Doctoral Degrees (Agronomy)

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Browsing Doctoral Degrees (Agronomy) by browse.metadata.advisor "Cairns, A. L. P."

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    Resistance of ryegrass (Lolium spp.) to paraquat and glyphosate in the Western Cape
    (Stellenbosch : Stellenbosch University, 2007-12) Eksteen, Frederik Heinrich; Cairns, A. L. P.; Pieterse, P. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: The origin of this study dates back to 2001 when ryegrass (Lolium spp.) from a vineyard near Tulbagh was found by the author to be resistant to glyphosate. Several other populations of glyphosate resistant ryegrass were found on nearby farms. In attempts to eliminate what was initially thought to be a very localised resistance problem, paraquat was applied at several of these sites. It soon became apparent that significant numbers of these ryegrass populations were also resistant to paraquat. Populations that were susceptible to glyphosate but resistant to paraquat were also found. This was the first recorded incidence of paraquat resistance in ryegrass. Further screening of Western Cape ryegrass resulted in the identification of populations that showed multiple resistance to glyphosate, paraquat and ACCase inhibitors. In laboratory trials this study established that the mechanism which confers resistance to paraquat is based on the failure of the herbicide to reach its site of action in the plant. This lack of trans location was ascribed to sequestration of the active ingredient in a non-physiologically active site in the plant, such as the vacuole. This form of resistance was overcome by applying glufosinate ammonium, either prior to, or together with the paraquat application. The same degree of synergy was observed using photosystem II inhibitors with paraquat. The resistance mechanism is overcome by these products by either preventing paraquat from being 'sequestrated and/or freeing up of herbicide which had already been bound. Mixtures containing paraquat, glufosinate ammonium and a photosystem II inhibitor such as terbuthylazine gave the best control of resi~tant ryegrass populations. Independent confirmation, of the findings in the laboratory perfonned trials, was done in field trials, conducted during the 2007 season by Syngenta SA on paraquat resistant ryegrass populations in the Western Cape.