Fears of ‘weed highways’ as summer rains spread invasive plants through rural Australia
Posters of Cowra’s most wanted hang from a fence near the shopping centre. The fugitives are invasive plants: fire weed, Chilean needle grass, parthenium and sticky nightshade. The descriptions are lengthy and the instructions clear: anyone who has seen the offending plants is to contact the authorities.
The posters show the big hitters in the New South Wales central west, but the national wanted list is long. There are 398 invasive plants in the Australiawide online weed database, of which 32 are considered weeds of “national significance”.
Tropical soda apple (Solanumviarum), mouse-ear-hawkweed (Pilosella officinarum), and parkinsonia (Parkinsoniaaculeata) are some of the worst offenders, each the subject of a dedicated plan to eradicate, control or contain their numbers.
But the unusually wet summer is wreaking havoc on those plans.
Andreas Glanznig, the chief executive of the Centre for Invasive Species Solutions, said floods and extreme weather could create “weed highways”.
“You’re getting more spread of weed propagules [seeds, buds and spores] over vast distances,” he said. “On top of that, you have mud [which means] weed seeds are being spread by cars, trucks and so on.
“The challenge is finding weeds early, so you can manage them or eradicate them from your local area.”
Glanznig said regions which experienced extreme wet weather over summer will need to remain on high alert for up to two years to see what weeds could germinate. He said WeedScan, an app created with the Centre for Invasive Species Solutions, the CSIRO, the Atlas of Living Australia, the NSW Department of Primary Industries and the South Australian, Queensland and Victorian governments, could help with early identification and detection.
“It comes back to people power,” he said.
The app, powered by CSIRO artificial intelligence to help identify weeds and alert the relevant state biosecurity officers, is one part of a broader national weed control strategy.
He said the battle started in people’s gardens.
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“The common definition of a weed is a plant out of place,” he said. “Twothirds of our weeds are garden escapes.”
In the NSW Central Tablelands, near-record rains have led to second and third germinations of weeds in back yards and farms.
“If you look at the rainfall totals for January this year and January last year, it’s chalk and cheese,” said Darren Gaffney, who owns Central West Weed Spraying. “This year, the growth of St
John’s wort has held on a lot longer – we’re still spraying it, last year it was done and dusted by Christmas.”
The most effective time to spray weeds with herbicide is usually in spring, before they have flowered. But this year Gaffney said landholders have had to do a second or third pass to control weed growth – if they can find a day free of rain or wind.
“The summer rains that we’ve had kicked everything into gear again; everything’s just growing,” he said.
“I kept weed spraying right through winter, and I’m going to be spraying right up to the end of March. It is difficult to get around to everyone when you lose two days for rain and another day with wind.
“Weeds are a huge cost, they’re going to break the country if we don’t get on top of them.”
Dr Marita Sydes, senior land services officer for the Central Tablelands, said a weed was “just something that’s growing where it’s not wanted”. “It changes with what side of the fence you’re on,” she said.
Sticky nightshade (Solanum sisymbriifolium), a nationally significant weed, can spread by broken root fragments, travelling hundreds of kilometres in contaminated soil, trucks or cultivation equipment. Its vibrant purple flowers and small edible fruits made it an attractive hedge plant to keep animals out, before it spread from Queensland to NSW, Victoria, the Australian Capital Territory and Western Australia.
“Once they become established, they get good, strong, root systems,” Sydes said. “It makes it harder to eradicate them because you can’t just dig them out.”
Sydes said the weed officers, landowners and biosecurity workers across the country “can’t deal with all weeds, there’s just not enough money or time”.
“We can’t be everywhere all the time, so you’ve got to join in and have a shared responsibility for a better outcome.”
A spokesperson for the NSW Department of Primary Industries said the state had some of the most “robust biosecurity programs in place to safeguard, build and strengthen” industries affected by weeds.
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