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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/50412 |
| Date | 12 1900 |
| Creators | De Wet, Hestia |
| Contributors | Cairns, A. L. P., Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 105 p. : ill. |
| Rights | Stellenbosch University |
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