NEW research shows that several weed species have grown resistant to the most widely used herbicide in farming, glyphosate.

Researcher Dr Todd Gaines of the Western Australian Herbicide Resistance Initiative (WAHRI) at the University of Western Australia, says research shows the weed species Amaranthus palmeri in the United States and Annual Rye-grass (Lolium rigidium) in Australia can become resistant to glyphosate.

UWA research is tackling the resistance of weeds to the common herbicide glyphosate / Image: Istockphoto

His paper, published in the Proceedings of the National Academy of Sciences, says a new mechanism of resistance is occurring in the weed species A. palmeri and that the same mechanism can be seen occurring in Annual Rye-grass, which grows in all wheat farming regions in Australia.

The new resistance mechanism involves the gene targeted by the glyphosate. The plant creates several copies of the gene and, as the herbicide at normal dosage levels can only attack a few copies of the gene, the plant manages to survive.

Dr Gaines says the mechanism has only been observed in a laboratory environment and not in the wild.

“It soaks up the herbicide like a sponge. Increasing the dosage will not work as you would need ten times the current dosage level and that is not economically viable.”

Current methods of coping with the situation include the additional use of other herbicides and targeted manual tillage.

According to Dr Gaines, the farmer is often not aware during the first year of herbicide resistance that other methods are required until the yield is unsatisfactory, as the herbicide is used prior to planting crops.

Glyphosate was first used in the 1970s and has been in constant common use since it is inexpensive, easy to use, and selectively targets weeds not crops.

It was originally thought that resistance to the chemical was unlikely to occur but resistance to it was first discovered in the 1990s.

Dr. Gaines says as a first step to dealing with the issue, farmers need to be warned about the dangers of over-use.

“This is good transgenic technology but we need to take care of it. Research has now shown that it is possible to develop a resistance to glyphosate.”

The WAHRI will focus its future research on solving the glyphosate resistance problem with the Australian weed species, Annual Rye-grass.

For further information, contact:
Dr. Todd Gaines: tgaines@plants.uwa.edu.au (08) 6488 7872

Reference information:

http://www.pnas.org/content/early/2009/12/10/0906649107
http://www.pnas.org/cgi/doi/10.1073/pnas.0913433107

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