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Herbicide resistance is manageable, says Australian expert

GREENSBORO, N.C. — Long before herbicide-resistant weeds were making headlines in the U.S., Australian wheat producers were taking steps to solve the problem.

Stephen Powles, weed expert and professor of plant biology at the University of Western Australia and the director of the Australian Herbicide Resistance Initiative, recently spoke at Syngenta’s headquarters on diverse weed management options.

“Basically what’s playing out here in the U.S. is similar to what played out with in Australia some time ago,” he said. “It wasn’t glyphosate. It was a different set of circumstances, but big-time resistance occurred in Australia from 1990 or so on.”

The herbicide resistance in Australia came about when the country was transitioning land from primarily large sheep farms to crop production.

“Wool was the big industry. There were a lot of sheep, and the profitability went out of that when people stopped wearing wool,” Powles said. “We planted ryegrass coast to coast when the sheep was king.”

As the wool industry declined, wheat became the major crop and high densities of ryegrass had to be removed.

Powles said to transform the pastures to cropland, one herbicide chemical was used “with no diversity in the system — and, of course, you get an evolution of resistance in the ryegrass.”

“As you contrast that to the U.S., it’s where the whole south and the Midwest got covered in one great big glyphosate field,” he said.

“So we got big-time resistance in the 1990s onward, and it has multiple resistances across several herbicides, so you couldn’t just reach for another jug to fix the problem. We just had to change our ways, and the U.S. farmer hasn’t learned that yet.”

In an interview with AgriNews , Powles said there were multiple strategies Australian farmers used to control resistant weeds.

“The first thing is the herbicides remain the single-best tool. The herbicide is the bit of crucial technology, but you can’t just rely on it, so we had to diversify our system,” he said.

“We had to never keep using the same chemical. We had to rotate crops. And we had to put some non-chemical tools in there that made sense.”

Diversity and not relying on any one herbicide are recommended, but make sure the strategies are within an economic reality.

“You might like to do something, but if you can’t do it profitably, you can’t do it,” Powles said. “As an example, we always use a pre-emergent residual herbicide — those that still work. We always use a burndown, but we wouldn’t rely just on glyphosate. We’d rotate it.

“The big thing that we do is at the end of the season we have some techniques to kill weed seeds during harvest time. That’s something no one does here.”

Harvest weed seed control provides an opportunity to target future weed populations. Problematic weed species are prolific seed producers capable of establishing a large viable seed bank in just one season.

However, very high proportions of weed seed are retained in upright stems and tillers of the weeds at crop maturity. This creates the potential to target these seed during harvest, thus restricting the inputs to the weed seed bank.

One method of weed seed control is with a chaff cart towed behind the headers during harvest to collect the material as it exits the harvester. The material is then either burned after harvest or used as a feed source for livestock.

Another option used in Australia is the Harrington Seed Destructor that collects the chaff behind the combine and destroys any weed seeds present. The nonviable weed seeds the exits the harvester.

“There are a range of techniques that we do to try to stop the weeds from producing seed,” Powles said.

Another option would be returning to the days of walking fields with hoes. During his recent visit to central Illinois, Powles said he heard of hand crews performing their own harvest weed seed control by chopping weeds at a cost of between $30 and $100 an acre.

“We have a range of mechanical ways of doing that,” he said.“I’m sure U.S. farmers are going to become much more familiar with all those sorts of things over the next few years.”

The key to all weed management is multiple modes of action and more.

“Don’t get me wrong. I love herbicides. I think herbicides are the absolute best way to control weeds. But they’re not much good when they don’t work,” Powles said.

“So the only way to insure they continue working is to use as much diversity as makes economic sense. I find that here in the U.S. pretty much the creativity is confined to one herbicide can I fix this problem with.

“‘Oh, I’ve got a problem. I have glyphosate resistance.’Well, what herbicide can I use to fix the problem when in fact the better question is how can I make my herbicide use sustainable in the long term.

“That just involves thinking about all of the possibilities. What good agronomy can you do? We keep seeing these very wide row soybeans. I bet the weeds love that.

“Some agronomic things will have a big impact. One of the problems right now is that the U.S. farmers don’t fear the weeds. They don’t have much respect for them. Well, a couple million years of evolution and they’re a pretty formidable opponent.

“I’ve learned to respect these weeds. You get something like waterhemp or pigweed, it’s a formidable opponent. You better be using all the control tools at your disposal if you want to get on top of plants like that.

“You should fear them and respect them because if you use any single tool against them, they’ll overcome it.

“I just spent a week in Illinois. What fabulous crops. What fabulous cropping country. What fabulous soils. They’re not going to stop farming, but they’re going to have to be more creative than they have been. And they can do it. That’s the main thing.

“Resistance is entirely a manageable problem. No need to get depressed. Just get on it and start handling it and don’t just rely on the next chemical.”

The original article was published by Agrinews.

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What to expect at WeedSmart Week 2021

Big 6 at WeedSmart Week 2021 – Double knock to protect glyphosate
The WeedSmart Forum is set for Tuesday 17 August, 2021 at the Civic Centre in Esperance WA. The program features growers, agronomists and researchers discussing ways to use the BIG 6 to beat crop weeds. You can register for the 3-day WeedSmart Week event here.
Greg Warren from Farm and General in Esperance will be sharing his thoughts on the control of weeds like summer-germinating ryegrass, marshmallow, fleabane and portulaca.
He says the growers around Esperance are tackling glyphosate resistance in annual ryegrass, along with brome and barley grass and other emerging weeds using a range of integrated control tactics. The double knock plays a key role in preserving glyphosate (and soil moisture) and providing a clean seed bed for planting crops.

Big 6 at WeedSmart Week 2021 – Increase crop competition
WeedSmart Week 2021 is set for Tuesday 17 to Thursday 19 August, 2021 in and around Esperance WA. The last two days feature local growers hosting visits to their farms and discussing how they use the BIG 6 to beat crop weeds. You can register for the 3-day WeedSmart Week event here.
One of the farms hosting a visit during WeedSmart Week is Warrakirri’s 12,800 cropping operation at Condingup. Farm manager Con Murphy has implemented a variety of tactics to combat their main weeds – annual ryegrass and wild radish. Since 2015 the farm has undergone an intensive soil amelioration program to improve the drainage and ameliorate the sandy soils across the farm.
Con says the benefits have been seen in better germination and establishment that sets their cereal, pulse and canola crops up to compete strongly with weeds. There is also a benefit at the end of the season where rain in August or September enters the soil profile without causing waterlogging, and providing a better finish for their crops.
Since 2016-17 about 80% of the farm has been ripped and a portion has been ripped 2 or 3 times because the sandy soils tend to slump after substantial rainfall events, recreating the hardpan.
Con will be showing the WeedSmart tour group how their ripping, drainage, liming and spading program has helped grow more crop and less weeds!
Listen to the podcast with Warrakirri’s Con Murphy talking about the impact of improved drainage on crop competition

Big 6 at WeedSmart Week 2021 – Implement harvest weed seed control
The WeedSmart Week machinery display is set for Wednesday 18 August, 2021 at Dave Campbell’s shed near Esperance WA. The 3-day WeedSmart Week program features growers, agronomists and researchers discussing ways to use the BIG 6 to beat crop weeds. You can register for the 3-day WeedSmart Week event here.
We’ve saved the harvest weed seed control discussion for the machinery session on Wednesday 18 August. Ben White from Kondinin Group will host the machinery session with spray and harvesting gear on display including impact mills from Seed Terminator, Redekop and iHSD (both hydraulic and belt-driven), Emar chaff deck, and spray technologies including Goldacres’ G6 Crop Cruiser series 2, and weed detection technologies using drones and weed identifying cameras (green on green).
Ben White, Kondinin Group (Photo: Melissa Powell, courtesy of GRDC)
Growers doing the WeedSmart Big 6
WeedSmart Week 2021 is set for Tuesday 17 to Thursday 19 August, 2021 in and around Esperance WA. The last two days feature local growers hosting visits to their farms and discussing how they use the BIG 6 to beat crop weeds. You can register for the 3-day WeedSmart Week event here.
One of the growers who will open up their farm for a visit is Adrian Perks who farms at Condingup, 70 km north-east of Esperance. Adrian runs a continuous cropping program on his 4300 ha property, growing canola, wheat, barley, faba beans and lupins. This diverse rotation allows him to mix and rotate both chemical and non-chemical weed control tactics. Over half of Adrian’s farm is sandplain, on which he has implemented a soil amelioration program to address non-wetting to increase the competitiveness of his crops. He currently uses chaff decks for harvest weed seed control and is introducing an impact mill this season. Adrian monitors the tramtracks for weed growth and if he feels the weed pressure is too high, he uses a shielded sprayer to reduce seed set. The bus tour will include four farm visits and a machinery display.
Listen to Adrian on the Regional Update podcast.
Adrian Perkins, Condingup WA


WeedSmart agronomist set to tackle high rainfall zone weeds

Every locality has its own spectrum of weeds, and growers face different opportunities and challenges regarding the control tactics they can employ.
The WeedSmart Big 6 approach is a practical way to ensure that an integrated weed management program is put in place that disrupts weed seed production and the evolution of herbicide resistance.
Commencing in January 2021, Jana Dixon has joined the WeedSmart team of extension agronomists, with a focus on applying the Big 6 to manage weeds in the high rainfall cropping systems of southern Australia – from Esperance in WA to south-eastern SA, Tasmania and south-western Victoria.
Jana will add to the dedicated and experienced extension agronomists on the WeedSmart team with Peter Newman in the Western region, Chris Davey in the South, Greg and Kirrily Condon in the East and Paul McIntosh in the North.
Jana Dixon has joined the WeedSmart team of extension agronomists, with a focus on applying the Big 6 to manage weeds in the high rainfall cropping systems of southern Australia – from Esperance in WA to south-eastern SA, Tasmania and south-western Victoria.
Jana hails from the Mid North of SA, and began working at Pinion Advisory (previously Rural Directions) while she was studying agriculture at the University of Adelaide. She has been employed full-time at Pinion Advisory since January 2019 as an agribusiness consultant, based in Clare, and spends most of her time delivering agronomy and farm business advice to clients from a wide range of cropping regions in South Australia.
Pinion Advisory is a foundation WeedSmart sponsor and Jana has been involved in two WeedSmart Week events already – the first as a participant and grower group organiser at the Horsham event in 2019 and then as the local organiser for WeedSmart Week 2020 in Clare.
In welcoming her to the WeedSmart team, program manager Lisa Mayer says Jana brings energy, commitment and insight to deliver communications focussed on the southern region’s high rainfall regions.
“Growers in the southern high rainfall zones are facing some serious issues with herbicide resistance influencing their farming decisions,” says Ms Mayer. “Jana will be engaging with agronomists, growers and researchers in each of the distinct high rainfall zones to understand the complexities and look for practical ways to apply the WeedSmart Big 6 in various cropping scenarios.”
“We plan to deliver WeedSmart Week in Esperance, part of Western Australia’s high rainfall cropping zone, in August 2021 and Jana will play a key role in the planning and delivering of our annual 3-day flagship event.”
Jana says her experience with the WeedSmart program has been very positive and she has been particularly impressed with the support the program has from all sectors of the grains industry.
Newly appointed WeedSmart extension agronomist, Jana Dixon (green cap) leading discussions with farm visit host, Ben Marshman, Owen SA, and growers and agronomists attending WeedSmart Week 2020 in Clare.
“I have spoken to many growers and agronomists who have found real value in the information that the WeedSmart program delivers,” she says. “For many it is as much about considering another operator’s philosophy on dealing with weeds, and taking a fresh look at their own systems, rather than just learning about a new tactic or the traits of a new herbicide in isolation from the big picture.”
She says the high calibre of industry people who contribute their time and expertise to the program is testament to the value WeedSmart has to agribusiness, growers, agronomists and researchers alike.
In taking on the responsibility for delivering information tailored for the high rainfall zones Jana says she is pleased to have an extensive network of contacts through Pinion Advisory, with offices in a number of high rainfall areas to provide easy access to local agronomists and growers. She is also aware that there are major differences in weed spectrums and farming systems in each high rainfall zone and plans to take full advantage of the opportunity this role presents to expand her understanding of different approaches to weed management.
“The long and favourable growing season and the associated prolonged periods of weed germination, is a key factor that I see potentially impacting on a grower’s weed management strategies in these regions,” she says. “On the other hand, access to highly diverse rotations and a focus on crop competition are two strategies that can play an important role in achieving excellent weed management in these regions.”
“I am keen to engage with anyone working and farming in the high rainfall zones to build my knowledge and understanding,” she says. “And to create opportunities to develop and extend the WeedSmart Big 6 strategies, both herbicide and non-herbicide, that work in each area and in different situations.”
WeedSmart is the industry voice delivering science-backed weed control solutions with support from the Grains Research and Development Corporation (GRDC), major herbicide, machinery and seed companies, and university and government research partners, all of whom have a stake in sustainable farming systems.
You an follow Jana on Twitter and keep up to date with the HRZ here.


Never cut the herbicide application rate

Scientific studies have demonstrated that resistance can rapidly evolve in weeds subjected to low doses of herbicide. Some weeds can develop resistance within a few generations.
Full rates when mixing herbicides too!
When mixing herbicides it is important that each product is still applied at the full label rate to ensure high mortality.
Applying different chemicals in one mix can provide an additive advantage. It is important to understand the mode of action of each herbicide on the plant when preparing a herbicide mix. This is just as important for pre-emergent grass weed mixes as it is for post-emergent mixes aimed at broadleaf weed control. ALWAYS READ THE LABEL.
Surrounding weed seeds with a combination of pre-emergent herbicides with different modes of action can give a high level of control and help extend the useful life of all the chemicals used. The high level of control must be supported with additional control measures for all survivors. All products with different modes of action must be applied at full label rates for this to be an effective strategy.

Mixing two chemicals with the same mode of action can achieve some additional efficacy, however, the mix should deliver the combined full rate to ensure a lethal dose. The amount of stubble present and crop safety are all important considerations when mixing chemicals. For example, when using a tank mix of Avadex® and trifluralin to control ryegrass in wheat, the rates used will vary depending on the sowing system and level of stubble retention. Be sure to get good advice.
Many herbicides on the market are a combination of two or more modes of action within the one product. These products must be applied at the full label rate to be effective. Having dual action does not negate the need to change herbicide products and rotate modes of action. Repeated use of any single strategy will reduce the effectiveness of that strategy over time.

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