‘One of Australia’s worst weeds’: CSIRO unlocks key to eradicating bitou bush from WA

Scientists are on the verge of eradicating “one of Australia’s worst weeds” in WA after groundbreaking new research that could have wider applications in agricultural settings.

Bitou bush was first detected in WA at Kwinana Port in 2012, prompting an urgent response from authorities who managed to contain it in the immediate area.

But it’s a different story on the eastern seaboard, where the dreaded weed has infested a 1600km stretch of coastline, smothering dune vegetation from Queensland to Victoria.

Exactly how bitou bush got to WA remained a mystery until now, after a team led by CSIRO principal research scientist Bruce Webber tracked the invader’s unique arrival pathway.

Dr Webber told Countryman the findings provided greater clarity to support the eradication of bitou bush in WA “in the near future”.

“We are just a couple of years away, fingers crossed, from annihilating this weed completely in the State,” he said.

“It’s on Australia’s Weeds of National Significance list . . . and bitou bush deserves its place there.

“It totally takes over dune ecosystems, smothers native vegetation and pushes out a lot of the animals that require that native vegetation.”

Native to South Africa, bitou bush was introduced to Australia via NSW more than a century ago before being intentionally planted for dune stabilisation along the east coast in the 1950s.

By the time the mistake was understood it was too late, with dense thickets of the perennial shrub now infesting nearly half the NSW coastline.

Using new detailed genetic analyses of plants from Australia and South Africa, Dr Webber’s team were able to confirm the closest relatives to the Australian plants were in the South African port city of East London.

Archival research of shipping records all but confirmed the likely entry pathway — via dry ballast discharged from ships sailing from East London into the portside suburb of Stockton, near Newcastle.

Genetic data then enabled the team to establish that the bitou bush found in WA came from eastern Australia and was not a new introduction from Africa.

Dr Webber said this finding was crucial, because knowing where any weed originated from was fundamental to managing it with effective biosecurity measures.

“One of the really long term, highly efficient solutions for managing weeds is classical biological control, which is basically just going back to where the weed’s from and looking for insects or fungi, or other natural enemies of the weed,” he said.

“It’s then a matter of testing them really carefully before we bring them into Australia — to make sure they only affect that weed — and then releasing them here, which then becomes a self-sustaining control.

“We’ve got two of those agents already introduced on the east coast but they don’t work very well; they impact bitou bush a little bit, but they’re not really an effective control solution.

“And the interesting thing we found is when we went back to the records and looked at where people searched for those agents, it was in a totally different place in South Africa to where the Australian plants were from.

“Because biological control agents are really specific, if we were to go back to South Africa and look in the area around East London, we’d probably be far more likely to find a new agent that would be far more damaging to bitou bush here in Australia.”

Dr Webber said new control options were not necessary in WA at this late stage of the eradication process.

Using aerial mapping, biosecurity officers have removed about 2000 plants over the past 11 years, with efforts now focused on removing seeds lying dormant in the ground, which can live for years.

And though bitou bush has never posed a major threat to agriculture, Dr Webber said the innovative research had important implications for tackling other weeds, including those that attack farms.

“If we look beyond bitou bush, that’s where there’s relevance to a whole range of industries, because weeds don’t discriminate — some impact on coastal ecosystems, others impact on agricultural ecosystems,” he said.

“So that was the other part of this research that was really useful to find out; how it got to WA was a really important question.”

Dr Webber said the research indicated it was “highly likely” mining company BHP’s activity at Kwinana Port introduced bitou bush to WA.

With BHP no longer operating in the area, the risk of reintroduction was greatly diminished.

All that remained now, Dr Webber said, was “a couple more years” of surveying and the continued removal of any newly established plants found.

When two years have passed without any detections, eradication will have been officially achieved.

Unfortunately, it remains a different story in the Eastern States.

“I think that it would be almost impossible to eradicate over east, just because it’s rampant over such a large area,” Dr Webber said.

“But the way we could transform control over east is through looking for that new biological control agent in the right spot back in South Africa.”