De Wet, Hestia (2005-12)
Thesis (MScAgric)--University of Stellenbosch, 2005.
ENGLISH ABSTRACT: Conyza bonariensis (flaxleaf fleabane) was reported for the first time, as a weed in California in 1893-1896. The first report of the occurrence of this weed in South Africa was made in May 1895 in Franschoek, South Africa. Paraquat resistance in C. bonariensis was first reported in the 1970s and early 1980s when resistance was observed from vineyards and citrus plantations in Egypt. More recently a report of herbicide resistance in South Africa was made in January 2003 when resistance occurred in C. bonariensis in the Breede Valley, South Africa. The resistance was to glyphosate, but recently reports of resistance to glyphosate and paraquat were received. C. bonariensis seeds were found to be positively photoblastic and germinated only under unfiltered white light and red light whilst no germination occurred under far-red light and in the dark. The optimum temperature range for C. bonariensis seed was found to be between 15 and 30°C, with no germination occurring at 0-5°C and at 35- 40°C. Optimum germination occurred at the soil surface. No germination occurred at depths of 2 cm and deeper. Although the optimum temperature range was found to be the same for the different biotypes tested. However, germination was highest in the susceptible biotype. Since farmers first reported paraquat and glyphosate resistance in C. bonariensis in the Breede Valley, South Africa, reports of resistance increase every year. Seed collected from populations suspected of being resistant to paraquat and glyphosate were obtained from the Breede Valley and screened for resistance. To determine the easiest, quickest, and most effective method to screen for paraquat and glyphosate resistance, two tests were evaluated viz. the petri dish assay method and the whoIeplant dose-response method. Both screening methods identified paraquat and glyphosate resistant biotypes. The petri dish assay method was found to be a more rapid method of screening for resistance in C. bonariensis. During this study it was found that both paraquat and glyphosate resistance does occur in the Breede Valley. The effect of growth stage on the level of herbicide resistance in C. bonariensis was tested. Herbicides other than paraquat and glyphosate were tested to determine if they could be used to control resistant C. bonariensis seedlings. The alternative herbicides tested included MCPA and Sorgomil Gold 600. The four herbicides were sprayed at different leaf stages. During the study it was found that growth stage does play an important role in the level of herbicide resistance. It was found that the control of different herbicides decreased with an increase in growth stage. The different herbicides showed varying levels of control depending on growth stage and resistant profile. Overall MCPA gave the best control at all leaf stages tested. What is gratifying was the finding that every biotype tested could be controlled by at least one of the treatments applied. This means that the producer using the most appropriate herbicide applied at the optimum application stage will be able to control most if not all the resistant populations of C. bonariensis that occur in the Western Cape.
AFRIKAANSE OPSOMMING: Conyza bonariensis (Kleinskraalhans) is vir die eerste keer as 'n onkruid gerapporteer in Kalifornia in 1893-1896. Die eerste waarneming van hierdie onkruid in Suid-Afrika is gemaak in Mei 189S in Franschoek. Parakwat weerstandbiedendheid in C. bonariensis is die eerste maal in die 1970s en vroeë 1980s waargeneem, toe weerstandbiedendheid opgemerk is in wingerde en sitrus plantasies in Egipte. Meer onlangs is 'n geval van onkruiddoder weerstandbiedendheid in Suid-Afrika aangemeld in Januarie 2003, toe 'n biotipe van C. bonariensis in die Breede Vallei weerstand-biedendheid getoon het teen 'n onkruiddoder. Die weerstand was teen glifosaat, maar onlangse berigte van weerstandbiedendheid teen glifosaat sowel as parakwat is ontvang. Daar is gevind dat die saadjies van C. bonariensis positief fotoblasties is en slegs ontkiem onder ongefiltreerde wit- en rooi lig, terwyl geen ontkieming voorkom onder ver-rooi lig en in die donker nie. Die optimum temperatuurreeks vir C. bonariensis saad is tussen IS en 30°C, met geen ontkieming wat by O-SoCen by 3S-40°C voorkom nie. Optimum ontkieming kom voor op die grondoppervlak. Geen ontkieming kom by dieptes van 2 cm of dieper voor nie. Alhoewel die optimum temperatuurreeks dieselfde is vir die verskillende biotipes wat getoets is, is daar tog 'n verskil in die persentasie ontkieming tussen die biotipes met die beste ontieming by die sensitiewe biotipe. Sedert boere die eerste geval van parakwat en glifosaat weerstandbiedendheid in C. bonariensis in die Breede Vallei, Suid-Afrika gerapporteer het, word meer gevalle van weerstandbiedendheid jaarliks aangemeld. Saad van populasies wat vermoedelik parakwat en glifosaat weerstandbiedend is, is in die Breede Vallei versamel en getoets vir weerstandbiedendheid. Om die maklikste, vinnigste en mees effektiewe metode van weerstandbiedendheidstoetsing te vind, is twee verskillende metodes van toetsing, naamlik die petribakkietoets en die heel plant dosis respons metode gebruik. Beide metodes van toetsing het parakwat en glifosaat weerstandbiedende biotipes geïdentifiseer. Daar is gevind dat die petri bakkie metode 'n vinniger manier van toetsing vir weerstandbiedendheid is. Die studie het ook bewys dat parakwat en glifosaat weerstandbiedendheid wel in die Breede Vallei, Suid-Afrika voorkom. Die effek van groeistadium op die vlak van onkruiddoder weerstandbiedendheid in C. bonariensis is ook tydens die studie getoets. Ander onkruiddoders buiten parakwat en glifosaat is getoets om te bepaal of hulle gebruik kan word vir die effektiewe beheer van weerstandbiedende C. bonariensis saailinge. Die alternatiewe onkruiddoders wat getoets is, was MCPA en Sorgomil Gold 600. Die vier onkruiddoders is gespuit by verskillende blaarstadiums. Gedurende die studie is daar gevind dat groeistadium wel 'n belangrike rol speel in die vlak van onkruiddoder weerstandbiedendheid. Die persentasie beheer van verskillende onkruiddoders neem af met 'n toename in die groeistadium. Die verskillende onkruiddoders se beheer het gewissel afhangend van weerstandbiedendheid en groeistadium. MCPA het die beste beheer by alle blaarstadiums wat getoets is getoon. Daar is ook gevind dat een of die ander van die onkruiddoders wat getoets is, gebruik kan word vir die suksesvolle beheer van onkruiddoder weerstandbiedendheid in elke biotipe wat getoets is. Dit beteken dat 'n produsent wat die korrekte onkruiddoder op die korrekte groeistadium toedien, in staat sal wees om die meeste, indien nie alle weestandbiedende C. bonariensis populasies wat in die Wes Kaap voorkom, te beheer.
Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/50412
Masters Degrees (Agronomy)44