Mimosa bush (Vachellia farnesiana)

Mimosa bush is a shrub to small tree. It occurs in the north-east and parts of north-west of NSW.

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How does this weed affect you?

Mimosa bush invades grasslands and is a major weed in some areas of northern NSW. It can:

outcompete desirable plants and form a monoculture
reduce available pasture plants
form dense thickets that limit movement of people and animals
restrict access to watering points
make mustering difficult
injure people and animals with its thorns.

What does it look like?

Mimosa bush is a spreading multi-stemmed shrub that usually grows 1–4 m tall and occasionally up to 7 m tall. It has sparse, feathery leaves and bright yellow flowers.

Leaves are:

sparse
fernlike
up to 30 cm long with a pair of whitish spines (2–45 mm long) at the base
alternate along the stem
divided twice with 1–7 primary pairs of leaflets, and further divided into 5–23 secondary pairs of leaflets which are:
- green or yellowish green
- 3-10 mm long and 0.5 - 2 mm wide
- narrow oblong
- opposite
- hairless or with very small hairs on the edges.

Flowers are:

bright yellow to orange-yellow
in round clusters 10–13 mm wide that look like fluffy pompoms
fragrant
on hairy stalks arising from the leaf forks
mostly present from June–September but occasionally throughout the year

Seedpods are:

green when unripe, turning brown to black when mature
50–70 mm long and 8–17 mm wide
cigar-like
hairless
woody
straight or curved.
brown and smooth
oval shaped and slightly compressed
7-8 mm long and 5-6 mm wide
separated by pith and lie across the pod.

Seeds are:

brown and smooth
oval shaped and slightly compressed
7-8 mm long and 5-6 mm wide
separated by pith and lie across the pod.

Stems are:

grey-brown
zigzagged
smooth or with fine grooves
covered with numerous obvious tiny whitish raised pores (lenticels)
often hairy towards tips when young
hairless when older.

Similar looking plants

Mimosa bush (Vachellia farnesiana) looks similar to:

Karoo acacia (Vachellia karroo) which has much larger spines up to 25 cm long and the seed pods are constricted between each seed.
Mesquite (Prosopis spp.) which has cylindrical greenish-cream flowers up to 8 cm long.
Prickly acacia (Vachellia nilotica) which has longer spines (usually up to 5 cm long) and longer seed pods that are constricted between each seed.
Parkinsonia (Parkinsonia aculeata) which has flowers with 5 petals, short, curved spines (up to 1 cm) and does not have fern-like leaves.
Cutch tree (Senegalia catechu) flowers are in long clusters, the seedpods are flattened, partly hairy, and dark brown when mature.

Where is it found?

Mimosa bush is most common in the North West and Western regions of NSW. However, it is also found in other regions of NSW.

It is native to Central America. It was most likely introduced to Australia pre-European settlement and was previously thought to be a native Australian plant.

What type of environment does it grow in?

Mimosa bush grows in tropical, sub tropical and warm temperate climates. It is drought tolerant and can grow in arid and semi-arid regions. It is found in open woodlands, shrublands and grasslands and near watercourses. It grows in alluvial clays and sandy loam soils.

How does it spread?

By seed

Seeds are mostly spread by livestock and other animals that eat the fruit and spread the seeds in their dung.

By plant parts

Mimosa bush produces suckers when its aboveground parts are damaged.

more info would be good in the long term

References

CABI (2020). Acacia farnesiana (huisache). In: Invasive Species Compendium. Wallingford, UK: CAB International. Retrieved 5 July 2022 from: https://www.cabi.org/isc/datasheet/2236

Cunningham G.M., Mulham W.E., Milthorpe P.L. and Leigh J.H. ( 1992). Plants of western New South Wales. (Inkata Press, Melbourne)

Dunlop, C.R., Leach, G.J. & Cowie, I.D. (1995). Flora of the Darwin Region Volume 2. (Conservation Commission of the Northern Territory: Darwin), as Acacia farnesiana.

Medlin, C. R., McGinty, W. A., Hanselka, C. W., Lyons, R. K., Clayton, M. K., & Thompson, W. J. (2019). Treatment life and economic comparisons of honey mesquite (Prosopis glandulosa) and huisache (Vachellia farnesiana) herbicide programs in rangeland. Weed Technology, 33(6), 763-772.

Moura, J., & Vieira, E. A. (2021). Responses of young plants of Vachellia farnesiana to drought. Australian Journal of Botany, 68(8), 587-594.

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 5 July 2022 from: http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Vachellia~farnesiana

Queensland, Department of Agriculture and Fisheries, (2020). Restricted Invasive Plant: Identification of Prickle Bushes. Retrieved 5 July 2022 from: https://www.daf.qld.gov.au/plants/weeds-pest-animals-ants/weeds/a-z-listing-of-weeds/photo-guide-to-weeds/mimosa-bush?a=72195

More information

PlantNET NSW FloraOnline, Vachellia farnesiana. Royal Botanical Gardens and Domain Trust.

Control

Successful weed control relies on follow up after the initial efforts. This means looking for and killing regrowth or new seedlings. Using a combination of control methods is usually more successful.

Physical removal

By hand

Hand-pull seedlings and dig out small plants. Remove as much of the roots as possible.

Machinery

It is difficult to remove all of the root structure using machinery. Mimosa bush grows quickly meaning mechanical control needs to be repeated within a few years and this can be expensive.

Fire

Fire can kill the above ground parts but plants will regrow from the roots.

Chemical control

Spot spraying

Apply to actively growing shrubs in full leaf. Cover all of the plant with herbicide.

Basal barking

This method can be used on plants with stems up to 5 cm in diameter at the base. Spray or paint the herbicide mix around the base of each stem from ground level up to at least 30 cm from the ground, wetting the bark to the point of runoff. Apply the herbicide mixture to dry stems because wet stems can repel the diesel or biodiesel mixture. Ensure all stems on multi-stemmed plants are treated.

Cut stump method

Cut trunks or stems less than 15 cm above the ground. Apply herbicide to the cut and sides of the stump immediately after cutting. See product labels for more detail on herbicide use in relation to stem size.

Herbicide pellets

Estimate the area within 30 cm beyond the drip zone of each tree or group of trees. Calculate the required dose. Distribute the pellets from the drip line to slightly beyond the dripline formed by the branches.

Herbicide options

WARNING - ALWAYS READ THE LABEL
Users of agricultural or veterinary chemical products must always read the label and any permit, before using the product, and strictly comply with the directions on the label and the conditions of any permit. Users are not absolved from compliance with the directions on the label or the conditions of the permit by reason of any statement made or not made in this information. To view permits or product labels go to the Australian Pesticides and Veterinary Medicines Authority website www.apvma.gov.au

See Using herbicides for more information.

PERMIT 14929 Expires 30/09/2029
Clopyralid 300 g/L (Lontrel®)
Rate: 500 mL in 100 L of water
Comments: High volume foliar application. Apply to actively growing plants in full leaf. Add a surfactant.
Withholding period: 1-12 weeks (see label).
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

PERMIT 13891 Expires 31/05/2028
Tebuthiuron 200 g/kg (Various products)
Rate: 2 g per square metre
Comments: Read and follow permit and label instructions thoroughly
Withholding period: Nil.
Herbicide group: 5 (previously group C), Inhibition of photosynthesis at photosystem II - D1 Serine 264 binders (and other nonhistidine binders) (PS II Serine 264 inhibitors)
Resistance risk: Moderate

Fluroxypyr 333 g/L (Starane™ Advanced)
Rate: 1 L in 55 L of diesel (or biodiesel).
Comments: Basal bark application
Withholding period: Do not graze failed crops and treated pastures or cut for stock food for 7 days after application. See label for more information.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

Triclopyr 240 g/L + Picloram 120 g/L (Access™ )
Rate: 1.0 L per 60 L of diesel (or biodiesel such as Biosafe).
Comments: Basal bark application for plants with stems up to 5 cm diameter at the base. Cut stump application can be used for plants with stems up to and in excess of 5 cm diameter at the base. Treat all stems on multi-stem plants. See label for information about biodiesel.
Withholding period: Nil
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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 pest 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.