The effects of fertilizers, herbicides and grazing intensity on the incidence of firewood (Senecio lautus) in sub-tropical pastures

Abstract

The incidence of fireweed (Senecio lautus) in carpet grass (axonopus affinis) dominant pastures was studied in two cutting experiments and a grazing trial at the Agricultural Research Centre, Wollongbar. Experiments were conducted on pastures initially dominated by carpet grass. Lower fireweed density resulted from higher herbage production or changes in botanical composition from carpet grass to the more competitive paspalum (Paspalum dilatatum) and kikuyu grass (Pennisetum clandestinum). These changes were rapidly achieved by the application of nitrogen fertilizer. Super phosphate application and management for clover development favoured invasion by fireweed in the initial stage. Subsequently the effect of superphosphate was similar to that of nitrogen fertilizer due to the response of more productive grasses to nitrogen fixed by clover. Under grazing, the density of fireweed was increased by high stocking rates, but was reduced markedly by a change to kikuyu grass dominance even under heavy grazing. Fireweed density was negatively related to per cent kikuyu grass. The densities of fireweed measured were not high and classification of fireweed as an undesirable species in these pastures is questioned. This conclusion may not apply to areas improved with temperate pasture species or in cultivations.