Call number: LD2668 .T4 1959 O38

Ph.D, Faculty of Science, University of the Witwatersrand, 2011 / Abstract Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae) (water hyacinth), a neotropic noxious weed of South American origin, is counted among the “big five” aquatic weeds in South Africa. The weed causes dramatic ecological and economic losses in infested areas. Its control is facilitated by the release of biocontrol agents, mainly Neochetina eichhorniae (Warner) and Neochetina bruchi Hustache (Coleoptera: Curculionidae). Control efforts via biocontrol are hampered, mainly by the climate incompatibility of the agents, aggravated further by the indiscriminate use of lethal doses of glyphosate based herbicides. The lethal doses interfere with the successful establishment and persistence of the biocontrol agents, thus undermining their impact. Continued use of herbicide kills the water hyacinth mat and as a result, the immature stages of the agents are killed. If biocontrol is to succeed as a control strategy, then low doses of the herbicide need to be advocated. It was hypothesized that a low dose will constrain the vegetative and reproductive capacity of the weed, while maintaining the habitat for the biocontrol agents. Consequently, this study was conducted to identify a retardant dose of glyphosate herbicide and test its effect on the Neochetina weevils. A concentration of 0.8% (0.11g m-² or 2880mg a.i /L) glyphosate based herbicide, sprayed at 150 L ha-1 was proved to retard the vegetative and the reproductive growth of the weed, in terms of leaf and ramet production. Further, the retardant dose did not have any detrimental effects on the adult weevils and its larval stages. Weevil herbivory was also enhanced by the retardant dose. Furthermore, the retardant dose did not have any detrimental effects on ‘plant quality’ as evidenced by % nitrogen level in plant tissues such as crown and leaves. Contrary to expectation however, the combined effects of the retardant dose and Neochetina herbivory (0.8%+Ne) did not result in the production of lower number of ramets or leaves than water hyacinth plants dosed with 0.8% herbicide alone. Water hyacinth biocontrol agents in South Africa are subjected to frosty winters with low temperatures which cause the biocontrol agents to decline to an overwintering larval population that fails to catch up with the weed as it rebounds from the frost in spring. This hypothesis was tested in this study at 12 water hyacinth infested sites, which were grouped as temperate and sub-tropical sites. At both the temperate and subtropical sites, water hyacinth plants produced ramets (daughter plants) through autumn and increased biomass during summer. However, weevil numbers were very low at these sites, as evidenced by adult counts and feeding scars, indicating a marked seasonal asynchrony between the phenologies of the weevils and water hyacinth. Hence, intervention by seasonal applications of the herbicide is crucial to constrain weed growth. Herbicidal applications during autumn and spring inhibited the growth of the weed without adversely affecting the adult weevils or immature, immobile stages. Continued use of herbicides raises concerns of effect on non-target species, such as amphibians. Results from this study indicate that a direct application of a retardant dose of glyphosate did not kill or affect the growth of the Xenopus larvae, as determined by survival and body lengths. However, under laboratory conditions, this study has shown for the first time that an invasive aquatic weed (water hyacinth) was more lethal to an aquatic vertebrate (Xenopus larvae) than a herbicide advocated for its control. This study conclusively shows that retardant dose of glyphosate herbicide can be integrated with biocontrol to provide a sustainable and eco-friendly technique with which to combat water hyacinth infestations in South Africa.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

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There is an ongoing and increasing interest in the significant and essential role that food plays in the health and survival of all people. As masticatory efficiency diminishes drastically in edentulous patients, many researchers in the past two decades have been studying how dietary intake varies when different types of oral rehabilitation are provided. Since the use of implants to support prostheses in edentulous mandibles has been shown to significantly improve masticatory performance, the question remains as to whether this improvement will influence nutritional status. In the present study, we used several nutritional markers to compare the nutritional status of edentulous patients who randomly received either mandibular conventional dentures or implant-supported overdentures one year previously. Although the conventional denture wearers reported having more difficulty chewing hard foods, no significant differences were detected in any of the nutritional markers. Therefore, even though chewing is more difficult for the patients wearing conventional dentures, it appears that the nutritional status of these two groups is similar.

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.

Bibliography: leaves 126-143. / x, 143 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--Adelaide University, Dept. of Applied and Molecular Ecology, 2001

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