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Weeds

Regional profile

About three-quarters of the VRD-Sturt region lies inside the Northern Territory, with the remainder in Western Australia. Land use in the region is dominated by pastoralism but Aboriginal lands and conservation reserves also occupy substantial areas. The area of intensive agriculture associated with the Ord River Irrigation Scheme is increasing, and there is also a large military training area.

Land degradation

The long history of pastoral use has left a legacy of land degradation in many of the region's most productive areas. There has been erosion and widespread replacement of preferred grasses by less palatable species including exotic weeds. In some areas, overgrazing and changes in fire regimes have combined to increase the density of native shrubs and trees and lower the land's carrying capacity. This combination has also left large areas vulnerable to invasion by weeds, including exotic woody species such as parkinsonia (Parkinsonia aculeata) and castor oil plant (Ricinus communis ).

Weed threats

Parkinsonia

Parkinsonia forms thorny thickets in the region
Photo Greg Calvert

Parkinsonia forms impenetrable thorny thickets that compete with and exclude native species and cut off access to creeks and rivers. It is widespread in the region. Castor oil plant, a tall branching shrub, displaces more desirable native species and can lead to significant losses in grazing land. It can become locally abundant after rains or flooding. Noogoora burr (Xanthium strumarium) is another weed that excludes native shrub species and the spines of the burr can cause injury to animals' feet.

Devil's claw (Martynia annua) is also present, and poses a major threat within the region. This plant invades disturbed ground where it prevents the regeneration of native species. The clawed fruits can work their way into soft body parts of animals, causing injury and discomfort. Lion's tail (Leonotis nepetifolia ) is another weed likely to become much more serious in the region.

Neem tree (Azadirachta indica), widely planted as a shade tree around settlements and towns, is spreading rapidly in the region. Rubber bush (Calotropis procera), sicklepod (Senna obtusifolia), coffee senna (Senna occidentalis), spiny head sida (Sida acuta) and flannel weed (Sida cordifolia ) are also causing concern.

Prickly acacia (Acacia nilotica) and mesquite have been reported in the region, and both have the potential to become major problems. Mimosa (Mimosa pigra ) also poses a serious threat to the region, although only a few occurrences have been reported so far.

Gamba grass

Gamba Grass is potentially a major problem

Weeds in National Parks

In Gregory National Park, devil's claw (Martynia annua), cobbler's peg (Bidens bipinnata), parkinsonia (Parkinsonia aculeata) and rubber bush (Calotropis procera) are the weeds causing most concern at present. Gamba grass (Andropogon gayanus) and mission grass (Pennisetum polystachion) are major potential problems, because they lead to very hot fires that can seriously damage native vegetation. Mimosa (Mimosa pigra) could also be a huge problem if it became established.

Weed management

Weeds are both a symptom and a cause of land-management problems. They interact with fire, feral animals and grazing management. Therefore it is vital that strategic weed management is fully integrated into all long term management programs.

As in all regions, prevention is the most desirable and cost-effective approach to weed management. Legislation prohibits introduction of potentially damaging weed species into the NT, but we also need to avoid moving weed seeds from infected areas into ones that are still 'clean'. It is important that we minimise an area's susceptibility to weed invasion. Examples are by reducing disturbance due to overgrazing, feral animals and unnecessary vehicle traffic, and rehabilitating and revegetating disturbed sites with local native plants.

Education and awareness are vital if we are to recognise weed infestations at an early stage when eradication is still practicable. Knowing how to deal effectively with existing infestations will minimise weed problems. Keep up to date with latest control methods, and implement long-term plans.

Contacts

Mr Murray Fuller
DPIF District Weeds Officer
Tel: (08) 8975 0307

Timber Creek, NT