Groundsel bush (Baccharis halimifolia) - a prolific menace
With its fluffy white flowers swaying in the breeze, this shrub appearing in coastal pastures and riverbanks may look like part of an idyllic country setting. However, it bears the hallmarks of a silent invader capable of smothering open land before you know it.
Groundsel bush is a menace of coastal floodplains, wetlands, forests and agricultural land. Its growing abundance means it may become so widespread that containment becomes increasingly difficult, allowing it to continue spreading throughout the region. Native to the southern United States, Groundsel bush is thought to have been introduced to Brisbane as an ornamental shrub in the 1800s. While it is no longer considered desirable, this hardy species has become invasive across northern NSW and southern Queensland.
Click play on the video to join our Biosecurity Officer, Matt Bell, in the field and learn more about this containment priority weed.
Where does it grow?
Groundsel bush thrives in high rainfall areas and tolerates a wide range of conditions, including acid and alkaline soils, salinity and waterlogging. It grows best in full sun but can also tolerate shade. It is commonly found along the edges of swamps, wetlands, estuaries and canals, as well as in coastal tea-tree wetlands, boggy or overgrazed pastures, roadsides, railway corridors and forest plantations. In urban areas it may establish in creek lines and coastal swamps, with wind-blown seeds spreading into nearby properties. Once a few plants are able to set seed, Groundsel bush spreads quickly through suitable habitat, taking over productive and marginal land and threatening sensitive environments.
Why is Groundsel bush a problem?
Why is Groundsel bush difficult to manage?
Groundsel bush has separate male and female plants, which look identical apart from their flowers. Male plants produce clusters of pale yellow flower heads, while female plants produce the familiar white, fluffy seed heads.
Their pollen and seeds are wind dispersed, allowing the plant to spread rapidly across the landscape.
A mature female plant can produce up to 1.5 million seeds each season. The seeds are attached to tufts of white hairs that act like tiny parachutes, allowing them to travel long distances in the wind. Seeds may be dispersed more than a kilometre from the parent plant in strong winds and can also spread during floods.
The light, fluffy seeds are notorious for sticking to machinery and can be transported long distances on farm or construction equipment, quickly establishing in new areas of disturbed ground.
How to indentify Groundsel bush
A multi-stemmed woody shrub that typically grows between 1.5 and 3 metres tall but can reach up to 6 metres under favourable conditions.
Leaves are waxy, around 5cm long by 3cm wide, and roughly diamond or oval-shaped with distinct blunt “teeth” around the tip.
Male flowers are 3mm wide and clustered at the ends of stems in creamy yellow heads, while female flowers are white and fluffy.
Young stems are glossy green, becoming darker and rougher with age as brown bark develops.
When are you likely to spot Groundsel bush?
Groundsel bush is flowering throughout April and May, making this one of the easiest times of year to identify infestations. Controlling plants in the early stages can prevent the development of large infestations and significant management costs in the future.
Groundsel bush is a containment priority weed that must be managed. If you think you have Groundsel bush on your property, contact Council’s Biosecurity Officer for advice on identification and control, and refer to NSW WeedWise for further information.
Image credits: Port Macquarie-Hastings Council & NSW WeedWise.
