It's not hard to get glyphosate resistant weeds on your farm, according to Chris Preston, from the Cooperative Research Centre (CRC) for Australian Weed Management at the University of Adelaide.

"Just use glyphosate intensively, conduct no tillage and use no other herbicides," Dr Preston says.

"Confirmed glyphosate resistance has occurred at 40 different sites in Australia and it's likely others haven't been formally reported.

"Resistance to glyphosate has occurred in cropping, horticulture and non-cropped areas, but the large number of populations recorded from chemical fallows illustrates risks that this type of glyphosate use poses for resistance.

"The factors that all these sites have in common are intensive use of glyphosate - every year or multiple times a year, often for 15 years or more - heavy reliance on glyphosate for weed control and little or no tillage."

Dr Preston will link up with NSW Department of Primary Industries (NSWDPI) weeds agronomist Andrew Storrie to lead a session on glyphosate resistance at Grains Research Updates for advisers and leading farmers at Dubbo and Goondiwindi over the next few weeks,

The Grains Research and Development Corporation (GRDC) works with the NSW and Queensland DPIs, CSIRO, universities, agribusiness and grower bodies to organise annual Updates and communicate the latest research results.

With the widely used glyphosate the key to environmentally friendly, conservation farming systems, reducing the risk of resistance development is one of the leading topics at Dubbo and Goondiwindi.

Dr Preston says that, although glyphosate has proved so far to be very robust with respect to resistance, it is important to understand where and why glyphosate resistance has occurred to prevent it developing in other areas.

"Any cropping system that has heavy dependence on glyphosate for weed control, few other herbicide options, no tillage and few other weed control options is at risk," he says.

"Experience in Australia shows that it takes about 15 years of glyphosate use for resistance to evolve, but experience in the United States demonstrates that, where the farming system is 'high risk', it is possible to get resistance earlier through seed movement if a neighbour has already got resistance.

"It's impossible to accurately predict which weeds will get glyphosate resistance next, but it is more likely in annual weeds that are widespread, are regularly controlled by glyphosate and have short-lived seed banks."

The Grains Research Updates for advisers and leading farmers will be held in Dubbo on February 22 and 23 and in Goondiwindi on March 8 and 9.

The Crop Doctor, Peter Reading, is managing director of the Grains Research and Development Corporation (GRDC), Canberra.