Fast-growing pasture: feed or weed? Experts respond

Farmers who use plant varieties that become invasive weeds should pay a levy to cover any environmental management costs, say the authors of a new study.

A summary of the research by author Assoc Prof Don Driscoll, ANU.

As breeding technologies produce faster-growing, more hardy pasture plants, the potential impact of wild-growing pasture in the wider environment grows, warn the authors of a new article published in PNAS. Their review of agricultural practices in eight countries, including New Zealand, reveals that governments impose few restrictions on pasture varieties planted by landowners.

The authors say governments should manage a list of prohibited varieties, not just species, develop a weed risk assessment, ensure rapid detection and control of invasive weeds, and develop an industry-pays system. If their pastures become invasive then agribusiness and farmers should be responsible for paying for any control or eradication, say the authors.

The SMC has collected the following expert commentary. Feel free to use these quotes in your reporting. If you would like to contact a New Zealand expert, please contact the SMC (04 499 5476;

Prof Philip Hulme, Professor of Plant  Biosecurity, Lincoln University is a co-author on the paper. He comments:

“Pasture species such a ryegrass and fescue may not strike people as major threats to the environment but they are regarded by the Department of Conservation as environmental weeds.

“Pasture is big business in New Zealand and a large part of our economic success arises from agribusiness developing ever more productive or persistent varieties. As a result there is a clear conflict between economic and conservation outcomes.

“[resolving] this will be difficult in a country as dependent as we are on dairy exports for economic prosperity. I imagine the environmental risks of pasture species are not at the front of the minds of farmers or policymakers”.

“It is probably those varieties being developed for greater persistence, especially in the face of drought, that might pose the greatest future risk”

These comments are excerpted from a release provided by Prof Hulme.

Dr Michael Dunbier,  is a research scientist with expertise in genetics and plant breeding. He comments:

“The authors correctly highlight the dilemma of enabling development of more productive pasture species or cultivars that have improvements in resilience to abiotic stress without increasing their potential weediness. They also highlight the negative externalities from this weed potential and suggest financial penalties for agribusiness to mitigate this risk. The positive externalities from more sustainable pasture industries (including savings in inputs, reduced nutrient leakage, less greenhouse gas emissions, enhanced animal welfare) also need to be taken into consideration. This is particularly so in New Zealand whose primary production industries are dependent on introduced species and whose economy is heavily influenced by the fortunes of the primary sectors.”The scrutiny of the biology of new plant species under the HSNO and Biosecurity Acts has markedly reduced importation of plant species, including potential pasture species. Additional constraints limiting the use of new species or cultivars with novel traits may limit innovation and result in increased environmental impact overall as weed potential is only one component of the possible negative impacts of pastoral production systems on the environment and society.”

[Dr Dunbier notes the above is a personal response and not made on behalf of any of the organisations he is associated with.]

Prof Jacqueline Rowarth, Professor of Agribusiness, University of Waikato, comments:

“Whether genetically-engineered or traditionally-bred through selection and hybridisation, new plant types have the potential to be more ‘fit’ for an environment than wild types – that is why they are created, and the aim is greater productivity than what is currently available. In 2009, Andy Coghlan in New Scientist pointed out the illogic of a system where introduction of novel plant traits were largely unregulated unless cross-border introduction or release of GMO were involved. Any novel trait has the potential to get away, hence the concern about GMO, but examples of them doing so are limited. The fact is that modification for a particular managed environment tends to make the plants less robust in the wild.

“In a paper in Grass and Forage Science (2011), Massey University scientist Professor Tony Parsons suggested  that a standard procedure to explore trait impacts and fitness should be applied whatever the origin of the plants. The overall goal should be to increase society’s confidence. Canada does have such a system, but it is expensive, and though the authors of the current paper do make recommendations on approaches to decrease the risk of native ecosystem invasion, the only costs mentioned are that industry should pay for any clean-up if a species escaped to become a weed.

“The problem with the ‘polluter pays’ principle is that it depresses innovation. For New Zealand the implications would be an increase in costs of development that are ultimately passed to the consumer. Eco-labelling of food is suggested so that consumers can support sustainable intensification, but labelling hasn’t for instance worked on cage and free range eggs – over 80% of consumers still buy cage eggs because they are cheaper.

“Another alternative is that plant breeding stops. As New Zealand’s environment is unique, which means that breeding and testing cannot be done overseas, ‘stopping’ would put considerable pressure on production systems already struggling with climate perturbation, disease and pest incursions, and nutrient limitations. Hence it is imperative for food production that developments continue.

“A possibility not mentioned in the current paper is the use of the colloquially named ‘terminator gene’. If new plants were unable to produce fertile seed, the environmental impact would be limited. The concept, however, didn’t go down well globally when it was first introduced.

“Hard choices ahead.”