How do you kill this native pest? By importing its natural enemy

In short: 

Until recently, the African boxthorn weed flourished in Australia without natural predators. 

The CSIRO has introduced a fungus in the hope it will effectively reduce the weed’s growth and reproduction. 

What’s next:

The weed is regulated across Australia except in Western Australia, so regions like the City of Greater Geraldton will have to wait to access the biocontrol agent. 

Researchers are pinning their hopes on a new fungus to control an invasive pest blighting the Australian landscape.

The fast-growing African boxthorn was introduced to Australia more than a century ago. 

It was used by early settlers to create hedges as cheaper alternatives to fences. 

The dense and thorny bush is difficult to destroy and has become a major weed regulated nationwide, except in Western Australia.

The definition of an invasive species can be complex and the African boxthorn is declared as one of 32 Weeds of National Significance everywhere in Australia except Western Australia.

Despite its prevalence in some areas, African boxthorn does not appear on WA’s list of declared weeds. 

Reuniting with its natural enemy

The CSIRO has introduced the fungus Puccinia rapipes from Africa to Australia to help control the weed.

However, it is only being trialled in NSW, with a hope it will reach WA one day.

Ben Gooden, a vegetation ecologist with the CSIRO, has been researching Puccinia rapipes to reduce boxthorn numbers without harming native Australian vegetation.

“The fungus doesn’t kill the plant but provides a complementary tool alongside herbicide control and mechanical removal,” Dr Gooden said.

“By reuniting the weed with its natural enemy, we aim to control its population in Australia.”

The weed stays dormant during summer. When winter rains come, it grows lush green leaves and produces fruit that contain seeds.

Dr Gooden said infection by the rust fungus could disrupt the photosynthetic capacity of the plant, reducing overall plant growth and reproductive output.

Plant knows no boundaries

Meagan Thompson, coordinator of environment and sustainability with the City of Greater Geraldton, highlighted the weed’s resilience and the need for community involvement.

The city has run workshops to recruit volunteers and is handing out kit bags to help manage new boxthorn growth.

“The boxthorn knows no boundaries, so community involvement is crucial,” Ms Thompson said.

Mic Payne, from the Northern Agricultural Catchments Council, has been working with the City of Greater Geraldton to demonstrate how to use the kit bags and gave tips on how to safely remove smaller plants in the community.

“You snip the base, apply the herbicide, and it rarely returns,” Dr Payne said.

He said many hands would make the work easier in helping to tackle the fast-spreading pest.

“They have this propensity to spread and take over and that’s really what they’ve been doing for the past 150 years,” he said.

“Particularly with this current wet winter we’re having, they are springing up everywhere,” he said.

Dr Payne said having access to CSIRO’s biocontrol rust spray would greatly assist in keeping the weed under control, but for now there was not enough funding for the spray to expand beyond NSW.

“I think the prospect of controlling this weed is really reliant on that biocontrol,” Dr Payne said.

Boxthorn seeds sold in 1895

Local amateur historians John and Lyn Sewell are long-time multigenerational farmers in the Midwest.

They have sourced a historic receipt addressed to Henry Sewell, not related to them, who sold the first seeds.

Henry Sewell operated a nursery in South Australia, selling various seeds to landowners.

This particular receipt, dated May 19, 1895, lists apricots, peaches, apples, guavas, and African boxthorn seed brought to the Midwest region by a local farmer.

“It’s the most horrendous looking thing ever and I don’t know why they imported it,” John Sewell said.

“If you look around Geraldton at the moment, it’s just flourishing everywhere.”

Mr Sewell said lots of introduced species were imported from South Africa that naturally came across with the ships as they came around the Cape of Good Hope.