Research NoteTebuthiuron residues remain active in soil for at least eight years in a semi-arid grassland, South Africa

The non-selective, soil-applied herbicide tebuthiuron (1-(5-tert-butyl-1,3,4-thiadiazol-2-yl)-1,3-dimethylurea) is registered for the control of the indigenous encroacher shrub Seriphium plumosum (Asteraceae) in South Africa. The use of tebuthiuron on a farm in the Cymbopogon–Themeda  veld type in the Zastron district of the Free State has led to the formation of bare patches in the grass layer. This study investigated patterns of emergence and survival of monocotyledonous oats (Avena sativa) and dicotyledonous cabbage (Brassica oleracea) in soils collected from bare patches resulting from the application of tebuthiuron between two and eight years earlier. Untreated soils provided a control. Both oats and cabbage emergence was high and not related to herbicide application. After about two weeks, plants growing in tebuthiuron-treated soil began to die, and after 60 d only four of the 299 emerged seedlings were alive, but showed signs of mortal phytotoxicity. Mortality in the control was low. It was concluded that tebuthiuron residues in the bare patches may preclude recolonisation by seed for at least eight years  following application.African Journal of Range & Forage Science 2012, 29(2): 85–9