Background
What is the weed problem?
Wandering trad (Tradescantia fluminensis) is an herbaceous groundcover plant native to South America that has become a significant environmental weed of temperate Australia, with hotspots in moist forests of eastern NSW, south-east Queensland and Dandenong Ranges region of Victoria. It forms dense swathes along the forest floor, particularly in moist riparian zones, where it reduces the diversity of native vegetation and alters the movement and behaviour of native animals. Wandering trad can also cause skin irritations to domestic pets, thereby reducing the recreational amenity of hikers and dog walkers using public pathways through infested forests.
Wandering trad primarily spreads via stem sections by water movement along creeks, soil disturbance and in dumped garden waste, meaning that it does not rely upon pollination and seed production for spread.
Close-up of wandering trad flowers.
How is the weed currently managed?
For small infestations, manual removal of wandering trad is the most suitable option for control, but it may cause disturbance to the soil profile and stimulate germination of other weed species. Wandering trad can regenerate rapidly from broken stem and root fragments, meaning that hand-pulling is ineffective in the long term unless all material is removed from a site. For large infestations, chemical control is considered more practical, although there is potential for non-target damage to native plants growing alongside wandering trad. Herbicide application is particularly problematic along creek lines in the presence of threatened native vegetation. There is increasing evidence that wandering trad can regenerate after primary chemical control, leading to the need for multiple follow-up herbicide treatments, which is considerably costly.
Dense infestation of wandering trad in Kangaroo Valley, NSW.
For more information see:
http://weeds.dpi.nsw.gov.au/Weeds/Details/141
What can biocontrol offer to the weed’s management?
Classical biological control is the only recognised sustainable solution to the suppression (but not eradication) of environmental weeds to reduce their impacts at a landscape scale in Australia. Use of mechanical or chemical control for wandering trad in sensitive rainforest settings, especially along creek lines comprising endangered plant species, is unviable over large spatial scales, because wandering trad can routinely regenerate unless long term intervention is undertaken. A biocontrol approach may offer a longer term, sustainable solution to controlling wandering trad in sensitive ecological communities with lower risks to native vegetation.
Historical context – the New Zealand biocontrol program for wandering trad
The fungus Kordyana brasiliensis was discovered on wandering trad during surveys in Brazil, as part of exploratory research that underpinned the biocontrol program for this weed in New Zealand. The fungus causes extensive necrosis on leaves, which progressively leads to leaf senescence and an overall reduction in the foliage of wandering trad. Under optimal conditions the fungus can complete its life cycle within 2-3 weeks.
Testing of the fungus performed in Brazil demonstrated it would not pose a risk to non-target plant species present in New Zealand. Based on these results, K. brasiliensis was approved for release in New Zealand. It was first released in early 2018 and successfully established. The dew that develops on the leaf surface within shady, moist situations where wandering trad is most invasive has likely facilitated its establishment. It is predicted that native vegetation will positively respond to a reduction in the competitiveness of wandering trad as a result of fungal infection. Monitoring of the fungus impacts is on-going.
The fungus complements the three insect biocontrol agents that have also been released in New Zealand: the tradescantia leaf beetle (Neolema ogloblini), tradescantia tip beetle (Neolema abbreviata) and the tradescantia stem beetle (Lema basicostata).
Details about the New Zealand biocontrol program can be found here:
Frequently asked questions
What support is provided to participants in the wandering trad biocontrol program?
CSIRO is Australia’s national science agency and leads the national weed biocontrol pipeline program. While CSIRO does not provide on-ground weed control services, it undertakes strategic research to develop and implement biocontrol programs that move approved agents from the laboratory into the Australian environment to reduce weed threats over time.
All CSIRO biocontrol programs are collaborative. CSIRO does not fund weed control directly. Instead, mass-release programs are delivered in partnership with stakeholders who contribute their own resources. This may include landholders releasing biocontrol agents on their properties or community groups undertaking releases as part of their volunteer activities.
To support these efforts, CSIRO provides:
- Biocontrol agent release kits free of charge,
- Training materials and online resources,
- Access to dedicated staff who can help design release programs tailored to local needs,
- Workshops and field demonstrations,
- Presentations of results at conferences and community forums.
We welcome expressions of interest and are happy to discuss how we can partner with you to deliver the project in your region.
How is the biocontrol fungus provided to participants, and are there limits on availability?
For the wandering trad biocontrol project, CSIRO provides participants with live stems of wandering trad (Tradescantia fluminensis) that are infected with the leaf-smut fungus Kordyana brasiliensis. These stems are carefully packaged and sent live in the post at a time when the fungal spores are viable and ready for release. Upon receipt, participants should either plant the stems at their intended release site as soon as possible, or, if not immediately ready, stand them in a bucket of water in a shaded area for up to two weeks until planting. Full instructions are included in every package.
Before sending any material, CSIRO will work directly with each participant to confirm that their site is eligible for release. This includes checking whether the fungus is already present at the site. If so, additional releases may not be necessary. We also collaborate with each participant to determine the appropriate quantity of infected stems and the best timing for release, considering local site conditions and climate.
All stakeholders are welcome to express interest in participating, and there is no set limit on the number of releases that can be requested. However, as with previous projects, distribution is managed to ensure equitable access and to maximise the impact of the program across NSW. The project is funded to run at least until June 2026, and we will work with participants throughout this period to support successful releases and ongoing engagement.
Is it safe to release the biocontrol agent into the Australian environment?
Yes, it is safe to release the leaf-smut fungus Kordyana brasiliensis for the biocontrol of wandering trad in Australia. The safety of this biocontrol agent has been rigorously assessed through extensive research and regulatory review.
CSIRO and its collaborators conducted comprehensive host-specificity testing in Australian quarantine facilities to determine whether Kordyana brasiliensis could infect native or ornamental plants closely related to wandering trad. These tests included a wide range of Australian species from the Commelinaceae family. The results showed that the fungus is highly host-specific: it attacks all tested populations of wandering trad, but non-target plants either showed no symptoms or only minor, transient flecks on leaves, indicating strong resistance to infection.
Following these scientific studies, an application to release Kordyana brasiliensis was submitted to the Department of Agriculture and Water Resources. The Department undertook a comprehensive risk assessment, including consultation with state and territory governments and the general public. The fungus was deemed to pose negligible risk to non-target plants and was officially approved for release from quarantine in December 2018.
What effect will the biocontrol agent have on wandering trad populations? How quickly does the fungus kill the weed?
The fungus has a significant impact on wandering trad populations, but it does not kill the weed instantly or eradicate it from a site. After the fungus is released, it infects wandering trad leaves, causing disease symptoms that progress from small chlorotic flecks to necrotic lesions and eventually leaf death. The reduction in wandering trad abundance is closely linked to the severity of fungal infection, with greater disease severity leading to a more pronounced decline in weed cover and volume. In favourable conditions (typically moist, shaded environments) the fungus can cause dramatic reductions in wandering trad within 18 months, especially in northern regions of New South Wales. However, the process is gradual, and it can take up to two years or more for the fungus to build up to high densities and have a noticeable impact on the weed population.
It is important to note that the fungus does not kill wandering trad outright. Instead, it suppresses the weed, allowing native vegetation to recover and thrive. Wandering trad can sometimes rebound after periods of favourable growth, requiring the fungus to “catch up” and suppress the weed again. The effectiveness of the biocontrol agent also varies by region and local climate, with slower or less pronounced impacts in cooler or drier areas. Overall, the fungus provides a sustainable and environmentally friendly tool for long-term management of wandering trad, but its effects are gradual and ongoing rather than immediate or absolute.
What are the impacts and benefits of releasing the biocontrol agent for wandering trad on the environment?
The release of the leaf-smut fungus Kordyana brasiliensis as a biocontrol agent for wandering trad has had a measurable and positive impact on the environment in New South Wales. Over the course of the previous 2020-2023 project, infected stems were distributed to hundreds of sites and monitored for changes in weed abundance and native vegetation recovery. In regions where the fungus established successfully, particularly in the warmer and more humid northern parts of the state, there was a dramatic decline in wandering trad cover and volume within 18 months of release. This reduction in weed abundance was closely linked to an increase in native plant species richness and abundance, especially in areas where wandering trad cover dropped below a critical threshold.
Prior to the release of the biocontrol agent, high levels of wandering trad cover were associated with a sharp decline in native species diversity. After the fungus became established, native vegetation began to recover, demonstrating the agent’s effectiveness in restoring ecosystem health. The project also showed that the impact of the biocontrol agent can vary depending on local climate, with the greatest benefits observed in regions with favourable conditions for fungal growth. In cooler or drier areas, reductions in wandering trad were slower or less pronounced, but the fungus was still able to become established in those areas.
Importantly, the fungus is highly host-specific and does not harm native or ornamental plants, making it a safe and sustainable alternative to chemical control methods. By enabling community groups and landholders to participate in the release and monitoring of the biocontrol agent, the project has fostered local stewardship and built capacity for ongoing weed management. Overall, the use of Kordyana brasiliensis has helped restore native plant communities, improve biodiversity, and support the recovery of valuable ecosystems affected by wandering trad.
Why is there an extension to the wandering trad biocontrol project if the fungus is already widely established in NSW?
Although the leaf-smut fungus is now established at many sites in New South Wales and has proven highly effective at suppressing wandering trad, there are several important reasons for extending the project. Firstly, the scale of the wandering trad problem is vast, and there is clear merit in expanding the biocontrol effort to cover the entire range of the weed across NSW. The previous phase of the project was delivered during the COVID-19 pandemic, which meant that many prospective stakeholders were unable to participate or receive the fungus for release at their sites. As a result, there are still many areas where the fungus has not yet been introduced.
Another key consideration is the biology of the fungus itself. While it can establish effectively at a site, it often takes up to two years to build up to high densities and have a noticeable impact on wandering trad populations. The fungus also has very limited capacity for long-distance spread without human assistance, so it can take years for it to reach new locations on its own. For example, after the fungus was released on the Kangaroo Valley River in March 2019, an extreme heatwave and drought caused it to die out, and it had to be reintroduced in late 2020 before it successfully established. In another case, the fungus was released on the southern side of the Illawarra Highway on the banks of the Macquarie Rivulet in late 2020, but it was not detected on the adjacent tributary (just 200 metres away) until June 2022. It then took a further year to extend through the upper reaches of the Macquarie Rivulet, a distance of about five kilometres.
The fungus is also sensitive to severe drought, which can cause local populations to die out and require reintroduction. Given these challenges, and the fact that the fungus can be easily and safely spread by people, there is a strong case for continuing the project. With funding secured for the next year, we encourage further participation from stakeholders to help identify new sites for release and to actively assist with spreading the fungus, rather than waiting for it to arrive naturally. This approach will help ensure that the benefits of biocontrol are realised more quickly and across a much broader area.
Can use of the biocontrol agent replace herbicide application or other control methods?
While the fungus has led to substantial reductions in wandering trad at many sites and enabled native vegetation to regenerate without the use of chemical herbicides, it cannot fully replace other control methods. The fungus is highly effective in moist, shaded environments, but there are many sites (particularly those that are very sunny or dry) where it does not establish well. In these areas, manual or chemical control remains necessary to manage wandering trad.
Even in favourable sites, the fungus does not eliminate wandering trad altogether. Wandering trad can rebound during periods of favourable growth, and the fungus must “catch up” to suppress the weed again, making the process dynamic and ongoing. This means that if complete removal of wandering trad is required, the fungus alone will not be sufficient.
The best way to integrate the fungus with other control methods is not fully understood. For this reason, the new project will focus on developing integrated management plans for wandering trad, aiming to provide guidance on how to combine biocontrol with manual or chemical approaches for more effective and sustainable weed management.
What happens if I cannot detect the fungus after release? Has it failed?
The fungus will only establish and spread effectively under optimal conditions; typically when the environment is warm and moist and the wandering trad plants are healthy and vigorous. As such, it is expected that the fungus may not establish in all instances, especially if the microclimate requirements for infection are not met. The fungal spores are delicate and need specific conditions to successfully infect wandering trad, and it can take many years of sustained releases by various participants for the fungus to become widely established in the Australian environment.
If you cannot detect the fungus within 6-12 months after release, it does not necessarily mean that the biocontrol agent has failed. It may simply be that the conditions were not suitable at the time of release, or that the fungus needs more time or additional releases to establish. Participants are encouraged to release the fungus on multiple occasions if initial releases do not appear to be successful. Over time, with repeated efforts and favourable conditions, the chances of successful establishment and impact will increase.
Can I collect and redistribute the fungus myself, or do I need to get it from CSIRO?
Yes, it is possible for people to collect and redistribute the fungus themselves, but there are important challenges to consider. The key to successful redistribution is collecting the fungus at exactly the right time, when the spores are viable and ready to infect new wandering trad plants. If the fungus is collected too early, the stems may die off before the fungus has a chance to establish at the new site. If it is collected too late, the spores may have already been released, meaning that infection transfer will not occur and the biocontrol will not be effective.
For this reason, we encourage anyone interested in redistributing the fungus to get in touch with us first. We can provide the fungus at the optimal time for release, maximising the chances of successful establishment. However, we recognise the need for ongoing redistribution when the project finished in June 2026. To support this, we will develop guidelines to help people identify the right time to collect and release the fungus, and to ensure best practice in redistribution.
If you wish to collect the fungus yourself, we recommend reaching out to us for advice on how to identify the fungus and determine when it is ready for collection. There are also useful resources available, such as records and photographs on iNaturalist, which can help with identification. Please remember that stakeholders are responsible for their own collection activities, including obtaining permission to access sites for both collecting and releasing the fungus.