Quick Facts

Quick facts

What Does It Look Like?

What is it?

Parthenium Weed (Parthenium hysterophorus) is a extremely fast growing, hairy, aromatic, resin-dotted, annual herb. The plant can produce a deep tap root. The juvenile or vegetative stage is when the plant germinates and forms a round basal rosette of many divided leaves laying flat on the ground. The adult stage is when the plant grows an erect ribbed stem (usually one stem, rarely more, and much branched above, usually about 0.5-1.5 metres tall to 2 metres In favourable situations producing flowers and fruits. It has much divided leaves with fine white hairs, leaves arranged alternately along the stem. The lower leaves 5–20 cm long; upper leaves decreasing in size towards the top of the plant.

The flowers heads are white or cream, about 4 mm in diameter, and borne in loose clusters (terminal panicles) on the tips of branches. The outer petals (ray florets with ligules) are about 0.7 mm long with a blunt apex (tip or end), and flowers are also resin-dotted.

The wedge-shaped seeds (known as achenes or cypselas) are obovate in outline (egg-shaped with the widest part nearer the tip or membranous white scales), black at maturity, about 2 mm long, and end in two broad membranous white scales about 0.5 mm long. In ideal conditions Parthenium Weed can germinate, grow, mature and set seed in four weeks (CRC 2003).

Recognition: This species can normally be recognised by the combination of the following characters; fast growing, hairy, aromatic, resin-dotted, annual herb usually about 0.5-1.5 metres tall to 2 metres; forming a rosette before producing taller erect ribbed stem; uch divided leaves with fine white hairs, leaves arranged alternately along the stem. The lower leaves 5–20 cm long; upper leaves decreasing in size towards the top of the plant; flowers heads are white or cream, about 4 mm in diameter, at the tips of branches; edge-shaped  black seeds about 2 mm long, with two broad membranous white scales about 0.5 mm long.

More detailed descriptions and informative illustrations of the species are available in Navie et al. (1998), Parsons & Cuthbertson (2001), CRC for Australian Weed Management (2003), Agfacts (2004), Navie (2004), and Natural Resources & Water, Queensland Government (2006). For further information and assistance with identification of Parthenium Weed contact the herbarium in your state or territory.

Flower colour

White or cream

Growth form (weed type/habit)

Herb

Where it currently grows? Preferred habitat

Parthenium Weed (Parthenium hysterophorus) can be prolific in disturbed situations, both natural and unnatural, and has a marked preference for highly fertile, black, alkaline, cracking clay soils but does grow on other soils, albeit not usually as vigorously. Climatically Parthenium Weed (Parthenium hysterophorus) is best suited to areas with an annual summer rainfall greater than 500 mm. Flooded country is also very prone to Parthenium Weed infestations (CRC 2003).

Are there similar species?

Parthenium Weed (Parthenium hysterophorus) is a distinctive plant which should be easily identified. When lacking flowers it may be confused with species of Ragweed (Ambrosia) but its ribbed stems and white flower heads distinguishes Parthenium Weed from these species (Navie 2004).

Why Is It A Weed?

What are its impacts?

Parthenium Weed (Parthenium hysterophorus) is a Weed of National Significance. It is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, economic, environmental and health impacts. All parts of the Parthenium plant at any stage of growth are toxic to humans and animals.

Agriculture: Parthenium Weed is a major problem in range-lands and summer-cropping areas (especially in Queensland), costing farmers and graziers over $22 million a year in reduced production and increased management costs. It has a serious impacts on the pastoral industry and readily colonises disturbed and heavily stocked areas, reduces both pasture establishment and potential, and is a host for crop viruses. It is somewhat toxic to livestock and taints meat and milk. Kaur (2014) reported that Parthenium Weed is toxic to animals causing dermatitis with pronounced skin lesions and is responsible for mouth-ulcers with excessive salivation on various animals including horses and cattle. Livestock do not usually eat Parthenium Weed but if no other feed is available, they may eat large amounts and this can cause kidney damage in ruminants (cattle, sheep and goats) (DPI NSW 2019). Kaur (2014) states that consumption is significant amounts of Parthenium Weed in cattle (10–50%) can kill. Young cattle are most susceptible to dying from parthenium poisoning (DPI NSW 2019). Parthenium Weed also contains chemicals and exerts strong allelopathic effects on different crops (prohibits the germination and growth of seeds), also affecting nodulation (production of nitrogen fixing bacteria) in legumes due to inhibition of activity of nitrogen fixing and nitrifying bacteria (Kaur 2014).

Native ecosystems:  Parthenium Weed can invade native vegetation. In Queensland it threatens biodiversity in the Einasleigh Uplands bio-region and native grassland in the central highlands. Parthenium Weed has been reported to to causing a total habitat change in native Australian grasslands, open woodlands, river banks, and flood plains (Kaur 2014).

Urban areas: Can invade urban areas and gardens further impacting people.

People: Negatively impacts humans with the pollen grains and airborne dried plant parts, causing severe allergic dermatitis in some, while in others the pollen may cause hay fever, asthma (CRC 2003). The best way to prevent an allergic reaction to Parthenium Weed is to avoid contact with it, especially breathing pollen from flowering plants (CRC 2003). Physical contact can cause great discomfort (Kaur 2014).

How does it spread?

Parthenium Weed (Parthenium hysterophorus) is a prolific seeder. Soil seed-bank studies in Australia reveal as many as 400 million seeds per hectare (Chamberlain & Gittens 2003). An average-sized plant producing about 15,000 seeds with a significant portion of buried seed remaining viable for six or more years. The seed can be dispersed by both water, with significant spread along waterways noted in central Queensland, and by wind. Similarly, they can be spread by livestock and other animals in the hair or mud attached to their bodies (CRC 2003).

Long-distance dispersal can take place by the movement of contaminated passenger vehicles, farm machinery, livestock, stock feed and pasture seed. In Queensland there is a legal requirement for suppliers of stock, machinery and other products to sign a declaration whether or not the material is clean of seed. Legislation is also in place which requires agricultural machinery moving from Queensland to New South Wales to be inspected at the border, a process considered to have greatly reduced the risk of further introductions into the latter state (Agfacts 2004).

What is its history in Australia?

Parthenium Weed (Parthenium hysterophorus) was first recorded in Australia at Toogoolawah, Queensland in 1955 and it is considered that it was probably introduced during World War II with American aircraft landing at a local airstrip. It was subsequently discovered in 1964 (or perhaps earlier) north of Clermont, this time introduced as a contaminant of pasture grass obtained from Texas (United States). It spread rapidly from this locality following good winter rains in 1973 (Kleinschmidt & Johnson 1987; Navie et al. 1998; National Weeds Strategy Executive Committee 2001; Parsons & Cuthbertson 2001).

It was first recorded in the Northern Territory in 1977 and in New South Wales in 1982 and Western Australia in 2011 (AVH 2020).

How To Manage It?

Best practice management

Parthenium Weed (Parthenium hysterophorus) can be controlled by chemical and physical methods, and management and cultivation. Quarantine methods, i.e. ensuring that farm machinery and other vehicles, grain and livestock that are moved between properties or imported are clean of Parthenium Weed seed, are important in preventing spread of seed.

Chemical control: Herbicides can be used to successfully kill plants. Spot and boom spraying are used to control the weed.  Herbicides, including rates of application, used for the control of Parthenium Weed are listed in web-based information sheets produced by the DPI NSW (2019); Queensland Government, Department of Agriculture and Fisheries (2020); and in Navie et al. (1998). For general information of the use of chemicals please visit the Australian Pesticides and Veterinary Medicines Authority at http://www.apvma.gov.au

Non-chemical control: Physical control is possible for small and limited plants in the rosette (juvenile) stage or before flowering and seed setting.  Don’t pull up mature plants by hand if they have already set seed as there is a danger that mature seeds will drop off the plant and increase the area of infestation. Warning: Hand-pulling of plants without using gloves and facial mask may result in allergic reactions.

Competition and management:  Pasture management the planting of vigorous pastures or crops provides competition to Parthenium Weed. The light grazing of pastures helps prevent invasion or re-establishment of Parthenium Weed. However, caution is advised as Kaur (2014) reported if Parthenium Weed eaten by animals is potentially toxic and can have negative impacts causing dermatitis with pronounced skin lesions.

Cultivation: It can also be controlled by cultivating before sowing and by subsequent use of herbicides.

Biological control: Parthenium Weed has also been recognised as a target for biological control through a cross-jurisdictional government process. This allows activities to be undertaken to develop effective biological controls. Biological control is one tool that forms part of an integrated management program for large-scale scattered and dense infestations. However, biological control on its own will not eradicate Parthenium Weed infestations. The leaf beetle Zygogramma bicolorata; and the stem moth Epiblema strenuana, cause the most damage.

Other biological control agents include: a stem boring weevil from Argentina, Listronotus setosipennis; a seed-feeding weevil, Smicronyx lutulentus, which lays eggs in the flower buds, leaving the newly hatched grubs to feed on the seed heads; a leaf mining moth, Bucculatrix parthenica, from Mexico, whose grubs feed on the leaves of Parthenium Weed; a stem-galling weevil, Conotrachelus albocinereus, from Argentina; and Carmentia ithacae, a stem boring moth from Mexico (CRC 2003).

Parsons & Cuthbertson (2001) give a general overview of control methods, and other overviews can be accessed in CRC (2003), Chamberlain & Gittens (2003), Agfacts (2004) and Natural Resources & Water (2006).

Does it have a biological control agent?

YES. Eleven biocontrol agents released: with the seed-feeding weevil (Smicronyx lutu- lentu), the stem-boring weevil (Listronotus setosipennis), and the root-boring moth (Carmenta nr. ithacae), the winter rust (Puccinia abrupta var. partheniicola), and the summer rust (Puccinia xanthii var. parthenii-hysterophorae) identified as priority agents for redistribution (Harvey,  et al 2023).

When does it grow? (lifecycle/growth calendar)

Parthenium Weed (Parthenium hysterophorus) normally germinates in spring and early summer, but with the right conditions plants can grow and produce seed at any time of the year, with no specific day length requirement for flowering.

In stressed conditions a plant can complete its life cycle in just four weeks. In contrast, in a good season four or more successive generations can emerge at the same site and plants in a favourable situation may live for six to eight months (CRC 2003).

Buried seeds remain viable for longer than those on the surface, an apparently significant portion remaining viable after six years and perhaps eight to ten years (CRC 2003). For more details, see Navie et al. (1998).

Where Is It Found?

Which states and territories is it found?

NSW, NT, QLD, WA

What areas within states and territories is it found?

Within Australia, Parthenium Weed (Parthenium hysterophorus) is widespread and seemingly entrenched in central Queensland. Around 2000 the core area of infestation in the central highlands of Queensland was estimated to be 8.2 million hectares. Scattered infestations also occur in Queensland from Cook shire in the north to Longreach in the west and south to the border towns of Goondiwindi and Mungindi.

In New South Wales, sporadic infestations have been reported from as far south as Deniliquin and Jerilderie. However, in a report by the National Weeds Strategy Executive Committee (2001) it was noted that the extent of Parthenium Weed in the state had been significantly reduced since its introduction in 1982 and in Agfacts (2004) it was recorded that Parthenium Weed has been prevented from establishing in New South Wales, although it is also evident that more outbreaks are inevitable (Chamberlain & Gittens 2003).

From published records the extent to which Parthenium Weed has been noted in the Northern Territory is unclear, but reports are few. Miller et al. (1998) reported that the original infestation of 1977 at Elsey Creek, in the Mataranka district, had almost been eradicated. At that time no other infestations were known. Since then, the Elsey population has been eradicated and sporadic outbreaks on rural blocks in the Katherine area have also been successfully treated. Seemingly, two outbreaks in the Northern Territory Gulf country in 1991 – one near Borroloola and the other at Limmen Bight – have also been satisfactorily dealt with (Chamberlain & Gittens 2003).

Fist collected from WA in 2008 from Wyndham-East Kimberley area (AVH 2020).

Where does it originate?

Parthenium Weed (Parthenium hysterophorus) was originally described and formally named from material gathered in Jamaica. The species is native to the Caribbean region (Parsons & Cuthbertson 2001), and according to some reports also other regions of central America, Mexico and parts of South America (e.g. CRC 2003; Navie et al. 1998).

It is considered to be an introduction to the United States (USDA undated) and introduced to many other regions, including Israel, Kenya, South Africa, Madagascar, Mauritius, Mozambique, the Seychelles, India, Bangladesh, Nepal, parts of China, Vietnam, Taiwan, many Pacific island (including Hawaii, New Caledonia, New Guinea & Tahiti) and Australia.

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

YES

Where is it a declared weed?

Declared in all Australian states and territories

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Parthenium hysterophorus

Other scientific names (synonyms)?

Parthenium lobatum Buckley

Does it have other known common name(s)?

Bitter Weed, Carrot Grass, Congress Grass (in India),  Escoba Amarga (Spanish, Caribbean), Feverfew  (Caribbean), False Ragweed, Fausse Camomile (French), Ragweed Parthenium (in USA), Whitetop (Jamaica).