World’s first glyphosate-resistant Capeweed found in Great Southern

Shannon VerhagenCountryman
Australian Herbicide Resistance Initiative Research Associate Yaseen Kahlil with Capeweed grown for herbicide resistance screening.
Camera IconAustralian Herbicide Resistance Initiative Research Associate Yaseen Kahlil with Capeweed grown for herbicide resistance screening.

Farmers are being urged to take a “double-knock” approach to Capeweed control following the discovery of the world’s first glyphosate-resistant strain in the Great Southern.

The detection by a local agronomist in the Albany port zone has raised alarm bells, with research from the Grains Research and Development Corporation-supported Australian Herbicide Resistance Initiative revealing it to have 13 times the survival rate of normal populations.

The sprawling annual herb with ‘daisy-like’ flower heads is widespread across the country’s grain growing regions and germinates during autumn and winter, favouring false breaks.

Competing for nutrients and water, as well as inhibiting emergence, it can have detrimental impacts on crops, with 7-90 plants per square metre demonstrated to reduce grain yield by 28-44 per cent in wheat crops.

University of Western Australia based AHRI research associate Yaseen Kahlil said seeds were collected from the site and seedlings screened for resistance in Perth, with glyphosate applied at a label rate of 540 grams of active ingredient per litre.

“We recorded survival rates four times higher than susceptible control populations, which were collected from six non-agricultural sites across the WA grainbelt,” he said.

Seed from the survivors was subjected to glyphosate dose response testing and this second generation exhibited a resistance level 13 times higher than the control population.

Dr Yaseen Kahlil

It is the first herbicide resistant strain found in WA, with diquat and paraquat (Group L) resistance strains detected in Victoria and 2,4-D (Group I) in South Australia.

The AHRI screening also found glyphosate resistance was co-occurring with resistance to the ALS-inhibiting herbicide metosulam (Bayer Eclipse® 100) and to the phytoene desaturase (PDS)-inhibiting herbicide diflufenican (Bayer Brodal® Options), with survival rates of more than 80 per cent in both cases.

While no other glyphosate-resistant populations had been reported, Dr Kahlil said it was likely they did exist.

However he said there were effective control measures farmers could use to tackle it.

The good news is that a paraquat-diquat mixture herbicide (Syngenta Spray.Seed® 250) was 100 per cent effective against this resistant population, so there is a control option.

Dr Yaseen Kahlil

An integrated weed management program based on the WeedSmart “Big 6,” including rotating crops and pastures, mixing and rotating herbicides, crop topping, patch management and cutting hay in the pasture phase was also recommended.

Harvest weed seed control — one of the “Big 6” strategies — was not considered effective for controlling capeweed due to the weed’s lack of height and significant seed dispersal.

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