A professional gardener is warning Aussies to know the signs of an invasive pest that could mean the end of their most beloved trees. Polyphagous shot-hole borer is a tiny beetle native to Southeast Asia that’s spreading throughout Perth, infesting thousands of trees.
The gardener, who asked to stay anonymous, first suspected something was wrong after noticing strange white marks on his forty-year-old avocado tree. Grown from seed, the species can take up to 13 years to bear fruit and live up to 100 years, so this was a difficult blow.
Although the insect has a symbiotic relationship with a fungus, what the man had noticed was something different. The white blobs were what’s known as “sugar volcanoes”, a sign the tree is excreting thick, sugary sap as a defence mechanism.
Across a half-acre garden, there have been several trees infected with the pest, including two large liquidambars, four camellias thought to be 40 years old, and six mango trees. Because of its invasiveness, all the trees are now earmarked for destruction.
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After the “sugar volcanoes” were cut away, tiny shot-hole borer burrows could be seen. Source: Supplied
According to the Department of Agriculture, other signs to look out for include tiny holes in the surface of the trunk or branches, little piles of sawdust, or lesions around the bark.
Shot-hole borers were first detected late in 2021, and now all of Perth has been quarantined to slow its spread.
Can trees be saved from shot-hole borer?
Internationally, more than 500 species of tree are known to be infested by the insects. That list includes native Australian species of fig, banksia and wattle.
Authorities have responded by chopping down trees, including 120-year-old Moreton Bay fig trees in the Botanic Gardens, but experts don’t believe the measure will eradicate the beetle as it’s only been successfully defeated once before, and that was in Europe when the weather cooled and the beetle became less active.
A shot-hole borer is tiny when compared to a 5 cent coin. Source: Department of Primary Industries
One council has had some success in saving trees by removing branches, then applying fungicide and insecticide. But success requires early detection and ongoing management.
Shot-hole borer is currently confined to Western Australia, but it’s important everyone around the country knows its signs to help stop its spread. Invasive beetles are a constant threat, with the varroa mite continuing to impact bee colonies in NSW, and fire ants marching south from Queensland.
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