AgResearch and Landcare Research have joined forces in a major new project that will build a national capability in weed management research.

AgResearch and Landcare Research already carry out most government-funded research on weed management across natural and productive ecosystems, but this collaboration is a new approach for the two crown research institutes. 

It will place a high priority on training a new generation of weed scientists through PhD programmes at Lincoln, Canterbury and Massey Universities, and will work closely with the ‘end-user’ pastoral industries and Regional Authorities in prioritising research and implementing the results..

The two CRIs have developed a research programme called “outsmarting weed populations using innovative bio-economic strategies,” which is aimed at providing the knowledge and understanding necessary to sustainably manage weeds at a range of scales from paddocks to whole farms and regions.

Led by AgResearch weed expert Dr Graeme Bourdôt, the Lincoln-based programme will provide the tools to manage weeds in New Zealand pastures in ways that are more effective, sustainable, environmentally friendly and in keeping with the agricultural biosecurity needs of the country.

There will be human and environmental welfare benefits to New Zealand through a shift away from the current short-term chemical-based approach to a long-term integrated approach that brings together existing and emerging weed control options. 

This new collaboration within the pastoral sector is the first step toward building a national capability in weed science, with further plans for a joint proposal on environmental weed management.

Dr Bourdot believes bringing together AgResearch’s expertise in weed population ecology and the use of naturally occurring pathogens in weed control, and Landcare’s skills in the science and implementation of classical biocontrol, will provide the rigorous scientific basis needed for developing weed control strategies that support sustainable pastoral development.

Dr Simon Fowler of Landcare Research adds combining new understanding of the population ecology of target weeds and potential biological control agents will enable us to explain our historical successes and failures.  “We can then identify the characteristics needed in future biocontrol agents for them to be successful”.

The programme is comprehensive, based on the understanding that weed growth and spread are complex processes that are influenced by many factors, and which require a thorough understanding for optimal economic management. 

Weeds under the joint venture spotlight initially will be Californian thistle, other thistles, giant buttercup and nasella tussock – weeds that collectively cost New Zealand hundreds of millions of dollars a year in control and in lost on-farm production.

The goals of the programme will be achieved by three inter-dependent basic and applied research objectives.  These are population dynamics of weeds, weed management tools and strategies, and adapting and improving weed management practice.

December 2003

Outsmarting Californian thistle

Pasture weeds are a significant constraint to farm profitability, but a multi-disciplinary long-term integrated approach will make a big difference to their management in New Zealand.

AgResearch and Landcare Research have just formed a joint research programme that brings together a comprehensive collection of research skills in weed research.  Such an integrated approach to weed management is expected to deal a big blow to such problematic weeds as thistles, giant buttercup and nassella tussock – weeds which cost the country millions of dollars a year.

For instance, a conservative estimate of the cost of Californian thistle control and its impact on agricultural production in New Zealand is $200 million a year.

Although considerable research has already been done on Californian thistle in New Zealand, a joint approach to the problem will accelerate knowledge and potential solutions. 

AgResearch and Landcare are already working to develop a new generation of biocontrols for Californian thistle.  Dr Simon Fowler from Landcare Research and his Lincoln-based team are presently studying a new weevil called Apion onopordi,a natural thistle predator that attacks the roots of the weed. 

But the weed is a difficult one to eradicate, so outsmarting Californian thistle will be an approach that integrates several strategies.

Scientists at AgResearch Lincoln, near Christchurch, have long had a multi-pronged strategy to understanding and controlling Californian thistle.  Such approaches include more traditional pasture management, chemical herbicides and mowing, and newer methods under research including mycoherbicides, classical biocontrol.

Computer modelling

Recent years have seen a move towards understanding what drives growth, or population dynamics as it’s known, which then allows a computer model to be designed to predict weed behaviour.

Computer models designed by the AgResearch team at Lincoln help to explain Californian thistle behaviour for a given situation, and suggest optimal control tactics for that specific environment.  This gives farmers the opportunity to select the best possible combination of control options available.

Understanding weed population dynamics, and how proposed control tactics will influence these dynamics, is necessary in selecting the long-term economically optimal management strategy.

Mowing and pasture management – a research success story

If there’s one important discovery made in recent years, it has to be the value of a planned thistle control programme over several years.

Scientist Dr Graeme Bourdôt, who has been studying what drives thistle growth, established that pasture populations of this weed increase solely by the growth and spread of its creeping root system and shoot formation on these roots.  Seeds, while produced in copious quantity each year, play no role in an established pasture.  More than 95 percent of the annual seed crop is lost to predation, and seeds that do enter the soil fail to establish seedlings. 

Mowing in spring, summer and autumn defoliates the plant, which in turn limits root production and growth, reducing the amount of over-wintering root, consequently reducing the size of the new season’s shoot population.  Repeat that over three years, and root production, and hence shoot population density, is close to zero.

While that obviously only suits farmland able to be mowed, it’s still a very positive control technique.  “Because we understand the mechanism, we can confidently predict that repeated defoliation over three consecutive growing seasons will dramatically reduce, if not eradicate, a Californian thistle population in a pasture”.

“Control costs alone for Californian thistle in pasture are estimated to be $140 million a year.  The control costs on arable cropping have not been quantified.  If farmers adopt long-term control approaches, it will ultimately bring control costs down, improve returns, and provide permanent improvements to the land and the environment for future generations.”

Not only do farmers spend millions trying to control the weed Californian thistle limits pasture growth and that impacts on dairy and sheep returns.  And it also causes animal health problems such as scabby mouth in sheep and the seed heads contaminate wool.

Combining mowing and herbicide approaches with pasture management may also prove effective.  Science has demonstrated competition from pasture significantly checks thistle growth, particularly with ryegrass.

Mycoherbicides

Another recent research focus is on mycoherbicides, which exploit natural diseases of Californian thistle.  One disease that is currently being evaluated is “watery soft-rot “ caused by a fungus called Sclerotinia sclerotiorum.

Studies over the last decade have shown that particular fungus can be cultured and applied as granules uniformly across a field using a fertiliser spreader.  Under conducive weather conditions it can provide very effective thistle control in pasture within a month or two of application without the damaging effects that chemical herbicides have clovers.

Development of this product is still in its final stages, and is expected to become commercially available in 2005 for use in dairy pastures.

“Again, this form of biological weed control potentially has a very important part to play in the objective of bringing Californian thistle under control in New Zealand,” Dr Bourdôt said.