Parthenium weed (Parthenium hysterophorus)

WEED ALERT: STATE PROHIBITED WEED
If you see this plant contact your council weeds officer, the NSW Invasive Plants & Animals Enquiry Line 1800 680 244 or email weeds@dpi.nsw.gov.au

Profile

Impact

The weed adversely affects human and animal health and can cause:

  • respiratory problems
  • severe dermatitis
  • tainted meat if stock eat the plant within one month of slaughter
  • tainted milk.

Landowners are advised to never touch the plant with bare hands and always use a dust mask if working near the weed for extended periods. Allergic reactions are not always experienced with the first contact with the plant but can develop after a number of exposures.

Once a reaction to parthenium weed develops, some individuals may show similar reactions to related plants such as sunflowers. This reaction can be so severe that allergic people can be forced to move away from parthenium weed-infested areas.

Distribution

Parthenium weed is native to the Caribbean region. It is thought to have been introduced to Australia from the USA on machinery during World War II and as a contaminant of imported pasture seed during the 1950s.

Parthenium weed is endemic to central Queensland and is spreading into southern Queensland.

NSW continues to be free from established populations of parthenium weed. Outbreaks occur on roadsides and particularly the Newell Highway but local government weeds officers have been very effective at finding and eradicating these infestations.

Outbreaks on private property occur in NSW but are not common. Headers and grain harvesting machinery from Queensland have previously been a source of new infestations on private property. However, compulsory NSW Department of Primary Industries (NSW DPI) inspections for harvesting machinery entering NSW from Queensland have minimised parthenium weed spread.

The potential for a permanent population of parthenium weed establishing in NSW is greater on private property than on roadsides due to the difficulty in finding new outbreaks at an early stage.

If you suspect a plant could be parthenium weed, note its location and report it to NSW DPI or your local council Weeds Officer for positive identification.

Distribution map

Spread

The weed is spread by seed and tolerates a variety of conditions.

The main pathways for introducing this weed to NSW are:

  • harvesting machinery
  • hay and grain
  • livestock floats, and
  • vehicles from infested areas of Queensland.

Good hygiene practices will reduce the risk of introducing parthenium weed to your property.

Parthenium weed becomes established in disturbed, degraded or bare soil sites such as:

  • overgrazed, heavily-stocked areas
  • stock yards and watering points
  • along roadsides and fencelines
  • neglected areas
  • cropping paddocks recently harvested by contract harvesters
  • areas where excavation machinery has been working.

Description

Parthenium weed is an annual plant with a deep taproot and an erect main stem. The weed usually grows to a height of 1–1.5m although it can grow to 2 m high.

Stem and leaves

The upper half of the main stem becomes highly branched at flowering. The deeply-lobed leaves are alternately branched on the stems, pale green and covered with soft, fine hair.

After flowering, most leaves die. Stems appear to be striped due to longitudinal grooves or ribs and they become woody with age.

Flowers

The creamy-white flowers occur at the tips of the stems. Clusters of male and female florets are grouped as five-lobed flowers on the terminal branches of the flower stem and measure 4–6 mm in diameter.

Seeds

Seeds are small (1–2 mm across), flattened, triangular and dark brown–black with two thin, white, spoon-shaped appendages.

Similar species

Prior to late-flowering, the plant can be easily mistaken for bishop’s weed (Ammi majus) and hemlock (Conium maculatum), after it has set seed and becomes woody it can then be mistaken for fleabane (Conyza spp).

Lifecycle

Parthenium weed is an annual plant that in favourable conditions, can germinate, flower, and set seed within four weeks. Seed set is continuous until the plant dies producing up to 15,000 seeds in a growing season.

Buried seeds can remain dormant for many years and seed close to the soil surface will germinate readily.

Conditions for the growth of parthenium weed are ideal in most areas of NSW with the exception of very arid or wet areas. Once established, plants will survive droughts and frosts.

Acknowledgements

Prepared by: Kirrily Condon; Reviewed by Philip Blackmore; Edited by Elissa van Oosterhout, Birgitte Verbeek

References

NSW Department of Primary Industries Parthenium Primefact 707

Other publications

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Control

Correct identification and quick action to prevent spread is important, however if you suspect you have found parthenium weed you SHOULD NOT attempt to control it yourself. Contact you local council weeds officer for assistance with identification, eradication and ongoing monitoring of infestations.

Biological control

Researchers in Queensland have located and tested numerous biological control agents against parthenium weed. These have included a gall-forming moth, leaf-miner, weevil, beetles, and two rust fungi. Five of these agents have established since their first releases in the 1980s but have not effectively controlled the weed. This work is now limited to the natural spread of these established agents or by landholders and community projects.

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.


2,4-D 300 g/L + Picloram 75 g/L (Tordon® 75-D)
Rate: 125 mL per 100 L of water
Comments: Spot spray. Rosette stage when plants are actively growing.
Withholding period: 1-8 weeks (see label).
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


2,4-D 300 g/L + Picloram 75 g/L (Tordon® 75-D)
Rate: 3.0 L/ha
Comments: Boom application.
Withholding period: 1-8 weeks (see label).
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Atrazine 900 g/kg (Various products)
Rate: 3.3 L/ha
Comments: Protects against emerging seedlings.
Withholding period: 28 days.
Herbicide group: C, Inhibitors of photosynthesis at photosystem II (PS II inhibitors)
Resistance risk: Moderate


Dicamba 500 g/L (Kamba® 500)
Rate: 40 mL per 100 L of water
Comments: Spot spray.
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Dicamba 500 g/L (Kamba® 500)
Rate: 600 mL/ha
Comments: Boom spray. Apply to young, actively growing plants.
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Hexazinone 250 g/L (Velpar® L)
Rate: 70 mL per 100 L of water
Comments: Apply uniformly over the area. When spraying single plants treat soil for 1 m around. Do not use near desirable trees.
Withholding period: No stated withholding period.
Herbicide group: C, Inhibitors of photosynthesis at photosystem II (PS II inhibitors)
Resistance risk: Moderate


Metsulfuron-methyl 300 g/kg + Aminopyralid 375 g/kg (Stingerâ„¢)
Rate: 10 g per 100 L of water
Comments: Hand gun application.
Withholding period: 3 - 56 days (see label)
Herbicide group: B, Inhibitors of acetolactate synthase (ALS inhibitors) + I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: High/Moderate


Metsulfuron-methyl 600 g/kg (Brush-off®)
Rate: 5 g per 100 L of water
Comments: Thoroughly wet all foliage to the point of run-off.
Withholding period: Nil (recommended not to graze for 7 days before treatment and for 7 days after treatment to allow adequate chemical uptake in target weeds).
Herbicide group: B, Inhibitors of acetolactate synthase (ALS inhibitors)
Resistance risk: High


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Legal requirements

The content provided here is for information purposes only and is taken from the Noxious Weeds (Weed Control) Order 2014 published in the NSW Government Gazette, detailing weeds declared noxious in New South Wales, Australia, under the Noxious Weeds Act 1993. The Order lists the weed names, the control class and the control requirements for each species declared in a Local Control Authority area.

Area Class Legal requirements
All of NSW 1 State Prohibited Weed
The plant must be eradicated from the land and that land must be kept free of the plant

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Parthenium weed
Parthenium weed (Photo: Bob Trounce)

Parthenium weed foliage
Parthenium weed foliage (Photo: J Gasparotto)

Parthenium weed at 6 leaf stage.
Parthenium weed at 6 leaf stage. (Photo: J.J. Dellow)

Parthenium weed seedling
Parthenium weed seedling (Photo: NSW DPI)

Parthenium weed infestation
Parthenium weed infestation (Photo: NSW DPI)

Parthenium weed flowers.
Parthenium weed flowers. (Photo: P. Blackmore)

Parthenium weed plant
Parthenium weed plant (Photo: Auld and Medd)