Charles Sturt University (CSU) researcher Dr John Broster said herbicide resistance in weeds was common in southern Australia and is a costly problem for the grains industry.

"Annual ryegrass has developed resistance to numerous chemicals and this research gives us insight into how resistance has evolved and how it's associated with different cropping practices," he said.

This research brought together scientists from the CSU School of Agricultural and Wine Sciences working on herbicide resistance and weed management with experts in data analysis from the CSU School of Computing and Mathematics.

It was based on the results of 4500 annual ryegrass samples collected across southern Australia in random paddock surveys and screened for resistance to commonly-used herbicides.

Using a GIS database the researchers studied the association between the extent of resistance to different herbicide modes of action, geographic distribution of resistance across southern Australia, and farming practices in particular regions.

"This research enabled us to quantify the management practices that were linked to specific resistances. For example, shires that grew a higher proportion of wheat had more Group A resistance and less Group C and M resistance than shires that grew a higher proportion of other crops."

Graham Centre plant systems research pathway leader, Professor Jim Pratley said the findings should serve as a timely reminder for grain growers.

"Herbicides are a tool for controlling weeds. Their misuse or overuse have consequences and herbicide resistance occurrence indicates that insufficient attention has been paid to the rotation of herbicide modes of action and that survivors of herbicide applications have been allowed to complete their life cycles," Professor Pratley said.