Mimosa (Mimosa pigra)

Mimosa is a branched, spiny, perennial shrub. It forms dense thickets that replace native vegetation. It is a Weed of National Significance.

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How does this weed affect you?

Mimosa is a branched, spiny, perennial shrub growing to 6 m in height. It forms dense thickets that replace native vegetation in northern Australia’s ecologically and economically valuable wetlands. It tolerates flooding, and can grow along roadsides, watercourses and seasonally inundated wetlands, and on a wide variety of soil types. It has the ability to invade ecologically sensitive areas and threatens indigenous cultural activities, and pastoral and tourism industries. Once mimosa becomes established, it dominates vegetation and is very difficult to control.

Where is it found?

Mimosa is a native of tropical America. It grows in moist areas in the humid and sub-humid tropics and has become a very serious weed of Africa, India, Southeast Asia and some Pacific islands.

In Australia the first mimosa plants were brought into the Northern Territory in the early 1890s for the Darwin Botanic Gardens. A large infestation was identified in 1952 on the Adelaide River, 100 km south of Darwin. This infestation was thought to be the primary site for further infestations in the Northern Territory. Sand containing mimosa seed was removed from the area in the 1950s and used at commercial building sites in the north.

Mimosa now occurs on an estimated 85 000 ha of wetlands across northern Australia. It has spread to some of the main river systems in the Top End of Australia (Finniss, Reynolds, Mary Daly, East Alligator and South Alligator) and is also found in the Victoria River in the west and the Phelp River in Arnhem Land. An outbreak was discovered in 2001 near Proserpine in Northern Queensland - outside the projected distribution and indicating that mimosa may be able to survive in areas further south. In late 2009 an isolated patch was identified in a seasonal billabong near Kununnurra in Western Australia.

Mimosa has not been recorded in New South Wales (NSW). Note: it is not the same plant as the commonly-called mimosa bush Vachellia farnesiana which is widespread in parts of NSW.

Distribution map

• NSW (image)

How does it spread?

The spread of mimosa occurs by seed. Large trees can produce up to 220 000 seeds per year. The seed pod segments (containing one seed per segment) float on water or attach to clothing or hair. Seeds can also be carried by water during floods, by animals (e.g. in cattle and horse manure or in mud attached to kangaroos and feral animals) and by humans (e.g. attached to clothing and machinery).

What does it look like?

Mimosa has large thorns (5–10 mm long) on the stem and smaller thorns on the branches between the leaves. The greenish stems on young plants become woody with age. Mimosa has a branching taproot which can reach a depth of 1–2 m.

Key identification features

• Leaves are green and fern-like. They are made up of many fine leaflets that occur in pairs along the branches. The leaflets fold together at night or when they are touched.
• Flowers (1–2 cm diameter) are round and made up of 100 individual pink-mauve flowers.
• Seed pods (6–8 cm long) are olive-green and covered in numerous fine hairs. Each flower head produces 10–20 pods. The mature pods turn brown and break into segments. There is one oblong-shaped seed (4–6 mm long) per segment.

What type of environment does it grow in?

Habitats such as the wetlands of Northern Australia are climatically suited to mimosa.

Acknowledgements

Adapted by AnDi Communications from the CRC for Australian Weed Management Weed Management Guide: Mimosa.
Reviewed by Peter Gray. Edited by Elissa van Oousterhout, Birgitte Verbeek

References

Lloyd SG & Vinnicombe TL (2010) Proceedings of the 17th Australasian Weeds Conference pp180-181.

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Control

You must report this plant if you see it anywhere in NSW. Call the helpline listed above. Help will then be provided to remove and destroy it. This serious weed could spread if control efforts do not follow all protocols. Not reporting it is a breach of your legal biosecurity duty.

Herbicide options

See Using herbicides for more information.

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PERMIT 9907 Expires 31/03/2025
Fluroxypyr 200 g/L (Starane™)
Rate: 35 mL per L diesel/kerosene
Comments: Basal bark
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate

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PERMIT 9907 Expires 31/03/2025
Fluroxypyr 333 g/L (Starane™ Advanced)
Rate: 21 mL per L diesel/kerosene
Comments: Basal bark
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Roundup®)
Rate: One part product to 1.5 parts water
Comments: Cut stump, drill, frill axe or injection.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L with Metsulfuron-methyl 600 g/kg (Various products)
Rate: 1:1.5 glyphosate to water + 1 g metsulfuron to 1 L water
Comments: Stem injection
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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Biosecurity duty

The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area	Duty
All of NSW	General Biosecurity Duty All plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
All of NSW	Prohibited Matter A person who deals with prohibited matter or a carrier of prohibited matter is guilty of an offence. A person who becomes aware of or suspects the presence of prohibited matter must immediately notify the Department of Primary Industries

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Reviewed 2018