Dave Crispin, senior arborist at Treeswest Australia and ArbWest member, highlights a serious problem which means WA is under attack.
Q. What do Israel, South Africa, California, and Perth all have in common?
A. They are all under serious attack from the PSHB.
It sounds like an eastern-bloc secret police. It’s not, but it’s equally as sinister. Polyphagos Shot Hole Borer (PSHB), has taken the west by surprise, first being detected in East Fremantle in August 2021.
Polyphagos Shot Hole Borer
The shot hole borer, Euwallacea fornicatus is native to Southeast Asia, and with Fremantle being a port, It’s a safe bet it came over via shipping. A resident noticed part of the canopy of their maple tree was dying back, so they contacted the Department of Primary Industries & Regional Development (DPIRD) through its great little app, and it took off from there.
DPIRD, our front line of defence in biosecurity, undertook extensive research into the beetle and the associated Fusarium fungus, and found several other countries have been battling the same pest. The Fusarium euwallacea, the fungus which the beetle feeds off, is carried around in a specialised cavity inside the beetle. As the beetle burrows through the tree, it creates hundreds of galleries, the Fusarium fungus lines the tiny tunnels and spreads throughout the tree in the conductive tissue, stopping the transportation of vital water and nutrients, slowly killing the tree. Females are the only ones that can fly, one single unmated female can fly up to 400m, although information on distances does tend to vary, and start a new colony alone.
The female has the ability lay unfertilised eggs, which can produce a male. She can then mate with that male and start a whole new colony.
The male of the species is smaller than the female. Females are brown to black, approximately two millimetres in length, while the males are marginally smaller at 1.6mm.
Below are some sobering statistics from DPIRD.
Department of Primary Industries and Regional Development
To date, in response since August 2021, DPIRD field surveillance staff have:
• Completed more than 1.4 million tree inspections
• Visited more than 48,000 properties to conduct surveillance
• Deployed more than 2800 traps
• Collected over 83,000 samples, and
• Travelled more than 640,000km.
Six-hundred-and-sixty-nine infested premises have been identified, with the majority of these in Perth’s western suburbs. There have been no detections outside of the Perth metropolitan area.
Arboricultural Association of Western Australia
The state industry body, Arboricultural Association of Western Australia, (ArbWest), was asked to attend a meeting with DPIRD to fully understand the implications of PSHB in our state. As one of the attendees at that meeting, it soon became clear the gravity of the situation. Understanding that there is no known defence against the beetle apart from: pruning infected wood (after the fact); removal of the whole tree depending on the severity of the infestation; and trapping, there is no effective means of elimination.
Working closely with DPIRD, a working committee was formed to answer the challenge from an industry perspective. In collaboration with the department, ArbWest presented a set of procedures that were workable (there was no point agreeing to something DPIRD wanted that couldn’t be adhered to):
• A quarantine area (QA) was to be set up that encompassed confirmed infestation locations, using the Local Government Areas, (LGAs)
• No wood of any kind will be transported outside of an infected LGA, unless deemed safe by a DPIRD inspector. This required an onsite inspection and the issuing of a permit to move
• All woody vegetation and leaf matter will be chipped to a size no greater than 25mm
• Any infected wood that is chipped must be disposed of at a DPIRD-sanctioned waste-disposal facility, and
• All equipment used while removing the infected material must be sanitised. This includes saws, and woodchippers – good cultural practices.
Currently, (July 2023) there are 25 LGAs in the QA in Perth, from Sorrento, north of Perth, heading east to Middle Swan and Forrestfield, then southwards down to Naval Base, near Kwinana.
From an Industry position, there are several challenges – quoting, for instance. Consider the 400 host species, the 100 reproductive host species, remembering to look for the signs that might give away the borer, then you have to price the job.
Common signs to look for are: upper canopy dieback; tiny entrance holes the size of the tip of a ballpoint pen; sugary exudate; volcanos or gumming; and sometimes frass at the entry holes.
Like most states, WA has a variety of borers, so before we raise the red flag, secondary indicators are a good idea.
Keeping abreast of the latest developments is key to combating PSHB, regular updates on the DPIRD website – agric.wa.gov.au/borer – and industry notifications sent out by ArbWest are critical in keeping the pest under control.
Perth parks and gardens
Recently, while undertaking an inspection of a 120-year-old Auracaria heterophylla, at a park in Perth, I noticed a white peppering over the trunk at about one metre up. It resembled a target that had been fired upon with shotgun pellets, speckled over a 2m square area. It turned out to be the tree’s response to the borer. The tree had secreted its white protective latex in response to the attack. Fortunately, I havn’t seen any progression by the beetle or the fungus in this magnificent specimen.
Speaking with a horticultural colleague who works throughout Perth recently, she lamented on the number of tree removals she’d witnessed due to one single infestation. It’s unprecedented. I asked if she’d noticed whether the beetle favours one species over another? “No!” she replied. Short and sharp, age or species, it does not differentiate.
Ficus does seem to be a popular genus. She was aware of a 100-year-old Ficus rubiginosa that had an amazing shape, and so much character, that had to be removed. Other popular species targeted in the CBD: Acer, Erythrina, Quercus, Robinia, Salix, Morus, Brachychiton, Platanus and the list goes on. Our natives are not immune, species include: Melaleuca, Casuarina, Corymbia calophylla, Eucalyptus globulus and some Banksia.
Most recently, I was asked to look at four very old Delonix regia, these had become infected to varying degrees, one unfortunately will have to be removed, but the other three are holding their own. The only management tool currently is the removal of the dead wood, and to monitor.
