Mistflower (Ageratina riparia)

Mistflower is a low growing herb with clusters of fluffy white flowers. It competes with native vegetation and pastures.

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How does this weed affect you?

Mistflower invades bushlands, riparian areas, and pastures in subtropical climates. Infestations can become a very dense mat of interwoven stems. Mistflower:

  • outcompetes native plants
  • reduces food and shelter for native plants
  • invades pastures reducing productivity
  • can reduce livestock movement
  • may cause lung damage in horses and sheep.

Livestock poisoning

Mistflower contains an unidentified lung-damaging toxin that affects horses. There are no field reports of death but laboratory tests show that it can kill sheep and horses.

What does it look like?

Mistflower is a low-growing perennial herb that is usually 40–60 cm high (occasionally up to 1 m tall). Plants die back after flowering and then re-shoot from the base. It grows very quickly in warm weather during summer.

Leaves are:

  • green
  • 3–13 cm long and 1–4 cm wide
  • spear-shaped with toothed edges and a pointed tip
  • prominently veined
  • on a stalk 1–2 cm long
  • opposite along the stem.

Flowers are:

  • white
  • 4–6 mm wide
  • fluffy-looking
  • tubular with 5 lobes
  • in clusters of up to 30 at the end of branches
  • present from July to October.

Seeds are:

  • dark brown to black
  • 1–2 mm long with 4–5 hairy ridges that run lengthwise
  • topped with a ring of 3–4 mm long bristles
  • shed 3–4 weeks after the flowers open

Stems are:

  • reddish or purplish
  • sometimes hairy
  • spreading and branched.

Roots are:

  • fibrous
  • short and thick
  • produced at stem joints where they touch the ground. 

Similar looking plants

Mistflower looks like crofton weed (Ageratina adenophora), which has wider, triangular leaves.

Where is it found?

Mistflower grows along the east coast, from Jervis Bay in NSW up to Yandina in QLD. Most NSW infestations are on the north coast.

Mistflower is native to Central America. In 1870 it was brought to Australia as an ornamental garden plant. It has been introduced to many countries as an ornamental plant and then become a weed.

What type of environment does it grow in?

Mistflower prefers humid subtropical climates with more than 1700 mm rainfall per year. It is shade tolerant but not frost tolerant. It often grows:

  • along creek banks
  • in rainforests
  • on damp south-facing hillsides
  • in gullies
  • in other moist, sheltered areas.

How does it spread?

By seed

A single plant can produce 10,000 to 100,000 seeds each year. Seeds germinate from late spring to summer. Most of the seeds are dispersed by wind and water. Seeds can also be spread in agricultural produce, sand and gravel and in mud stuck to vehicles, machinery, shoes and clothing.

Existing infestations increase in size and density by forming a mat of layered and interwoven stems.

References

Harvey, K.J., McConnachie, A.J. Sullivan, P. Holtkamp, R. and Officer, D. (2021). Biological control of weeds: a practitioner's guide for south east Australia. New South Wales Department of Primary Industries, Orange.

Hosking J.R., Sainty G.R., Jacobs S.W.L. & Dellow J.J. (in prep) The Australian WeedBOOK.

Identic Pty Ltd. and Lucid central (2016). Environmental Weeds of Australia Fact sheet: Ageratina riparia. Retrieved 18 October 2021 from: https://keyserver.lucidcentral.org/weeds/data/media/Html/ageratina_riparia.htm

McKenzie, R. (2012). Australia's poisonous plants, fungi and cyanobacteria: a guide to species of medical and veterinary importance. CSIRO.

Parsons, W.T., & Cuthbertson, E. G. (2001). Noxious weeds of Australia. CSIRO publishing.

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 30 June 2020 from: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Ageratina~riparia

More information

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Control

Successful weed control relies on follow up after the initial efforts. This means looking for and killing regrowth or new seedlings. Using a combination of control methods is usually more successful.

To manage mistflower:

  • control the weed when plants are young and before flowering to prevent seed set
  • check for flushes of seedlings after rain
  • control infestations when infestations are small when possible.

Pasture management

When: Year round.

Follow up: Spot spray regrowth or new seedlings with herbicides.

Dense pastures help prevent mistflower from establishing and assist in preventing re-establishment following control. Follow good pasture management practices and in particular avoid overgrazing. Avoid overgrazing pastures and manage pastures to maintain 100% ground cover.

Physical removal

By hand

When: Before flowering in August.

Follow up: Within 6 months to keep infestations under control.

Hand pull or dig out plants before they flower. In pastures sow pasture seed in the space where the mistflower was removed to provide competition for mistflower seedlings.

Cultivation

When: Before flowering in August.

Follow up: Plant competitive pasture species or native vegetation.

Larger or dense infestations can be slashed or cultivated where the terrain is suitable. This may not be possible in steep or rocky areas. 

Biological control

There are two biological control agents available for mistflower:

  • White-smut fungus (Entyloma ageratinae) is widespread from south-eastern QLD to the south coast of NSW. This fungus prefers wet, cool (10 - 20°C) areas. It affects the lower leaves of the plant first, eventually causing the leaves to die. If plants are severely affected they will not flower.
  • Mistflower gall fly (Procecidochares alani), feeds on the upper leaves. It limits growth but does not control the plants. The gall fly is more suited to warmer drier sites than the white smut fungus.

Both of these agents are widespread in NSW. Redistribution is usually not necessary but in some cases it can accelerate dispersal. Contact your local council weeds officer for advice on using biological control agents for mistflower.

Chemical control

Spot spraying

When: Any time before flowering.

Spray actively growing plants. Cover all of the foliage with herbicide.

Splatter guns

Splatter guns can be used for dense infestations of weeds that are difficult to reach. The specialised nozzle produces large droplets that allow plants up to 10 m away to be sprayed with limited chance of spray drift. Spray small amounts of concentrated herbicide onto the weeds. It is not necessary to cover all of the foliage.

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: 650 mL per 100 L of water
Comments: Actively growing bushes.
Withholding period: 1-8 weeks (see label).
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Fluroxypyr 140 g/L + Aminopyralid 10 g/L (Hot Shot™ )
Rate: 700mL per 100 L of water
Comments: Apply to actively growing plants from October to April.
Withholding period: Not required for pastures when used as directed. Do not graze or cut crops for stock food for 7 days after application. See label for export restrictions.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Fluroxypyr 200 g/L (Comet® 200 herbicide)
Rate: 500 mL per 100 L of water
Comments: Actively growing seedlings and young bushes before flowering.
Withholding period: Do not graze failed crops and treated pastures or cut for stock feed for 7 days after application. See label for further information.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Fluroxypyr 333 g/L (Starane™ Advanced)
Rate: 300 mL in 100 L of water
Comments: Apply to actively growing seedlings and young plants before flowering
Withholding period: Do not graze failed crops and treated pastures or cut for stock food for 7 days after application. See label for more information.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Glyphosate 360 g/L (Various products)
Rate: 5 mL per 1 L of water
Comments: Actively growing bushes with full foliage.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate


Glyphosate 360 g/L (Various products)
Rate: 1.0 L per 9 L water (3 mL per m2)
Comments: Low volume application.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate


Metsulfuron-methyl 300 g/kg + Aminopyralid 375 g/kg (Stinger™)
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 (Various products)
Rate: 5 g per 100 L of water
Comments: Apply when bush is actively growing and before flowering.
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


Picloram 100 g/L + Triclopyr 300 g/L + Aminopyralid 8 g/L (Grazon Extra®)
Rate: 350 mL in 100 L of water
Comments: Foliar application from spring to autumn on actively growing bushes
Withholding period: Where product is used to control woody weeds in pastures there is a restriction of 12 weeks for use of treated pastures for making hay and silage; using hay or other plant material for compost, mulch or mushroom substrate; or using animal waste from animals grazing on treated pastures for compost, mulching, or spreading on pasture/crops.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Triclopyr 300 g/L + Picloram 100 g/L (Various products)
Rate: 350 mL per 100 L of water
Comments: Spring to autumn on actively growing bushes.
Withholding period: Nil.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Triclopyr 300 g/L + Picloram 100 g/L (Various products)
Rate: 500 mL per 10 L of water
Comments: Gas gun / Splatter gun application. Apply to actively growing bushes.
Withholding period: Nil.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


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Biosecurity duty

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

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For technical advice and assistance with identification please contact your local council weeds officer.
For further information call the NSW DPI Biosecurity Helpline on 1800 680 244 or send an email to weeds@dpi.nsw.gov.au

Reviewed 2021