Wagga Wagga, NSW - herbicide resistance in wild oats
This New South Wales scenario is set in Wagga Wagga between 2008 and 2010.
This is a barley - canola - wheat rotation with wild oats and a few annual ryegrass.
In the original scenario, all herbicides are working and all there is no harvest weed seed management (all chaff is spread out the back of the header) (see Table 3 below for management events). In the modified scenario, wild oats has almost complete resistance to clethodim (Select™, a Group A herbicide) which was sprayed once on 15/06/2009.
| Date | Management events for the original and modified scenarios |
|---|---|
| 18/04/08 | Spray: Glyphosate 450 |
| 23/04/08 | Sow: Barley, disc seeding |
| 23/04/08 | Spray: Trifluralin |
| 22/05/08 | Spray: Axial (pinoxaden) |
| 11/12/08 | Harvest: Barley harvested, 2.3t/ha of potential yield, all chaff spread/normal harvest used |
| 12/04/09 | Spray: Glyphosate 450 |
| 11/05/09 | Spray: Sprayseed/Trifluralin |
| 12/05/09 | Sow: Canola, disc seeding |
| 15/06/09 | Spray: Select (clethodim) |
| 10/11/09 | Harvest: Canola harvested, swathing used |
| 14/04/10 | Spray: Glyphosate 450 |
| 24/04/10 | Spray: Trifluralin |
| 24/04/10 | Sow: Wheat, disc seeding |
| 24/06/10 | Spray: Atlantis (mesosulfuron) |
| 11/11/10 | Harvest: Wheat harvested, 3.4t/ha of potential yield, all chaff spread/normal harvest used |
What happens when wild oats develop resistance to clethodim?
In the first scenario (Figure 5 - left and Figure 6 - top), there is no herbicide resistance in wild oats and it is controlled well. There is a reduction in yield in the canola rotation due to the dry season and late sowing (shown by the red bars - with weed competition).
In the second scenario, (Figure 5 - right and Figure 6 - bottom), the wild oats has almost complete resistance to clethodim (Select™, a Group A herbicide) but is susceptible to all of the other herbicides. There is a substantial decrease in the canola yield, followed by a reduction in the wheat yield in the following season (shown by the red bars - with weed competition).
But by looking at the plant numbers of wild oats (Figure 6) in the two scenarios, you can see that there are more wild oat plants at the canola harvest in the scenario with clethodim resistance. This led to more seed set and more wild oat plants in the wheat rotation.
What can you do once wild oats is resistant to clethodim?
There are many integrated weed management techniques that can be used (and are available in the Weed Seed Wizard). These might include:
- rotating herbicides (after doing a resistance test on the wild oats to determine which herbicides still work)
- increasing crop seeding rates for greater crop competition
- changing the crop rotation with different herbicide modes of action
- having a fallow year
- having a pastures phase with grazing
- changing the time of sowing and herbicide application
- using harvest weed seed management, for example, a chaff cart.
For more information refer to integrated weed management links in See also section or look at the Integrated Weed Management manual (External links section) and discover how they may fit into your farm.