The extent of Mission grasses and Gamba Grass in the Darwin region of Australia's Northern Territory

Abstract

Mission grasses Pennisetum polystachion (L.) Schult. and P. pedicellatum (Trin) and Gamba Grass Andropogon gayanus (Kunth) are three weed species that are thought to be spreading rapidly in the vicinity of Darwin and may pose a major threat to ecosystems in northern Australia. The distribution of the species was assessed from a vehicle along 913 km of roads near Darwin. The study provided data on the potential source of further spread and an analysis of the potential habitat of the weeds. For analysis, roadsides were divided up into 200 m cells and the distributions of the grasses were compared against land tenure and broad land unit maps, Mission grasses were present in approximately 52% of cells, and were particularly common around the rural residential/horticultural area of Humpty Doo. They occurred equally commonly in all broad land units, but differed among tenures, being particularly common on freehold land. Gamba Grass occurred in 15% of cells, with hot spots in a number of areas. It was most common on freehold land, and was rare on conservation reserves. It also showed an association with broad land units reflecting wetter areas. Mission grasses are so widespread in the Darwin region that control can only be contemplated in very small areas requiring frequent treatment of re-invading plants. It may be possible to control Gamba Grass in conservation reserves and Crown land if prompt action is taken. For all three species, preventing their spread to new areas should be a high priority.