Rust Fungus a tool in the fight against African boxthorn, says CSIRO - trial sites needed

Rust Fungus is the latest tool in the fight against African Boxthorn. Image: CSIRO.

By Krista Schade

A tough, thorny weed called African boxthorn is causing major headaches for farmers and the environment across regional Australia, but a fungus is the latest tool being used in the fight.

Originally from South Africa, the boxthorn grows into dense, tangled thickets that are nearly impossible to get through.

Spread by birds and foxes, it pops up everywhere, making it a real threat to the environment and to primary production.

Right now, the ways we try to eradicate the weed – like digging it up or spraying chemicals – can be pretty damaging to the land, especially in delicate natural areas, such as along waterways or among established native trees and plants.

These methods are also costly, take a lot of effort and aren't a long-term fix for such a widespread problem.

Enter the CSIRO’s Weed Management Systems Team.

Dr Ben Gooden is a plant scientist and team leader, and he recently visited Hay to address the Riverina Local Land Services Rangeland Production Forum.

Dr Gooden spoke about the success of the release of the rust fungus in the Hay, Booroorban and Deniliquin regions last year, including one site north of Carrathool, where the weed population has significantly declined.

“In the long term, we predict this rust fungus will reduce the reproductive output and growth of African boxthorn under conditions supporting fungal growth,” Dr Gooden said.

“This can help reduce further spread of the weed.”

Dr Gooden explained that biocontrol agent release sites are still being sought.

He invited interested stakeholders to submit expressions of interest to participate in the biocontrol release program by emailing boxthornbiocontrol@csiro.au.

Right: Dr Ben Gooden and Caroline Delaisse visited Hay recently, to present the rust fungus success story at the Riverina Local Land Services forum.

Image: The Riverine Grazier / Krista Schade.

The fungus was rigorously tested and is not able to reproduce on native plant species.

It was deemed by regulators to be safe for release into the Australian environment in 2024.

Once released, rust fungus causes yellowing of the leaves of the boxthorn, followed by the development of dark brown pustules that swell up and release fungal spores.

These fungal spores then go on to infect nearby boxthorn plants.

CSIRO says the fungus will take several years to establish.

CSIRO highlights that the fungus will complement but not replace the need for traditional control tools, like herbicides.

Dr Gooden explained that biocontrol is not a “silver bullet” and is another “tool in the toolbox”.

Broader biocontrol benefits may only be apparent over years or even decades once the fungus is found far and wide across Australia.