Paraquat and glyphosate resistance in Conyza bonariensis in the Western Cape in the Republic of South Africa

[摘要] ENGLISH ABSTRACT:Conyza bonariensis (flaxleaf fleabane) was reported for the first time, as a weed inCalifornia in 1893-1896. The first report of the occurrence of this weed in SouthAfrica 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 wasobserved from vineyards and citrus plantations in Egypt. More recently a report ofherbicide resistance in South Africa was made in January 2003 when resistanceoccurred in C. bonariensis in the Breede Valley, South Africa. The resistance was toglyphosate, but recently reports of resistance to glyphosate and paraquat werereceived.C. bonariensis seeds were found to be positively photoblastic and germinated onlyunder unfiltered white light and red light whilst no germination occurred under far-redlight and in the dark. The optimum temperature range for C. bonariensis seed wasfound 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 atdepths of 2 cm and deeper. Although the optimum temperature range was found to bethe same for the different biotypes tested. However, germination was highest in thesusceptible biotype.Since farmers first reported paraquat and glyphosate resistance in C. bonariensis inthe Breede Valley, South Africa, reports of resistance increase every year. Seedcollected from populations suspected of being resistant to paraquat and glyphosatewere obtained from the Breede Valley and screened for resistance. To determine theeasiest, quickest, and most effective method to screen for paraquat and glyphosateresistance, two tests were evaluated viz. the petri dish assay method and the whoIeplantdose-response method. Both screening methods identified paraquat andglyphosate resistant biotypes. The petri dish assay method was found to be a morerapid method of screening for resistance in C. bonariensis. During this study it wasfound 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 wastested. Herbicides other than paraquat and glyphosate were tested to determine if theycould be used to control resistant C. bonariensis seedlings. The alternative herbicidestested included MCPA and Sorgomil Gold 600. The four herbicides were sprayed atdifferent leaf stages. During the study it was found that growth stage does play animportant role in the level of herbicide resistance. It was found that the control ofdifferent herbicides decreased with an increase in growth stage. The differentherbicides showed varying levels of control depending on growth stage and resistantprofile. Overall MCPA gave the best control at all leaf stages tested. What isgratifying was the finding that every biotype tested could be controlled by at least oneof the treatments applied. This means that the producer using the most appropriateherbicide applied at the optimum application stage will be able to control most if notall the resistant populations of C. bonariensis that occur in the Western Cape.

[发布机构] Stellenbosch University