- Title
- Ecology and management of a tropical invasive weed, Cyperus aromaticus (Navua sedge) in Queensland, Australia
- Creator
- Chadha, Aakansha
- Date
- 2022
- Type
- Text; Thesis; PhD
- Identifier
- http://researchonline.federation.edu.au/vital/access/HandleResolver/1959.17/191410
- Identifier
- vital:17794
- Abstract
- Cyperus aromaticus (Ridley) Mattf. & Kükenth, commonly known as Navua sedge is an invasive C4 perennial sedge species of the Cyperaceae family found predominantly in tropical environments. A native of tropical Africa, it has spread widely and become problematic in many southwest Pacific islands and in tropical north Queensland, Australia. It is a principal weed infesting pastures, sugarcane, banana and root crops, which causes significant damage across a range of industries including dairy, beef, sugarcane and banana in the highly fertile and productive areas of Queensland. The primary objective of this thesis was to contribute to a significant weed management problem at a stage where intervention is cost effective, efficient and environmentally sensitive. At the centre of this work, was a contribution to fundamental knowledge regarding the ecology of the species. The first objective was to examine the global literature on rhizomatous weeds and C. aromaticus in particular to identify the research problems and knowledge gaps. As C. aromaticus has dual mode of reproduction, via seeds and rhizomes, both these aspects were taken into consideration in the experimental chapters. The project critically addressed the issues related to (i) understanding the fundamental ecological aspects of reproduction via seeds in C. aromaticus, (ii) the regeneration of C. aromaticus from its rhizomes, and (iii) control of C. aromaticus using herbicides. A stepwise approach, involving multiple objectives was used to meet the primary objective of this project. Three experiments were conducted to understand the fundamental ecological aspects of reproduction via seeds. (i) A study was conducted to understand the soil seed bank dynamics of pastures invaded by C. aromaticus. It was found that C. aromaticus is the dominant species in the soil seed bank of pastures invaded by C. aromaticus and can contribute between 62% and 95% of the total seed bank. In this respect, the abundance of C. aromaticus seed in the soil seed bank is positively correlated with the aboveground biomass of C. aromaticus and 83% of the total C. aromaticus seeds was found in the top 0-5 cm layer of soil. (ii) The lifespan of C. aromaticus seeds was estimated by artificial ageing technique in the laboratory whereby the results indicate that long-term management is required to control the recruitment from the soil seed bank even in the absence of additional seed deposition. (iii) Seed germination ecology was investigated to understand the effect of various environmental factors on the germination of C. aromaticus seeds. It was found that light is absolutely required for C. aromaticus seed germination, and there was no germination of seeds above 150 mM NaCl concentration and -0.8 Mpa osmotic potential, or from seeds buried greater than 2 cm below the soil surface. Focussing on the regeneration from C. aromaticus rhizomes, an experiment was conducted to investigate the effect of rhizome size and burial depth on the emergence from rhizomes in different soil types. A positive correlation was found between the total emergence of tillers and rhizome fragment size of C. aromaticus, but a negative correlation was found between the total emergence of tillers and burial depth of rhizomes. Importantly, it was also found that rhizomes when reduced to 10 cm or smaller fragments and buried 15 cm or deeper will prevent emergence. A further two glasshouse experiments were conducted to explore chemical options to control both the aboveground biomass and the belowground rhizomes. (i) The herbicide sensitivity of various rates of halosulfuron-methyl was evaluated at different growth stages using plants with and without established rhizomes. Mortality of 27.5%, 0% and 5% was recorded when treated with 75 g ai ha-1 of halosulfuron-methyl at the mowed, pre-flowering and flowering stages, respectively in plants with established rhizomes. The herbicide was effective in controlling the aboveground growth, however, subsequent emergence of new growth from the rhizome confirms the failure of the herbicide to kill the rhizome. In contrast, application of 75 g ai ha-1 of halosulfuron-methyl provided 100% mortality in plants treated at seedling and pre-flowering stage in plants without established rhizomes. (ii) Another herbicide with an alternate mode of action, florpyrauxifen-benzyl, was assessed at different growth stages again using plants with and without established rhizomes. Results indicate that a single application of florpyrauxifen-benzyl is effective at controlling C. aromaticus seedlings, but not effective at controlling plants with established rhizomes. In summary, this thesis has increased the fundamental knowledge about the ecology of C. aromaticus which will feed into designing of management strategies. Likewise, new tools established in the form of mechanical and chemical control and improving the methods currently used to manage populations will advance the capacity to effectively manage C. aromaticus in the future. Although this investigation is based on a relatively focussed suite of issues relevant to tropical north Queensland, where there is an immediate application of the research outcomes from this study, it is anticipated that they will also inform weed management strategies more broadly in a range of similar environments throughout the world.; Doctor of Philosophy
- Publisher
- Federation University Australia
- Rights
- All metadata describing materials held in, or linked to, the repository is freely available under a CC0 licence
- Rights
- Copyright @ Aakansha Chadha
- Rights
- Open Access
- Subject
- Weed ecology; Halosulfuron-methyl; Florpyrauxifeb-benzyl; Artificial ageing; Soil seed bank; Seed ecology; Rhizome, Sedge
- Full Text
- Thesis Supervisor
- Florentine, Singarayer
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