Restoration and Conservation Biology, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa; Agricultural Research Council (ARC), Plant Protection Research Institute (PPRI), Hilton, South Africa
Goodall, J.M., Restoration and Conservation Biology, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa, Agricultural Research Council (ARC), Plant Protection Research Institute (PPRI), Hilton, South Africa; Witkowski, E.T.F., Restoration and Conservation Biology, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa
We report on the performance of the registered herbicides picloram and metsulfuron-methyl on the control of Campuloclinium macrocephalum (pompom weed) in grasslands. Herbicide trials in hydric and xeric grasslands were treated for three consecutive years in either summer (February) or autumn (April) and monitored for an additional 3 years after spraying ceased. Uncontrolled factors such as a host-specific rust, fire and drought were observed from the second year of the study. Metsulfuron-methyl and picloram did not differ in efficacy according to the timing of applications, but average mortality of marked plants was <80% expected of registered herbicides. Populations of C. macrocephalum in plots were reduced proportionately to the percentage mortality of marked plants. Picloram and metsulfuron-methyl applied at 252 g a.i. ha-1 and 45 g a.i. ha-1, respectively, were not detectable by gas chromatography in the upper 25 cm of the soil profile during any of the sampling intervals from 0 to 56 days after treatment. Three annual applications of registered herbicide did not reduce C. macrocephalum successfully, and it is estimated that between five (summer) to seven (autumn) annual treatments are required to reduce weed density to <1 plant per plot (25 m2). Future research should focus on rust-herbicide interactions, the role of fire in seedbank management and fire as a treatment that could be integrated with chemical control. © 2014 European Weed Research Society.