Toxic 'superweed' spreading across Northland sparks concern for pastoral farming sector
Perennial Madagascar ragwort (Senecio madagascariensis) can grow up to 50cm tall in ideal conditions, and has multiple branches, long leaves and many flowers.
Photo:
SUPPLIED/Northland Regional Council
The Northland regional council and farming groups are developing a plan to try to control an invasive weed known as the "mad rag" or "fireweed", amid fears it could spread to other regions and even into the South Island.
Madagascar ragwort (Senecio madagascariensis) is a poisonous and sometimes fatal plant for livestock with bright yellow, daisy-like flowers, now considered widespread in the Far North particularly on cattle farms.
Dubbed the "fireweed" in Australia, that originated from southern Africa, adult plants could produce up to 10,000 seeds that could be viable for up to a decade, and germinated in as little as six weeks across most soil types.
AgResearch principal scientist and weed management expert, Dr Trevor James said the plant suppressed other pasture species and spread by wind, posing many challenges for farmers and landowners trying to control it.
"There is no easy way to manage it once it gets established, but the main problem is its toxicity to cattle and horses," James said.
"Poisoning doesn't seem to be the problem per se, because stock don't eat it once they learn that it's horrible.
"But poisoning could be a problem if it's made into hay and is fed out as hay or possibly silage and the poison toxins are still there."
James said climate modelling showed it had the potential to go further afield of Northland.
"And if climates get warmer and drier, definitely it has the potential to move
further south
."
Some fields along SH10 in the Far North are now dominated by Madagascar ragwort.
Photo:
RNZ / Peter de Graaf
Farmers were being urged to get to know the weed, pull it out by hand and
work with their neighbours
to keep on top of it.
Will Burrett, chief operating officer of Crown-owned Pāmu Farming formerly Landcorp Farming, said Madagascar ragwort was prevalent on its Northland farms.
He said it resulted in lost production of up to 35 percent over seven years at its Rangiputa site, where it was costing on average up to $200 per hectare to control, in addition to the increased use of agrichemicals.
"We've obviously got herbicide applications and we're trying to limit those as much as we can because we are starting to impact overall pasture production," Burrett said.
"It is highly toxic, so we can spray out of paddock and then the fresh seedlings that re-sprout and come back through, if animals do graze those, they're highly toxic to their liver, so that does cause animal health considerations that we have to try and manage as well."
He said Pāmu were actively trying to manage it by pulling the weeds out by hand as they came through, but it was such a "fast, prolific grower".
"There's no silver bullet for this, and it's got a significant risk across the north in that it's been proven to have the ability to spread to other regions throughout Aotearoa in terms of the cattle systems and the dairy systems out there. It's a massive risk."
Burrett said the next steps were about committing industry to a plan, to take to the biosecurity minister in the next month or two.
Takou Bay farmer Ian Sizer studies an infestation of Madagascar ragwort.
Photo:
RNZ / Peter de Graaf
Beef farmer Ian Sizer
of Tākou River had dealt with the pest for around four years, and said it spread across a whole paddock within just four weeks on discovering the first plant.
He spent up to two hours a day hand-weeding it to keep on top of it and maintain his herd's health.
"It's everywhere. It's a problem all the way across our farm and of course, neighbouring farms, and we're all trying to do our part on containing it," Sizer said.
"Part of my daily routine when I'm moving cattle is one eye is always kept on the Madagascar ragwort, and if I see it, the priority is to get off and hand-weed it."
Sizer said it came at a significant cost to the business.
"It's costing me probably in the region of $70,000 a year to try and deal with this, but the impact on farmers throughout the whole of New Zealand, it could easily be put into millions," he said.
Sizer said there were very few effective herbicide for farmers, which had to change, and a collective, national approach to fast-track the development of longer-term biological controls was vital.
The Northland Regional Council led a
working group
to address the challenge of controlling Madagascar ragwort, including the Ministry for Primary Industries and the Department of Conservation, as well as farming sector groups like Beef and Lamb New Zealand and Dairy NZ.
A 2023 Manaaki Whenua Landcare Research feasibility study for biocontrol of Madagascar ragwort found the potential agents used in Australia would be unsuitable in New Zealand.
Jack Craw, chairman of the regional council's Biosecurity and Biodiversity Working Party, said it had $20,000 allocated towards developing a business case for its long-term management and further research.
He hoped industry groups would help co-fund the programme that would explore the use of biological controls such as beneficial insects for the long-term management.
"We've highlighted this to the national level, and we believe it's something that the regional councils, plural, of New Zealand should be funding this, along with all the sector organisations."
Madagascar ragwort grows up to 60cm tall and has yellow, daisy-like flowers.
Photo:
RNZ / Peter de Graaf
He said its spread outside of Northland was "inevitable", as the seeds travelled by wind, so a controlled area notice to restrict the movement of vehicles in and out of the region would be "a futile gesture".
"There's probably no point in the Ministry for Primary Industries putting a controlled area notice on the upper half of Northland because even if we did, we can't inspect every single vehicle and then water blast them all. It's just not possible.
"We need to focus much more on finding a long-term control solution for this weed."
Madagascar ragwort was "a national issue," he said.
"We've done the climate matching and this thing will grow as far south as Canterbury, and invade most pasture types."
Farmers were not currently receiving any financial assistance for its control, he said.
Biosecurity Minister Andrew Hoggard said the management of Madagascar ragwort would require a "collective effort", but the responsibility of long-term management of it in the north, where it was well-established, sat with the regional council.
"A working group involving regional council and industry sector representatives has been established with the intention of identifying management options to mitigate the risk of further spread and to reduce known infestations," Hoggard said in a statement.
"The working group will be developing a Madagascar ragwort action plan for the region. Nearby regions are involved in this too.
"Biosecurity New Zealand and MPI's On Farm Support team will support this group."
The matter would be discussed at the next regional biosecurity manager's forum, he said.
Recent genomic DNA testing revealed the plant that many thought to be the similar endemic Gravel groundsel species, was the faster-spreading Madagascar ragwort.
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