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 both an environmental and a forestry weed because it readily invades open to densely vegetated forests and bushland. Thousands of hectares of pine plantations in New South Wales (NSW) and Queensland are heavily infested.

Thick stands of groundsel bush can inhibit the movement of stock and reduce the productivity and carrying capacity of agricultural land. Therefore, the spread of the weed is of great concern to rural communities, especially where annual rainfall exceeds 1000 mm per year.

At the moment, it has not spread to its potential range, but threatens to do so. If coordinated control programs are not maintained it may rapidly fulfil this potential.

Groundsel bush is reputed to be poisonous to livestock although it seldom causes a problem because they rarely eat enough. However, livestock will lose condition rapidly if forced to graze it.

Groundsel bush is a serious weed of horticulture, cropping and grazing agricultural industries as well as forestry. It is also an environmental weed.

Groundsel bush is particularly invasive in some specific situations. These situations include:

• badly-drained, poor, coastal wetlands;
• abandoned cane farms;
• undeveloped land subdivisions which have been bulldozed;
• areas where groundcover has been disturbed;
• all grazing land that is overgrazed or undervegetated – newly-cleared land is prone to invasion by groundsel bush, as is land which has suffered from fertility rundown and neglect;
• abandoned banana and stone fruit plantations, because of the effects of consistent, bare-ground management during the life of the plantation;
• open or poorly-developed forest areas after logging when canopy cover is reduced and soil disturbance is at a maximum; groundsel bush can grow and form a canopy faster than the forest species regrowth;
• coastal pine forests where there is little groundcover to compete with seedlings;
• occasionally, even in dense pasture.

What does it look like?

Groundsel bush is a densely-branched shrub, usually 1.5–3 m high, although it sometimes grows into a small tree up to 7 m high.

Leaves are dull or pale green, waxy to touch, alternate, 2.5–5 cm long, 1–2.5 cm wide, wedge-shaped and prominently-toothed, particularly near the tip.

Stems are green at first but turn brown with age and have a characteristic striped bark.

Numerous male and female flowers grow on separate plants.

Male flowers are cream and occur in globular heads. Female flowers are white and grow in head clusters at the ends of branches.

Seeds are very small and light, about 3 mm long and weighing only about 0.1 mg. On the top of each seed grows tufts of white hairs (the pappus) which give the female plant its characteristic fluffy appearance when in full flower.

Mature groundsel bush have a deep branching taproot, with numerous fibrous lateral roots.

Where is it found?

Groundsel bush was first introduced into Australia as an ornamental plant and by 1900 had become naturalised in Queensland.

By 1930, it was a serious weed in south-eastern Queensland. By the mid-1960s, it was present in the Tweed, Richmond and Clarence catchments in northern NSW. Since then, it has gradually spread southwards along the coastal fringe to the Taree area. It is likely that groundsel bush will spread further in Australia.

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?

Each female plant can produce more than 1.5 million seeds annually. The seeds are adapted for dispersal by wind and water because of the pappus, which remains attached to the seed for several days after release from the head. Under windy conditions during flowering, groundsel bush seed can be transported over long distances.

Seeds can also be spread by:

• water
• contaminated agricultural produce
• contaminated sand or gravel
• machinery.

Half of the seed usually falls within 100 m of the parent bush, forming dense, impenetrable stands of the weed. 

What type of environment does it grow in?

Groundsel bush is found in humid warm-temperate to subtropical regions. It is mostly found in disturbed areas such as coastal swamps, degraded pastures and forests where the understorey has been removed.

Groundsel bush tolerates a wide range of soil types and pH levels from 3.8 to 8.2 and is very tolerant of waterlogged, acid and saline conditions. It is also resistant to damage from salt spray.

Groundsel bush is frost-tolerant and occurs naturally in North America where there are regular winter snowfalls. This means that in Australia it could spread inland to colder climates where the habitat is favourable.

Acknowledgements

Author: Rod Ensbey, Regional Weed Control Coordinator, Grafton

Editing and reviewing: Birgitte Verbeek, Annie Johnson, Annette McCaffery, Bill Smith.

References

• Parsons, W.T. and Cuthbertson, E.G. (1992) Noxious Weeds of Australia, 2nd ed. CSIRO publishing.

More information

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Control

A variety of measures are available for controlling groundsel bush effectively.

Mechanical control

Young plants are easy to pull out as they have a shallow root system. Care should be taken, however, to remove all the roots to prevent regrowth.

Widespread infestations of young plants can be controlled by cultivation, but seedling regrowth can occur if competitive pastures or crops are not sown soon afterwards.

In the case of very large bushes, bulldozing may be the most effective first step.

Slashing

Large infestations of young groundsel bush are slashed in some areas. Slashing suppresses flowering and reduces the spread of seed.

Frequent, regular slashing will eventually kill groundsel bush. in many large infestations, groundsel bush grows in association with blady grass and bracken fern and regular slashing of the three species together encourages a more vigorous growth of pasture. this in turn suppresses groundsel bush seedling regrowth. regular slashing of large groundsel bush infestations is often part of a long-term program of eradication involving spraying, slashing and pasture improvement.

Grazing with goats

Control of widespread infestations of groundsel bush by goats is also worth considering. However, investment in goats as a control measure will require goat-proof fencing and some knowledge of goat husbandry. Goats are only effective if the infested area is grazed intensively. They can also destroy other desirable vegetation unless precautions are taken to protect it with effective tree guards or other deterrents. Goats are not suitable where wild dogs are a problem. 

Pasture improvement

Pasture improvement is an important part of any program to control groundsel bush. Well-managed, competitive pastures help to reduce the establishment of groundsel bush seedlings. abandoned banana plantation areas, newly-cleared land and overgrazed infertile paddocks, especially in swampy areas, are all less susceptible to groundsel bush invasion after the establishment of a vigorous pasture.

Pasture improvement costs should be compared with the cost of future weed control costs. consult your local agronomist or your agronomic advisor for advice on the pasture plants and establishment techniques most suitable for your situation.

Reafforestation

Reafforestation to control groundsel bush has been tried in a number of situations. this is only successful when good forest management methods are adopted.

Chemical control of groundsel bush during the establishment of the plantation may be necessary. Groundsel bush is also shade-tolerant and can still grow and produce seed under heavy canopies. therefore, once the plantation is established it will be necessary to continue to undertake a chemical management program during this stage as well.

Biological control

In Australia, groundsel bush does not suffer from predation by the range of natural enemies which are found in its native habitat. Biological control of groundsel bush involves introducing these natural enemies to reduce its vigour and competitive ability. Six insects have established in Australia, three of which, a fly and two stem-boring agents, have had a minor impact on groundsel bush in NSW. a rust fungus has also been released in NSW.

Biological control of groundsel bush is only a management tool in core infestation areas. at this stage, biological control cannot be relied upon for short-term, comprehensive control; other techniques should be used, including mechanical and chemical means.

Gall-forming fly

The gall-forming fly (Rhopalomyia californica), lives for only 4–5 hours, in which time it emerges from its pupal stage, mates, finds another groundsel bush, lays eggs and dies. Eggs are laid on the shooting tips and stems and after hatching from the eggs the larvae burrow into the stems.

The plant then forms a gall of spongy tissue around the burrowing larvae, which grow and develop into pupae and eventually emerge as adults.

The effect of the galls is to reduce the growth and vigour of the plant and prevent flowering. Once flowering stops, the spread of seed is reduced, making it easier to eventually control the weed.

Stem borers

In the mid-1980s, two stem boring agents, a beetle (Megacyllene mellyi) and a moth (Oidaematophorus balanotes), were introduced into northern NSW. Larvae of both agents tunnel into the stems of groundsel bush, causing dieback and even death of the plants in some cases.

The stem borers, particularly O. balanotes, have successfully established and can be found over a wide area. However, their effect has been sporadic, mainly reducing the vigour of the plant or causing partial dieback.

Another stem borer (Hellinsia balanotes) is also widespread and established. It is very damaging to groundsel bush but unfortunately the plant rapidly recovers.

Rust

A rust fungus (Puccinia evadens), was first released into south-eastern Queensland in 1998. During the following years, numerous releases were undertaken, including a number of sites in northern NSW. Early indications showed promising results for the establishment of the rust. It is hoped this rust will be able to complement other biological control agents and assist with the longterm, integrated management of the weed.

Chemical control

Spraying

Spray actively growing plants. Type of herbicide and rates vary depending on the size of the plants. See details below and labels for details.

Basal bark application

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

Cut stump application

Liquid herbicide mix: Stems should be cut less than 15 cm above the ground. Apply herbicide mixture to the cut surface and the sides of the stem immediately.

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 or cut for stock food for 7 days after application.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
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: I, Disruptors of plant cell growth (synthetic auxins)
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: I, Disruptors of plant cell growth (synthetic auxins)
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: I, Disruptors of plant cell growth (synthetic auxins)
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: M, Inhibitors of EPSP synthase
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: M, Inhibitors of EPSP synthase
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: I, Disruptors of plant cell growth (synthetic auxins)
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: I, Disruptors of plant cell growth (synthetic auxins)
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: I, Disruptors of plant cell growth (synthetic auxins)
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: I, Disruptors of plant cell growth (synthetic auxins)
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: I, Disruptors of plant cell growth (synthetic auxins)
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: 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 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