A good, early break to the 2014 cropping season provided many Western Australian grain growers with optimal conditions to apply the ‘double knock’ weed control technique prior to seeding.
As farmers know, the ‘double knock’ technique usually involves two applications of knockdown herbicides applied at full label rates, with researchers recommending paraquat-based products be used as the second spray, to give glyphosate a break.
But with Grains Research and Development Corporation (GRDC) supported surveys indicated escalating weed resistance to herbicides including glyphosate, it is likely some weeds will nevertheless have survived knockdown sprays.
A targeted (not random) WA grainbelt survey, conducted by Sally Peltzer of the Department of Agriculture and Food (DAFWA) in 2013, found that more than 40 per cent of 172 annual ryegrass samples tested had some level of resistance to glyphosate.
So what do growers do if they find weedy patches on their farm?
Growers who find weeds surviving herbicide application should send samples to commercial services for a ‘Quick Test’ in which plants (mainly grasses) are tested for herbicide resistance.
Resistance testing can be useful in developing a plan to contain the problem, and in developing strategies to prevent the resistance evolving further.
Information about the Quick Test service is available at www.plantscienceconsulting.com.
If you suspect you have glyphosate resistant weeds on your property or roadsides, the Australian Glyphosate Sustainability Working Group (AGSWG) advises landholders to contact their local agronomist and an AGSWG representative.
Details of AGSWG representatives are available on the website www.glyphosateresistance.org.au. They can provide information and advice on sampling suspect plants for testing.
Growers who find surviving weedy patches on their farm should also prevent the surviving weeds from setting seed.
Researchers also recommend that growers develop a long-term plan to declare war on the weed seed bank using a combination of chemical, cultural and mechanical methods.
There is only one true answer to all resistance problems and that is to farm with a low weed seed bank.
Growers who take this approach are having a win.
Information about sustainable integrated weed management (IWM) practices is available at the Australian Herbicide Resistance Initiative (AHRI) website www.ahri.uwa.edu.au
For information on herbicide sustainability, visit the WeedSmart information hub at www.weedsmart.org.au. It outlines a 10-point plan - including information on testing for resistance - to help you win the battle against weeds.
Useful information is also available in the Integrated Weed Management in Australian cropping systems manual, available at www.grdc.com.au/miniIWMM