Yellow oleander (Cascabela thevetia)

Assessment ID: 4679
Jurisdiction: North Territory
Methodology: Northern Territory Weed Risk Management System - terrestrial
Management area: Katherine Region

Notes: Technical report available at https://territorystories.nt.gov.au/10070/372956

Status: PUBLISHED
Last updated: 11/6/2025 3:18:29 pm AEST

Questions answered: 39 / 47

Weed Risk: 290.39 (Very high)
   Invasiveness (raw/adjusted): 7.00 / 5.831
   Impacts (raw/adjusted): 12.00 / 6.312
   Potential distribution (raw/adjusted): 15.00 / 7.890

Feasibility of Control: 195.73 (High)
   Control costs (raw/adjusted): 7.00 / 6.363
   Current distribution (raw/adjusted): 5.00 / 5.000
   Persistence (raw/adjusted): 8.00 / 6.152

Result: Prevent entry, contain regional spread, protect priority sites

Invasiveness

A1. What is the ability of the plant to establish amongst intact native environments?
Answer: High

Comments: Yellow oleander is at Mataranka, Litchfield shire, McMinns Lagoon (monsoon forest), Katherine (creeklines), and at every defence facility except Humpty Doo. It is invading undisturbed riparian areas and monsoon forests (P. Jeffery & M. Fuller, pers comm. August 2007). Yellow oleander or Thevetia peruviana has escaped from manicured gardens and gone bush. (Savanna Explorer 2007). Yellow oleander is able to establish in relatively undisturbed habitats. Most of the plants seen in the Katherine River corridor growing beneath established trees, with the main type of disturbance present from flooding (NT WRM Technical Committee 2015). Captain Cook tree [Cascabela thevetia] has become a highly invasive weed in parts of Queensland, especially along creek systems (QDEEDI 2009). Occurs near old habitations or in creeks (Forster & Williams 1996). Large bushy shrub to 3-4 m high; forming dense thicket covering ca 50 m; dominating a section of vine thicket, East Point, Darwin (R Booth, NT Herbarium record, 05/03/1993).

A2. What is the reproductive ability of the plant?

(a) Time to seeding
Answer: 1 year or less

Comments: For land managers trying to prevent establishment of C. thevetia or to control seedling regrowth once initial infestations have been treated, this study indicates that young plants have the potential to flower and produce seeds within 268 and 353 days, respectively. However, with plant growth and reproduction most likely to be slower under field conditions, annual surveillance and control activities should be sufficient to find and treat plants before they produce seeds and replenish soil seed banks (Bebawi et al. 2014).

(b) Annual production of viable seed /m2 or /plant
Answer: High

Comments: Maximum pod production per pot was observed under natural light conditions where the yellow biotype produced significantly more pods (775 pods) than the peach biotype (371 pods) across all plant densities. Under shaded conditions, pod production was low, averaging 96 or less pods per pot over the study period, and there was no significant difference between the yellow and peach biotypes (Bebawi et al. 2014). Plants of both biotypes were capable of producing pods all year round once they reached reproductive maturity (Bebawi et al. 2014). One plant produces 400–800 fruits/year, depending on rainfall and plant age (Schmelzer 2006). Fruits are fleshy and broadly pyramidal with a raised, grooved ridge around the middle, 20-27 mm long and 28-30 mm wide, changing colour from green to black when ripe, and contain four flattened winged seeds (McKenzie 2012). Fruit drupaceous, syncarpous, pyriform. Seeds 4, compressed, ellipsoidal, winged, ecomose (Forster & Williams 1996). Seed can be stored for up to 3 months before sowing; the germination rate is about 80% (Schmelzer 2006).

(c) Vegetative reproduction
Answer: None

Comments: Examining yellow oleander in flood zone at Scott Creek in conditions that would be conducive to vegetative reproduction, no evidence of vegetative reproduction was found. New stems resprouting from fallen trees remain attached to the parent plant (R. Eastick, Weed Management Branch, pers. comm. 2017). Current known garden escapes can be attributed to recruitment by seed (R. Eastick, Weed Management Branch, pers. comm. 2017). It spreads into new areas mainly through dispersal of seeds by animals and water (Bebawi et al. 2014).

A3. Do propagules of the plant have properties that allow them to be dispersed long-distance by natural means?

(a) Flying animals (birds, bats)
Answer: Yes

Comments: Yellow oleander is spread by birds (P. Jeffery & M. Fuller, pers comm. August 2007). A few of a flock of approximately ten Oriental White-eyes Zosterops palpebrosus were observed feeding on the unripe fruit which was still on the tree, of the poisonous yellow oleander tree on 7 December 2009. This is an addition to the list of birds reported to have fruits of yellow oleander as part of their diet—Asian Koel Eudynamys scolopacea Indian Grey Hornbill Ocyceros birostris, Common Myna Acridotheres tristis, Lesser Coucal Centropus bengalensis, Red-vented Bulbul Pycnonotus cafer, White-headed Babbler Turdoides affinis, White-browed Bulbul P. luteolus, Red-whiskered Bulbul P. jocosus, Brahminy Starling Sturnus pagodarum, and domestic fowl. The ground below was littered with half eaten fruit indicating that the birds avidly ate the fruits (Turaga 2011). The fruit-pulp appears to be virtually non-toxic, at least to humans (Everist 1981).

(b) Other wild animals
Answer: No

Comments: Toxic to animals (Childrens Health Queensland 2018, Pahwa & Chatterjee 1990). Livestock generally refuse to eat the plant under normal circumstances but have occasionally been observed grazing shoot tips and consuming fruit (F. Bebawi pers. obs.). (Bebawi et al. 2014).

(c) Water
Answer: Yes

Comments: The fruit were tested to see if they float in water and they do (N. Rossiter, CDU, pers comm. 2017). Yellow oleander fruit float in water (N. Cuff, NT Herbarium, pers comm. 19/11/2015, R. Eastick, Weed Management Branch, pers comm. 19/11/2015). It spreads into new areas mainly through dispersal of seeds by animals and water (Bebawi et al. 2014).

(d) Wind
Answer: No

Comments: Propagules are not adapted to wind dispersal (NT WRM Technical Committee 2015).

A4. How likely is long-distance dispersal by human-assisted means?

(a) Deliberate spread by people
Answer: Occasional

Comments: In Australia, it is commonly grown as a garden plant in warm areas, thriving in a variety of environments ranging from wet coastal regions to dry inland areas on soils ranging from sandy loam to black clay (Everist 1981). Widely cultivated in the subtropics and tropics (Forster & Williams 1996). In the Northern Territory, due to the fact that it is known to be a weedy plant, it is no longer being sold in commercial nurseries, and has not been since around 2000. There are reports of yellow oleander being occasionally sold at markets (L. Elliott, NT Weed Management Branch, pers. comm. 27/06/2018).

(b) Accidentally by people and vehicles
Answer: Occasional

Comments: This plant reproduces only by seeds. These are commonly spread in dumped garden waste.

(c) Contaminated produce
Answer: Unlikely

Comments:

(d) Domestic/farm animals
Answer: Unlikely

Comments: Toxic to animals (Childrens Health Queensland 2018, Pahwa & Chatterjee 1990). Livestock generally refuse to eat the plant under normal circumstances but have occasionally been observed grazing shoot tips and consuming fruit (F. Bebawi, pers. obs., Bebawi et al. 2014).

Impacts

B1. What is the plant's competitive potential?
Answer: Medium

Comments: The allelopathic effect of Thevetia nerifolia on understorey vegetation was studied. The effect of decaying leaves, leaf leachates from Thevetia nerifolia and soil from below the test trees was examined on the germination and seedling growth of herbaceous test species. Leaf litter of the trees was inhibitory for the radicle growth of herbaceous species (Goel & Sareen 1986). Well established infestations in Katherine forming monocultures, replacing native vegetation and forming thickets (NT WRM Technical Committee 2015). Yellow oleander has demonstrated capacity to outcompete bellyache bush at Scott Creek (R. Eastick, Weed Management Branch, pers. comm. 2017).

B2. What is the plant’s potential to modify the existing fire behaviour and alter the fire regime?
Answer: Some potential

Comments: Fire resistant plant (Bolton 1991, PIER 2006). Yellow oleander in Katherine seems to change the fuel characteristics of the vegetation. Nothing else grows under it, so there is little horizontal fuel, reducing fire frequency (NT WRM Technical Committee 2015). Fire will cause some damage to the plant, but regrowth is normally rapid and few plants are killed. Seedlings may be more susceptible to fire but the survival of mature plants means the problem will persist (QDEEDI 2009).

B3. What is the plant’s potential to restrict the physical movement of people, animals, vehicles, machinery and/or water?
Answer: Medium

Comments: Difficult to ride a horse through thickets in Katherine (R. Eastick, Weed Management Branch, pers comm. 19/11/2015).

B4. What is the plant’s potential to negatively affect the health of animals and/or people?
Answer: High

Comments: Toxic effects of yellow oleander seed kernels were evaluated against the roof rat (Rattus rattus Linn). Major signs of poisoning observed were hind limb paralysis, rolling of the body on the long axis, circular flailing of the tail, muscular twitch, tetanic convulsions, tremors, collapse and death. Significant reduction in the rats weights were observed (Pahwa & Chatterjee 1990, PIER 2006). All parts of the plant are toxic if eaten, particularly the fruit and seeds. This species has been responsible for the deaths of several children. Symptoms may include a burning sensation in the mouth, vomiting, diarrhoea, dizziness and a slow or irregular heartbeat. The sap may be an irritant and cause dermatitis or blistering (Childrens Health Queensland 2018). The yellow oleander contains at least eight different cardiac glycosides. All parts of the plant are poisonous especially the seeds. Ingestion of oleander seeds or leaves is a common cause of accidental poisoning worldwide, particularly among children. Cases have been reported from places as diverse as Hawaii, the Solomon Islands, Southern Africa, Australia, Europe, the Far East and the United States (Eddleston & Warrell 1999). Although not present in large numbers yet, it could be dangerous to firefighters if they were to inhale fumes from this weed during grassfires. Breathing smoke, eating any part of the plant or even stirring your tea with a twig can result in severe poisoning (Savanna Explorer 2007). A wide range of birds including Oriental White-eyes, Asian koel, Indian Grey Hornbill, Common Myna, Lessa Coucal, White-headed Babbler, various Bulbuls, Brahminy Starling and domestic fowl are recorded as eating the fruits of yellow oleander without apparent ill-effect (Turaga 2011). More references available at https://territorystories.nt.gov.au/10070/372956

B5. Does the plant potentially have negative effects on natural and cultural values?

(a) Reducing habitat quality for native animals?
Answer: Medium

Comments: Yellow oleander is replacing riparian scrub along the Katherine River corridor (Elliott 2014, NT WRM Technical Committee 2015). Captain Cook tree has become a highly invasive weed in parts of Queensland, especially along creek systems (QDEEDI 2009). Cascabela thevetia (L.) Lippold (Apocynaceae) is an invasive woody weed that has formed large infestations at several locations in northern Australia. The most at-risk part of the landscape may be open areas that receive maximum sunlight, particularly within riparian habitats where plants would consistently have more favourable soil moisture conditions (Bebawi et al. 2014). Field observations by the authors across the sites in North Queensland revealed not only an absence of pasture species under the canopy of dense infestations of C. thevetia plants but also absence of any native vegetation and other ground cover species (Bebawi et al. 2014).

(b) Threatened species or communities
Answer: One

Comments: Transforming the riparian grass layer will have severe negative impacts on the endangered purple crown fairy wren (Malurus coronatus), (D. Liddle, DLRM Flora and Fauna, pers comm. 19/11/2015, NT WRM Technical Committee 2015).

(c) Sites of natural or cultural significance
Answer: More than one

Comments: Sites of Cultural Significance (SOCS) that are being affected by yellow oleander include; (1) Victoria River middle reaches, (2) Daly River middle reaches, and (3) Mataranka and Bitter Springs (NT WRM Technical Committee 2015).

B6. Is the plant presumed to have negative effects on environmental health?

(a) Soil chemistry/stability
Answer: No

Comments: The alleopathic effect of Thevetia neriifolia [Cascabela thevetia] on understorey vegetation was studied. The soil did not inhibit the seed germination and seedling growth of the test species (Goel & Sareen 1986). Field observations by the authors across the sites in North Queensland revealed not only an absence of pasture species under the canopy of dense infestations of C. thevetia plants but also absence of any native vegetation and other ground cover species (Bebawi et al. 2014).

(b) Water quality
Answer: No

Comments:

(c) Hydrology
Answer: No

Comments:

Potential distribution

C1b. What is the Climatch suitability score (which indicates the proportion of the NT environment that is suitable for the plant)?
Answer: 10

Comments: The shrub Thevetia peruviana (also named Cascabela thevetia) (yellow oleander), are locally naturalised on creeklines at Koolan Island, an island off the north-west coast of Western Australia (Randall 2007). Patchy infestations of Thevetia peruviana are known in the Wet Tropics Bioregion in Queensland (Werren 2001). It is a very common garden plant in Brisbane and has naturalised on ex-pasture land on St. Helena Island National Park near Brisbane, at Burleigh Heads and Rockhampton, Queensland (Csurhes & Edwards 1998). The Climatch model used by the NT WRMS predicts that 97% of the Northern Territory is climatically suitable for yellow oleander (Bureau of Rural Sciences 2009, GBIF 2018, Rossiter-Rachor et al. 2012). In Australia, it is commonly grown as a garden plant in warm areas, thriving in a variety of environments ranging from wet coastal regions to dry inland areas on soils ranging from sandy loam to black clay (Bebawi et al. 2014). Yellow oleander is invading riparian areas in the Katherine River corridor and woodland around Mataranka (Elliott 2014). It has invaded natural areas and formed dense thickets along creek lines and floodplains particularly in Charters Towers, South Townsville, Will Creek, Two-mile Creek, Douglas River, Silver Valley, and the Cook Shire (Bebawi et al. 2014).

C2. How many broad habitat types in the NT will the plant potentially naturalise in (up to 5)?
Answer: Three

Comments: The broad vegetation types that yellow oleander will potentially naturalise in are: * Tropical riparian areas * Tropical open forests/savanna woodlands * Rainforests The favoured habitat is tropical riparian areas (NT WRM Technical Committee 2007, Rossiter-Rachor et al. 2012).

C3. What is the potential of the plant to occur throughout its favoured habitat in the NT (as identified in question 2)?
Answer: Some

Comments: Potential to occur throughout some of its favoured habitat (NT WRM Technical Committee 2015).

Control costs

A1. How detectable is the weed?

(a) Distinguishing features
Answer: Always distinct

Comments: Yellow oleander is always distinct (P. Jeffery & M. Fuller, pers comm. August 2007). Yellow oleander has distinctive tubular, yellow flowers and round, green fruit (QDEEDI 2009). The sweetly perfumed flowers are funnel-shaped, bright yellow or peach coloured, 5.5-7 cm long and 2.5-4 cm wide, grouped in clusters at the end of the branches. The fruit are angular, green when immature, ripening black, broader than long and somewhat triangular in outline, with a raised ridge around the middle, about 3–4.5 cm in diameter. The fruit is fleshy and soft like a plum and encloses a “stone” comprising two starchy kernels (Childrens Health Queensland 2018). The origin of the name is from the Spanish, cascabel, cascabela for a small bell, jingle bell, tinkle bell, snake's rattle, rattlesnake, possibly referring to the fruit or to the flowers of these plants (Quattrochhi 1999). Shrub to 4 m tall. Leaves with petiole 1-3 mm Jong; lamina linear-lanceolate to Janceolate, to 15 cm long, to 15 mm wide, attenuate, acute or short- to long-acuminate, discolorous; upper surface glossy dark green, with venation obscure; lower surface pale green, with venation just visible but not prominent. Flowers 50-60 mm long, 24-35 mm diam.; pedicels 20-37 mm long. Corolla yellow or orange; tube 25-28 mm long, 10-15 mm diam. at throat; lobes obovate, 27-33 mm long, 13-15 mm wide. Disc annular. Fruit 20-27 mm long, 28-30 mm wide, black when ripe (Forster & Williams 1996). This species is still widely cultivated in Australia, and is most commonly in sub-tropical and tropical regions. In addition to the relatively common yellow- and orange-flowered forms of this species, there is also a relatively rare white-flowered cultivar known as Cascabela thevetia 'Alba' (Biosecurity Queensland 2016).

(b) Active growth period
Answer: >8 months

Comments: The active growth period > 8 months (P. Jeffery & M. Fuller, pers comm. August 2007). Flowers and fruits throughout the year (Forster & Williams 1996).

(c) Height at maturity
Answer: >2 m

Comments: Yellow oleander is a large spreading shrub usually 2.5-3.5 m tall (Childrens Health Queensland 2018). Shrub to 4 m tall (Forster & Williams 1996). The adult plant of C. thevetia is a shrub or tree capable of growing up to 10 m tall with milky sap (Bebawi et al. 2014).

A2. What is the general accessibility of infestations at the optimum treatment time?
Answer: High

Comments: The general accessibility of yellow oleander infestations is high (can treat at any time of year) (P. Jeffery & M. Fuller, pers comm. August 2007). The most at-risk part of the landscape may be open areas that receive maximum sunlight, particularly within riparian habitats where plants would consistently have more favourable soil moisture conditions (Bebawi et al. 2014).

A3. How expensive is control of the weed in the first year of targeted control, for an infestation that has reached maximum weed density?

(a) Chemical costs
Answer: High

Comments: Yellow oleander is difficult to kill when young because it has waxy bark. Total: $250-500 per hectare. [Note: This would place yellow oleander control in the high chemical costs category] (P. Jeffery & M. Fuller, pers comm. August 2007). It is particularly susceptible to fluroxypyr-based herbicides using foliar, basal bark or cut stump applications (Bebawi et al. 2014). Some herbicide treatments may take more than a year to kill Captain Cook tree (QDEEDI 2009).

(b) Labour cost
Answer: High

Comments: Yellow oleander is controlled using the basal bark method. [Note: This method would place yellow oleander control in the high labour costs category] (P. Jeffery & M. Fuller, pers comm. August 2007). Yellow oleander is difficult to control and labour intensive. Some herbicides including Starane are not effective. The main method of control in the Katherine River corridor is basal barking using Access and diesel. Fire is not effective because plants resprout from the base (similar to rubber bush). We don't recommend foliar spraying because it doesn't seem to be effective (N. Mills, NT Weed Management Branch, pers. comm. 29/06/2018).

(c) Equipment cost
Answer: Low

Comments: Yellow oleander is controlled using the basal bark method. [Note: This method would place yellow oleander control in the medium equipment costs category] (P. Jeffery & M. Fuller, pers comm. August 2007).

A4. What is the general community perception of this weed within the region?
Answer: Medium

Comments: The general community motivation to control yellow oleander is low (P. Jeffery & M. Fuller, pers comm. August 2007). The general community motivation to control yellow oleander is still low in Darwin but is increasing in Katherine (NT WRM Technical Committee 2015).

Current distribution

B1. What is the current pattern of the species’ distribution across the weed management region?
Answer: Scattered

Comments: Yellow oleander’s distribution in the Darwin and Katherine region is scattered (P. Jeffery & M. Fuller, pers comm. August 2007). Yellow oleander has always been restricted in Darwin but is becoming more present in scattered infestations around Katherine (NT WRM Technical Committee 2015). There are historic infestations at East Point, Darwin, as early as 1993 (R Booth, NT Herbarium record, 05/03/1993). Many homesteads in the Victoria River District and Barkly have yellow oleander as a cultivated plant in gardens. Yellow oleander has naturalised and is spreading along the Keep, Katherine and Mainoru Rivers (N. Mills, NT Weed Management Branch, pers. comm. 29/06/2018).

Persistence

C1. How long will it take to reach the maintenance period?
Answer: Medium

Comments: It is likely to take 2-5 years to reach the maintence period. It has taken approximately 3 years in the past (P. Jeffery & M. Fuller, pers comm. August 2007).

C2. What is the minimum time period for reproduction of sexual or vegetative propagules?
Answer: <1 years

Comments: For land managers trying to prevent establishment of C. thevetia or to control seedling regrowth once initial infestations have been treated, this study indicates that young plants have the potential to flower and produce seeds within 268 and 353 days, respectively. However, with plant growth and reproduction most likely to be slower under field conditions, annual surveillance and control activities should be sufficient to find and treat plants before they produce seeds and replenish soil seed banks (Bebawi et al. 2014).

C3. What is the maximum longevity of sexual or vegetative propagules?
Answer: 2-5 years

Comments: Short seed longevity of generally less than 24 months (QDAFF 2013).

C4. What is the threat of reinfestation from outside the management region?

(a) Long-distance (>100m) dispersal by natural means
Answer: Occasional

Comments: Yellow oleander is spread by birds (P. Jeffery & M. Fuller, pers comm. August 2007). Birds are clearly a major agent of spread, but water dispersal through floating seeds is also a mechanism that is contributing (NT WRM Technical Committee 2015).

(b) Long-distance (>100m) dispersal by human means
Answer: Rare

Comments: In Australia it is commonly grown as a garden plant in warm areas, thriving in a variety of situations from wet coastal regions to dry inland areas on soils ranging from sandy loam to black clay (Everist 1981). Because the nursery industry is aware that it is a potential weed, yellow oleander is no longer sold in nurseries in the Northern Territory, although it is occasionally sold in markets (L. Elliott, NT Weed Management Branch, pers. comm. 27/06/2018).

References

Bebawi FF, Campbell SD & Mayer RJ (2014). Effect of light conditions and plant density on growth and reproductive biology of Cascabela thevetia (L.) Lippold. The Rangeland Journal, 36: 459-467. Biosecurity Queensland (2016). Weeds of Australia - Biosecurity Queensland Edition Fact Sheet: Cascabela thevetia, <https://keyserver.lucidcentral.org/weeds/data/media/Html/cascabela_thevetia.htm>, accessed 27 June 2018. Bolton, J. (1991). Firescaping. Horticulture 69: 54. Bureau of Rural Sciences (2009). Climatch. Department of Agriculture, Fisheries and Forestry, Canberra, viewed 6 June 2009,<http://adl.brs.gov.au:8080/Climatch>. Cebra C & Sisson D (2014). Diseases of the Cardiovascular and Hemolymphatic Systems, in 'Llama and Alpaca Care', eds. Cebra C, Anderson DE, Tibary A, Van Saun RJ, Johnson LW, Elsevier, <https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/oleandrin>, accessed 25/06/2018. Childrens Health Queensland (2018). Yellow oleander (Cascabela thevetia), <https://www.childrens.health.qld.gov.au/poisonous-plant-yellow-oleander-cascabela-thevetia/>, accessed 22/06/2018. Csurhes, S. & Edwards, R. (1998). Potential Environmental Weeds in Australia: Candidate species for preventative control. Queensland Department of Natural Resources, Brisbane. Downer J, Craigmill A, Holstege D (2003). Toxic potential of oleander derived compost and vegetables grown with oleander soil amendments, Vet Hum Toxicol, 45: 219-221. Eddleston, M. & Warrell, D. A. (1999). Management of acute yellow oleander poisoning. Q J Med 92: 483-485. Elliott LP (2014). Yellow oleander (Cascabela thevetia) in the Katherine River corridor: recent field observations relevant to a reconsideration of NT Weed Risk Assessment determinations, July 2014, NT Department of Land Resource Management, Darwin. Everist SL (1981). Poisonous plants of Australia. Angus and Robertson, Sydney. More references available at https://territorystories.nt.gov.au/10070/372956