Glyphosate resistance an issue along fence lines

Author: | Date: 26 Nov 2010

Chris Preston

Fence lines and crop margins can be problem areas on grain-growing properties as weeds, if not controlled, grow freely in these locations.

This can lead to weed infestations moving into cropped paddocks and these weeds can also harbour pests and pose a fire risk.

It is therefore understandable why growers are keen to control weeds along fence lines and crop margins.

However, a problem can arise if glyphosate is the only tactic used to control weeds in these areas. The latest information from the Australian Glyphosate Sustainability Working Group (AGSWG), which is supported by the Grains Research and Development Corporation (GRDC), shows that there are currently 119 sites with documented glyphosate resistant annual ryegrass in Australia. Of these, 33 are located along fence lines or crop margins.

AGSWG Chairman Dr Chris Preston, from the University of Adelaide’s School of Agriculture, Food and Wine, says the main factors that contribute to glyphosate resistant weeds are: intensive use of glyphosate; lack of competition; no other effective herbicides employed; and little or no other weed control practices employed. Many fence lines fit all these criteria.

“Many growers prefer to use glyphosate alone for weed control on fence lines due to its ease of use and low cost,” Dr Preston said. “Using glyphosate as the only weed control practice along fence lines will result in glyphosate resistant weeds evolving.

“The lack of competition on fence lines and crop margins means that any plant surviving treatment will produce a large amount of seed. If this plant happens to be resistant to glyphosate, then a lot of glyphosate-resistant seed will enter the soil seed bank.”

Dr Preston said a further problem with glyphosate-resistant weeds appearing along fence lines was the ease with which seed could be moved into the cropped area with farm operations.

“As glyphosate resistant weeds are occurring along fence lines due to intensive use of glyphosate, no competition and no other effective weed control, it should be possible to reduce the risk of glyphosate resistant weeds by changing some of these practices.
“For example, where fence lines are no longer useful, removing the fence and cropping the area will provide both competition and a change in weed management practices.

“Other practices that could be employed would be mowing or slashing the weeds along the fence line, with herbicide employed only for the area immediately under the wire.

“Cropping as close to the fence line as possible and cutting a fire break late in the season will reduce the area treated solely with glyphosate.”

Dr Preston said many growers would continue to want a herbicide option to keen fence lines clean of weeds. His research has involved a number of products and product mixtures being applied to a site with a very large population of glyphosate-resistant annual ryegrass along a fence line. He said glyphosate, even at high rates, provided little control of the resistant ryegrass, while some mixtures with glyphosate were more effective.

Dr Preston and his research colleagues are continuing to assess new options for fence line weed management.

Funded by the GRDC, on behalf of growers and the Australian Government, the AGSWG is a collaborative industry initiative aimed at promoting the sustainable use of glyphosate in Australian agriculture. More information is available from the AGSWG website

The GRDC has published a new Glyphosate Resistance Fact Sheet, focusing on management of resistance on fence lines and crop margins. It is available via It can also be ordered free of charge (plus postage and handling) from GRDC Ground Cover Direct, freecall 1800 11 00 44 or email

Growers seeking more information on integrated weed management can access the GRDC’s online resource hub at


Caption: AGSWG Chairman Dr Chris Preston, from the University of Adelaide, at a glyphosate resistance trial at the Hart Field Site in SA’s Mid North.

GRDC project code: UA00104

Peter Reading is the Managing Director of the Grains Research and Development Corporation. Contact the GRDC on (02) 6166 4500 or visit

This Crop Doctor and other media products are available at

GRDC Project Code UA00104