Calls are being made for the formation of a nationwide approach to preventing the spread of economically damaging plants capable of costing farmers eye-watering sums.
Classified as a ‘sleeper weed’, Chilean needle grass was the subject of a recent report by Crown Research Agency AgResearch which identified the relatively unknown plant as costing the pastoral sector between $192 million and $1.16 billion depending on how long it takes to spread.
The low end of that model involves the grass taking 201 years to reach 90 percent occupation of its potentially suitable range, while the higher end, which tops a billion, is based on it taking 100 years to take over 90 percent of its range.
Found in the Auckland, Horizons, Canterbury and Marlborough regions. it is currently in just a sliver of its possible range expected to grow with climate change.
“It is a nasty plant,” says Hawkes Bay Regional Council’s Iain Maxwell, responsible for environmental management in the area.
“I’ve got the luxury of living on a lifestyle block that’s surrounded by it. I’ve had two seeds removed from my dog and it costs a lot of money. When it gets in your own skin it’s pretty painful, let alone what it does to stock.”
Potential stock injuries involve blindness and pelt and flesh damage which, coupled with a loss of grazing area, lead to serious productivity losses and animal welfare issues.
Currently afflicted regional councils control the pest through regional pest plans created under the Biosecurity Act, with landowners and councils required to perform certain acts and precautions on land where Chilean spiky grass is present.
The plant grows in river corridors in the region, and Cyclone Gabrielle may have facilitated its spread and upped the workload of Maxwell and his team.
Sleeper weeds
Chilean needle grass has been present in New Zealand since about 1930, but Maxwell says it has only become a prominent problem in recent years as it’s found in increasingly more areas.
Chilean needle grass is just one of between 22,000 and 25,000 (depending who you ask) introduced plants in New Zealand, many of which in gardens, which Auckland University biological sciences professor Margaret Stanley describes as a “conveyor belt” for new pest species.
There are currently about 1800 introduced plant species living wild in New Zealand, with around 20 making the jump out of cultivation each year.
These plants, known as sleeper weeds, reproduce in the wild in small numbers with no noticeable impact, often unrecognised by the public who would have a better chance of identifying new animal species.
However, they have the potential to be activated years or decades after introduction and begin spreading, defying the usual biosecurity attention placed on intercepting new species at the border.
Manaaki Whenua Landcare Research ecology researcher Dr Angela Brandt said due to New Zealand’s unique environment we were often the first to find out that a plant considered harmless could take off as a weed.
The triggers can be many, with climate change the most obvious and imminent risk.
“If tropical or subtropical species seedlings die in frost, then that’s obviously going to prevent them from establishing, but as we get fewer frosts they can suddenly grow and you get reproduction in the wild,” Brandt said.
Other factors include the introduction of pollinators allowing for wild reproduction, as was the case with fig species after the fig wasp appeared in New Zealand, but also in horticultural and ornamental plant species where only one sex is grown, with the accidental introduction of the opposite sex allowing for fertilised seed production and spread.
Another risk factor, and one that’s far harder to predict, is propagule pressure, essentially a threshold where enough of a species are planted and distributed that they can make a leap to the wild.
“Knowing what that threshold is is much trickier than knowing whether a pollinator is present,” Brandt said.
With so many potential threats already introduced to the ecosystem, getting ahead of weeds is an increasingly difficult task.
Stanley said common weeds such as moth plant and gorse stand out in large infestations.
“These weeds cause great harm to our ecosystems, but while we focus all our attention on getting rid of one or two widespread weed species, there are five or even 10 sleeper weed species sneaking in behind us and ramping up their numbers and impact.”
Getting rid of weeds before they take off gives the best chance of eradication.
“All too soon we realise our error in ignoring these species when we end up with five-10 new weeds causing massive impacts in our ecosystems. Some clear strategies and roles are needed to prevent managers and community volunteers running around like headless chooks,” Stanley said.
AgReaserch report co-author Dr Chris Buddenhagen said AgResearch’s new modelling method taps multiple climate change scenarios and automatically searches scientific literature for weediness and invasiveness of species.
Previously risk assessment for plant species had been done manually, but the new algorithmic approach can handle thousands of species at a time, which Buddenhagen said prevented species only being identified as problematic after they start becoming problematic.
Nationwide approach
AgResearch’s report says there is a case for a nationally co-ordinated approach to controlling Chilean needle grass, rather than the decentralised status-quo.
They believe the potential economic impacts of between $192 million and $1.16 billion justify an annual spend of $5.3m and $34m respectively to prevent its spread.
It’s an idea Hawkes Bay’s Maxwell is highly supportive of.
“This isn’t something you should look to try and manage at one place necessarily, this is a plant you need to manage in a consistent and coordinated way across the whole country, and it’s an area we need to explore in more detail with the Ministry for Primary Industries and farming industry groups.”
The Ministry for Primary Industries, which previously had a Chilean needle grass working group, were unable to comment in time for publication.
Maxwell said the thorny issue was who would pay for it.
“Should Hawkes Bay continue to pay for essentially protecting the rest of the country and bear those costs or should they be distributed in a slightly different way? Or do we all kind of say, well we’re all kind of managing pests that other regions aren’t to protect those that don’t have it?”
He said the paper presented an opportunity to step back and look at whether national coordination was needed and how to tackle the problem more efficiently and effectively than it currently was.
Buddenhagen said it was clear a cost sharing agreement would be applicable, but it would be a long-term commitment.
“The reason I wanted to do this paper was because there’s a concern that regional councils could decide to abandon this problem because it’s a difficult thing to manage, yet the benefits accrue to everyone in New Zealand to some extent.
“They are underestimating the benefits by only considering their regions, which means they will underinvest in management.”
He said with the dollar figure on what this could do to an important part of the New Zealand economy out in the ether, councils could make a case to the Ministry for Primary Industries to come to some sort of agreement for better sharing of the costs between regional councils and central government for incipient invaders.
“In every case getting ahead of the problem is the most cost-effective way of dealing with a weed, rather than when it’s too late. The issue to be considered is whether or not a weed is serious enough for New Zealand taxpayer dollars to go towards it,” Buddenhagen said.
Biodiversity
Chilean needle grass is accepted primarily an agricultural pest, thriving in areas already disturbed by humans rather than competing on a large scale with native plants and posing a major biodiversity risk.
It’s that agricultural focus that gives AgResearch the licence to research its risk profile and come up with an eye-grabbing figure for potential disruption and to develop risk modelling processes for it and other risks to agriculture.
The economic impact lays the foundations for a strong discussion on how best to mitigate the impact of an invader, but what about those plants that pose a risk to New Zealand’s wider ecosystem?
Manaaki Whenua’s Dr Brandt said weeds don’t respect boundaries.
“There are plenty of weeds that cause problems in agricultural systems as well as threatening biodiversity or native ecosystems. So there’s definitely overlap there.”
She said harming the environment wasn’t good for New Zealand’s economy or international brand, so biodiversity had a value, but quantifying it was far more difficult and potentially problematic.
Buddenhagen said similar methodology could be applied, with some difficulty to sites that had high biodiversity values.
“I don’t know whether you really want to put a dollar value on biodiversity because it is priceless.”
He said subtropical plants with limited distribution in New Zealand such as the Australian umbrella tree and strawberry guava, which have a track record of being bad weeds overseas, could easily awaken as frosts become less frequent.
“To measure their actual impacts is a bit pointless because we’re trying to prevent its future impact.”
Dollar signs or not, weight has been thrown behind the cause.
In his 2021 ‘Space Invaders’ report on the biodiversity risk posed by pest plants, Parliamentary Commissioner for the Environment Simon Upton warned they smothered, outcompeted and prevented the regeneration of native plants.
“If left to their own devices, these weeds will transform our ecosystems beyond recognition.”
The report recommended, among other things, including the development of a national policy direction on native ecosystem weeds and greater leadership from the Ministry for Primary Industries and the Department of Conservation.
Once long ago every council had a noxious weeds officer and people where compelled to keep weeds on their properties under control and then the idiot reformers of the 1980s and 90s decided that market forces would look after this problem much better than dedicated staff and so these positions were disestablished. So weeds have had a free reign in the intervening decades. Also we have really daft and rigid rules around pest management that replaces the good old pest control boards – I live in Moeraki and we have an abundance of rabbits – which the locals quite enjoy shooting – at worst they are a minor nuisance – otherwise are a great resource for recreational hunters. The same land is infested with Box thorn – this is one of the nastiest weeds going – it grows with its roots in the ocean – it hangs off the cliffs – it is the dominant coastal vegetation across all of north otago and infests all of the limestone outcrops up the waitaki valley – it has edible berries so birds spread it – rabbits browse the seedlings – along with the seedlings of briar and gorse and a lot of weeds so the rabbtis are doign more good than our local regional council. The regional council’s pest management officer – likely who has never used a herbicide or shot a rabbit writes us letters advising us that our rabbits exceed level 3 on the relevant infestation scale and that we should rabbit proof our boundary fences – now this is a 1.5 ha block with an odd shape that results in the boundary fence being 500metres long it would cost thousands, it would not make any difference to the rabbit population. One boundary runs along the coastal cliff and is impossible to effectively fence another boundary is shared with a small block owned by a Maori trust with 1500 nominal owners. It is pointless doing any rabbit control unless it is done on a community wide basis – fences are a waste of money but our regional council would rather spend a bundle counting rabbits and writing letters. But they only write letters to land owners with landholdings over 1 hectare where most of the rabbits live and breed in the urban area – this is an exercise in futility – meanwhile the boxthorn flourishes untroubled by the attention of the regional council – who are far too busy building themselves anew 30Million dollar office to do anything useful – boxthorn has spines on it the will puncture a truck tire and give you a nasty infection if one spikes you, it is highly resistant to herbicides – it laughs at fire and ripping it out with an excavator simply encourages the roots left in the ground to send up a veritable thicket of new shoots. The same regional council has simply shrugged and looked away while wilding pines and douglas fir spread far and wide across the high country tussock. It has always been cheaper to control a few weeds than an infestation because weeds tend to spread exponentially . We are now confronted with the cost and environmental harm caused by these three decades of neglect and this is a problem that requires a communal response as in many areas it will be beyond the resources of the individual Land owner