Assessment of the impact of Mikania micrantha Kunth. ex. H.B.K. on crop production systems in Viti Levu Fiji

Apaitia Ravaga Macanawai (2011). Assessment of the impact of Mikania micrantha Kunth. ex. H.B.K. on crop production systems in Viti Levu Fiji PhD Thesis, School of Agriculture and Food Sciences, The University of Queensland.

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Author Apaitia Ravaga Macanawai
Thesis Title Assessment of the impact of Mikania micrantha Kunth. ex. H.B.K. on crop production systems in Viti Levu Fiji
School, Centre or Institute School of Agriculture and Food Sciences
Institution The University of Queensland
Publication date 2011-11
Thesis type PhD Thesis
Supervisor Professor Steve Adkins
Michael Day
Dr Tessie Diete-Tumaneng
Total pages 302
Total colour pages 24
Total black and white pages 278
Language eng
Subjects 07 Agricultural and Veterinary Sciences
Abstract/Summary Mikania micrantha Kunth. ex. H.B.K (here after, mikania) is an alien invasive plant species in the Asia and Pacific region and is currently one of the major weeds of plantation crops and home gardens in this region. The purpose of this research project was to assess the current and potential impacts of mikania on crop production systems in Viti Levu, Fiji. To help such an assessment, the distribution and infestation density were assessed, as were aspects of its asexual and sexual reproductive biology, the germination and establishment requirements of its seeds and the soil seed bank dynamics of the weed were investigated. In addition, farmers’ views on its management and potential losses caused by mikania were also assessed. The distribution survey demonstrated that mikania is widespread in Viti Levu and is to be found in 18 other islands in Fiji. It was revealed that mikania was the most frequently occurring weed species on the edges of Saccharum officinarum L. (sugarcane) fields. Mikania was ranked the second most frequently occurring weed in traditional Colocasia esculenta (L.) Schott (taro) production systems in Tailevu and in Naitasiri and was also the most frequently occurring weed in Musa spp. (banana) plots in the two provinces. It was found that 96, 95 and 89% of the weeds found in sugarcane, taro and banana crops respectively were introduced species. A study on the growth potential of the vegetative stem sections of mikania revealed that long stem sections (≥ two nodes) had a greater chance of survival than shorter stem sections. Mature mikania stem sections (with nodes) had a greater chance of survival than young stem sections when buried horizontally or vertically with a node exposed. The growth capacity at the edges and within the central area of a Manihot esculenta Crantz (cassava) and a taro crop showed mikania to grow aggressively at the edges, however to a lesser extent in between the rows of the crops. The lower soil nutrients and light intensity levels within the crop may have played a role in this behaviour. A study on the sexual reproductive capacity of mikania revealed that the flowering season in Viti Levu occurs between April to October coinciding with the cool, drier period of the year which presumably favours insect pollination. It was found that Apis mellifera L. (the honey bee) was the most frequent insect floral visitor. The number of seed produced in each flower head (capitulum), ranged from one to seven with the highest proportion of capitula (95%) carrying four seeds. The number of viable seed produced per m2 was determined to be 90,825 and 98,134 for the high and the moderate rainfall regions, respectively. When determining the conditions for germination, it was found that the optimum constant temperature was in the range of 14 to 29°C, with between 87 to 94% of the seed germinating in this temperature range. Under alternating temperature regimes, mikania seed germination was best at 30/20°C (96.9%) and possessed no primary dormancy. It was observed that c. 50% more mikania seed germinated in a salt solution (150 mM) than did Bidens pilosa L. or Synedrella nodiflora (L.) Gaertn.) seeds indicating a moderate tolerance to germination inhibition in saline soils. There was a greater species richness in the soil seed bank in the high than moderate rainfall region suggesting that rainfall had a role to play in this variation. Sixty percent of the germinable mikania seed emerged more rapidly (within the first 8 days of imbibitions) than A. conyzoides and Ludwigia spp. There were greater numbers of germinable mikania seed and a greater species richness in the traditional, as compared to the mechanised taro plots, indicating that mikania was effectively controlled in the mechanised cropping system. Seed longevity studies demonstrated that seed could live for at least 3 years in the soil seed bank and this was seen for three contrasting collection environments. Finally, the questionnaire and the interview survey indicated that mikania had been present in the root crop and sugarcane farming systems for between 20 to 50 years. Chemical control was the most frequently used method for controlling mikania and farmers controlled the weed to prevent crop losses. Farmers did not control mikania in the non-production areas mainly because they considered this to be a waste of their time and money. Beneficial aspects of mikania mentioned by farmers included the improvement of soil fertility, use as a traditional medicine, use as a livestock feed and as a ground cover. The presence of mikania has caused losses of c. AUD $0.21 million for root crop production and for sugarcane production c. AUD $0.99 to 2.10 million. The findings of this research and its implications on mikania management justify the need to formulate a cost-effective and sustainable management of the weed in Fiji.
Keyword Mikania micrantha
Viti Levu Fiji
Manihot esculenta
Colocasia esculenta
Saccharum officinarum
vegetative reproduction
relative growth rate
soil seed bank
seed germination
weed survey
Seed ageing
Additional Notes xiv, 9, 10, 13, 16, 18, 33, 46, 47, 50, 53, 58, 59, 62, 75, 108, 127, 131, 133, 135, 136, 146, 149, 171. Landscape page 251

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