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Herbicide resistance is a global problem

Like Canadians, Australian farmers are planning their strategies to manage herbicide resistance

Troy Missen stands beside his single disc planter. Low soil disturbance is a key part of his ryegrass management strategy.

Andrew Morrison’s family bought their farm, southwest of Melbourne, Australia, in 1910. His family home is built from bluestone, a volcanic rock used by earlier generations to construct buildings and fences.

Morrison’s farm was originally a livestock operation. After a drought in 1982, the Morrisons started continuous cropping. These days it’s a mixed farm, with about 4,500 acres of cropland and crossbred sheep. Gum trees edge the crop and pastureland. Morrison’s always wanted a legume to slide into his canola, wheat and barley rotation, he says, and fababeans seem to fit.

If there’s an early “break” (Australian farmer slang for seasonal rains), Morrison will sow red wheat in March or early April to graze sheep before harvesting. Otherwise, fababeans and canola go in by April, followed by the rest of the wheat and barley.

Harvest begins in November or December. “So if all goes well we usually finish by Christmastime,” says Morrison.

Morrison contends with many of the same problems that have plagued farmers since they first planted wheat. They all get frustrated by difficult seasons, he says.

Andrew Morrison poses in his canola field. Morrison’s farm has been in the family since 1910.
Andrew Morrison poses in his canola field. Morrison’s farm has been in the family since 1910. photo: Lisa Guenther

“We’ve had a run of very dry years over the last 15 years. We’ve probably had normal years a couple of times out (of that),” he says. Normally 18.5 inches of rain fall on his sandy loam. Since the soil is susceptible to wind erosion, he’s gone with zero till since he first started cropping.

And, of course, like every farmer before him, Morrison deals with weeds. But these days he’s facing a very modern problem: herbicide resistance.

Resistance is an Australian problem

Australian farmers are facing weed species that are resistant to “three, four, five modes of action,” says Stuart McLaverty of Bayer CropScience. McLaverty, who manages Bayer’s broadacre, rice and seed treatment portfolio, is giving us an overview of Australian farming in Bayer’s Melbourne office.

Some growers have one or two modes of action left to control certain weeds, he adds. In fact, Australia only has three chemical groups with no known resistance, although McLaverty cautions that’s not the situation on each farm. It means there’s at least one weed population with resistance to one or more modes of action.

Bayer is working on a Google map to pinpoint resistant weed populations, based on data from Australian researchers, he says. “What we’re trying to do is to highlight to the guys that it’s not just a neighbour’s problem. It’s an Australian problem,” says McLaverty.

Australian farmers face a host of resistant weeds, including everything from wild oats to wild turnip. But topping that least wanted list is annual ryegrass, with over 20,000 sites reporting ryegrass resistant to Group 1 herbicides. Ryegrass has also developed resistance to six other chemical groups to varying degrees, including over 20,000 sites with Group 2 resistant weeds.

Back on Andrew Morrison’s farm, Paul Crack, sales manager with Bayer, picks up a clump of ryegrass, pointing out the purple at the base of the stem.

Annual ryegrass, freshly plucked from one of Andrew Morrison’s canola trials.
Annual ryegrass, freshly plucked from one of Andrew Morrison’s canola trials. photo: Lisa Guenther

Morrison knows he has resistant ryegrass. Raised beds, once used to try to reduce water-logging, “stirred up” the ryegrass, says Morrison. Post-emergent herbicides don’t control it anymore. Triazine Tolerant (TT) canola isn’t an option because of ryegrass — any time he’s went back to it he’s “always hit the wall,” and regretted it, he says.

But genetically modified varieties, only allowed in Victoria since 2008, have helped, he says. Morrison was an early adopter of GM canola, and he can’t see why more farmers haven’t adopted Roundup Ready canola. After seeding RR canola in all his fields with ryegrass issues, he saw a 50 per cent yield jump and a bump in oil content, he says.

“Everything was good about it. And we had this clean paddock. Fantastic,” he says. This year he used RT (glyphosate and triazine tolerant) canola to clean up a bad paddock of radish, to great success, he says.

Old fences, made of bluestone, line paddocks on the drive from Morrison’s place to Troy Missen’s farm, a couple of hours southwest of Melbourne.

Much of the landscape in this part of Victoria is flat, with distant (inactive) volcanoes visible on the horizon. As we get closer to Missen’s farm, we see heaps of earth in fields. Paul Crack explains they’re remnants of old gold mines.

Missen is off working cattle when we pull into his yard. A few minutes after a quick call to his cell we hear his ATV roaring from the field.

When it comes to ryegrass, Missen’s ditched post-emergents, too. “It’s all about knock downs and pre-emergents for us,” he says of his herbicide regime for ryegrass.

But you’ll find a key part of his ryegrass strategy in an unlikely place — the machinery shed. There sits his single disc planter. The machine’s key strength, says Missen, is that it is low disturbance.

“Ryegrass loves to be buried, loves to have soil thrown on top of it because then it just keeps coming up. And it comes up later in the season in-crop,” Missen explains. No effective post-emergents mean any in-crop ryegrass is a problem.

Missen’s land has been in minimum tillage for seven years, he says. He also practices controlled traffic farming, calling it a “no brainer.” He still has ryegrass. But because it’s not buried, it germinates earlier in the year and the early herbicide applications hit it.

While the conventional wisdom is that narrower rows mean more crop competition and better weed suppression, Missen has taken the opposite approach. Wider rows mean less soil disturbance, he says, which is good for suppressing ryegrass.

Gum trees and canola are features of Andrew Morrison’s farm in Teesdale, Victoria. After the drought of 1982, the Morrisons started a continuous cropping regime.
Gum trees and canola are features of Andrew Morrison’s farm in Teesdale, Victoria. After the drought of 1982, the Morrisons started a continuous cropping regime. photo: Lisa Guenther

When GM canola came in, Missen didn’t think they needed it. But he’s found it works well as part of his weed management strategy. Thirty to 40 per cent of his rotation is legumes, so he has to watch his chemistries. He doesn’t grow a lot of canola right now but it’s an important crop on his farm, he says.

Missen seems optimistic that he can handle herbicide resistance on his farm. He has less ryegrass now than he did when he switched to the disc drill, he says. And this year, he had a couple of paddocks where he says he was able to skip the pre-emergent herbicide entirely.

Morrison also hits weeds with everything he can. He funnels chaff into windrows and burns it, to kill any weed seeds. He’s going to try spray-topping canola — applying herbicide to stop in-crop weeds from going to seed. He uses the “double knock” — glyphosate followed a few days later by paraquat to burn off any surviving weeds.

He’s starting to see the first hints of glyphosate resistance, so he’s also moving away from Roundup. During our visit he recites the herbicides that he can use on different crops — a list of Australian brands that, when I look up their chemical names, come from several different chemical groups.

He’s not particularly scared of herbicide resistance, says Morrison.

“I don’t think we’ve got to the stage where we need to go out of cropping to a pasture phase. We hope that we’ll be able to continue our rotation with cropping,” he says.

About the author

Field Editor

Lisa Guenther

Lisa Guenther is field editor for Grainews based at Livelong, Sask. You can follow her on Twitter @LtoG.



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