For all survey populations, the results have been classified into three categories for comparisons between surveys:
- Susceptible populations were classified as those having 0% plant survival,
- Resistant populations were classified into two groups, those having between 1 – 19% survival and,
- Those resistant populations with greater than 20% plant survival.
This generally reflects a management relevant system of classification, as farmers often visually recognise resistance at a level of around 20% survival, at which point they may stop using the herbicide or consider alternative management options. Known susceptible and resistant biotypes were used as controls in all experiments.