Mimosa weed invades the east Kimberley

26 Nov, 2009 12:55 PM
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Mimosa pigra, a Weed of National Significance, has been found for the first time in Western Australia, near Kununurra. The weed is a threat to the pastoral industry and other native plant species. Anyone finding suspect plants is urged to call the department’s Pest and Disease Information Service on 1800 084 881.
Mimosa pigra, a Weed of National Significance, has been found for the first time in Western Australia, near Kununurra. The weed is a threat to the pastoral industry and other native plant species. Anyone finding suspect plants is urged to call the department’s Pest and Disease Information Service on 1800 084 881.

East Kimberley land holders and the public are urged to be on the lookout for an invasive weed which has been discovered for the first time in Western Australia.

Mimosa pigra, a Weed of National Significance which poses a threat to the northern pastoral industry and competes with native plants, has been found near Kununurra.

The Department of Agriculture and Food is assisting the land holder to eradicate the destructive weed.

The department’s Kununurra District Office manager Noel Wilson said the prickly weed could spread easily, outcompeting native plant species.

“Mimosa has been identified as a key threat to the pastoral industry, tourism and recreation,” Mr Wilson said.

“The weed thrives particularly in wetlands of the north, forming dense stands that replace native vegetation.

“It displaces native animals and indigenous cultural activities such as hunting. It can also be a refuge for feral animals such as pigs.”

The weed is already widespread in the Northern Territory and found in one area of northern Queensland.

“Preventing the spread of mimosa is essential in protecting northern wetlands,” Mr Wilson said. “Once established, it is very difficult to control.”

Mimosa reproduces by seed with one plant capable of producing about 9100 seeds per square metre per year. The highest known production from a plant is 220 000 seeds annually.

Seeds are spread by water, animals and human activities. Floodwaters in particular can spread the seeds over huge distances.

“Depending on soil type, moisture, temperature and other factors, seeds can remain dormant in the soil for at least five years, often much longer,” he said.

Mr Wilson said the size of the plants found in WA and the fact they had set seed indicated the infestation had been there for about three years.

“Fortunately, conditions at the site are not ideal so spread has been less than what might have occurred if water was present year-round,” he said.

Mimosa is a branched, prickly shrub, growing up to six metres. The stem is greenish in young plants but becomes woody as the plant matures. It has fern-like green leaves, which fold together at night or when touched. Thorns up to 10mm long are found on the stem, with smaller thorns on branches between leaves.

Round flower heads, 10 to 20mm in diameter, are composed of numerous pink-mauve individual flowers. They each produce 10 and 20 olive-green seed pods, up to 80mm long, which turn brown and break into segments when mature.

Mimosa in small patches can be controlled by hand pulling, bulldozing or spraying herbicides. Larger infestations should be aerially sprayed.

* Anyone with information is urged to call the department’s Pest and Disease Information Service on 1800 084 881. More information on Mimosa pigra can be found at www.weeds.org.au or www.agric.wa.gov.au.

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