Farmers along the north coast of New South Wales are at war with a noxious weed that has sprung out of the ground following the 2019 bushfires.
- Tropical soda apple is one of only two weeds in NSW with a biosecurity control order
- Native to South America, tropical soda apple is a species that prefers wet environments
- Increased rain during the current La Niña brings with it increased risk of spread
Tropical soda apple (Solanum viarum) was first identified in Australia in 2010 by beef cattle enterprise owners Caroline and David Duff near Armidale.
“This thing is more aggressive than anything I’ve ever witnessed,” Mr Duff said.
“It grows all year round, so it’s not like those annual weeds.”
With seeds germinating in six to 12 weeks and each fruit containing up to 400 seeds, Mr Duff said controlling this “weed from hell” was a daily battle.
“We can do the best that we can to control it, and every time we get a rise in the river, if it is not being controlled upstream, then we reseed it again,” he said.
Kempsey Shire Council weeds officer Greg Egan said the amount of seed tropical soda apple produced from just one fruit was what made it such a threat.
“Two-hundred to 400 seeds per fruit, that’s potentially a lot of plants from just one fruit,” he said.
“When we got the rain events after the bushfires, tropical soda apple jumped out of the ground like we’ve never seen it before.
Department of Primary Industries state priority weeds coordinator Philip Blackmore said the sharpness of the weed’s spines and its capacity to dominate in subtropical environments made it very undesirable in a grazing situation.
Mr Blackmore said when the weed’s sample was submitted to botanists in 2010, they were not entirely sure what it was.
“One botanist who’d been in Florida recognised it as tropical soda apple,” he said.
“In Florida, which has a similar climate to the north coast of New South Wales, it is possibly the most serious weed of grazing industries in the United States.
“That is the potential for tropical soda apple in warm-temperate to subtropical areas.”
NSW Local Land Services regional weed coordinator Kylie Van der Kolk said the north coast region had the most tropical soda apple in the state.
“Its potential distribution across NSW is quite large; it could end up impacting heavily on the [agriculture] industry and environment.”
One of only two weeds in NSW with a biosecurity control order, tropical soda apple is recognised as a serious threat.
The most common way for tropical soda apple to spread is being eaten by stock, floating downstream or being stuck to vehicles.
Rachel Gallagher, a senior lecturer at Macquarie University’s Department of Biological Science, is working with the Weed Futures Project which looks at the potential for weeds to spread under climate change.
The majority of infestations of tropical soda apple are around the Brisbane area and northern NSW.
“Modelling for the decade centred on 2050 and 2070 shows that there is a lot of climatically suitable habitat in the south of the continent, making for larger areas of potential infestation of this species,” Dr Gallagher said.
Native to Argentina and tropical areas of South America, tropical soda apple is a species that prefers wet environments.
Increased rainfall during the current La Niña cycle brings with it increased risk of spread.
“It is really important we get in and control weed species and that we dedicate the resources that are required to slow the potential extinction of native species which are competing with invasive species,” Dr Gallagher said.
Mr Duff said he had been fighting the weed for 10 years and questioned if enough had been done to control it.
“It is no use just one farmer trying to control it; everybody’s got to be on the bandwagon to control it.”