Growers and advisers need to monitor now for suspect weed populations and control them before the weeds are too large to handle with selective herbicides or non-glyphosate knockdowns.
That’s the strong message from Andrew Storrie, Australian Glyphosate Sustainability Working Group (AGSWG) chief executive officer for growers who have been relying heavily on glyphosate for weed management.
Mr Storrie says 82 confirmed cases of glyphosate-resistant annual ryegrass have been recorded in winter grain crops including wheat, canola and pulses from NSW to Western Australia.
“This is the tip of the iceberg, as our most valuable herbicide, glyphosate, has been used for long enough to prime weed populations for resistance,” Mr Storrie said.
“More glyphosate resistant weed populations are certain to show up in 2012.
“Now the crops are in the ground and growers are getting ready for post emergent weed control spraying, it is time for action.”
The message is supported by the Grains Research and Development Corporation (GRDC) which provides funding for AGSWG and has put a high priority on managing herbicide resistance in the crop-weed population.
Mr Storrie says the problem of glyphosate resistance has been rapidly expanding across southern Australia and large areas have been dry sown making the early discovery of resistant infestations tricky.
While glyphosate resistant populations have become relatively common in eastern states in recent years, most WA growers have only had to deal with resistance to other modes-of-action to date, Mr Storrie says.
“This is all about to change as a random survey of crops in WA in 2010 conducted by Mechelle Owen, Australian Herbicide Resistance Initiative (AHRI), found seven per cent of ryegrass samples were resistant to glyphosate, which is best described as a ‘scary’ figure for a random survey,” he said.
“Most of these infestations were from the Esperance region.”
A survey of WA glyphosate-resistant canola crops in 2011 by Mike Ashworth, AHRI, collected a further eight populations while another three ryegrass populations were confirmed from NSW and Victoria.
“If there is ryegrass still alive after two applications of glyphosate in a canola crop, you have a fair indication they are resistant, but it is a good idea to get a Quick-test™ done as well for suspected problem weeds from other crops and fallows,” Mr Storrie said.
“If you know what herbicide modes-of-action still work, you can save a lot of money and stomp on the problem fast.
“Testing is important and saves wasted money on ineffective herbicides.”
Mr Storrie said testing had a four to six week turn-around, allowing growers to make decisions about controlling resistant weeds this season before they set seed creating an even bigger and more persistent problem.
“If you have run out of selective herbicides you might have to manure or hay the crop instead of taking it through to harvest.”
Mr Storrie says growers should check high risk paddocks first, such as those with a 10-year or longer history of no-till and those where fences and firebreaks have been repeatedly sprayed with glyphosate.
Patches of problem weeds will be easiest to spot when the crops are small before cereals start to tiller and canola gets cabbage-growth, he said.
For more information on managing glyphosate resistance visit the AGSWG web site www.glyphosateresistance.org.au.
PHOTO CAPTION: Glyphosate resistant annual ryegrass in stubble following an application of glyphosate.
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