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QUIK STATS (last updated Aug 04, 2003 )
NOTES ABOUT THIS BIOTYPE
Paraquat-resistant Conyza bonariensis in the Western Cape.
In January 2003 reports were received from the Breede Valley (about 100km
north east of Cape Town) of glyphosate failing to control Conyza bonariensis at
registered dosage rates. During the course of these investigations paraquat was
evaluated as an alternative treatment to control the glyphosate-resistant weeds.
It soon became clear that several of the control populations evaluated, which
were susceptible to glyphosate, were resistant to paraquat. A paraquat dose
response pot trial was carried out on one of these populations. Dosage rates
applied were 0.6, 1.2, 1.8, 2.4, 3.0, 3.6, 4.2, and 4.8 kg a.i. paraquat ha-1.
Seed was collected on the University of Stellenbosch’s experimental farm,
Welgevallen which is situated about 40km from Cape Town. A population
originating from seed collected at Goudini in the Breede Valley was used as a
control. The trial was carried out on transplants in the rosette growth stage.
Four replications of 4 plants per pot were used. From Table 1. it is clear that
the Welgevallen population was resistant to paraquat. Virtually no dose response
was observed in the Welgevallen population. The Goudini control population was
well controlled by paraquat.
1. Dose response of two Western Cape populations of Conyza bonariensis to
Provisional screening of 12 C. bonariensis populations from the Western Cape
showed that 7 of them showed significant resistance to paraquat. Generally
speaking, all populations evaluated were controlled by either paraquat or
glyphosate. However, one Breede Valley population appeared to be resistant to
both herbicides. This population is the subject of further investigation.
Department of Agronomy
University of Stellenbosch
CONTRIBUTING WEED SCIENTISTS