Control measures for the encroacher shrub Seriphium plumosum

Abstract

Seriphium plumosum encroachment in South Africa has converted extensive areas of grassland into less productive shrubland–grassland, but its control is not being seriously addressed at present. Therefore, the short-term response of S. plumosum to different applications of nitrogen (N), phosphate (P), lime, sodium chloride (NaCl) and a soil-applied suspension herbicide, Molopo (active ingredient tebuthiuron), was examined. The lime and P-fertiliser treatments lead to no deaths of S. plumosum for any of the concentrations. The smaller the shrubs, the more sensitive they were to both N and NaCl applications. The minimum N-fertiliser applications of 30, 60, 120, 1 000 and 2 000 kg ha−1 were responsible for 100% death of shrubs with heights of 200, 300, 400, 500 and 600 mm, respectively. Sodium chloride application of only 100 kg ha−1 lead to 100% death of shrubs smaller than 400 mm high. Although high applications of NaCl led to total death of shrubs 600 mm high, the enormous problem of saline/sodic soil accompanying it must not be disregarded. Molopo successfully killed all shrubs up to a height of 600 mm. As the plant reaches maturity, the root:shoot ratio increases significantly. It was proved that S. plumosum encroachment is not linked to overgrazing. These results confirm the vulnerability of S. plumosum in semiarid areas, following changes in soil characteristics, which can be used in the control of this invasive plant. A combination of methods is recommended for S. plumosum control.