THE FIRST sign that herbicide resistance is a problem in a field is usually that the herbicide either does a poor job or fails to kill the target weeds altogether. However, for a herbicide to fail, it usually means that the number of resistant individuals ill the population has already grown to a high level.
If herbicide-resistant weeds could be detected at an early stage of development, it would enable farmers to implement control strategies while the size of the resistant population is still small, before it becomes a signiticant problem.
The Agricultural Molecular Biotechnology Laboratory (AMBL) at the Gatton Campus of the University of Queensland has recently developed a molecular marker tool that can distinguish between weeds that are susceptible and resistant to triazine herbicides.
Trials conducted on triazine-resistant canola, common groundsel, barnyard grass and blackberry nightshade showed that the test is able to discriminate between triazine-resistant and susceptible plants with 100 per cent accuracy.
The test is reliable, simple, fast and accurate and can test a large number of samples from a single paddock within a day. This enables early detection of resistant biotypes when still present in low numbers. Resistance in weeds can also be tested in cotyledon stage plants and results could be available within two days. This means that the farmer can decide if triazines can be used on that paddock or not, and still apply the herbicide spray at the optimum weed growth stage for maximum kill.
The research was conducted by PhD student Wenjie Liu and her supervisor Dion Harrison, and was supported by growers and the Federal Government through the GRDC.
The hope is that this method will be developed into a useful management tool. Similar tests are also being developed to detect resistance to other herbicide mode-of-action groups. Dr Harrison says that, while they are not in a position to offer a commercial testing service at the moment, if someone has what they suspect are resistant samples, they are welcome to contact him and send in seeds, and these will be incorporated in the research. The team would be very interested to learn of areas of suspected resistance.
Program 3 Contact: Dr Dion Harrison 07 5460 1313 email firstname.lastname@example.org