Groundsel bush (Baccharis halimifolia)

Groundsel bush is a densely branched, woody shrub with white to yellowish flowers. It invades pastures, plantations, wetlands and forests.

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How does this weed affect you?

Groundsel bush is an environmental and agricultural weed that can form dense thickets. It:

• outcompetes native plants
• reduces the amount of shelter and food for native animals
• reduces pasture productivity
• impedes stock movement
• is poisonous to animals
• causes allergies in people
• invades pine plantations, reducing productivity

Human health

The pollen from groundsel bush can cause allergies in some people.

Livestock poisoning

Groundsel bush is thought to be poisonous to cattle, though it seldom causes poisoning because animals rarely eat enough of the plant.

What does it look like?

Groundsel bush is a densely-branched perennial shrub usually 1.5–3 m tall, but can grow to up to 7 m. There are separate male and female plants. When in full flower, the female plants are easily identified by their fluffy white appearance.

Leaves are:

• dull or pale green
• up to 7 cm long and 4 cm wide (upper leaves smaller)
• diamond or oval shaped
• coarsely toothed on the upper half (leave higher up the stem are less toothed or have smooth edges)
• waxy and hairless
• alternate along the stem.

 Flowers are:

• abundant
• enclosed at the base by green bracts
• are in branched clusters at the end of the stems
• present from December–May
• male and female flowers are on different plants.

Male flowers are:

• cream or yellowish
• 3 mm wide
• in globular heads.

Female flowers are:

• white and fluffy
• 3-5 mm wide
• mature later than the male flowers.

Seeds are:

• straw-coloured or brown with 8-10 ribs
• light and easily blown by the wind
• topped with a tuft of white hairs up to 12 mm long (pappus)
• shed in April–May.

Stems are:

• multi-branched with lengthwise ribs
• green when young
• brown and woody when mature.

Roots:

It has a deep branching taproot and fibrous lateral roots.

Where is it found?

In NSW, groundsel bush grows in coastal areas from the Queensland border to the South East region. Plants have also been found in the Central West, North West and Northern Tablelands.

Groundsel bush is native to North America. It was first introduced as an ornamental plant. Plants on the Australian east coast are thought to derive from ornamental plantings in Brisbane in the mid1800s.

What type of environment does it grow in?

Groundsel bush mostly grows in humid warm-temperate to subtropical regions, though it can tolerate frost and snowfalls. It is most common in areas with at least 1000 mm of rain per year.

Plants grow in a wide range of soil types including acid and alkaline soils. They are very tolerant of waterlogged, and saline conditions including salt spray. Groundsel grows in full sun and shade and can still produce seed under heavy canopies.

Groundsel bush is particularly invasive in disturbed areas where the understorey has been removed or the canopy cover has been cleared or reduced. Common sites include:

• poorly-drained areas and coastal wetlands, especially where Melaleuca grow
• abandoned cane farms, banana and stone fruit plantations
• pastures, especially those that are overgrazed
• newly cleared land
• forestry plantations and open or poorly-managed forest areas after logging.

It can also grow in open woodlands, forests and along waterways in areas that have not had severe disturbance.

Maps and records

• Recorded presence of Groundsel bush during property inspections (Map: Biosecurity Information System - Weeds, 2017-2023)
  These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.
  
  

How does it spread?

By seed

Plants mature and produce seed in their second year of growth. Each female groundsel bush plant can produce more than 1.5 million seeds per year.  Most new seedlings appear between July and October. About half of the seeds usually fall within 100 m of the parent bush, which results in very dense, impenetrable stands of groundsel bush. Buried seeds can survive in the soil for two years.

Seeds are spread:

• by wind over long distances
• by water
• in contaminated agricultural produce
• in contaminated sand or gravel
• by sticking to machinery.

Plant parts

Groundsel bush can resprout from roots left in the ground.

References

Department of Agriculture, Water and the Environment. (2011). Weeds in Australia. Baccharis halimifolia. Australian Government. https://www.environment.gov.au/cgi-bin/biodiversity/invasive/weeds/weeddetails.pl?taxon_id=5654 Retrieved 10/3/2020.

Ensbey, R. (2009). PRIMEFACT 734: Groundsel bush. NSW Department of Industry and Investment 

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 16 May 2023 from: http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Baccharis~halimifolia  

Queensland, Department of Agriculture and Fisheries (2020). Restricted invasive plant:. Groundsel bush Baccharis halimifolia. Retrieved December 2020 from: https://www.daf.qld.gov.au/__data/assets/pdf_file/0009/75366/groundsel-bush.pdf

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

More information

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Control

Successful weed control requires 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.

Physical control

By hand

Young plants are easy to dig out as they have a shallow root system. Remove all the roots to prevent regrowth.

By machine

Bulldozing can be an effective first step for very large groundsel bushes.

Slashing and mulching

Slashing can suppress flowering which reduces seed production. Frequent, regular slashing will eventually kill groundsel bush. Groundsel bush sometimes grows in association with native blady grass and bracken fern. Regular slashing of the three species together encourages more vigorous pasture growth which can outcompete groundsel bush seedlings.  Slashing can form part of a long-term program of eradication that also includes spraying and pasture improvement.

Do not slash plants with seeds as this will spread the seeds.

Cultivation

Infestations of young plants can be controlled by cultivation. Sow competitive pastures or crops soon afterwards to suppress the growth of new groundsel bush seedlings.

Pasture management

Competitive pastures help reduce the establishment of groundsel bush seedlings. Pasture improvement methods such as managing stock numbers and fertilising pastures can help control groundsel bush. Your local agronomist for advice on the pasture plants and establishment techniques most suitable for your situation.

Reafforestation

Replanting areas with local native trees can help to control groundsel bush by restricting the amount of light available for groundsel bush to grow. Depending on the reafforestation location and species selected, physical removal of plants, slashing between planted rows or chemical control of groundsel bush may be required as part of an ongoing management program or until the trees become established and shade out the ground layer.

Biological control

Six insects and a rust fungus have established in Australia. However, the only two that help with control are the gallfly, (Rhopalomyia californica), which reduces growth and limits flowering and the stem boring beetle, (Megacylene mellyi), which has caused dieback on plants in coastal regions.

While biocontrol agents can be damaging to localised populations of groundsel bush in difficult to access areas, they should not be considered the solution to large infestations.

Chemical control

Herbicides can be effective in managing groundsel bush. Follow-up treatments may be needed.

Spraying

Spray actively growing plants. Ensure that all of the foliage is covered with the herbicide mix. The type of herbicide and rates vary depending on the size of the plants. See details below and labels.

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.

Basal barking

Use basal bark application for plants with stems up to 5 cm diameter at the base. Liberally spray the bark all the way around the stem from ground level to 30 cm high, wetting thoroughly to the point of runoff.

Cut stump method

Gel herbicide: Cut stems horizontally preferably no higher than 10 cm above the ground. Apply a 3–5 mm layer of gel for stems less than 20 mm and 5 mm layer on stems above 20 mm 

Herbicide options

See Using herbicides for more information.

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2,4-D 300 g/L (Affray 300®)
Rate: 100 mL in 10 L of water
Comments: Thorough even coverage of the plant is necessary
Withholding period: Do not 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

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2,4-D 300 g/L + Picloram 75 g/L (Tordon® 75-D)
Rate: 650 mL per 100 L of water
Comments: Thorough coverage required on active growth.
Withholding period: Do not graze or cut crops (except sugar cane 8 weeks) or pastures for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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2,4-D amine 625 g/L (Various products)
Rate: 320 mL per 100 L of water
Comments: Spray actively growing bushes. Thorough coverage.
Withholding period: 7 days withholding for grazing
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Clopyralid 600 g/L (Lontrel® Advanced )
Rate: 165 - 250 mL per 100 L of water
Comments: Handgun application for active growth, lower rate on seedlings, higher rate on bushes over 2 m high.
Withholding period: 7 days to 10 weeks see label for details.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Glyphosate 360 g/L (Various products)
Rate: 700 mL to 1.0 L per 100 L of water
Comments: Actively growing bushes. Do not apply during winter or summer drought stress.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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Glyphosate 360 g/L (Various products)
Rate: 1 part per 9 parts water
Comments: Gas gun / Splatter gun application. Apply 2 x 2 mL doses per 0.5 m of bush height
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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Picloram 100 g/L + Triclopyr 300 g/L + Aminopyralid 8 g/L (Grazon Extra®)
Rate: 250 or 350 mL in 100 L of water
Comments: Use lower rate on bushes 1–1.5 m high in spring and summer; use higher rate on bushes over 1.5 m high in the autumn.
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: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Picloram 44.7 g/L + Aminopyralid 4.47 g/L (Vigilant II ®)
Rate: Undiluted
Comments: Cut stump. Apply a 3–5 mm layer of gel for stems less than 20 mm. Apply 5 mm layer on stems above 20 mm .
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Triclopyr 240 g/L + Picloram 120 g/L (Access™ )
Rate: 1.0 L per 60 L of diesel (or biodiesel such as Biosafe).
Comments: Basal bark application for plants with stems up to 5 cm diameter at the base. Cut stump application for plants with stems up to and more than 5 cm diameter at the base. Apply herbicide immediately after the cut. See label for information about using biodiesel.
Withholding period: Nil
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Triclopyr 300 g/L + Picloram 100 g/L (Various products)
Rate: 250 or 350 mL per 100 L of water
Comments: Use lower rate on bushes 1–1.5 m high in spring and summer; use higher rate on bushes over 1.5 m high in the autumn.
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Triclopyr 600 g/L (Garlon® 600)
Rate: 160 mL per 100 L of water
Comments: Spray seedlings 1 to 2 m tall.
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Triclopyr 600 g/L (Garlon® 600)
Rate: 320 mL per 100 L of water
Comments: Spray plants 2 - 3 m tall.
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
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 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.
Greater Sydney	Regional Recommended Measure* (for Regional Priority - Eradication) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
Hunter	Regional Recommended Measure* (for Regional Priority - Eradication) Notify local control authority if found. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant.
North Coast Exclusion (eradication) zone: Clarence Valley LGA, Lord Howe Island, Port Macquarie-Hastings LGA. Core infestation (containment) zone: Ballina Shire LGA, Bellingen Shire LGA, Byron Shire LGA, Coffs Harbour City LGA, Kempsey Shire LGA, Kyogle Shire LGA, Lismore City LGA, Nambucca Valley LGA, Richmond Valley LGA, Tweed Shire LGA.	Regional Recommended Measure* (for Regional Priority - Containment) Whole of region: Land managers should mitigate the risk of the plant being introduced to their land. A person should not buy, sell, move, carry or release the plant into the environment. Exclusion zone: Notify local control authority if found. Land managers should eradicate the plant from the land and keep the land free of the plant. Core infestation: Land managers should mitigate spread of the plant from their land. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
South East	Regional Recommended Measure* (for Regional Priority - Eradication) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
	*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here

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Disclaimers

Pasture improvement may be associated with an increase in the incidence of certain livestock health disorders. Livestock and production losses from some disorders are possible. Management may need to be modified to minimise risk. Consult your veterinarian or adviser when planning pasture improvement. The Biodiversity Conservation Act 2016 and Local Land Services Amendment Act 2016 restrict some pasture improvement practices where existing pasture contains native species. Contact Local Land Services for further details.

Reviewed 2023