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Narrow row spacing: is it worth going back?

Narrow row spacing can deliver an average 6% yield increase along with a 98% decrease in annual ryegrass seed heads—more crop, less weeds.

Forward thinking DAFWA researcher Glen Riethmuller has recorded significant yield benefits in wheat sown at narrow row spacing, along with a remarkable suppression of weed numbers in a 28-year long trial at Merredin Research Station.

Forward thinking DAFWA researcher Glen Riethmuller has recorded significant yield benefits in wheat sown at narrow row spacing, along with a remarkable suppression of weed numbers in a 28-year long trial at Merredin Research Station.

Nearly thirty years ago, forward thinking researchers in Western Australia laid out a row width trial at Merredin Research Station to investigate the effect of stubble retention versus stubble burning. Ten years into the trial they found herbicide resistant annual ryegrass was becoming a problem in the wide row plots.

The research team decided to introduce rotation crops to the trial site in an effort to rotate chemical groups and bring the weeds under control. While the thinking was sound it was not very successful in the wide row plots.

This scenario has played out on minimum tillage farms around Australia, eking away the potential gains through better moisture conservation.

Glen Riethmuller is the Department of Agriculture and Food acting Technical Services Manager responsible for the design and management of this long-term trial in WA that Steve Porritt initiated in 1987.

“The average yield from the 15 wheat crops has been 5.7% higher in the retained stubble plots compared to plots where the stubble is burnt,” he said. “When it comes to row width we find yield decreasing by an average 0.4% for every centimetre, or 1% loss per inch, as the row spacing increases over 180 mm (7 inches).”

For wheat crops sown at 360 mm (14 inches) this equates to an average 6.8 per cent yield loss due to increased row width when sown into burnt stubble and a huge 7.9 per cent loss in stubble retained situations. Left: wide rows. Right: narrow rows.

Left: narrow rows. Right: wide rows.

For wheat crops sown at 360 mm (14 inches) this equates to an average 6.8% yield loss due to increased row width when sown into burnt stubble and a huge 7.9% loss in stubble retained situations. In the six pulse crops (2 field pea, 1 faba bean, 1 lentil and 2 chickpea) the retention of stubble and row spacing had little effect on yield. The two canola crops showed little response to stubble management but a sizeable response to row spacing with yield declining 1% for every centimetre row spacing increase over 180 mm.

Left: narrow rows. Right: wide rows.

Left: narrow rows. Right: wide rows.

Further narrowing the rows to 90 mm increased yields in most stubble situations, indicating that very narrow rows can improve yields even in the low rainfall zones.

When these yield results are considered together with the effect of narrow rows on weed seed heads, the case for narrower rows becomes very compelling. All plots were treated with full rates of herbicide yet annual ryegrass remained a problem in the wider row plots while there was a 98% reduction in ryegrass seed heads in 2013 in the narrow rows plots.

In the narrow row stubble retained plots, ryegrass head counts in 2013 were very low at 0.17 heads per m2 compared to 7.67 seed heads per m2 at 360 mm row spacing. This is a great example of how well herbicides work in the presence of competition.

“Our experience with managing weeds in the trial sites has been that none of the available herbicide options are able to overcome the extra weed pressure in wider rows,” he said. “We typically used trifluralin pre-sowing at 1 L/ha for ryegrass control in the trial. In two years we tried 2 L/ha and it made no difference to ryegrass control in the wide row plots.”

In recent years the researchers have switched to using full label rates of the new herbicides Sakura® and Boxer Gold® pre-sowing.

“Finding ways to practically sow through stubble at the narrowest row spacing possible is the way to grow more grain, reduce herbicide costs and combat herbicide resistance in weeds.”

These results were confirmed across the country when researchers examined data from 89 wheat experiments measuring the effect of row width. “The consistent message from the data was that widening row spacing is an enabling method of dealing with high stubble load but there is always a yield penalty in doing so,” said Mr Riethmuller. “The penalty is greatest in high production areas where the yield potential is highest. There is no question that growers are best off sowing at the narrowest practical row spacing possible.”

“At narrow rows and lower seeding rate along the row we see the highest germination rate and overall plant density,” he said. “High seeding rates along wider rows has lower establishment rates as the crop plants compete for resources or are affected by high fertiliser rates close to the row. In canola, planting on narrow rows could cut seed costs in half while increasing yield.”

Crops sown on narrow rows achieve full canopy cover quickly, reducing evaporation from the soil. With precision planting equipment now available Mr Riethmuller believes planting between rows can achieve great benefits in disease and soil nutrient management.

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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.


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.


Spray well – correct nozzles, adjuvants and water rates

Spray application is a technical field and growers need to make sure their equipment and application techniques are spot-on. The GRDC Spray Application GrowNote provides detailed information and about 80 videos to demonstrate key skills.

Prevent spray-drift
The focus of spraying herbicide needs to be on doing the job right so the weeds receive the correct dose and die, and this includes reducing the air borne fraction to a bare minimum.

Bill Gordon’s 10 Tips for Reducing Spray Drift

Choose all products in the tank mix carefully.
Understand the product mode of action and coverage requirements.
Select (and check) the coarsest spray quality that will provide effective control.
Expect that surface temperature inversions will form as sunset approaches and will likely persist overnight and even beyond sunrise on many occasions. DO NOT SPRAY.
Use weather forecasts to inform your spray decisions.
Only start spraying when the sun is about 20 degrees above the horizon and when the wind speed has been above 4–5 km/hr for more than 20–30 minutes, and clearly blowing away from any adjacent sensitive crops or areas.
Set the boom height to achieve a double overlap of the spray patterns.
Avoid higher spraying speeds.
Leave buffers unsprayed if necessary and come back.
Continue to monitor conditions, particularly wind speed, at the site during the spray operation

High water rates don’t have to slow you down
Some growers are concerned that increasing the water rate when applying herbicide will slow down their spray operation and cost them money. However, the biggest financial loss during spraying usually comes from a failed spray job.
To keep your spray operation as time efficient as possible when using more effective and reliable application volumes, you can:

Use nurse tanks around the farm to reduce the time spent travelling back to a central re-fill point.
Use a larger pump, e.g. 2.5 inch, to make re-filling quicker.
Pre-mix the batch while the sprayer is operating. Many mixes can be held in the mixing tank for up to 6 hours. However, wettable granules and suspension concentrates will need agitation to keep them in solution.

For pre-emergent herbicides in high stubble situations, carrier volume has a large effect on the level of control achieved. Across four trial sites Dr Borger’s research demonstrated that ryegrass control with trifluralin or Sakura® increased from 53% control when the carrier volume was 30 L/ha to 78% control when the carrier volume was increased to 150 L water/ha in high
Water quality and mixing order
Water quality is often overlooked as a possible contributor to herbicide failure and can lead to confusion over the herbicide resistance status of weeds on a property.
Water should be considered as one of the chemicals in any mix, given that water quality varies markedly depending on its source. Getting the mixing order right is essential for effective spray results.

Don’t start mixing until the water quality is right
Podcast – Mixing herbicides

Sometimes adding an adjuvant is beneficial and sometimes it is detrimental; and there is an art to knowing how to best deploy these additives.
When weeds are susceptible to the applied herbicides, the effectiveness of adjuvants generally goes un-noticed. Correctly applied adjuvants can reduce the impact of low level herbicide resistance by helping to maximise the amount of herbicide taken up by the plant.

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