An invasive beetle which is killing Perth's tree canopy has been effectively managed in avocado crops in the United States without the need to remove infected trees, according to an expert who has been monitoring the pest for a decade.
The detection of the polyphagous shot-hole borer in Perth three years ago triggered a $41 million biosecurity response.
Significant funding was also dedicated to trying to stop the spread of the beetle in the United States after it was found on a backyard avocado tree in Los Angeles in 2012.
Efforts are underway in Kings Park to curb the spread of the shot-hole borer. (ABC News: West Matteeussen)
The Department of Primary Industries and Regional Development (DPIRD) is using a range of measures to try and eradicate the beetle in Western Australia.
But in California, the focus has instead been to learn to live with shot-hole borer.
Pruning branches early
University of California Davis Assistant Professor of Forest Pathology Shannon Lynch said the key to this was careful pruning and strict sanitation standards.
Shannon Lynch is an assistant professor of forest pathology and plant disease ecology with the University of California Davis. (Supplied)
"We were finding that even though it was spreading rapidly through these [avocado] groves, over time, with good sanitation practices, if they did good pruning practices of their grove and everything like that, the beetle could actually be managed," she said.
Dr Lynch said the borer favoured the secondary branches of California's avocado crops instead of the trunks, making it possible to remove infected branches before the pest spread.
The beetle burrows into the wood and cultivates a fungus which blocks the transport water and nutrients to its branches, causing the tree to die.
Children learn about the shot hole borer at the Perth Royal Show where bits of wood are on display to show the markings left by the beetle. (ABC News: Kate Forrester)
But Dr Lynch said the shot-hole borer in WA carries a different type of fungus than that found in California, and suggested more research was needed into the pest affecting Perth.
Can plastic wrap work?
Dr Lynch has been touring WA to share the latest research and lessons in the management and treatment of the pest.
She said methods like wrapping infected trees with a copper-infused plastic material had shown little promise overseas.
Despite its small size, the shot-hole borer beetle can destroy a tree in just two years. (ABC News)
"As soon as that hole gets plugged up, the female beetle, the mother, will immediately go to the entry hole and open it up," she said.
"She can easily chew through plastic to open up those holes … we've seen this time and time again."
There are concerns the pest could escape the Perth quarantine zone and enter orchards in the state's south west.
A large tree infected with polyphagous shot-hole borer being pruned or chopped in Perth's Kings Park. (ABC News: Grace Burmas)
Dr Lynch encouraged growers to remain cautious but not fearful of the pest.
"Take the pest seriously, but there's no need to panic," she said.
"I think [with] good integrated pest management practices, good sanitation practices … applying good, tried and true, well-tested treatments [and] the things that we've learned in California to reduce the beetle populations, it can be managed."
'Trees coming down every week'
In early September DPIRD extended the shot-hole borer quarantine area to try and stop the pest from spreading outside the metropolitan area.
DPIRD deputy director of sustainability and biosecurity Mia Carbon said removing infected trees remained the only proven method to stopping the beetle in its tracks.
Mia Carbon is involved in the biggest biosecurity response ever undertaken in WA to control the shot-hole borer. (ABC News: Kate Forrester)
"No one likes chopping down trees … that's a really big impact on a community, but unfortunately, at the moment, it's the only tool we've got available to us in eradication," she said.
"We've got a team of more than 160 people, and we've got 100 people out in the field every day… we've got trees coming down every week, unfortunately, but there's lots of activity going on."
A shot hole borer awareness exhibition is running at the 2024 Perth Royal Show. (ABC News: Kate Forrester)
Dr Carbon was speaking with Perth Royal Show goers about the beetle this week, saying the public played a key role in tracking shot-hole borer.
"You often can't tell just by looking at a tree what kind of borer it is so the best thing people can do, if they've got a suspicion, is call it in, and we will get somebody out to look at it," she said.
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