‘It’s absolutely devastating’: Urgent biosecurity warning for Sydney’s street trees

Sydney’s majestic Moreton Bay and Port Jackson figs could be decimated, along with up to 4000 plane trees casting shade and greenery along the city’s streets, if an invasive tunnelling beetle hitches a ride across the Nullarbor from its stronghold in Perth.

Last month, the Western Australian government admitted it had lost a multimillion-dollar fight to eradicate the polyphagous shot-hole borer, a tiny beetle originally from South-East Asia that has devastated 4500 trees in Perth, including 20 towering much-loved figs that were chainsawed and mulched.

Now plant pathologist and chief scientist of Botanic Gardens of Sydney, Professor Brett Summerell, has sounded the alarm over the urgent biosecurity threat the beetle poses to Sydney.

“I was just starting to do the numbers, and thinking about how much impact this could have if it got here was just absolutely devastating,” he said.

“We have a lot of heritage figs in the botanic gardens, Centennial Park, Hyde Park, pretty much in every major park and garden within Sydney is heavily populated with fig trees, which seem to be extremely susceptible to the beetle.”

Summerell’s warning comes after senior botanist at Curtin University Professor Kingsley Dixon said no plant material from WA should be allowed into eastern Australia, fearing more trees would be “king-hit”.

Plant pathologist Professor Brett Summerell, chief scientist of Botanic Gardens of Sydney.Credit: Janie Barrett

Many of the CBD’s trees are plane trees, which are also at risk of attack. Losing the trees would cause a massive loss of amenity and turbocharge urban heating; street trees slash summer temperatures in cities by as much as 12 degrees.

Figs, plane trees and box elder maples are all known targets alongside crops such as mango, macadamia, avocado and apple trees. Trees grown for timber, including ash, elms and oak, are also vulnerable.

“The other big concern I have is that we have no idea at all what the susceptibility of our native species will be to this, particularly in the nice warm coastal forests up and down NSW,” Summerell said.

Control measures would be “impossible to administer” if the beetle takes hold in native forest, he said.

The beetle is the size of a sesame seed and isn’t a killer by itself, but it carries Fusarium ambrosium fungus for its larvae to feed on.

The shot-hole borer is an invasive beetle the size of a sesame seed.Credit: Wikimedia Commons

The fungus spreads into a tree’s vascular system, blocking the water-carrying xylem and the nutrient-transporting phloem, which starves the tree of hydration and energy.

There’s little choice but to cut down infected trees and kill the beetles in the remaining wood with fumigation or fire.

The beetle probably arrived in Perth as a stowaway in imported wood. Following its detection in 2021, it jumped to Rottnest Island, possibly via infected mulch.

Tiny holes in trees are a sign of infection.

Containment measures across Perth have seen 2.6 million trees inspected and swaths of greenery destroyed to rein in the beetle’s spread, leaving parks, Perth’s botanic garden and treasured leafy regions such as the Mount Eliza escarpment marred by brown scars where dozens of trees once grew.

The beetles can fly about 400 metres, but Summerell said they would probably spread to Sydney via transported wood.

“I could imagine that you have people camping near Perth and then coming across the Nullarbor, driving to eventually end up in Sydney with some infested firewood. That’s one potential way it could get here,” Summerell said.

“We’ve been assuming it’s going to be coming any day for a year or two now. We’re working on the assumption that it could be tomorrow.”

Shot holes in plane trees photographed by Summerell in South Africa, another country where the invasive beetle has taken hold.Credit: Professor Brett Summerell

Surveillance measures using traps that attract the beetles with pheromones have ramped up across the botanic gardens in collaboration with the Department of Primary Industries.

Summerell urged people to familiarise themselves with the symptoms of shot-hole borer infestation and report suspected sightings to the department’s biosecurity hotline.

Signs of infection include trunks riddled with tiny holes, as if the tree was stabbed with a pen. Sometimes, the beetles leave behind white powdery frass around the holes.

Other symptoms include lesions of discolouration caused by the fungus and the wilting and dieback of branches, starting with the upper canopy.

Signs of shot-hole borer infestation

• Tiny exit or entrance holes in bark.
• Holes are often surrounded by water-soaked lesions, white powdery frass, or “frass tubes”, which look like matchsticks poking out of the hole.
• Beetle galleries or dark squiggles may be seen under bark or within the wood.
• Infected trees wilt or have dead branches. In severe cases whole trees die.
• The beetle can attack a range of trees but only completes its entire life cycle in certain trees, mainly hardwoods.
• These major hosts include maples, figs, oaks, willows, plane trees and coral trees.
• Native species at very high risk include river sheoaks, swamp paperbarks and wedding bush.
• Visit the NSW government’s biosecurity page for more information.

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