Roadsides the next frontier for glyphosate resistant weeds

Glyphosate resistant annual ryegrass has recently been confirmed along several kilometres of roadside in semi-rural South Australia. This roadside, like much of Australia’s 810,000 kilometres of roads, has a 20 year history of using glyphosate alone for weed control. More cases of glyphosate resistance are likely if management practices don’t change.

This is the first recorded case in Australia of a weed becoming resistant to glyphosate due to roadside management practices and is a highly significant discovery. The infestation was first observed in 2008 and seed was collected and tested for resistance at the University of Adelaide.

The herbicide glyphosate plays a critical weed control role in all parts of Australian agriculture as well as other sectors of the community including roadsides, railways, parks and gardens and environmentally sensitive areas.

Over-reliance on glyphosate for control leads to weed populations being dominated by resistant individuals, with the herbicide no longer effective. Weed seeds then spread to other areas by water, wind and machinery creating problems for roadside management and adjacent landholders.

Currently there are glyphosate resistant populations of annual ryegrass, awnless barnyard grass, and liverseed grass in Australia. Overseas there are another 4 grasses and 8 broadleaf weed species that have developed resistance to glyphosate.

“Although the South Australian infestation was first noticed in 2008 it had clearly been there for some time for it to have spread so far” said Associate Professor Chris Preston, Chair of the Australian Glyphosate Sustainability Group. “Roadsides are routinely treated with glyphosate herbicide alone with few other effective weed control techniques being used, which should be ringing alarm bells with roadside managers”.

Associate Professor Preston says authorities, councils and communities must start looking at a range of roadside weed management techniques to prevent the development and spread of glyphosate resistant weeds along roadsides and movement into other sectors of the community.

Associate Professor Preston believes more planning needs to go into roadside vegetation management to prevent the development of glyphosate resistant weeds, while meeting road safety requirements.

“Preventing the seed set of those weeds surviving the herbicide application is critical to the management of herbicide resistance,” stated Professor Preston. “This applies as much to roadside weed management as it does in farming.”

Anyone suspecting glyphosate resistant weeds should contact their state expert with details available from the Australian glyphosate Working Group web site -

The Australian Glyphosate Sustainability Working Group, which is supported by the Grains Research & Development Corporation and sponsored by Syngenta, has a web site with all the information you wanted to know about glyphosate resistance including a register of glyphosate resistant weed populations as well as guides and links for management of glyphosate resistance in different industries.

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