Harvest the time to get on top of resistant weeds
With herbicide resistance an increasing problem across the southern cropping region, grain growers are being urged to get on top of the issue at harvest as part of a sustainable approach to weed control.
University of Adelaide weed management expert Dr Chris Preston says herbicide resistance has eroded many of farmers’ chemical in-crop weed control options, placing more emphasis on what they do before and after plants are in the ground.
With that in mind, he says starting to tackle seed set at harvest is a good way of leading into a long-term strategy of methodically tackling weeds through pre-emergent herbicides and depleting seed banks.
“If you don’t stop seed set, you don’t make any headway. Managing seed-set is crucial for managing herbicide resistant weeds,” said Dr Preston, whose research into herbicide resistance is supported by the Grains Research and Development Corporation (GRDC).
“Because herbicide resistance has had such a significant impact on our post-emergent weed control tactics, the combination of a pre-emergent herbicide and then coming back and stopping seed-set at the end of the season is where we’re going to have to go with a lot of our cropping rotations.
“In much of the southern region, especially in the case of ryegrass, we’ve lost our post-emergent chemical options. In the absence of post-emergent herbicides, we’ve only got pre-emergent chemical options.
“What we’re seeing is that getting the most out of your pre-emergent herbicides is essential for making the whole thing work, and then we’re looking at seed-set control. For all of your seed-set control tactics, whether it’s crop-topping, weed seed management at harvest, windrow burning or any other similar options, if you don’t have so many weeds to start with, they will work much better: you will drive your seed banks down faster.”
In 2014 and 2015, Dr Preston and his team are investigating a range of emerging herbicide resistance issues in the southern cropping region with GRDC support, including new pre-emergent herbicide options available to growers and control tactics for specific weeds like brome grass, Indian hedge mustard, ryegrass and wild radish.
He said the last several years had seen growers around Australia’s grain growing regions become more open to using non-chemical weed control options to tackle seed set at harvest, and taking a more flexible approach would be crucial for growers in implementing more sustainable cropping and weed-management strategies.
“One example of something we’ve seen is widespread adoption of windrow burning by growers around the country. We’ve also seen growers cutting really badly infested crops for hay, and 15 years ago nobody would cut a grain crop for hay, and now they will,” he said.
“That’s the changing mindset that has allowed people to get on top of their weeds, and it’s a multi-year mindset. It doesn’t take just one year: you need to fix it over a series of years.”
The GRDC and its industry partners have a broad range of resources available to growers to assist with their integrated weed management strategies:
- The comprehensive Summer Fallow Weed Management manual is available for viewing and downloading via the GRDC website at www.grdc.com.au/GRDC-Manual-SummerFallowWeedManagement or hard copies can be ordered through the GRDC’s Ground Cover Direct, free phone 1800 11 00 44 or email email@example.com.
- To assist growers with pre-harvest herbicide application to control weeds in winter crops, and post-harvest control of summer weeds, the GRDC has also produced an updated Pre-Harvest Herbicide Use Fact Sheet which is now available at http://www.grdc.com.au/GRDC-FS-PreHarvestHerbicide.
- Further information on effective weed control is available at the GRDC’s new Integrated Weed Management Hub, www.grdc.com.au/IWMhub, which has been developed specifically to help Australian grains industry advisers and growers find the latest weed research and management advice quickly and efficiently, as well as the WeedSmart website, www.weedsmart.org.au.
- For more information on herbicide resistance and management options, see GRDC’s Herbicide Resistance Fact Sheet at http://www.grdc.com.au/Resources/Factsheets/2012/05/Herbicide-Resistance.
- Guidance on pre-emergent herbicide application can be found in GRDC’s Pre-emergent Herbicides Fact Sheet at http://grdc.com.au/Resources/Factsheets/2014/10/Preemergent-Herbicide-Use-Fact-Sheet.
For further information
Christopher Preston, University of Adelaide
(08) 8313 7237
Tristan Price, Porter Novelli
(03) 9289 9555
Caption: University of Adelaide weed management expert Dr Chris Preston says harvest can be an ideal time to address herbicide resistant weeds.
GRDC Project Code UA00113, UA00121, UA00144, ICN00009, ICN00013, ICN00012
Region South, North