Herbicide-resistant weeds spreading on public land 31 Oct 2012

Once thought to be a problem restricted to Australia’s farms, weeds resistant to the popular chemical herbicide glyphosate have now been found across Australia along highways, railways and around buildings.

Research led by Associate Professor Christopher Preston at the University of Adelaide, as part of the Australian Government’s National Weeds and Productivity Research Program, has identified that herbicide resistance is far wider spread than first thought.

The research found that weed management practices on public lands were routinely adding to the risk of herbicide resistance developing, due largely to ignorance of the problem and alternative herbicides.

“Non-agriculture sectors where glyphosate is used exclusively for weed management have a high risk of glyphosate-resistant weeds evolving,” Dr Preston said. 

“These weeds will cause serious management difficulties for those sectors and pose a risk of spread to other areas. Weed management practices other than glyphosate need to be adopted to reduce this risk.

“And there is a need for accurate information on herbicide resistance risks and alternative management practices to be provided to weed managers in non-agricultural areas.” 

Dr Preston’s research discovered 136 glyphosate resistant populations of annual ryegrass and fleabane along roadsides from Queensland to Western Australia - this was approximately 50 per cent of all populations tested during the first-ever roadside weed survey. 

The potential problem for Australia’s public land managers is huge - Australia has 612,000km of roads considered at risk of developing weeds with glyphosate resistance.
Weeds are one of the major threats to Australia’s primary production and to the natural environment. Weeds cost Australian agriculture more than $4 billion dollars each year, including control costs and lost production.

Under the National Weeds Program, the Australian Government provided $12.4 million to Rural Industries Research and Development Corporation (RIRDC) to support more than 50 research projects, with the program ending on 30 June 2012.

The National Weeds Program supported 11 research projects which dealt directly with herbicide resistance issues and delivered new weed control measures to reduce the need for chemical treatments.

Dr Preston, who is also chair of the Australian Glyphosate Sustainability Working Group, said alternative practices need to be used to manage the risk of glyphosate resistant weeds on Australia’s public lands.

“A worrying result was the lack of formal record keeping on herbicide efficacy. There were very few examples of formal monitoring programs in place to determine the success or failure of the spray application, which could potentially delay the detection of resistance following weed control activities,” he said. 

“Nearly 60 per cent of interviewees were in the poor to moderate categories regarding their level of understanding of herbicide resistance and its development, but a 92 per cent positive response was recorded from survey respondents acknowledging that additional staff from their respective organisations would benefit from herbicide resistance training on weeds.

“Management risks were particularly high for water authorities, railways, aviation areas and local government. Conversely, private contractors and consultants and transport authorities (for example, Main Roads) nominated the lowest risk strategies on average.”

Dr Preston said many authorities were challenged by budgets that had not kept pace with inflation over the last decade, while high turnover of staff had resulted in a loss of “corporate knowledge” in the area of weed control.

He recommended the development of training programs for both authority managers and those at the frontline of weed management, as well as an encouragement of the rotation of a wider range of herbicides and weed control methods. 

“Glyphosate is an excellent herbicide that helps keep management costs down, however there are no easy replacement options currently available,” Dr Preston said. 
“The rapid development of glyphosate resistant weeds and species shift to glyphosate tolerant species will have a large impact on budgets and logistics.”

Dr Preston said further work was required to monitor the glyphosate resistance and to develop information packages for managers of non-agricultural land, specific to their region and the types of weeds they were treating.

A fact sheet with general tips for managers of roadsides and railway lines is available at