Cha-om (Senegalia pennata subsp. insuavis)

Also known as: khang, stinky leaf, Petai duri, Rau thoi

Cha-om is a prickly shrub with fern-like leaves that smell foul when crushed. It can form dense thickets and outcompetes native plants.

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How does this weed affect you?

Cha-om is an invasive shrub that:

  • can form prickly thickets, which limit movement of people and animals
  • has spines that can injure people and animals
  • outcompetes native plants
  • competes with pastures reducing productivity
  • can increase the risk of erosion by shading out ground covers
  • can damage fences or other structures that it climbs over.

What does it look like?

Cha-om is a prickly shrub up to 5 m tall. It can climb like a vine if there are other plants or structures, such as fences, nearby to support it.

Leaves:

The leaves are fern-like and divided into 17-28 primary leaflets each 3-10 cm long. These are further divided into many pairs of secondary leaflets which are:

  • green
  • oblong shaped
  • 4–6 mm long and 0.5–1 mm wide
  • sometimes fold together longwise
  • smell foul when crushed
  • have glands at the base of the leaf stalk.

Prickles are:

  • up to 10 mm long
  • scattered along the stems
  • straight or curved backwards.

Flowers heads are:

  • white, cream or pale yellow
  • pompom like
  • on the end of the stems.

Fruit are:

  • pods containing up to 8 seeds
  • green ripening to brown.
  • 12–23 cm long and 1.5–3 cm wide
  • flattened, thin and oblong shaped (straight or slightly curved)
  • papery to leathery
  • hairless.

Similar looking plants

Cha-om looks like:

  • Leucaena (Leucaena leucocephala), which does not have prickles and does not smell pungent when the leaves are crushed. It also has larger flowerheads (2 cm diameter).
  • Common sensitive plant (Mimosa pudica), which is a ground cover with pink flowers and the leaves close together when touched.
  • Poinciana (Delonix regia), which grows taller to 10 m, has red flowers and the leaves do not smell when crushed. It also has much longer seed pods up to 60 cm.

 

Where is it found?

Plants have been found in food gardens on the North Coast.  

In Queensland it has been found in disturbed areas, often near rainforests. 

Cha-om is native to Myanmar, Indonesia, southern China and India. 

What type of Environment does it grow in?

Cha-om grows in tropical and sub tropic climates. It is often found on disturbed sites near rainforests.

Maps and records

  • Recorded presence of Cha-om during property inspections (Map: Biosecurity Information System - Weeds, 2017-2023)
    These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.

How does it spread?

By seeds

Cha-om plants can produce seeds within a year. Pods are eaten by cattle and seeds are spread in their dung. Seeds could also be spread by moving water.

By plant parts

Cha-om reproduces via stem fragments and where branches come in contact with the ground.  

Stem fragments can be spread by moving water.

References

Hassan, R. A., & Hamdy, R. S. (2021). Synoptic Overview of Exotic Acacia, Senegalia and Vachellia (Caesalpinioideae, Mimosoid Clade, Fabaceae) in Egypt. Plants10(7), 1344.

Maslin, B. R. (2012). New combinations in Senegalia (Fabaceae: Mimosoideae) for Australia. Nuytsia22(6), 465-468.

Maslin, B. R., Ho, B. C., Sun, H., & Bai, L. (2019). Revision of Senegalia in China, and notes on introduced species of Acacia, Acaciella, Senegalia and Vachellia (Leguminosae: Mimosoideae). Plant diversity41(6), 353-480.

Queensland (N.D.) Prohibited invasive plant: Cha-om. Retreived from November 2022 from: https://www.daf.qld.gov.au/__data/assets/pdf_file/0005/1396472/cha-om.pdf

Queensland Government.  (2018). Cha-om alert Retreived 09 July 2021 from: https://www.business.qld.gov.au/industries/farms-fishing-forestry/agriculture/land-management/health-pests-weeds-diseases/weeds-diseases/invasive-plants/prohibited/cha-om

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Control

If you suspect you have seen Cha-om call your local council weeds officer for help with identification and control.

Wear personal protective equipment when controlling cha-om including gloves to protect from the spines.

Physical

Individual smaller plants can be dug out by hand.

Chemical control 

Cut stump

Cut the stump and apply herbicide to the remaining stump within 15 seconds. To reach the stump branches may need to be cut away to get access to the stump and avoid injury.

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.


Picloram 44.7 g/L + Aminopyralid 4.47 g/L (Vigilant II ®)
Rate: Undiluted
Comments: Cut stump application: Apply a 3–5 mm layer of gel for stems less than 20 mm. Apply 5 mm layer on stems above 20 mm.
Withholding period: Nil.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
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.
North Coast Regional Recommended Measure* (for Regional Priority - Eradication)
Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here

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For technical advice and assistance with identification please contact your local council weeds officer.
For further information call the NSW DPI Biosecurity Helpline on 1800 680 244 or send an email to weeds@dpi.nsw.gov.au

Reviewed 2022