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On the lookout for new resistant weeds with Rohan Rainbow

Herbicide resistance is well-established in populations of several weed species across Australia but many more are at risk of evolving resistance if they are given the opportunity. Dr Rohan Rainbow says the two main risks are that new species will evolve resistance to the chemicals currently available and that weeds already known to have evolved herbicide resistance will spread to new areas.

“It is not likely that any new chemistry or modes of action will become available any time soon,” says Dr Rainbow. “We have to do whatever we can to conserve the chemistry that we have now and this must be done on a regional and farm by farm basis.”

“Weeds will continue to spread by wind and water and on vehicles and there is a significant risk that herbicide resistance can simply arrive in a region or on a farm even if farmers have been diligent with their herbicide management.”

“The weeds that are hard-seeded and can stay dormant for many years are the most difficult to control once herbicide resistance evolves,” he says


How do I know if the weeds on my farm are becoming resistant to the herbicides I use?

Short answer: Spray applications will seem ineffective.

Longer answer: After applying herbicide it is important to assess the effectiveness of the operation. Herbicide resistance usually becomes apparent as patches of weeds that ‘survive’ the application of herbicide. If you notice patches of weeds, take seed samples and have them tested for herbicide resistance. Even while the herbicides are still effective, implement strategies such as collecting and destroying weed seed at harvest, preventing seed set and rotating chemicals with different modes of action to reduce the risk of resistance evolving. Information about herbicide resistance testing is on the WeedSmart website.

Are there areas on the farm where herbicide resistance might evolve unnoticed?

Short answer: Yes.

Longer answer: Herbicide resistance may evolve in weeds that have always been present on your farm or in your district. These are likely to be noticed in-crop. Other weeds may spread to your farm or district and already be resistant to herbicides. Take notice of the plants growing along fence lines and road ways and on neighbouring properties that are upstream or upwind. Taking action across the landscape is the most effective way of reducing the economic and environmental damage associated with herbicide resistance.


Can I assess the risk of weeds on my farm becoming herbicide resistant?

Short answer: Yes.

Longer answer: On the WeedSmart website you will find the WeedSmart app and the Glyphosate Resistance Toolkit (for northern growers). These are free digital tools that farmers can use to assess the risk of herbicide resistance evolving in their current farming system. Answering a set of questions about your farming system and target weeds will highlight potential risks. Recommendations will be offered to minimise the risk of herbicide resistance. Take action early and implement the WeedSmart 10 Point Plan.

How to ask a WeedSmart question

Ask your questions about the spread of herbicide resistance, or any herbicide resistance management strategy, using this blog or using Twitter @WeedSmartAU.

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