside + arbutin; 4-nitrophenyl--Dglucopyranoside + hydroquinone; and 4-chlorophenyl--D-glucopyranoside + salicin) and one antagonistic blend (4-nitrophenyl--D-glucopyranoside + 4- chlorophenol--D-glucopyranoside). The response surface model for the average dry mass response contains two synergistic blends (4-nitrophenyl--Dglucopyranoside + hydroquinone; and 4-chlorophenol--D-glucopyranoside + salicin) and the same antagonistic blend as for germination response. For both germination and average dry mass responses, the most synergistic blend was found to be the combination of 4-chlorophenyl--D-glucopyranoside and salicin. Two additional tests were conducted and both confirmed the results obtained from the screening designs. These tests involved the identification of the two components responsible for the synergistic activity that resulted in the suppression of the germination of the tubers and growth of the seedlings. The experimental response measuring the longest shoot proved to be erroneous and was excluded from the statistical analysis. In summary, this study has clearly shown that statistically designed experiments based on mixture designs can be used as a powerful tool in identifying and quantifying synergistic (or antagonistic) effects of chemicals on the germination ability of plant seeds.

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Womack, Jonathan G. "Development of a mycoherbicide for bracken control." Thesis, University of Strathclyde, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336477.

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Prus, J. L. "New methods of risk assessment for the release of transgenic plants." Thesis, Cranfield University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360068.

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Bentivegna, Diego Javier. "Integrated management of the invasive weed, cut-leaved teasel (Dipsacus laciniatus L.) along a Missouri highways." Diss., Columbia, Mo. : University of Missouri-Columbia, 2008. http://hdl.handle.net/10355/5549.

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Thesis (Ph. D.)--University of Missouri-Columbia, 2008.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on July 22, 2009) Includes bibliographical references.

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Mayonado, David James. "Field, greenhouse, and laboratory studies on the efficacy and action of the herbicides SC-0051 and SC-0774." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/53586.

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SC-0051 and SC-0774 are two experimental herbicides of undisclosed chemistry. A three year field study was conducted to evaluate SC-0051 and SC-0774 for weed control in conventional and no-till corn in Virginia. SC-0051 applied preemergence or postemergence, controlled common lambs-quarters (Chenopodium album L.), common ragweed (Ambrosia artemisiifolia L.) horseweed (Conyza canadensis (L.) Cronq.), common chickweed (Stellaria media (L.) Vill. and was safe to corn. SC-0051 did not control smooth pigweed (Amaranthus hybridus L.) or giant foxtail (Setaria faberi Herrm.). SC-0774 effectively controlled the rye (Secale cereale) cover crop and large crabgrass (Digitaria sanguinalis (L. Scop.) but did not control broadleaf weeds or giant foxtail. SC-0774 also caused considerable but temporary corn injury when applied at rates above 1.1 kg/ha. Combinations of SC-0051 and atrazine provided broad spectrum weed control and yields comparable to atrazine plus metolachlor. Field and laboratory studies were conducted to evaluate the effect of soil pH on the soil mobility of SC-0051 and SC-0774 in sandy loam soils. SC-0774 was applied to soils amended to high and low pH and samples were collected by depth throughout the growing season. A method was developed for extracting and quantifying SC-0774 from collected soil samples. Large crabgrass was also used as a bioindicator species for qualitative detection of SC-0774 residues. These studies showed that SC-0774 was significantly more mobile in high pH soil than in low pH soil. Also, the decreased mobility of SC-0774 at low soil pH lead to decreased corn injury but it increased the soil residual activity of this herbicide. Soil column studies with SC-0774 and SC-0051 showed that the soil mobility of both herbicides increased with increasing soil pH. These herbicides cause reductions in chlorophyll and carotenoid levels in susceptible species resulting in a bleached appearance. The mechanism of this bleaching action is not known. Studies were conducted which examined the effect of SC-0051 on the pigment content and quantity in the susceptible species soybean. High performance liquid chromatography was used to separate, quantify, and identify pigments present in extracts of bleached tissues. The bleaching herbicide norflurazon was also examined for comparison purposes. SC-0051 and norflurazon inhibited the biosynthesis of carotenoids while causing an accumulation of the carotene precursor phytoene and an additional, unidentified pigment that appears to be structurally related to phytoene. This indicates that SC-0051, like norflurazon, inhibits carotenoid formation by blocking the desaturation of phytoene to phytofluene. The uptake and translocation of ¹⁴C-SC-0051 into tolerant corn and susceptible soybean seedlings was examined under growth chamber conditions to investigate the basis for the selectivity of this herbicide. Herbicide uptake was similar in both species but the susceptible soybean translocated a higher percentage of the ¹⁴C-SC-0051 to the growing point of new tissues than did the tolerant corn. It is proposed that differential translocation plays a role in the crop selectivity of the herbicide SC-0051.
Ph. D.

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Jones, Brandon Tyler. "An Evaluation of a Low-Cost UAV Approach to Noxious Weed Mapping." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd2146.pdf.

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Stock, Daniel. "The Dynamics of Lantana Camara (L.)Invasion of Subtropical Rainforest in Southeast Queensland." Thesis, Griffith University, 2005. http://hdl.handle.net/10072/366732.

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Lantana Lantana camara L. is a highly aggressive exotic environmental weed that is weestablished throughout eastern Australia and is reportedly able to displace native vegetation under a range of conditions. Whether lantana is able to displace native vegetation in the absence of anthropogenic disturbance is subject of some disagreement in the literature. The question remains, however, as to what is the future for the Gold Coast hinterland rainforests in the face of invasion by lantana? This study is mainly directed at addressing the dynamics at the lantana/rainforest interface, especially lantana's capacity to invade and ability to compete with the wetter subtropical rainforests of the MacPherson Ranges of southeast Queensland, where the studies are centered on the Springbrook Plateau and the Springbrook and Lamington National Parks. The aims of this research are to determine: whether lantana can displace rainforest; whether rainforest can reclaim the space lost to lantana; and what are the mechanisms and processes involved. To investigate these questions a conceptual framework was determined where key processes at the rainforest/lantana interface were determined and set in a logical context. A wide variety of possible processes whereby lantana could resist or displace rainforest or forest could resist or replace lantana were identified. The framework questions were addressed by observations made at lantana patches in Springbrook and Lamington National Parks in southeast Queensland. These answers/conclusions indicate that lantana is not invading further into intact rainforest and is seemingly isolated to canopy gaps, suggesting that rainforest is suppressing further expansion of lantana. Even though lantana may not commonly occur thriving in subtropical rainforest, it was determined that the issues/interactions that need to be pursued via experimentation were as follows: (i) how common is lantana in the national parks of southeast Queensland; (ii) what limits lantana expansion (is it physical shading, processes attributable to biological effects, such as allelopathy or a combination of both) and; (iii) what physical/biological conditions suppress lantana health and aggressiveness. Although some previous work has looked at the correlation between lantana density and tree cover in dry rainforest and savanna woodland, there have been no reported studies looking specifically at the quantity and abundance of lantana throughout a forest community. An extensive transect study in subtropical rainforest in southeast Queensland assessed habitat variables and the density of the lantana at numerous points along four transects running through rainforest and other mesic communities. The study was conducted in national parks to ensure that the typical disturbances present were, as much as possible natural rather than anthropogenic. From this study the extent of lantana infestation in particular forest types was determined and forest variables such as canopy density and canopy type were compared with lantana density providing indications of the current extent of infestation and the types of forest especially prone to infestation by this environmental weed. The density of lantana in intact rainforest was low and only slightly more lantana was observed in secondary forest than in primary forest. These differences are however driven by the density of the forest rather then the nature of the forest. Finally, lantana appears to be disturbance-dependent in that there is significantly more lantana in disturbed areas than undisturbed areas of the forest: these differences were attributable to the more open canopies above disturbed sites, rather than the disturbance itself. According to previous work the germination of lantana seeds is significantly reduced in low light conditions, such as occur under intact rainforest. A germination experiment investigated the contributions of shading and canopy type to the germination of lantana seeds. The experiment permitted the separation of shading and species-specific effects and the study of rainforest seeds under lantana. Seeds were bagged and placed under rainforest canopy trees and lantana, above and below the leaf litter for a six-month period or until maximum likely germination was achieved. The amount of germination was compared with the amount of shading, the position relative to leaf litter and the species of canopy they were placed under, to determine the relative contributions of shading, litter cover and canopy species. The results of this study show that native rainforest seeds germinate differently under rainforest canopies than under lantana with most showing a higher level of germination under rainforest canopies. This difference was found to be attributable to both the nature of the canopy (canopy species) and the changing level of shading (canopy openness). For most rainforest species, the difference attributable to the level of shading and nature of the canopy was indicative of greater germination capacity under the rainforest canopy than under lantana. Thus, lantana reduces the germination of natives and therefore, in this manner, reduces the forest's capacity to replace lantana. Lantana seed did not germinate in this study and thus their capacity to out-compete native species is, based on this work, unknown. It appears that the competitive ability of lantana seedlings may gives them the edge over rainforest seedlings when colonising canopy gaps. It is therefore important to examine the survival and growth of lantana seedlings compared to rainforest seedlings and the effect of canopy species and shade levels on lantana seedling survival, growth and thus competitive ability. Lantana and rainforest seedlings were planted under rainforest trees and lantana, and their survival and rate of growth over a period of 24 months compared. The survival and rate of growth was compared with the amount of shading and the species under which the seedlings were planted, to determine the contributions of shading and canopy species to survival and growth. The results of this study suggest that, as a seedling, lantana survival was greater under secondary forest canopies and lantana, than under the primary forest species. The growth of lantana seedlings was significantly different under different forest canopies, but differences in growth were not attributable to the different canopy openness ranges with each canopy species and better explained by the actual canopy species themselves. This suggests that there aren canopy specific differences in seedling growth beyond that explicable by canopy openness. As a canopy, lantana does not appear to suppress the survival and growth of rainforest seedlings and thus as a canopy, lantana may not prevent the establishment of native forest seedlings that were studied here. In the rainforests of southeast Queensland, lantana is able to maintain large and dense patches apparently for long periods, leaving open the question of whether lantana in these forests is able to displace the forest or whether the rainforest displaces lantana. In this study, lantana was observed in a number of different locations in the border ranges between New South Wales and Queensland and there is little evidence of its capacity to displace forests in the absence of additional disturbances. The study here explored the reasons for the apparent inability of lantana to displace forest and focused particularly on the shading of lantana by the forest and the capacity of forest species to grow through patches of lantana. Lantana's inability to successfully expand its patch size, under intact rainforest, appears to be due to two main reasons: (i) the increased level of shade provided by the intact canopy of the rainforest compared to the open canopy of the disturbance; and (ii) the particular nature of (species in) the intact rainforest. The results suggest that lantana has little capacity to adapt to shading, only developing slightly larger leaves, longer petioles and longer thinner internodes in moderate shade. Conversely, there is a marked degradation of most health characteristics when lantana is growing in low light conditions. Where the canopy is denser than 75%, lantana will be unthrifty, probably unable to grow and certainly unable to flower. Therefore, maintaining at least 75% shading should prevent the successful encroachment of lantana and early achievement of this level of canopy density should be aimed at in revegetating disturbed sites. This thesis suggests that lantana does not appear to have the ability to competitively displace rainforest. Conversely reclaiming the land taken over by lantana is very slow. More research is required to fully understand the rainforest's ability to recolonise lantana infestations. Although lantana thrives in the canopy gaps created by disturbances, it appears to be restricted (to these gaps) and seems unable to expand the patch beyond the canopy gap. If rainforest reclamation can be confirmed to take place at such a pace that gaps can be closed in an ecologically reasonable time, little active control of lantana maybe required. If active intervention is desired then control efforts should focus on the physical removal of the lantana from initially, small gaps, accompanied by the planting of fast growing rainforest species that can increase the shade at a disturbed site to prevent the reestablishment of the weed.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environmental and Applied Science
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Dissertations / Theses on the topic 'Weeds'

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