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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Susceptibility towards selected herbicides of two insect biocontrol agents for water hyacinth

Ueckermann, Claudia 23 November 2005 (has links)
Please read the abstract in the section 00front of this document / Dissertation (MSc (Botany))--University of Pretoria, 2005. / Plant Science / unrestricted
22

Tick control in Tswana, Simmental and Brahman cattle by means of Neem seed extracts (Azadirachta indica)

Davidi, Matayo 17 February 2006 (has links)
Please read the abstract in the section 00front of this document / Dissertation (MSc Agric (Animal Science))--University of Pretoria, 2006. / Animal and Wildlife Sciences / unrestricted
23

Factors affecting the establishment of a classical biological control agent, the horehound plume moth (Wheeleria spilodactylus) in South Australia

Baker, Jeanine. January 2002 (has links) (PDF)
Includes bibliographical references (leaves 168-198) The horehound plume moth (Wheeleria spilodactylus Curits), an agent introduced to control the invasive weed horehound (Murrubium vulgare L.), was used as a model system to investigate factors believed to influence the successful establishment of an introduced natural enemy. Retrospectively tests the use of generic population viability analysis and decision making tools for determining optimal release strategies for the horehound plume moth in South Australia and to compare outcomes with the emprical data collected during the course of this project
24

Factors affecting the establishment of a classical biological control agent, the horehound plume moth (Wheeleria spilodactylus) in South Australia / by Jeanine Baker.

Baker, Jeanine January 2002 (has links)
Includes bibliographical references (leaves 168-198) / xiv, 204 leaves ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The horehound plume moth (Wheeleria spilodactylus Curits), an agent introduced to control the invasive weed horehound (Murrubium vulgare L.), was used as a model system to investigate factors believed to influence the successful establishment of an introduced natural enemy. Retrospectively tests the use of generic population viability analysis and decision making tools for determining optimal release strategies for the horehound plume moth in South Australia and to compare outcomes with the emprical data collected during the course of this project / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied and Molecular Ecology, 2002
25

Influence of mite predation on the efficacy of the gall midge Dasineura sp. as a biocontrol agent of Australian myrtle Leptospermum laevigatum (Myrtaceae) in South Africa

Mdlangu, Thabisa Lynette Honey January 2010 (has links)
Dasineura sp. is a gall forming midge that was introduced into South Africa for the biocontrol of the Australian myrtle, Leptospermum laevigatum. It causes galls on both the vegetative and reproductive buds of the plant. Although Dasineura sp. was initially regarded as a potentially successful agent, galling up to 99 percent of the buds of the host plant, it has been preyed on by native opportunistic mites, which caused a decline in the performance of the midge as a biocontrol agent of L. laevigatum. This raised a concern about whether this fly will be able to perform effectively in the presence of its new natural enemies. Therefore, the objectives of this study were to: 1) ascertain whether mite abundance has seasonal variations; 2) determine if plant density and plant size have an effect on midge predation by the mites; and 3) determine if midge predation varies in different locations. The study was conducted at three sites in the Hermanus area, Western Cape Province. Every three weeks for thirteen months, galls were collected and dissected so as to count and record the numbers of midge larvae, pupae, adults and mites that were found. Data collected showed that predation varied with season, and the mites were scarce during the flowering season. Predation also varied among the study sites and plant density had an effect on midge predation. Midges in smaller plants (saplings) were more vulnerable to predation than those in the bigger plants (plants from isolates and thickets). It was concluded that although mites have an effect on midge populations, they do not prevent their establishment on the plant. Therefore, a survey should be done in two to three years time to check if the midges are still persisting on the plant, vi and recommendations are that a new agent should be released to supplement the midges.
26

Ecology and biological control of an apomictic invasive plant, Chondrilla juncea (Asteraceae) /

Campanella, Donald Michael. January 1900 (has links)
Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 112-121). Also available on the World Wide Web.
27

Plant-insect interactions between yellow toadflax, Linaria vulgaris, and a potential biocontrol agent, the gall-forming weevil, Rhinusa pilosa

Barnewall, Emily C, University of Lethbridge. Faculty of Arts and Science January 2011 (has links)
Yellow toadflax, Linaria vulgaris (L.) Mill. (Plantaginaceae), is a non-native invasive plant. Rhinusa pilosa Germar (Coleoptera: Curculionidae) is a proposed biocontrol agent. Gall development by R. pilosa was described using histological methods and compared between plant populations from native and introduced ranges. Key stages of oviposition were isolated histologically to determine their importance in gall induction. Rhinusa pilosa galled and developed on four geographically distinct Canadian populations in a pre-release quarantine study. Low agent densities only negatively affected one population. High densities of R. pilosa reduced potential reproductive output and plant biomass. Conducting detailed investigations into the biology, impact, and development of R. pilosa on populations from invasive and native ranges may help predict the efficacy of R. pilosa in the field if approved for release and.goes beyond current pre-release testing requirements. / ix, 168 leaves : ill. (chiefly col.) ; 29 cm
28

The interaction of two different fungi, Colletotrichum graminicola and Gloeocercospora sorghi, as a biological herbicide for the control of shattercane

Racine, Scott R. January 2007 (has links)
Greenhouse and laboratory experiments were conducted on the fungal bioherbicides Colletotrichum graminicola and Gloeocercospora sorghi on shattercane (Sorghum bicolor), to evaluate any potential interactions among and between these two plant pathogens for management of this weed. Intraspecific interactions were evaluated with back to back applications of C. gramincola or G. sorghi, and results indicate additive or no effects. Results indicate that interspecific interactions between C. graminicola and G. sorghi lower expected disease incidence when C. gramincola is applied first, while the opposite effect occurs when G. sorghi is applied first. Tank mixtures were also evaluated, and results indicate that no synergistic relationships occur when both species are applied simultaneously. When using spores in conjunction with the chemical herbicide RoundUp (a.i. glyphosate), applying spores with or before glyphosate results in decreased biomass loss, while applying glyphosate prior to spore application results in increased weed biomass loss. Data from intra- and interspecific interactions evaluated in vitro support these findings. / Department of Biology
29

Evaluation of the potential use of antagonistic microbes on grass species, turf and pasture, for disease control and growth stimulation.

Cunningham, Debra M. January 2003 (has links)
Public tendency, of late, is to reduce liberal use of harmful synthesized chemicals for promoting plant health. Today, biological control is becoming a commonly cited disease control option. Biological control agents (BCAs) not only control disease , but also promote plant growth. Application of biological control is based largely on knowledge of control mechanisms employed by antagonists, as well as the means of application that will ensure that an antagonistic population is established. Knowing the advantages is not the only factor that should be considered before application commences as, the disadvantages must be clearly outlined and explored further before a constructive decision as on implementation of biological control. A literature review was undertaken to provide the necessary technical information about biological control, its potential uses, methods of application, mechanisms of action employed, advantages and disadvantages associated with biological control application, public perceptions and the potential future of biological control. Diseases encountered within the KwaZulu-Natal Midlands on pasture and turf grasses were determined by a once-off survey conducted over 1999/2000. The aim of the survey was to determine broadly the management practices of farmers and groundsmen in KwaZulu-Natal and the potential impact of these on the occurrence of weeds, insects and diseases. The survey also addressed the level of existing knowledge about biological control and willingness to apply such measures. In the pasture survey, farmers were questioned about: soil type, grass species common used, irrigation , fertilization and liming, grazing programs and weed, insect and disease occurrences and control measures implemented. The same aspects were addressed in a survey to a representative sample of groundsmen (turfgrass production) , including also: topdressing, greens base used, drainage systems, mowing practices and decompaction principles. The survey showed correlation between pest incidence and management practices implemented. In terms of pest control, both farmers and groundsmen indicated a stronger preference to the use of herbicides , insecticides and fungicides. Use of fungicides for disease control by farmers is considered an often unfeasible expense, rather more emphasis was placed on implementing cultural control methods. At present farmers do not apply biological control strategies, but they did indicate much interest in the topic. Alternatives to current, or lack of current, disease management strategies are important considerations, with two new diseases identified in the KwaZulu-Natal Midlands just within the period of this thesis. Biological control strategies are implemented by 8% of the groundsmen surveyed, with emphasis being placed on augmenting the already present natural predators rather than the introduction of microbial antagonists. Although often mis-diagnosed by farmers Helminthosporium leaf spot is a common disease in the KwaZulu-Natal Midlands on Pennisetum clandestinum (kikuyu), This disease reduces pasture quality and detracts from the aesthetic appearance and wearability of turfgrasses. Helminthosporium leaf spot is incited by a complex of causal agents , Bipolaris was confirmed as the casual agent of Helminthosporium leaf spot on kikuyu at Cedara. Disease control by two BCAs, Bacillus (B. subtilis Ehrenberg & Cohn.) and Trichoderma (T. harzianum Rifai), as commercial formulations was tested against the fungicide, PUNCH EXTRA®. In vitro, Trichoderma was shown to be aggressive in controlling Bipolaris sp. In vivo, disease control achieved with Trichoderma kd was comparative with PUNCH XTRA® but not statistically different (P>=0.05). Trichoderma and Bacillus provided better disease control in comparison to an untreated control. Improved growth of Lolium sp. was determined in vitro, with Trichoderma kd and Bacillus B69 treatments. The microbe-based treatments accounted for growth stimulation, with significant (P<=O.05) growth differences noted. A microbial activator, MICROBOOST®was added to the treatments to improve microbial efficiency. Improved plant growth with MICROBOOST® applications was shown. Improved growth associated with microbial treatments, Trichoderma harzianum kd; Bacillus subtilis B69 and Gliocladium virens Miller, Gibens, Foster and con Arx. ,was also determined in vivo at Cedara, on L.perenne L., Festuca rubra L. and Agrostis stolonifera L. Establishment of a suppressive soil with antagonistic microbes resulted in significant (P<=O.05) effects on final grass coverage (except G. virens), as well increased root and shoot lengths (P<=O.05). Increased germination rates, as expressed in vitro, were not shown in vivo. Microbial activity with the application of MICROBOOST® showed little effect on germination but increased root and shoot lengths significantly (P<=O.05). Increased weed growth associated with the treatments (except G. virens) was considered a drawback of the microbial-treatments. Microbial treatments were also applied to pasture grasses. An in vitro grazing trial was established at Cedara, using L. multiflorum L. to evaluate the microbe-based treatments Trichoderma kd, Bacillus B69 and G. virens for improved pasture establishment and for increased grazing preference by Dohne Merino sheep. Trichoderma kd was associated with increased dry and wet biomass , but lower dry matter yields in comparison to the control. Only G. virens accounted for a higher dry matter percentage than the control. However, differences between the control and the microbial treatments was very small and not significant (P>=0.05). Of the three grazing observations made, sheep showed no grazing preference to plots with or without microbial treatments In general, the body of this research has shown that microbial treatments have the potential for increased disease control and growth stimulation of grasses. However, lack of significant differences between microbial treatments and controls has raised the question as to effect of external factors on microbial activity and survival, especially in vivo. This raises the question as to the validity of the use of microbial treatments where growth conditions cannot be controlled , remembering that the cost of establishment must be covered by the economic returns from utilization. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.
30

Ecology of the predatory mite, Pergamasus quisquiliarum Canestrini (Acari: Mesostigmata)

Groth, Eric M. 25 September 1997 (has links)
Pergamasus quisquiliarum Canestini is a polyphagous predatory mite that has been shown to feed on the economically important arthropod, Scutigerella immaculata Newport (Symphyla: Scutigerellidae), Collembola, Diptera larvae, Enchytraeid worms, and miscellaneous other soil organisms. This study examined the feeding behavior of P. quisquiliarum, the effects of cover cropping and tillage practices on P. quisquiliarum populations, the biology and ecology of P. quisquiliarum in agricultural and non-agricultural sites, and the seasonal dynamics of P. quisquiliarum. The interaction of cover crop and tillage treatment was statistically significant for P. quisquiliarum populations (P<0.001). Tillage treatment was the primary factor for P. quisquiliarum populations, as very low densities of P. quisquiliarum were recovered from green manure plots, regardless of the cover crop treatment. Among no-till plots, Monida oats had the greatest densities of P. quisquiliarum, while control (fallow) and white mustard plots had the lowest densities. The two non-agricultural sites had higher densities of P. quisquiliarum than the agricultural site. Among the non-agricultural sites, P. quisquiliarum density was higher in Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) litter than in Oregon white oak litter (Quercus garryana Dougl.), suggesting that the nature of the chemical and physical micro-environment was more suitable under Douglas-fir trees. In all sites, P. quisquiliarum attained it's greatest density in August, with a second peak in October. Minimum P. quisquiliarum densities were observed in January and February. Seasonal P. quisquiliarum densities were significantly synchronized with seasonal dynamics of it's prey items. / Graduation date: 1998

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