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Non-herbicide weed control in the Northern region

Diversity in cropping systems and diversity in weeds in the northern GRDC grains region of NSW and Queensland calls for diversity in weed management solutions, including non-herbicide tactics.

Survey work in the region has identified over 70 different weed species that impact on grain production and over 10 per cent of these weed species have confirmed populations within Australia that are resistant to glyphosate and several other chemical modes of action (MOA).

DAF weeds researchers Annie van de Meulen and Michael Widderick.

DAF weeds researchers Annie van de Meulen and Michael Widderick.

Confirmed herbicide resistance in weed populations found in NSW and Queensland.
Source: adapted from a table prepared by M Widderick, DAF.

Mode of Action Resistant weeds
A (fops, dims, dens) wild oats, paradoxa grass, annual ryegrass
B (SUs, imis etc) annual ryegrass, wild oats, paradoxa grass, Indian hedge mustard, charlock, wild radish, turnip weed, African turnip weed, common sowthistle, black bindweed
C (triazines, ureas, amides etc) awnless barnyard grass, liverseed grass
D (DNAs, benzamides etc) annual ryegrass
I (phenoxys, pyridines etc) wild radish
L (bipyridyls i.e. diquat, paraquat) flaxleaf fleabane
M (glycines i.e. glyphosate) annual ryegrass, awnless barnyard grass, liverseed grass, windmill grass, feathertop Rhodes grass, sweet summer grass, flaxleaf fleabane, common sowthistle
Z (dicarboxylic acids etc) wild oats

A recent survey of common sowthistle determined populations as glyphosate resistant if treated seedlings were surviving and reshooting 21 days after glyphosate application. In this testing, glyphosate was applied at the upper label rate for small sized plants (up to 5 leaf).

While the majority of common sowthistle samples collected from central Queensland to central NSW were still susceptible to label rates of glyphosate applied to small seedlings, resistant populations were found throughout the study area, showing that this is not a localised problem but rather the inevitable result of over-reliance on a particular herbicide.

Most northern region weeds are self-pollinated so resistant plants will produce resistant seed. To reduce the likelihood of resistance, a key approach is to use multiple tactics to maintain low weed numbers. While weed numbers are low so too is the risk of resistance genes being present in the population.

To keep these ‘difficult to control’ weeds in check will clearly require other, non-herbicide, tactics to reduce germination and weed seed set. Queensland Department of Agriculture and Fisheries (DAF) researchers in Queensland have been studying common weeds, particularly feathertop Rhodes grass, barnyard grass and common sowthistle, to find weaknesses in each weed’s ecology to help identify non-chemical control tactics that could be part of an effective management system.

Dr Michael Widderick and the DAF weed research team are investigating non-chemical options, including various cover crops, crop competition, strategic tillage, strategic burning and harvest weed seed control options.

He says that although growers are making good use of chemical strategies such as double knock, residual herbicides, spot spraying and weed sensing technology to preserve herbicide efficacy, there is an urgent need to investigate non-chemical options that can be added to a weed management program to target resistant weeds in the northern region, as outlined in the WeedSmart 10 Point Plan.

Strategic tillage

“Most growers are keen to preserve their zero or minimum tillage farming systems that have delivered significant benefits and so are very reluctant to re-introduce cultivation for weed control purposes,” says Dr Widderick. “We are currently researching ways to use cultivation that will have maximum effect on driving down weed numbers while having least impact on the min-till farming system.”

The aim of this research is to investigate the impact of different tillage operations in situations where the weed population has blown out and intensive patch or paddock-scale management is required.

“The key is to understand weed ecology, particularly how seed in the soil seed bank responds to different types of cultivation,” he says.

The team used small plots to determine the effect of burial at different depths on weed seed persistence (long-term viability) and emergence. They also conducted experiments to determine the displacement of seed (glass beads were used to represent the seed) throughout the cultivated zone using four different types of machine—harrows, gyral, off-set discs and one-way discs—compared to the zero till control treatment.

Sowthistle emergence occurs primarily from seeds close to the soil surface with up to 30% of viable seeds emerging over 5 months. Seed can emerge from a depth of up to 2 cm with approximately 4% emergence after 6 months. Seed buried below 5 cm is unable to emerge and can persist at depth.

Seed persistence (the percentage of viable seed after burial) in fleabane was most reduced when seed was buried to a depth of 2 cm and not disturbed for at least two years. Seed buried to a depth of 10 cm remained viable for over 3 years. Feathertop Rhodes grass seed persisted for only 12 months regardless of being left on the surface or buried to 10 cm depth. Barnyard grass however, persisted on the soil surface for up to 2 years and when buried to 10 cm depth remained viable for over three years.

The Gyral machine placed the majority of weed seed in the 0–2 cm and 2–5 cm zones while the offset discs and one-way discs achieving burial of about half the seed below 5 cm depth.

“All species responded to increased tillage intensity with reduced germinations,” says Dr Widderick. “The message here is that infrequent but intense cultivation can be a useful weed management tool within an otherwise zero tillage farming system. Generally, once a deep cultivation has been done there should be no cultivation of that area or paddock for at least four years to avoid the risk of bringing seed back to the soil surface.”

Strategic burning

Feathertop Rhodes grass is known to colonise around mature plants and potentially spread to form distinct weedy patches. Killing the large plant at the centre of the colony is usually not possible using chemical treatments.

Strategic burning of early infestations of this weed can effectively reduce the biomass of the survivor plant and reduce the amount of viable seed present on the soil surface from 7500 seeds per m2 to less than 500 seeds per m2.

Growers have made effective use of a flame-thrower to burn large feathertop Rhodes grass plants during the fallow.

Strategic burning of early infestations of feathertop Rhodes grass in a fallow can effectively reduce the biomass of the survivor plant and reduce the amount of viable seed present on the soil surface.

Strategic burning of early infestations of feathertop Rhodes grass in a fallow can effectively reduce the biomass of the survivor plant and reduce the amount of viable seed present on the soil surface.

Crop competition

Crop competition through narrower row spacing and or increased planting density provides an effective offensive against common sowthistle and flaxleaf fleabane.

“Our experiment looked at the effect of crop competition on its own, however, in commercial situations crop competition would be used in conjunction with herbicide applications,” says Dr Widderick. “Narrowing wheat rows from 50 cm to 25 cm spacing had the most marked effect on fleabane seedhead production with an additive advantage if the crop density is also increased from 50 plants per m2 to 100 plants per m2.”

ws-fleabane-seed-heads

Fleabane seedhead production (Source: M Widderick, DAF)

Project work is continuing to investigate the options for increasing crop competitiveness in sorghum, winter and summer pulses and wheat.

“We are particularly keen to identify ways to improve the competitiveness of sorghum crops, which are often a weak link in northern farming systems,” he says. “Highly competitive summer grasses that also have high tolerance and or resistance to herbicide can gain the upper hand in sorghum crops that often do not achieve canopy closure.”

Crop competition through narrower row spacing and or increased planting density provides an effective offensive against common sowthistle and flaxleaf fleabane.

Crop competition through narrower row spacing and or increased planting density provides an effective offensive against common sowthistle and flaxleaf fleabane.

Cover crops

Summer fallow periods are heavily reliant on glyphosate for summer grass control. Preliminary research has explored the potential role of cover crops in place of a chemical fallow for control of summer grass weeds. Summer cover crops such as cowpea, lablab and French millet have the potential to smother summer growing weeds, particularly barnyard grass and feathertop Rhodes grass and return large amounts of organic biomass to the soil.

French millet planted on its own, or in combination with the legumes, increased the amount of biomass produced. The higher the biomass production the greater the suppression of weeds. Cover crops will tend to use fallow stored moisture so the team investigated the effect of two termination dates on both subsequent crop yield and on weed numbers.

“Feathertop Rhodes grass germination was minimal after all the cover crop treatments, and the yield of the following wheat crop was comparable to the chemical fallow control and no yield differences were found between treatments,” says Dr Widderick. “For barnyard grass, late termination of the cover crop reduced weed emergences before and after the following wheat crop, however there was a trend toward slightly reduced wheat yield compared to the early termination treatments that tended to boost yield compared to the chemical fallow control.”

“The reduction in barnyard grass emergence and wheat yield are both likely due to reduced soil water following the late terminated cover crops,” he says. “Much more work is required to identify suitable cover crops and define the parameters for their use as a weed management tactic.”

Harvest weed seed control

Harvest weed seed control (HWSC) is known to be an effective strategy and is widely adopted in Western Australia and increasingly in South Australia, Victoria and southern NSW. The efficacy of the current tools such as narrow windrow burning, chaff carts, tramlining or chaff decks, bale direct systems and the new integrated Harrington Seed Destructor to control weeds found in the northern growing region is largely unknown.

Trial work in winter crops to date have revealed that these tools can effectively collect and concentrate brassica weeds growing in wheat and chickpea crops in the northern region. The DAF weed research team is conducting further HWSC trials this winter with a focus on collecting wild oats seed. They are also keen to hear from growers planning to plant sorghum this summer where the team will be assessing the efficacy of various HWSC tools against barnyard grass and feathertop Rhodes grass.

More information – Read the full published paper here: Non-chemical tactics for improved control of key northern region weeds and listen in to the webinar recording with Michael Widderick and Annie van de Meulen.

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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
 

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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.

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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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