The Association runs, or contributes to a number of weed programs annually. These programs are focused on highly invasive weeds such as prickly acacia and mesquite that are still located over relatively small areas. They were selected based on the likelihood that if funds were allocated to their control it would be beneficial to the whole of the Kimberley in the longer term. The four weeds the Association currently contributes to are -
Currently these weeds are restricted to just a single or few locations and have been assessed as weeds that could potentially be eradicated from those location/s.
The target weeds in the Association’s current programs all met the following assessment criteria to qualify –
(Important note: Mimosa bush (Vachellia farnesiana) is a widespread plant in the Kimberley that looks like, and is often called prickly acacia. However, its thorns are generally much smaller, and there are subtle differences in overall plant appearance.)
Prickly acacia is a Weed of National Significance and is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts. Currently, more than 6.6 million hectares of Queensland are infested. It is also found in scattered populations across the Northern Territory, with a substantial infestation in the southern Victoria River district.
Prickly acacia is a thorny, spreading tree that generally grows to around 4–5 m high and occasionally up to 10 m. A pair of stout spines, 10–50 mm long, grows at the base of each group of leaves on young stems. The flowers are yellow, fluffy, round clusters about 10 mm in diameter. Seed pods are grey-green, covered in fine hairs and typically 100–200 mm long. Seeds may be washed downstream in fast-flowing water, but long-distance spread in Australia is mainly attributed to consumption and dispersal by animals such as cattle.
Only two sites are known in Western Australia, both in the East Kimberley. The smaller site has been controlled by the land manager. The larger site covers more than 10,000 hectares. The Association began its work program on this site in late 2010, following on from a previous program led by DAFWA that commenced in 2006. In that first year (2010), nearly 10,000 plants were controlled. In the 2024/25 wet season—when control activities are carried out—the number of plants found and controlled totalled 60.
This work remains ongoing and eradication is an expected outcome.
Mesquite is a Weed of National Significance and is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts. Four species and several hybrids occur in Australia, and all are collectively known as mesquite. The weed is widespread across northern Australia, particularly in Queensland. The Mardie Station infestation (150,000 ha) in the Pilbara is the largest single core infestation in Australia.
Mesquite’s economic impacts stem from its ability to form impenetrable thickets which, combined with its large thorns, prevent stock from accessing watering points and make mustering difficult. Mesquite also reduces the productivity of pastoral land by overtaking grasslands and consuming valuable water resources.
Mesquite leaves are fern-like and occur in groups of one to three pairs, often accompanied by one or two thorns up to 50 mm long. The greenish cream-yellow flowers resemble a ‘lamb’s tail’ and are 50–80 mm long. The seed pods, which can be up to 200 mm in length, are straight or slightly curved. The bark is smooth and dark red-green on young stems, becoming rough and grey as the plant ages. The taproot is large, highly branched, and generally grows to a depth of around 20 m. Identification of mesquite is often complicated due to significant variation in growth form, even within the same species, and the presence of hybrids (or crosses) between the main species.
A combination of a long life cycle, drought tolerance, high seed production, and seed dormancy makes mesquite an extremely resilient invader capable of rapidly exploiting suitable conditions and dominating entire ecosystems.
There are two main mesquite infestations in the Kimberley, one in the east and one in the west. The West Kimberley infestation covers approximately 8,000 hectares, while the East Kimberley infestation covers around 16,000 hectares. Plans were made to introduce a biological control agent into the West Kimberley infestation in 2019. Whilst this didn't occur, in 2022 the agent was found in some West Kimberley plants having spread to the region naturally. In 2025 the agent is still active but only on small numbers of plants indicating the agent is yet to establish itself properly on the site.
The Association began its work program at the East Kimberley site in 2012, following on from a previous program led by DAFWA. In the first year, nearly 6,000 plants were controlled. During the 2018/19 wet season, when control activities are undertaken, the number of plants found and controlled had reduced to 75. This work remains ongoing, and eradication is the expected outcome
Rubber vine is a Weed of National Significance and is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts. Its main impact on pastoralism is the loss of grazing country, which in 1995 was estimated to cost the Queensland beef industry $18 million. It also increases the costs of mustering and fencing. Rubber vine has a potential distribution covering all of northern Queensland, the northern half of the Northern Territory, and most of the Kimberley region. The total area of rubber vine infestation in Queensland was estimated at over 700,000 hectares, and it was present across an area 50 times as large.
Rubber vine is a many-stemmed shrub that can climb up to 30 metres into tree canopies. The stems are greyish-brown with smooth bark. A typical feature is the formation of a “whip” that extends onto adjacent vegetation. The plant exudes a milky sap when scratched or broken. The leaves occur in pairs and are glossy dark green. The trumpet-shaped flowers are large—up to 50 mm long and wide—with five light-purple to white petals. The seed pods are rigid and usually occur in opposing pairs at the end of short stalks, reaching up to 120 mm long and 40 mm wide. The roots can grow to a depth of 12 metres.
There are two significant infestations in the Kimberley: one at the top end of Lake Argyle in the East Kimberley, and another along the Fitzroy River in the West Kimberley. Both infestations are being controlled by partnership groups involving landholders, state agencies, and the Association.
In 2024, a significant infestation was found in Manguel Creek, adjacent to the existing infestation in the West Kimberley. It currently extends approximately four kilometres along the creek and is believed to be at least twenty years old. Land occupier sensitivities have, for the time being, ruled out affordable methods of control, making work on the site not possible at this point in time.
Gamba grass is a Weed of National Significance and is regarded as one of the most significant threats to northern Australia because of its invasiveness, potential for spread, and economic and environmental impacts. It is a large perennial grass that grows up to 4 metres tall, with tussocks up to 70 cm in diameter. Its leaves are 30–60 cm long and up to 3 cm wide, covered in soft hairs with a distinctive white midrib. The stems are robust and also covered in soft hairs. Seeds are contained in a fluffy, V-shaped seed head consisting of up to six groups of branches, each containing 2–18 primary branches.
Gamba grass currently affects up to 15,000 square kilometres of the Northern Territory, with the potential to affect a further 380,000 square kilometres. Most infestations are north of Katherine. There is also an estimated 60,000 hectares spread across northern Queensland.
Introduced into Australia in the 1930s, gamba grass was trialled at the Katherine Research Station from 1946 specifically for use as cattle fodder. Since then it has proved to be highly invasive, with the ability to negatively impact savanna landscapes in northern Australia. It is now considered a serious bushfire threat, carrying fuel loads up to eight times higher than those of native forests and pastures. As a result, bushfires become more extensive and more intense, affecting tree canopies and transforming woodlands into grasslands. It also poses a serious threat to people and property. Where gamba grass continues to be used as fodder, it requires careful management to maximise productivity, limit seed production, and control spread.
There is one known infestation in Western Australia. It is located in the East Kimberley and covers 433 hectares. Work on this site is being undertaken by a partnership group involving landholders, state agencies, and the Association.
Weed subsidies are available to all land holders within the area managed by the Kimberley Rangelands Biosecurity Association who pay annually the Declared Pest Rate. The rate is determined on property value and is raised to fund the control of established declared pests.
Currently the amount a land manager can claim per lease is up to $7,500 and is payable for the purpose of the purchase of chemicals and the use of registered and licenced contractors to carry out the control.
The following conditions apply to the subsidy
Regarding providing proof of chemical or contractor use there are a number of methods that could be used. It is extremely important that anybody considering applying for the subsidy contacts a staff member before to discuss the options so they can be agreed on prior to any purchase or application. Examples of what have been used in the past include –
Please note that random audits of the work done will be undertaken annually for verification purposes.
