Agricultural
17 February, 2026
Act now to manage Harrisia cactus
If you’re on the hunt to deal with the invasive pest Harrisia cactus, now is your best chance. The plant is currently in bloom, making it easy for landholders to identify as it is usually difficult to spot amongst tall grass and other vegetation.
Harrisia cactus (Harrisia martinii, Harrisia tortuosa and Harrisia pomanensis) are category 3 restricted invasive plants under the Biosecurity Act 2014.
They can form dense infestations that will reduce pastures to a level unsuitable for stock, and choke out other pasture species when left unchecked.
The plant produces large quantities of seed that is highly viable and easily spread by birds and other animals.
Seedlings quickly produce swollen tuberous food storage roots that develop as the plant grows, and bears bright red fruit with scattered bumps, hairs and spines, containing 400-1000 small black seeds.
The pest is native to South America and was introduced to Queensland as a pot plant in the 1890s.
MANAGEMENT
The general biosecurity obligation (GBO) requires a person to take reasonable practical measures to minimise the biosecurity risks posed by harrisia cactus.
Control of this plant is difficult as it has a deep underground root system and use of a combination of physical, biologic and herbicide controls is recommended.
Physical control:
Dig out plants and completely burn, ensuring all tubers that can grow are removed and destroyed.
Ploughing is not considered an effective means of control unless followed by annual cropping.
Herbicide control:
Foliar application of registered herbicides provides effective control but can be costly over large areas.
Biological control:
Two introduced insects have become established in the field - a stem-boring longicorn beetle (Alcidion cereicola) and a mealy bug (Hypogeococcus festerianus).
The stem-boring beetle only attacks older woody stems.
The most successful biological control agent is the mealy bug which is present in harrisia cactus in the Goondiwindi district with smaller colonies established at Millmerran and Greenmount.
The mealy bug aggregates and feeds in the tips of stems and buds, where it limits growth and causes distortion.
This results in the knotting of the stem.
While mealy bug disperses naturally via wind, landholder assistance is necessary for its continuous spread, particularly between patches.
The bug is manually spread by cutting infected stems and placing them into healthy plants.
The best pieces for starting new colonies are large knobs of twisted and distorted cactus that contain many mealy bugs well protected inside knots.
Stem tips covered by white, woolly masses of bug are also good.
To collect the bug, cut infected stems approximately 15cm from the distorted knot and place segments in green, plump sections of the health plant.
Don’t forget to use tongs!
Cut pieces can be transported in boxes or open vehicles, and should be put out within three days.
Mealy bugs are generally more active and effective on harrisia cactus growing underneath shrubs and trees, so results will be seen more quickly in these areas than in cactus growing in the open.
Best results are obtained when infesting plants that have actively growing new shoots.
Dry weather does reduce the effectiveness of the mealy bug.
The maximum growth and spreading of mealy bug infestations occurs in the summer months of December to February.
During the drier and colder months of April to August, the mealy bug does not die but little growth and multiplication occurs.
If your introduction of mealy bug occurs during that time, little effect will be seen until the following summer.
For more information on managing Harrisia cactus contact Toowoomba Regional Council or visit biosecurity.qld.gov.au
Alternatively, touch base with Millmerran Landcare by emailing millmerranlandcare@bigpond.com
