Ten new populations of glyphosate resistant annual ryegrass, including three on fencelines in South Australia and Victoria, have been confirmed in 2006. 

The national Glyphosate Sustainability Working Group (GSWG) reports the incidence of glyphosate resistance in annual ryegrass, although double last year’s, is still proportionally low, but such jumps are timely reminders for growers to adopt practices to minimise the risk of developing resistance.

The GSWG, initiated by the Grains Research and Development Corporation (GRDC) and supported by the CRC for Australian Weeds Management, aims to minimise the development of resistance to glyphosate and maximise the effective life of this key herbicide. 

GSWG member, Dr Chris Preston, University of Adelaide, maintains the register of glyphosate resistant populations in Australia. 

"All new cases are from where glyphosate was used intensively to control annual ryegrass and follows the general pattern, with 18 of the 54 current annual ryegrass glyphosate resistant populations recorded where chemical fallow is practiced," he said.

"Three of the new cases are from fencelines and five are from vineyards. In both cases glyphosate is often the only weed control used, but alternatives do exist."

In broadacre agriculture, glyphosate resistance in annual ryegrass on fencelines is a particular problem as the resistance can be moved into the cropped area by farm equipment. Farm hygiene to prevent the movement of resistance seeds is important. If resistance on fencelines is suspected, action should be taken early to stop the resistant weeds from setting seed.

The use of the double knock, effective in-crop weed control, alternative herbicides, crop topping and non-herbicide weed control techniques, such as hay and weed seed collection, can help reduce the risk of developing resistance in broadacre cropping. 

Continually using glyphosate and allowing weed numbers to increase amplifies the risk of glyphosate resistance occurring and should be avoided, if possible.

“Currently, no glyphosate equivalent is in development and even if one was found today, it would take approximately 10 years before registration was completed. It’s therefore essential growers use glyphosate responsibly to prevent glyphosate resistant weeds developing," Dr Preston said

The GSWG’s website www.weeds.crc.org.au/glyphosate/ has useful information and resources about weed management techniques to minimise glyphosate resistance. There are answers to frequently asked questions, fact sheets, information on identifying and testing for glyphosate resistance and a database of glyphosate resistant weed populations. Growers and agronomists are encouraged to visit the site and use and share the information widely.

“If herbicide resistance is suspected, samples should be tested to help future weed control decisions. Information about testing is also on the website,” he said.