Weed survivors could signal resistance issues

Growers urged to test weed survivors for herbicide resistance

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Adelaide University researcher Peter Boutsalis at a brome grass trial site at Balaklava, South Australia. PHOTO Rebecca Barr

Adelaide University researcher Peter Boutsalis at a brome grass trial site at Balaklava, South Australia. PHOTO Rebecca Barr

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Southern region growers have been urged to send in-season weed survivors for testing.

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Grain growers in Victoria, South Australia and Tasmania who detect weeds that have survived herbicide applications are encouraged to have those weeds tested in-season for herbicide resistance.

Research scientist Peter Boutsalis says screening of weeds during the winter crop growing season to determine their resistance status provides growers with valuable information about the effectiveness of herbicides on target weeds, potentially preventing the costly use of ineffective herbicides and reducing the spread of herbicide resistance.

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A 'Quick Test' - the only in-season test of its kind in which plants (grasses and some broadleaf weeds) are tested for herbicide resistance (or susceptibility) - can assist growers in understanding the extent of resistance on their properties.

"The Quick Test works on plants from seedlings to advanced tillering, as long as the plants are green and healthy," says Dr Boutsalis, who conducts research into herbicide resistance as part of a GRDC investment.

"The test usually takes about four weeks to complete, provided the weeds received are in good condition."

The Quick Test works on plants from seedlings to advanced tillering, as long as the plants are green and healthy. - University of Adelaide and Plant Science Consulting research scientist Peter Boutsalis

Location details

Dr Boutsalis, of the University of Adelaide and Plant Science Consulting, says it is important to provide accurate details about the location from which weeds were collected for sampling during registration for the test.

"Growers should collect 50 to 100 plants per paddock, aiming to collect 20 plants per herbicide test - fewer plants are needed if they are tillering," he says.

"After carefully pulling out plants, soil should be shaken from the roots and it is also critical that growers do not wash or wet plants.

"They should be placed in a small plastic sandwich bag or wrapped in cling wrap."

GRDC has produced a video with University of Adelaide weed researcher, Chris Preston, outlining how to take a sample for Quick Test services.

More information about the Quick Test service, including a video on how to prepare and send samples for testing, is also available on the Plant Science Consulting website.

Herbicide resistance is a priority issue for southern region grain growers, as identified by the GRDC Southern Region Panel and the GRDC Southern Regional Cropping Solutions Network.

Annual resistance surveys conducted by Dr Boutsalis and his colleagues through a GRDC research investment have shown concerning levels of herbicide resistance in some weed species in many parts of the southern cropping region.

"The surveys provide resistance status information on a regional basis, informing growers' integrated weed management strategies," Dr Boutsalis says.

"In-season testing of weeds that growers suspect are resistant adds another layer of knowledge to support growers in combating the spread of resistance and extending of the longevity of existing chemistries, and the employment of effective chemical and non-chemical weed control tactics."

Information about herbicide resistance and weed management is available via the GRDC's Integrated Weed Management hub and the GRDC-supported WeedSmart resource centre.

More information: Peter Boutsalis, Plant Science Consulting, 0400 664 460

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