Sleeper Weed Poses Potential Billion-dollar Threat; New Tools To Focus Response

The “sleeper weed” Chilean needle grass, if nothing was done to stop it, could spread through most of New Zealand and eventually cost the country over a billion dollars, according to newly published research.

Chilean needle grass (Nassella neesiana) is known to have already taken hold in 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.

It is one of approximately 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.

“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,” says AgResearch principal scientist Dr Graeme Bourdt.

“We’ve worked with Manaaki Whenua - Landcare Research on analysing various 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 Dr Bourdt 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% 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 Chris Buddenhagen says: “This bio-economic modelling reveals that a nationally coordinated 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 advisor biosecurity, Imogen Bassett, welcomed research that improved the ability to tackle sleeper weeds.

“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,” Dr Bassett says.

“But with so many potential weeds in the country, we are reliant on good information to help us prioritise. Auckland Council and other 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.”

You can read the full research paper, The cost of doing nothing about a sleeper weed – Nassella neesiana in New Zealand, at: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0295574

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