Perennial ragweed (Ambrosia psilostachya)

Perennial ragweed is a herb up to 2 m tall. It is a weed of crops and pastures and can cause skin allergies.

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How does this weed affect you?

Perennial ragweed, is not eaten by stock and competes with pastures and crops. It has an extensive root system making it difficult to control. Many people are allergic to the pollen, which causes flu-like symptoms. Contact with the plant can also cause skin allergies.

What does it look like?

Perennial ragweed is a herb up to 2 m tall. Leaves are alternate along the stem. They are up to 12 cm long and 4 cm wide and divided into pointed lobes. The cream or greenish male flowers are in spikes at the top of the plant. The female flowers are small and cup-shaped.

Where is it found?

In NSW, perennial ragweed grows in many regions including the Central Tablelands, Central West, Hunter, Greater Sydney and North West region.

Perennial ragweed is native in on the American continent from Canada to Mexico.

How does it spread?

Plants spread by movement of seed and stolons, which sends up shoots to form large dense colonies.

More information

Control

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.

Dicamba 750 g/L (Kamba® 750)
Rate: 400 mL per 100 L of water. Add a surfactant.
Comments: Spray prior to flowering. For non crop situations.
Withholding period: Do not harvest, graze or cut for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

Dicamba 750 g/L (Kamba® 750)
Rate: 5.9 L/ha Use a minimum of 1500 L water per ha. Add a surfactant.
Comments: Boom spray for non-crop situations. Spray prior to flowering.
Withholding period: Do not harvest, graze or cut for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

Dicamba 750 g/L (Kamba® 750)
Rate: 87 mL per 15 L of water. Add a surfactant.
Comments: Spot spray prior to flowering. For non-crop situations.
Withholding period: Do not harvest, graze or cut for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

Biosecurity duty

The content provided here is for information purposes only and is taken from the NSW 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 pest 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.

For technical advice and assistance with identification please contact your local council weeds officer.

Reviewed 2021