Preliminary results from a Western Australian research project suggest some grain growers are under-estimating herbicide resistance levels in cropping system weeds present on their farms.

A ‘resistance estimation’ study, involving a limited number of growers and advisers, was conducted as part of a GRDC research project designed to demonstrate the value of proactively testing herbicide resistance levels for a range of key production weeds and herbicides.

“Results show that many people are confident in their resistance status assumptions for some types of resistance but not for others, and this points to where resistance testing can add the most value,” Australian Herbicide Resistance Initiative (AHRI) researcher Roberto Busi said.

“In addition, a significant number of the participants have not previously tested weeds for herbicide resistance, which is concerning as it is important to know if there are even developing levels of resistance (up to 20 per cent weed survival to full rate herbicides) in order to be aware of emerging issues and to plan accordingly.”

Findings from the herbicide resistance testing, conducted by AHRI, and results from the resistance estimation study, carried out by The University of Western Australia and CSIRO, will be presented at coming workshops for growers and advisers in each of WA’s four port zones.

Dr Busi said about 230 weed seed samples, collected from 60 grower properties across the WA grainbelt, were being tested for herbicide resistance and these growers, as well as 17 agronomists and four grower groups, were being surveyed.

Weeds tested included annual ryegrass, which most survey respondents identified as their most prevalent winter weed, along with wild radish, brome grass, barley grass and capeweed.

Dr Busi said levels of resistance in annual ryegrass remained high with more than 85 per cent of samples demonstrating resistance to Group A and Group B post-emergent herbicides.

“In addition, glyphosate resistance in annual ryegrass was found in 12 per cent of samples tested. Paraquat was fully effective in the samples tested,” he said.

“From the wild radish samples, there is significant resistance to the herbicide groups B, F and I. In brome grass, resistance to sulfonylurea (Group B) herbicides is an issue, having been identified in about 40 per cent of samples tested.”

Dr Busi will present the herbicide resistance results at the workshops, while CSIRO group leader for integrated agricultural systems, Rick Llewellyn, and UWA School of Agriculture and Environment research fellow, Fiona Dempster, will deliver the findings on where resistance testing information was found to have the most potential value in informing management decisions.

Each event will be organised by a local grower group and coordinated by a leading agronomist.

Workshops will be held at:

• Neridup Fire Shed, 2-5pm, Tuesday, June 22 – organised by the South East Premium Wheat Growers Association and coordinated by agronomist Garren Knell
• Green Range Country Club, 40521 South Coast Highway, 12.30-3.30pm, Wednesday, June 23 – organised by Stirlings to Coast Farmers and coordinated by agronomist Garren Knell
• Merredin Community Resource Centre, 110 Barrack Street, 2-5pm, Thursday, June 24 – organised by the Merredin and Districts Farm Improvement Group and coordinated by agronomist Geoff Fosbery
• Liebe Group Agricultural Research and Education Facility, Dalwallinu, 9am-12 noon, Thursday, August 5 – organised by the Liebe Group and coordinated by the Liebe Group.

Information on herbicide resistance and weed management is available via WeedSmart, which has investment from GRDC and commercial companies and delivers science-backed weed control solutions.

The WeedSmart ‘Big 6’ provides practical ways for growers to fight herbicide resistance by farming with diverse tactics within both summer and winter cropping systems.

More information: to register for these free events visit GRDC's events.