Northern barley grass has been confirmed as resistant to key herbicide glyphosate on the Yorke Peninsula, the first location in Australia, and the University of Adelaide’s associate professor of weed management Chris Preston said the discovery was a concern for the industry’s farming practices.
Barley grass plants that had not yet reached flowering, 20 centimetres in height, were found along a property’s fenceline near livestock yards, and researchers were alerted by the farmer.
Dr Preston said it was first located in 2016 but extensive testing and seed propagation was needed to confirm the type of resistance present.
The farmer managed the resistant barley grass with an application of Paraquat-based herbicide, but researchers were left a small amount of barley grass to test. Dr Preston said because plants needed to be grown out to set seed, it extended the time taken to confirm resistance.
“Barley grass has already been confirmed as resistant to herbicide groups A, B and L, so we needed to make sure the resistant result was accurate,” he said.
“When we get our first example of a weed species that is showing resistance we take it through to seed, then spray those and test the new seed to be really confident – plants only set seed once a year.”
Dr Preston said the weed was hard to manage because the seeds were a lot more mobile than other species.
“It moves into cropping areas easily with equipment, livestock and people,” he said.
“We are running out of options to control it and the minimal pre-emergent chemistry which can be used in some crops is also causing an increase in barley grass populations.”
Australian Glyphosate Sustainability working group executive officer Andrew Storrie, Albany, WA, said the resistance was damaging to growers because the chemical was under two pressures, biologically and politically.
“If we lose glyphosate because of consistent use without the addition of other strategies, the chemical cupboard is getting pretty bare,” he said.
Mr Storrie wants farmers to be more inquisitive.
“Instead of just continuing to spray, stop and ask why plants are not dying,” Mr Storrie said.
“Glyphosate is the linchpin for no-till farming and it has brought a host of benefits including higher crop yield. If we have to go back to cultivation because of chemical resistance that will be disastrous for farming systems across Australia,” he said.
Instead of just continuing to spray, stop and ask why plants are not dying.
- ANDREW STORRIE
YP producers have a cause for concern according to YP Ag agronomist Chris Davey, but through the use of existing management tools for other weeds, growers can manage barley grass.
Mr Davey said barley grass was considered the third most obnoxious weed on the YP, behind brome grass and wild oats, but it would rank higher for mixed enterprises because of wool contamination during spring.
“In the short-term not much will change in management but it is another example of how constant applications of glyphosate can induce resistance in a weed population,” he said.
“It is a timely reminder that everyone needs to rotate their chemical group usage at this time of year.”
Dr Preston there was no evidence to suggest the population had spread and local growers were told about the resistance at GRDC updates earlier this year.
“We have recently collected samples in the area to be tested soon,” he said.