Masters Degrees (Agronomy)

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Browsing Masters Degrees (Agronomy) by Author "Bester, Dirk Wouter"

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    The use of Flucarbazone-sodium to control wild oats (Avena spp.) in cultivated wheat fields of the Western Cape of South Africa
    (Stellenbosch : Stellenbosch University, 2017-03) Bester, Dirk Wouter; Kempen, Estelle; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Wild oats (Avena spp.) is a prominent weed in cultivated wheat fields of the Western Cape Province of South Africa. For the sustainable production of wheat, it is crucial to apply the correct herbicide rates at the correct growth stages of both wild oats and wheat in order to achieve maximum weed control. Flucarbazone-sodium has shown to provide excellent activity against wild oats when applied as a post-emergence herbicide to wheat in field experiments conducted in Canada and the USA. Flucarbazone-sodium acts as an inhibitor of the enzyme acetolactate synthase (ALS) also known as acetohydroxyacid synthase (AHAS), an important enzyme that acts as a catalyst in the biosynthesis of the branched-chain amino acids leucine, isoleucine and valine. This product, known as Everest® 2.0, is a new sulfonylaminocarbonyltriazoline herbicide on the South African market. Flucarbazone-sodium has not yet been tested scientifically under South African conditions. The environment, soil, wheat cultivars and cultivation techniques between South Africa and North America differ immensely. In this study flucarbazone-sodium was evaluated under South African conditions in the Western Cape. The first part of the study aimed to evaluate the phytotoxic effect of flucarbazone-sodium on the locally grown wheat cultivars of the Western Cape, as herbicides have no use if they reduce yield potential, regardless of how effectively they control weeds. For this study the internationally accepted BBCH scale was used to describe the different growth stages of the crop. Flucarbazone-sodium was applied at half, one and double the recommended rates at three different plant growth stages ([12-13], [14-15] and [16-17]; BBCH scale on five cultivars (SST 88, SST 027, SST 056, SST 015 and Pannar 3408) in a phytotoxicity field trial. Yield and grain quality (protein content, hectolitre mass and thousand kernel mass) was examined at the end of the growing season. Wheat yield was not negativly affected by flucarbazone-sodium applications, however, double the recommended rate showed a significant (p < 0.05) reduction in yield and hectolitre mass for cultivar SST 056. Appart from SST 056 there is no statistical evidence to discard flucarbazone-sodium in a weed management system, as long as the application guidelines on the product label are followed. To date, no studies have been published on the effectiveness of flucarbazone-sodium in controlling wild oats biotypes in South Africa. For this study, three sites in the Swartland area (Moorreesburg and Piketberg) with severe wild oats infestations were chosen. Flucarbazone-sodium was applied at half, recommended and double the recommended rates at three different growth stages ([12-13], [14-15] and [16-17]; BBCH scale of the wheat. The results showed that flucarbazone-sodium was very effective in controlling wild oats in cultivated fields at all sites except one. At the Pools site near Piketberg in the Western Cape very low levels of wild oats control by flucarbazone-sodium was recorded. Resistance was suspected and seeds were harvested for further investigation. Glasshouse and molecular trials were conducted in order to prove that the biotype present at Pools is resistant to flucarbazone-sodium and to investigate the possible mechanism responsible for this resistance. Results showed that the sampled wild oats biotype at Pools is clearly resistant to flucarbazone-sodium. Even at eight times the recommended rate, flucarbazone-sodium could not control a single wild oats plant. Flucarbazone-sodium appeared to have some effect on the wild oats biotype sampled at Pools, since the dry mass (DM) of the wild oats was negatively v affected as the dosage rate was increased. PCR results showed the sampled wild oats biotype had homozygous resistance mutations Ala-205-Val and Trp-574, and heterozygous resistance mutations Pro-197 and Ser-653. This is the first documented case of Ala-205-Val, Trp-574 and Pro-197 mutations present in Avena spp. worldwide.