Castor oil plant (Ricinus communis)

Castor oil plant is a medium to tall shrub with large star-like leaves. It is poisonous to humans, dogs and livestock.

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How does this weed affect you?

Castor oil plant:

  • is poisonous to people and animals
  • invades pastures, reducing productivity
  • can out compete native plants
  • reduces habitat and food for native animals.

Human poisoning

Castor oil plant contains a toxin called ricin. It is toxic to humans, capable of causing serious illness and death. Flowers, leaves and especially the seeds are poisonous. Eating castor oil plant causes:

  • a burning sensation in the throat and mouth
  • vomiting, abdominal pain, diarrhea and bleeding
  • bleeding from the eye and mucous membranes
  • respiratory and cardiac distress and failure.

Temporary blindness may occur if the sap gets into the eyes. Touching leaves and seeds can cause dermatitis in people with sensitive skin.

 What to do if a person is poisoned:
  • If the patient is unconscious, unresponsive or having difficulty breathing dial 000 or get to the emergency section of a hospital immediately.
  • If the patient is conscious and responsive call the Poisons Information Centre on 13 11 26 or your doctor.
  • If going to a hospital take a piece of the plant for identification.

Animal poisoning

Castor oil plant is poisonous to dogs and livestock including cattle, horses, pigs, sheep and poultry. Livestock rarely eat this weed due to the odour of the leaves. However, poisoning can occur if grain is contaminated with seeds. Symptoms are similar to human poisoning. It may take a few hours or days for symptoms to appear.

Honey bees have been poisoned by castor oil plants.

What does it look like?

Castor oil plant is a fast-growing shrub usually 3 m tall (occasionally up to 12 m). It is a perennial plant unless it is growing in areas with regular severe frosts where it will die in winter.

There is a lot of variation in this plant. The flowers or leaves on one plant may be a different colour to other plants, even when growing in the same area.

Leaves are:

  • dark red-brown, turning green-blue when older
  • 10-40 cm in diameter
  • star shaped with toothed edges
  • divided into 7-9 lobes
  • glossy and hairless with prominent midveins
  • strong smelling
  • attached underneath to stalks 10-30 cm long.

Flowers are:

  • clustered in spikes at the end of stems
  • red (female) or creamy-yellow (male) both without petals
  • present year round, mainly summer.

Fruit are:

  • egg-shaped or rounded
  • 2.5 cm long
  • covered in soft spines
  • reddish-green with 3 segments, each containing one seed.

Seeds are:

  • oval
  • mottled brown or grey with a yellowish knob at one end
  • smooth and shiny
  • 10-15 mm long and 6-10 mm wide.

Stems are:

  • hollow and hairless
  • dull, pale green sometimes tinged red
  • grey when older.

Roots:

Castor oil plant has a strong tap root and thick fibrous side roots.

Similar looking plants

Castor oil plants looks similar to two other weed species:

  • bellyache bush (Jatropha gossypiifolia)
  • physic nut (Jatropha curcas).

Both of these plants have leaves with 3-5 lobes and flowers with petals.

Where is it found?

Castor oil plant is common along the coastal regions of NSW but it is also found in scattered populations throughout NSW.

It is native to Africa and Eurasia.

What type of environment does it grow in?

Castor oil plant grows in warm temperate and sub-tropical climates in a wide variety of soils. It is drought tolerant but grows best in soils with high moisture. It is not frost tolerant. It grows:

  • along gullies and waterways
  • in coastal areas including sand dunes
  • along roadsides
  • in pastures especially on flood plains
  • in gardens
  • in neglected areas or areas with disturbed soil.

How does it spread?

When the fruit pods dry out the seed shoots out, sometimes landing many metres away. Seeds germinate in autumn to spring or can stay viable for at least four years. Seeds are spread:

  • in water
  • by birds, ants and rodents
  • by people dumping garden waste
  • in contaminated soil on shoes, vehicles and machinery.

References

Parsons, W.T. and Cuthbertson, E.C. (2001). Noxious weeds in Australia 2nd Edn, CSIRO Publishing, Collingwood.

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 2020 from: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Ricinus~communis

Sasidharan, R. & Venkatesan, R. (2019). Seed elaiosome mediates dispersal by ants and impacts germination in Ricinus communis. Frontiers in Ecology and Evolution7, 246.

More information

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Control

Be careful when controlling this plant as it is poisonous. Wear protective clothing including gloves and eye protection before starting control work.

Castor oil plant can be controlled by:

  • hand pulling or digging out seedlings and young plants
  • slashing, mowing and cultivation
  • herbicides.

 The key is to follow up any control work to treat plants that have re-grown or stop new plants from growing and seeding. Check sites for at least four years.

Slashing, mowing and cultivation

Large areas of castor oil plant can be slashed or mown, followed by cultivation. Keep cultivation shallow to stop seeds from being buried deeply. Deeper burial can cuase dormacy in seeds and this could make control difficult in future. Check the area and control any regrowth or new seedlings.

Physical removal

Young plants can be hand pulled or dug out quite easily. Larger plants can be removed if the soil is damp. It is important to remove as much of the roots as possible to stop the plant from re-growing. Contact your local council for advice on disposal.

Chemical control

If possible spray before plants set seed. If plants have fruit, collect and dispose of the fruit. If there are too many to collect follow up control of seedlings will be needed. Check controlled areas within one month of treatment.

Spraying

This method is best before plants get too tall and when there is no risk of spraying desirable plants nearby. Cover all foliage with herbicide.

Cut stump

Cut trunks or stems and apply herbicide within 15 seconds.

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 9907 Expires 31/03/2025
Glyphosate 360 g/L (Various products)
Rate: 1 part glyphosate to 50 parts water
Comments: Spray seedlings and coppice shoots.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate


PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Various products)
Rate: 1 part glyphosate to 1.5 parts water
Comments: Cut stump/scrape stem application for saplings. Stem injection application large trees and shrubs.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate


2,4-D amine 625 g/L (Various products)
Rate: 340 mL per 150 L of water, or 3.4 L/Ha
Comments: Apply to young, actively growing plants.
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Picloram 44.7 g/L + Aminopyralid 4.47 g/L (Vigilant II ®)
Rate: Undiluted
Comments: Cut the stump close to the ground (no higher than 10 cm). 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


Triclopyr 600 g/L (Garlon® 600)
Rate: 1.0 L per 60 L of diesel
Comments: Basal bark application for plants up to 5 cm basal diameter. Cut stump application for plants with larger basal diameter.
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.

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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 2021