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Wise up to your weed status

Landholders are urged to monitor the effectiveness of herbicide sprays and to act quickly to test surviving patches of weeds for resistance.

Dr Michael Widderick, Department of Agriculture, Fisheries and Forestry Queensland (DAFFQ) principal research scientist says knowing the status of weed populations may surprise some farmers but allows them to devise a better weed management strategy.

“Herbicide resistance testing is very important; you need to know what herbicides are still effective on the weeds you are trying to control,” Dr Widderick said.

“For example, if you’ve been relying on glyphosate for a number of years to control awnless barnyard grass and you find it’s not working as well as it used to and leaving patches of survivors, testing samples can give you a better picture of what herbicides are and aren’t working.

“From there you can devise a strategy for stopping seed set but if you apply herbicides that are not effective you might as well pour your money down the drain.”

There are two testing services available in Australia: Charles Sturt University (CSU), Wagga Wagga, NSW predominately tests weed seed samples; and Dr Peter Boutsalis’s Plant Science Consulting in South Australia tests both seed and plant samples.

Dr Widderick advises farmers who are concerned or already experiencing herbicide failures in-paddock to collect seed from the suspected resistant patch or across the paddock in order to evaluate a range of different herbicides on their efficacy in controlling the weed species.

“If you’ve had a herbicide failure you’ll often see patches of weeds that survive so collect seeds from several plants,” he said.

“For a species such as barnyard grass, for example, you’ll need to collect about two tablespoons of viable seed. You’ll know they are if viable if they fall off the barnyard plant quite easily.

“Collect the seeds and place them in an envelope or paper bag, but not in something that will sweat and keep the seed moist, and send for testing.”

The Quick Test is a plant test predominately used for grass weed species such as awnless barnyard grass.

“Collect plants that are between the early to late tillering stage. About 50 to 100 plants will need to be pulled up, quite a large number,” Dr Widderick said.

“Wash off the roots and wrap in a moist but not drenched paper towel, put those samples in a plastic bag to retain the moisture and send it to the testing service.”

DAFF weed researchers have teamed with the Northern Grower Alliance (NGA), funded by the Grains Research and Development Corporation (GRDC), NSW Department of Primary Industries, Tamworth to launch a survey of awnless barnyard grass glyphosate resistance levels.

An alarming 50 per cent of populations tested in the pre-glyphosate application random sample were resistant to glyphosate, Dr Widderick said.

A second survey was done following the treatment of glyphosate and survivors were gathered.

“From that survey we found that 90pc of the populations came back as having glyphosate resistant plants,” he said.

The next step is to explore further the level of resistance within these populations and extend the survey to cropping areas in western NSW and Queensland and into Central Queensland.

“We always suspected there were barnyard grass populations with high levels of glyphosate resistance but to get 50pc from that first survey was quite alarming because we didn’t expect it to be that high,” Dr Widderick said.

The recommendation to test for resistance is an important part of the WeedSmart campaign which aims to galvanise the Australian cropping industry against herbicide resistance.

WeedSmart brings together industry organisations including GRDC, research providers and major crop input firms to deliver the message that herbicide resistance is a difficult but not insurmountable problem – but changes need to occur on-farm.

For more information on testing services, visit or

For more information on herbicide sustainability practices, visit

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