IT has been revealed that spraying glyphosate on fence lines is one of the major contributors to glyphosate-resistance on WA farms.
Grains Research and Development Corporation (GRDC) crop protection manager Rohan Rainbow said the latest information from the Australian Glyphosate Sustainability Working Group (AGSWG) showed fence lines and paddock margins represented the largest number of situations where glyphosate-resistant annual ryegrass occurred.
"There are currently 119 sites with documented glyphosate-resistant annual ryegrass in Australia and of these 33 are located along fence lines or crop margins," he said.
Mr Rainbow said many growers preferred to use glyphosate alone for weed control on fence lines due to its ease of use and low cost.
"But using glyphosate as the only weed control practice along fence lines will result in glyphosate-resistant weeds occurring which can easily spread to cropped areas," he said.
Mr Rainbow said strategies growers could use to reduce the risk of glyphosate-resistant weeds, included removing fences which were no longer useful and cropping the area, mowing or slashing weeds along fence lines with herbicide used only in the area immediately under the wire or cropping as close to the fence as possible and cutting a firebreak late in the season to reduce the area treated solely with glyphosate.
He said GRDC-supported research by the University of Adelaide in collaboration with the Hart Fieldsite Group had helped to identify effective herbicides strategies for paddock boundaries and fence lines.
"Trials showed that while glyphosate applied even at high rates provided little control some mixtures with glyphosate were more effective," he said. "Mixtures with Spray Seed or Alliance were effective as were two applications of Spray Seed, 14 days apart."
Dr Rainbow said growers needed to ensure residual herbicides were not used where they might damage desirable plants such as trees.
Australian Herbicide Resistance Initiative (AHRI) extension agronomist Neree Martinez said AHRI's last herbicide resistance survey completed in 2003 showed there was widespread resistance to ryegrass throughout the State particularly in the northern agricultural region.
"A total of 67 per cent of populations displayed resistance to the group A herbicide diclofop and 88pc of populations were resistant to the group B herbicide sulfometuron, while 24pc of populations were developing resistance to trifluralin and eight per cent of populations were developing resistance to clethodim," Ms Martinez said.
Ms Martinez said populations were considered to be resistant if more than 20pc of the population survived the herbicide and if it was less than 20pc the AHRI studies considered it to be developing resistance.
According to AHRI senior research officer, Mechelle Owen, a just-completed survey on 2010 figures was likely to reveal group A and B resistance will be the same if not higher than last time.
"Whereas we expect both trifluralin and clethodim to be significantly higher, we also expect to see that clethodim resistance will now be widespread throughout the State whereas in the last survey it was more confined to the northern agricultural region," Ms Martinez said.
AHRI would continue to monitor for glyphosate resistance in the GRDC-funded survey and growers should be aware of the increased number of cases of glyphosate-resistance which occurred in the Eastern States along roadsides, fence lines and firebreaks.
She also said growers should understand that using glyphosate as the only means of control on fence lines and firebreaks will lead to the development of glyphosate resistance.
Ms Martinez also advised that Integrated Weed Management should be applied to all parts of the paddock including fence lines and firebreaks because resistant weeds on fence lines, roadsides and firebreaks could quickly spread into cropping paddocks.
"Glyphosate is not limited to broadacre agriculture, there are more cases of glyphosate resistance being reported from horticulture, viticulture and roadside locations including railways," Ms Martinez said.
The GRDC Glyphosate Resistance
Fact Sheet is available at www.grdc.com.au/GRDC_GlyphosateResistance or www.grdc.com.au/ weedlinks.
