2020-2023

This project was supported by the NSW Government’s Environmental Trust (Stage 3 Implementation Plan 2 – Biocontrol research for weed management, 1 July 2020 to 30 June 2023)

This project focused on the releases and evaluation of the approved biological control agent for wandering trad, the leaf-smut fungus Kordyana brasiliensis, in New South Wales (July 2020 to June 2023).

Key activities of the project were to:

  • Supply material of the agent for community releases in NSW via post or at workshops.
  • Establish monitoring plots throughout the range of the weed in NSW and gather baseline vegetation data.
  • Assess establishment, spread and impact of the agent at monitoring plots one, two and three years post-release.

Establishing monitoring plots and baseline vegetation surveys

Study sites

Between July and October 2020, we established a total of 97 monitoring plots (dimensions: 5 m x 2 m) across 14 sites along a ~750 km latitudinal gradient in NSW, located between the townships of Dorrigo in the north and Bega in the south. Plots were located in subtropical and warm temperate wet sclerophyll forest communities on the coastal plains, foothills, and escarpment of the Great Dividing Range.

Monitoring plots were assigned to one of three experimental treatments: (1) biocontrol release plots dominated by wandering trad (50 plots); (2) experimental control plots dominated by wandering trad where the biocontrol agent was not released (27 plots); (3) plots dominated by native vegetation with only minimal level of wandering trad invasion, acting as a benchmark against which the recovery of desirable native vegetation in the biocontrol release plots will be assessed (20 plots).

Vegetation surveys

The composition of resident vegetation with each 10 m2 plot was censused between July and October 2020, mostly when each plot was first established. Vegetation was identified to species level following the NSW Flora available through PlantNET. Abundance (% cover) for each species was estimated visually to the nearest 1 %. A total of 249 vascular plant species, consisting of 191 native and 58 alien species, were identified across the 97 monitoring plots prior to release of the biocontrol agent.

Native species richness was strongly negatively associated with wandering trad cover (see graphs below). However, there was an apparent negative threshold change in native species richness, such that richness values remained high as wandering trad cover increased to about 60 %, then decline dramatically when wandering trad cover exceeded 60 %. There was no significant difference in native species richness between low and medium wandering trad cover, yet richness declined significantly by 80 % on average where wandering trad cover exceed 60 %. There was also a significant decline in native species abundance with increasing wandering trad. However, the richness and abundance of other alien plant species were not associated with wandering trad cover.

Example of (a) plot arrangement at Kangaroo River, (b) plot configuration at Macquarie Pass and (c) a native reference plot at Yarranabee.

Effects of wandering trad cover on (a) native and alien species richness and (c) native and alien cover abundance (n = 93). Blue curves represent non-linear (i.e. negative quadrat function) lines-of-best fit for significant effects. The vertical black arrow denotes likely position of an invasion threshold (~ 60%) above which native species richness declines precipitously with increasing wandering trad cover. The histogram (plot b) represents mean (± SD) native species richness in three categories of wandering trad cover: low (< 20%, n = 16), medium (20 ≤ x < 60 %, n = 23), high (60 ≤ x ≤ 100 %, n = 54); letters above each bar denote significant differences amongst means based on Tukey’s Honestly Significant Difference test.

Biocontrol agent release

Releasing the biocontrol agent at monitoring plots

Between August and October 2020, wandering trad stems infected by the biocontrol agent were harvested from a nursery release site established in March 2019 at Brogers Creek, near the township of Berry on the South Coast of NSW. Each plot was divided into 10 contiguous 1 m2 subplots, in which we planted five infected wandering trad stems (one in the centre, and four in each corner) by inserting at least one basal stem node into a small hole in the soil. This resulted in a total of 50 infected stems planted per plot.

Monitoring the biocontrol agent

We quantified the incidence and severity of disease symptoms caused by the biocontrol agent at each release plot approximately six months after the infected stems were first. Symptoms initially appeared as small chlorotic flecks that enlarge with time, forming whitish lesions on the underside of leaves and yellowish areas on the upper surface of leaves. As the lesions aged, they became reddish-brown and coalesce, eventually resulting in leaf death.

Disease incidence was calculated in two ways: (1) as the percentage of 50 stems showing signs of infection; and (2) the percentage of infected leaves per stem, as an average of the 50 randomly selected stems per plot. Disease incidence and severity, wandering trad cover and volume, and associated vegetation richness and cover were assessed on several occasions up to 2. 5 years post-release of the fungus.

Variation in disease severity over time

Kordyana brasiliensis disease severity varied significantly across time and was dependent on region and treatment. Maximum levels of disease severity were observed across the three northern regions after 18 months (stabilising at 24 months). The rate of increase in disease severity was significantly higher at the three northern regions, with maximum severity at the southern sites only reached after 24 months. Disease severity was always significantly lower in the south coast region. By 30 months, disease severity began to decline to a lower level in all regions, commensurate to a decrease in the cover of wandering trad (see below).

Kordyana brasiliensis disease severity over 30-months across four different regions (north to south: Coffs Harbour, Port Macquarie, Illawarra, and the South Coast). Points represent mean values and error bars represent standard errors from the predictions from the generalised linear mixed model.

Infection of wandering trad by Kordyana brasiliensis across monitoring sites 18-months post release. (A) Infection of a single leaf, (B, C, D) different levels of infection of stems across sites, (E) significant leaf death on stems at Bega Anabranch, (F) examples of leaf death and missing leaves observed on stems across sites, predominantly at sites in Port Macquarie and Coffs Harbour where disease infection was greatest.

Variation in wandering trad abundance over time

The change in wandering trad abundance over time varied significantly amongst the four regions. In this analysis, abundance was represented by wandering trad volume. In the two northern regions, wandering trad volume declined dramatically (approaching zero) in the biocontrol-release plots between 0 – 18-months post release, before stabilising between 18- 30- months after release of the fungus. In the two southern regions (Illawarra, South Coast), wandering trad volume increased significantly in the biocontrol release plots between 0 and 6-months after release before declining significantly in the Illawarra region. In the south coast region of NSW, wandering trad volume never decreased below the pre-release level.

This result highlights that host plant responses to infection by a biocontrol agent are context specific and can vary spatially, likely as a result of broad regional climate context (warm, humid in northern NSW and relatively cool and dry in the southern region).


Variation in wandering trad volume over 30 months in each of four regions; Coffs Harbour (n = 102), Port Macquarie (n = 86), Shoalhaven/Illawarra (n = 140) and the South Coast (n = 87). Points represent mean values and error bars represent standard errors.

Photo point monitoring showing a reduction in wandering trad cover at three plots, approximately 18-months following release of K. brasiliensis. Values represent the percentage reduction in wandering trad cover over time.

Relationship between wandering trad volume and disease severity

The percentage change in wandering trad volume was calculated between each monitoring period and the baseline volume that was measured immediately prior to release of the fungus. The magnitude of decline in wandering trad volume increased with increasing disease severity – i.e., the higher the disease severity, the greater the reduction in wandering trad abundance.

The effects of disease severity varied regionally, with the greatest reduction in wandering trad volume observed in the northern regions of NSW and the lowest rate of decline in the south coast region. There were impact thresholds of infection on wandering trad volume in the Illawarra and south coast regions, where wandering trad volume only declined where disease severity exceeded approximately 20 % and 40 %, respectively.

Relationship between percentage change in wandering trad volume and Kordyana brasiliensis disease severity over 30 months in each of four regions, Coffs Harbour (n = 63), Port Macquarie (n = 51), Shoalhaven/Illawarra (n = 88) and South Coast (n = 69). Points represent raw data and lines represent the predictions from the linear mixed model bound by 95 % confidence intervals. Zero values along the y-axis represent no change, positive values represent an increase and negative values represent a decline in wandering trad volume between each time point.

Community engagement and large-scale release of the biocontrol agent

Biocontrol agent release methods

Between October 2020 and June 2021, wandering trad stems infected by the biocontrol agent were delivered to registered participants. Stems were stored in plastic bags and posted to registered participants along with a booklet containing information about the biocontrol program and instructions on how to release the agent in a wandering trad infestation (instructions published online here: https://research.csiro.au/wandering-trad/wp-content/uploads/sites/173/2020/09/Wandering-Trad-Biocontrol_Release-Information_NSW-Enviro-Trust_07.09.20.pdf).

Participants were instructed to make a small hole in the soil, insert a couple of inches of one of the infected wandering trad stems received and gently press the hole closed. We advised participants to plant at least five stems in a single patch of wandering trad about 1 m apart, in areas with dense cover of the weed, usually in deeply shaded, moist environments.

In exchange for the agent, we requested that participants return the following information to CSIRO researchers via email: name of participant and associated community group, release date, release location (in the form of a GPS coordinate), number of stems planted at each location, a general description of habitat and weather conditions during the week in which the stems were planted.

Results of biocontrol releases across NSW

Altogether, between October 2020 and June 2023, we distributed > 11,000 healthy, viable units of the biocontrol agent to a total of 248 participating entities for release at 425 unique sites. Releases were targeted to areas of highest frequency and abundance of wandering trad, especially in areas of high conservation value (e.g., national parks, reserves, remnant rainforests with high potential for natural recovery from the seed bank), ensuring that releases were made across the entire range of the weed in NSW.

Participants were drawn from 73 community groups, usually for release in reserves and national parks, and 175 private citizens for release on private properties. Participation in the biocontrol release program remained steady over the three years, with generally high demand for releases in the peak weeding seasons of spring and autumn. All levels of government and the volunteer sector were invited to participate in the program; predominantly Landcare and Bushcare groups, key local government partners and NPWS.

This represented one of the largest community-based mass-release, monitoring and evaluation programs for any biocontrol agent across Australia. The CSIRO is sincerely grateful to all participants for engaging with us on this high-impact project to help tackle this damaging weed. Results have contributed significantly to further optimising the release of the biocontrol agent in potential future projects.

Geographical distribution of 425 sites (blue dots) where the biocontrol agent Kordyana brasiliensis was released on infestations of wandering trad throughout NSW over three years, between October 2020 and June 2023. Orange dots represent major urban centres; large grey dots represent verified wandering trad occurrence records obtained from Atlas of Living Australia in July 2021.

Next steps

The CSIRO is sincerely grateful to all participants for engagement on this biocontrol agent release program.

The CSIRO acknowledges that it was not possible to meet face to face with most participants between2020-2022, during the establishment phase of this project, due to COVID-19 travel restrictions. The CSIRO also acknowledges that many participants who expressed interest in participating in the program could not be provided with fungal material, due to very high demand for participation. Managing very high demand for participation in the midst of ongoing lockdowns to our laboratories and inability to travel in the field also meant that some participants to whom we promised the fungus were not provided with a biocontrol agent release kit.

In terms of next steps, the CSIRO welcomes ongoing interactions with community members who retain interest in the wandering trad biocontrol program. Participants are invited to engage as follows:

  1. Participants who were promised to be sent a biocontrol agent release kit, but were missed during COVID-19, are very welcome to reach out to Dr Ben Gooden via email for assistance (Ben.Gooden@csiro). The CSIRO will consider sending such participants the fungus for release into the environment over spring and early summer 2023 and autumn 2024. As our stocks of the fungus are limited, we will only consider providing the fungus to participants who were missed during the main project.
  2. The biocontrol agent can be collected from the field and redistributed to new locations on the proviso that:
          1. Participants seek and are granted permission from site custodians to enter areas to collect the fungus for redistribution (note that the CSIRO does not provide advice or hold liability for on-ground activities pertaining to collection or redistribution of the fungus or any other on-ground activities related to this biocontrol program). The location of all known established populations of the fungus located on public land (private land excluded for privacy reasons) will be uploaded to the Atlas of Living Australia’s Biocontrol Hub in December 2023. https://biocollect.ala.org.au/biocontrolhub
          2. Participants are encouraged to record any new biocontrol agent release locations. This can be done via iNaturalist (preferred by most community members). The iNaturalist platform already has > 260 recorded populations of the fungus (search for Kordyana brasiliensis), along with photographs etc. Verified observations of the fungus uploaded to iNaturalist will eventually be uploaded to the Atlas of Living Australia Hub.
          3. The fungus can be released following the previous methods described here: Wandering Trad Biocontrol_Release Information_NSW Enviro Trust_07.09.20