Tākou Bay farmer Ian Sizer studies an infestation of Madagascar ragwort. Photo: RNZ / Peter de Graaf
A toxic weed spreading like wildfire through Northland pastures has a farmer so worried he's petitioning the government to take urgent action against the threat.
Ian Sizer, of Tākou Bay, north of the Bay of Islands, said the invasive weed Madagascar ragwort arrived in the Far North on farm machinery about 20 years ago and was now spreading inexorably south.
He said it was now south of Whangārei with nothing to stop it from spreading to the bottom of the South Island.
The Northland Regional Council shares his concern but with as yet no known biological or herbicide controls, there is little it can do.
Sizer said he first noticed a few yellow-flowered weeds when moving cattle four years ago.
He thought little of it until he returned to the same paddock three weeks later and found a sea of yellow flowers.
He sent a sample away for identification and was told it was Madagascar ragwort (Senecio madagascariensis), a fast-spreading plant toxic to livestock.
Sizer said he pulled the plant out by hand, a laborious method but the only one that worked.
His neighbour hired someone two days a week simply to hand-weed Madagascar ragwort.
"It disperses really easily with the wind. One plant seed head will have thousands of seeds, and it takes over. It colonises areas.
"It's not good for stock, if they're forced to eat it because there's no grass, it can cause serious health problems."
When Sizer noticed the plants spreading down State Highway 10 this spring - some fields around Waipapa were entirely yellow with the flowers - he decided it was time to act.
Madagascar ragwort grows up to 60cm tall and has yellow, daisy-like flowers. Photo: RNZ / Peter de Graaf
He contacted Northland MP Grant McCallum, also a farmer, and started a petition calling on the government to take urgent action.
Sizer said the first thing that was needed was an awareness campaign.
"A lot of people see it in their pasture, on their lawn, and they don't know what it is and how deadly it is, or that if they leave it, the seeds will spread everywhere.
"So we need a national campaign to make sure that farmers, growers, landowners and the community are aware of how bad this weed is."
Fast-tracking of research into biological and herbicidal control was also required, as was financial help for Northland farmers carrying the cost of dealing with the weed.
"The problem is that if one farmer controls it and the other farmer does not, as soon as the wind blows, you're back to square one again.
"So it has to be a Northland-wide approach, and eventually a nationwide approach, so that we deal with it quickly, efficiently and effectively," he said.
The seeds could also be spread with hay, so Sizer wanted Northland designated a "controlled area" for feed to help prevent seed dispersal. That would ban the movement of hay or baleage out of the region.
Without a proper national action plan, Sizer said the weed would take over the landscape and dominate pasture.
"I have nightmares about it. That's how bad it is. But I'm determined that we're going to get rid of it."
Some fields along SH10 in the Far North are now dominated by Madagascar ragwort. Photo: RNZ / Peter de Graaf
Northland Regional Council biosecurity manager Joanna Barr said Madagascar ragwort was spreading aggressively through the region.
Some farms in the Far North, where the weed was first identified, already had high-density infestations similar to those of ragwort (Jacobaea vulgaris) before biocontrol agents were introduced in the 1980s.
Barr said Madagascar ragwort contained toxins that caused permanent liver damage when grazed, resulting in illness, low milk production and slow growth, and sometimes stock deaths.
Cattle and horses were particularly susceptible, she said.
It was toxic when green or dry, so contaminated hay or silage could also be harmful.
There was also no effective treatment for Madagascar ragwort poisoning.
Initially, the weed was thought to be an almost identical species known as Gravel groundsel (Senecio skirrhodon).
However, genetic analysis in late 2022 made the distinction apparent.
Barr said Madagascar ragwort was significantly more invasive than Gravel groundsel and a major threat to the agricultural sector.
It was already a serious problem in Hawaii and Australia, where it was known as "fireweed" and classed by the Australian government as a Weed of National Significance.
It was difficult to control, with dense infestations requiring expensive and repeated intervention.
The best way to protect pasture was by early identification and intervention, Barr said.
The Ministry for Primary Industries was notified once the plant was confirmed as a new species for New Zealand.
The ministry concluded the weed was not yet widespread throughout the country, but had been present for up to 20 years so eradication was not feasible.
Barr said cattle were usually reluctant to eat Madagascar ragwort, so poisoning was most likely when plants were dense and stock could not feed selectively, or when there was a shortage of pasture and stocks were less selective about food.
Sheep and goats were more inclined to eat Madagascar ragwort than cattle and were also less susceptible to poisoning.
The weed had a wide environmental tolerance and competed strongly with pasture species.
An average Madagascar ragwort plant could produce more than 10,000 seeds per year and growth from seed to flowering could take as little as six weeks.
In 2023 the council commissioned a study to discover if some form of biocontrol was feasible.
Unfortunately, potential biocontrol agents tested in Australia proved to be unsuitable.
The next phase of biocontrol research would be to carry out a genetic analysis of Madagascar ragwort across its native range, to work out where the New Zealand and Australian infestations originated from.
That area could then be surveyed for new insect and pathogen agents for further testing, but that would require substantial extra funding.
Barr said pasture improvement and reduced grazing pressure reduced germination rates, and mixed grazing with sheep could also help manage Madagascar ragwort, but that was not always practical.
Biosecurity Minister Andrew Hoggard has been contacted for comment.
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