Chilean needle grass (Nassella neesiana) is known to have taken hold in Hawke’s Bay and Central Hawke’s Bay.
Chilean needle grass (Nassella neesiana) is known to have taken hold in Hawke’s Bay and Central Hawke’s Bay.
Newly published research says Chilean needle grass, if nothing is done to stop it, could spread through most of New Zealand and eventually cost the country over a billion dollars.
Chilean needle grass (Nassella neesiana) is known to have already taken hold in Hawke’s Bay and Central Hawke’s Bay, Canterbury, and Marlborough.
Its sharp, penetrating seeds cause blindness in livestock, pelt and carcass damage, and the loss in pasture quality and grazing access leads to farm production taking a financial hit.
Chilean needle grass is one of about 22,000 species of introduced plants in New Zealand. The scientific challenge is to identify those that pose an economic or environmental threat before they become widespread.
These “sleeper weeds” can then be prioritised by authorities such as regional councils and the Department of Conservation for management to prevent their spread.
Sleeper weeds are introduced plant species that are reproducing in the wild, but in small numbers with no noticeable impact. Their populations tick along in the background until the right pollinator or environmental conditions activate them.
The sharp, penetrating seeds of Chilean needle grass cause blindness in livestock, and pelt and carcass damage.
Once the sleeper weeds “awaken” and become more noticeable in the environment, it can be too late, and their populations explode.
“The exciting part is that we now have the ability through our research to develop models and tools to identify sleeper weeds, predict how and where they will spread in a changing climate, and estimate the economic and environmental damage that would result,” AgResearch principal scientist Dr Graeme Bourdot said.
“We’ve worked with Manaaki Whenua-Landcare Research on analysing management scenarios for sleeper pests in general. We are currently working with regional councils, DoC and the Ministry of Primary Industries to develop a web-based tool that will enable informed decisions about investing in sleeper weed management programmes.”
The newly published research about Chilean needle grass in the science journal PLOS One, by Bourdot and AgResearch colleague Dr Chris Buddenhagen, combined climate niche modelling (to estimate the potential range of the species in New Zealand) and a spread model (to estimate the future economic losses under a “do nothing” scenario) to determine the benefits of stopping the spread.
Under realistic low and high estimates of this weed’s spread rate, where it takes either 201 or 100 years to reach 90 per cent occupation of its potential climatically suitable range covering 3.96 million hectares, the loss to the pastoral sector is $192 million and $1.16 billion respectively.
These losses would justify annual expenditures to prevent the spread of $5.3m and $34m respectively, AgResearch senior scientist Buddenhagen says.
“This bio-economic modelling reveals that a nationally co-ordinated approach to managing Chilean needle grass makes best economic sense. This would include surveillance in susceptible regions and control measures in the infested regions”.
Auckland Council principal adviser biosecurity Dr Imogen Bassett welcomes the research.
“We know it is much more cost-effective for us to act early, to prevent future weed invasions than to deal with them once they become widespread,” Bassett says. “But with so many potential weeds in the country, we are reliant on good information to help us prioritise. Councils around the country are working hard to prevent the spread of Chilean needle grass, and this new research highlights just how important that work is.”
