The aim of this project was to provide sound scientific underpinning for the development of new weed management strategies in sugar cane by exploring competition from the major weeds, and explaining the different mechanisms of weed interference from Paspalum paniculatum and P. urvillei. Critical periods of weed control (CPWC) were studied in six field trials. In ratoon cane, CPWC with natural weed infestations started between 228 and 916 growing degree days (GDD), and ended between 648 and 1311 GDD, depending on the site and cane variety. These results represented a maximum CPWC of 12 to 28 weeks after harvest (WAH). In plant cane, the CPWC started earlier (6 WAP) and was longer than those in ratoon cane. Relative competitiveness ‘q’ values of eight common weed species showed that sugar cane was a stronger competitor than most of the weeds tested. The adverse effect of weed competition in sugar cane is not experienced before several weeks following weed emergence. Weeds transplanted 10 WAP caused no significant change in cane yield response as compared to those transplanted 4 WAP. Paspalum paniculatum was often found to be more competitive than P. urvillei, although the latter produced more leaf area and grew taller to intercept more light within the canopy. This indicated that other mechanisms of weed interference were involved and competition for light was more important during the earlier (tillering) growth stages. Root competition was shown to be as important as shoot competition. Root competition effects were observed several weeks after imposing competition, suggesting that it was more important than competition for light in the post-tillering phase. Application of root exudates from the two grasses to sugar cane confirmed an allelopathic effect on the root biomass of sugar cane. One chemical identified in the leachates from both Paspalum species for the allelopathic effects was 2-propenoic acid, 3-(4-methoxyphenyl). The main implications of the above findings for the Mauritian sugar industry would involve a change in the timing of application of herbicides. A new tank-mix consisting of trifloxysulfuron + ametryn and amicarbazone has been found to meet this objective. This strategy will enable a saving of at least one herbicide treatment per season. / Thesis (PhD)--University of Pretoria, 2011. / Plant Production and Soil Science / unrestricted

本文目的為探討影響東亞九個經濟體（台灣、香港、韓國、中國、及東南亞國協五國─印尼、馬來西亞、菲律賓、新加坡、泰國）在國際旅遊觀光市場之相對競爭力的因素及利用國際旅遊觀光統計資料，透過三階段最小平方法（3SLS）及迴歸分析，分別針對東亞九個經濟體，探究相對價格、匯率及供給面變數，對其主要來源國家觀光客─美國、日本做實證分析。實證結果發現：(1) 如果旅遊目的為商務或探親，或者是以觀光團型態旅遊，則國際觀光客對於相對價格變動並不敏感。(2) 如果大部分在目的地國家的旅遊支出是以來源國家貨幣計價，則國際觀光客對於匯率變動並不敏感。(3) 供給面因素的確對經濟體之國際旅遊觀光市場佔有率具有決定性影響，然而其影響視來源國與各目的地國家之相關性而定。

本文分別針對東南亞七經濟體，探究相對價格及供給面變數，對其主要來源國家觀光客-美、日、英、澳，選擇旅遊地點的影響，並了解各經濟體間替代及互補關係。實證結果發現：（1）大陸開放對香港、新加坡吸引英國觀光客呈現統計上顯著互補效果；而台灣、菲律賓對爭取美國觀光客上，呈現競爭替代關係。（2）天安門事件對香港國際旅遊，統計上皆存在顯著負面影響，且其在美、澳觀光客的明顯競爭對手為新加坡。（3）馬來西亞的國際觀光年在統計上皆是十分正面的效果，替代對象就美國觀光客部分為新加坡及菲律賓；就日本觀光客部分為台灣；就英國觀光客部分為新加坡及香港；就澳洲觀光客部分則為香港。（4）印尼的國際觀光年在統計上亦有顯著的成果。