Darwin-Kakadu: Weeds and Wetlands


 Mimosa Pigra

Mimosa pigra

Wetlands and riparian systems are amongst the most productive of the regions' ecosystems and are particularly vulnerable to weed invasions.  Mimosa (Mimosa pigra) is regarded by many as the most serious problem weed in the region. It is a woody invasive shrub that originated in tropical America, and now infests about 80,000 hectares of coastal floodplain in the NT. It affects pastoral enterprises, traditional Aboriginal activities and conservation values, and has the potential to irreversibly alter the ecology of the world-heritage Kakadu wetlands. Many millions of dollars have been spent on its control, and on eradicating infestations such as one near Oenpelli. Control of outlying satellite infestations is vital to prevent the spread of mimosa into Arnhem Land, Kakadu National Park, Daly River and other parts of Australia. Click here to see a list of mimosa research findings.

Salvinia molesta now occurs widely in the Darwin region
Photo: Greg Calvert

Salvinia molesta

Infestations of Salvinia (Salvinia molesta) have occurred widely in the Darwin-Arnhem region. Salvinia is a water weed that can affect fish populations and make water bodies useless for water supply or recreation. Infestations on Rapid Creek, the Adelaide River and Mary River have been eradicated using physical and chemical means. Other infestations have been diminished and controlled biologically by the salvinia weevil, but this method has not been very successful in Magela Creek in Kakadu National Park. To see a recent list of research findings on salvinia click here .

Water hyacinth

Water hyacinth (Eichhornia crassipes) is a serious water weed throughout much of the world. Fortunately the six field infestations reported in the NT have all been eradicated using hand removal and nets. To see a list of research findings on water hyacinth click here .

Weeding out para grass
Photo: Deborah Bisa

Para grass

Para grass (Brachiaria mutica ) was introduced to the NT as a pasture grass for wet and seasonally flooded areas. However, it spreads vigorously, choking out native species and hindering establishment of more desirable species. It has the potential to be one of the most serious weeds in wetlands surrounding the Mary River and in Kakadu National Park. Olive Hymenachne (Hymenachne amplexicaulis) is another grass being tested as a ponded pasture species. It has the potential to smother native vegetation by forming dense monocultures in seasonally flooded areas, and it would appear wiser to use native alternatives such as Hymenachne acutigluma .

Other threats

Other weeds that pose a potentially serious threat to the region's wetlands include alligator weed (Alternanthera philoxeroides), barnyard grass (Echinochloa glabrescens), dense waterweed (Egeria densa), Fanwort (Cabomba caroliniana), lagarosiphon (Lagarosiphon major), and Salvinia natans. Luckily, most of these species have not yet been found in the NT, but all have the potential to spread rapidly and have a major impact on the region's ecology. Click on any of the species names above to see recent lists of research findings.