Castor oil plant

Castor oil plant is a declared Class B and Class C weed.

Another name for this plant is Ricinus communis.

Castor oil plant - infestation 

Identification

You should use this as a guide. There may be other plants or weeds that look similar.

If you are unsure, contact the Weed Management Branch.

Habit

habit image

These features describe the habit of this plant:

  • tall, branching shrub
  • 2 to 3m high
  • can grow taller in favourable conditions.

Castor oil plant - habit 

Stems and branches

stems and branches image

These features can identify the stems and branches:

  • hollow
  • change in colour from a pale green-red to grey when mature.

Castor oil plant - stems and branches 

Leaves

leaves image

These features can identify the leaves:

  • arranged alternately along branches
  • glossy
  • maturing from dark red-brown to green
  • distinctive unpleasant odour when crushed
  • divided into seven to nine triangular toothed lobes with a central vein.

Castor oil plant - leaves 

Flowers

flowers image

These features can identify the flowers:

  • red-green
  • form as crowded, rigid spikes in the forks of upper branches
  • females at the top of the spikes, males at the bottom
  • neither type has petals.

Castor oil plant - flowers 

Fruit and seeds

fruit and seeds image

These features can identify the fruit and seeds:

  • egg-shaped fruit
  • three-lobed
  • about 2.5cm long
  • covered in red or green soft spines
  • each lobe contains one seed
  • fruits explode when mature, throwing seeds several metres
  • seeds are toxic to animals and humans.

Castor oil plant - fruit and seeds 

Similar looking plants

The following plant species look similar to castor oil plant:

Impact

Castor oil plant can have all of the following impacts:

  • invade pastures, rarely grazed
  • seeds contain an extremely poisonous substance called ricin
  • ricin in seeds is toxic to horses, cattle, sheep, pigs, poultry and humans
  • the consumption of two to eight seeds can lead to death in humans.

Habitat and distribution

Castor oil plant is native to Asia and Africa. It was probably first introduced as a medicinal plant. Castor oil plant is now found in all Australian mainland states, generally along creek lines and in disturbed areas. Dense colonies may develop, particularly following heavy rains or flooding.

In the NT castor oil plant has mainly been confined to the arid centre and the Victoria River District.

Spread prevention

Castor oil plant seeds can be spread by flooding, in mud adhering to vehicles or machinery and in garden waste and soil. It is often abundant along watercourses and floodplains.

You can prevent the spread of castor oil plant by doing all of the following:

  • map infestations to help develop a management plan
  • control minor infestations, isolated outbreaks or seedlings first
  • designate wash down areas and actively work to prevent contamination of clean areas
  • monitor areas that you have treated and watch for re-infestations.

Castor oil plant - spread 

Castor oil plant spread. 

Control

Caution should be taken when attempting any control and removal of this weed. Wear protective clothing, gloves and eye protection before starting control work.

Chemical control

The best time to treat castor oil plant is from December to April. Below is a list of treatment methods that can be used.

Chemical and concentration Rate Situation, method and notes
2, 4-D amine 625 g/L
Various trade names
320ml / 100L Seedling (individuals or infestation) + adult (infestation):
Foliar spray - apply when actively growing
For boom rate contact WMB
Triclopyr 600 g per litre
Various trade names
1L / 60L (diesel)Seedling (individuals or infestation) + adult (infestation):
Foliar spray - apply when actively growing
For boom rate contact WMB

It is vital that follow up works are carried out to control seedling recruitment and regrowth after a site has been treated. Treatment areas must be revisited no less than four weeks after spraying, but prior to seed-set.

Seeds in the soil can remain viable for at least four years, and up to seven years under dry conditions, so follow-up control to kill any regrowth or new germinants should be done for at least four years after treatment.

Areas should be checked for two years after eradication. 

If left uncontrolled, seedlings and regrowth may develop into a bigger problem than the initial infestation.

Non-chemical control

Hand pulling and grubbing

Weeds, including their roots, are physically pulled out of the ground by hand or using hand tools. 

This is an effective method of control for individual weeds and recent outbreaks that haven’t released seeds yet, but it requires a lot of labour.

Last updated: 27 June 2017