Para grass management and costing trial within Kakadu National Park

Para grass (Urochloa mutica (Forssk.) T.Q.Nguyen) is an environmental weed that forms dense monocultures on Australia’s tropical floodplains. It is a weed of particular concern for Kakadu National Park managers and the Indigenous Traditional Owners. To inform the design of a large-scale management program of para grass in Kakadu, we collected distribution and control data. This information will be incorporated into a weed risk and management model for Kakadu. Here we report on the initial data collection findings. The large-scale aerial survey to map the distribution of para grass across the Kakadu floodplains showed extensive areas of infestations in a range of density and size classes. The cover of para grass in Kakadu is now estimated to be over 3200 ha. A field trial was established using six management plots (6.25 ha) to estimate the cost and effectiveness of para grass control. The density of infestations ranged from low (1–10%), medium (10–50%) and high (>50%). Following the current ‘best practice’ management, plots were burnt and sprayed one month later with glyphosate. Data including labour, vehicle and chemical costs were recorded. Treatment cost for high, medium and low density plots was approximately $2770, $1150 and $520, respectively. Based on the current distribution of para grass it would cost over $2.3 million for an initial treatment of all infestations in the park. Because of the large costs of this approach, this information is now being used to explore more cost effective management strategies including containment areas and aerial spraying.