Farm Management

Time right to conduct resistance testing

Georgia Megirian - GRDC Crop Protection Officer - West
Georgia Megirian - GRDC Crop Protection Officer - West. Image courtesy of GRDC

Herbicide resistance testing of weed seeds before harvest can help grain growers identify effective herbicide options and target areas where resistant weeds need to be managed.

Grains Research and Development Corporation (GRDC) crop protection officer – west, Georgia Megirian, said this knowledge would enable growers to plan targeted, cost-effective weed management strategies for 2019 and beyond.

“It will allow growers to diagnose any resistance issues and help guide future management to limit weed infestations and prevent weed seed set occurring in the next season in the affected patches,” Ms Megirian said.

“Test results can also allow growers to understand which herbicides are still effective, including any older and often cheaper chemistries, to help inform weed management planning for 2019.

“Ultimately, the information will assist growers in using an integrated weed management (IWM) approach, and to take steps to preserve the effectiveness of herbicides that are still options for them.”

Ms Megirian said understanding the herbicide resistance status of weeds at a local level had been identified as a high priority by members of the GRDC Regional Cropping Solutions Network groups in WA.

“Results from extensive herbicide resistance surveys conducted across the WA grainbelt by the Australian Herbicide Resistance Initiative (AHRI) provide a good indication of the resistance status of western region weed populations, but knowing your local situation, at an individual field level, is also very important,” she said.

Results from the last WA herbicide resistance survey conducted by AHRI, during the 2015 harvest, are available in a GRDC Grains Research Update paper.

Also, resistance to pre-emergent herbicides from a total of three mode of action groups has recently been confirmed in Australian annual ryegrass populations.

National weed resistance surveys of growers’ paddocks have identified populations resistant to the Group D, Group J and Group K herbicides and combinations of these herbicides.

Therefore, testing for resistance to trifluralin, propyzamide, Avadex® Xtra, Boxer Gold®, Butisan® and Sakura® should be considered to understand which pre-emergent herbicides will still work on the sampled population in the future.

Ms Megirian recommended samples be taken from areas where growers suspect herbicide resistant weeds might be present – such as where spray failures have occurred.

“If a paddock contains more than one suspect area, samples from each area should be tested separately because resistances can vary across a paddock,” she said.

Testing herbicides of differing modes of action can be helpful in identifying those herbicides that are still effective.

GRDC grower relations manager – west Lizzie von Perger said a GRDC investment in WA, centred in the western part of the Kwinana port zone, aimed to demonstrate the value of growers testing for herbicide resistance in major weeds on their farms.

“The project, being led by AHRI researcher Roberto Busi, is looking at the herbicide resistance status of weeds on ‘focus farms’ and agronomic practices that can help growers deal with any resistance issues,” she said.

“A number of workshops will be held prior to seeding in 2019, at which AHRI researchers, ConsultAg staff and local growers will discuss diverse and economical on-farm practices that can help manage any local resistance issues found.

“This weeds project is one of a number of targeted western region ‘development and extension’ projects addressing grower priorities identified through extensive industry consultation, including by the GRDC Regional Cropping Solutions Network (RCSN) and GRDC Western Regional Panel.”

Source: GRDC

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