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Windrow burning: it’s got to be hot

Growth Farms Australia manager, Chris Bunny, knew that the company was buying a property with herbicide resistant weeds when they purchased ‘Glaisnock’ near Young in 2008.

“The ryegrass on the property was known to be resistant to both Group A and Group B herbicides,” he said.

Chris and Elise Bunny, ‘Glaisnock’, Young believe narrow windrow burning is an effective non-chemical tactic to add to their weed control strategy.

“Twenty-five years of continuous wheat-canola cropping had taken its toll and changes to the farming system were obviously required.”

Over the last few years Mr Bunny has implemented drastic changes—reintroducing livestock into the system, changing herbicide application tactics, modifying the rotation and adopting narrow windrow burning—all to address the problem of herbicide resistance in weeds.

The 970 ha red earth property, ‘Glaisnock’, located between Young and Temora is well suited to cropping but continuous cropping practice has generated an unsustainable level of weed pressure. Mr Bunny is in the process of fencing paddocks and installing stock waters as they move around the property planting lucerne for stock grazing.

“About 20 percent of the property is under lucerne in any one year,” he said. “Lucerne gives us the opportunity to earn income off these paddocks while also winter cleaning with heavy grazing and paraquat in at least 3 of the 5 years of pasture.”

They run trade stock, either steers or prime lambs, so they are able to be flexible with the timing and stock density. The lucerne is also breaking up the hard pan that had developed over so many years of continuous cropping.

Triazine tolerant canola and wheat are currently sown 50:50 across the remaining farming area. Mr Bunny said the triazine-tolerant canola had proven to be a useful way to introduce different modes of action to the assault on resistant weeds. He hopes eventually to reduce the area sown to canola but for now it is playing an important part in their integrated weed management program.

During the summer fallow Mr Bunny employs double knock herbicide applications at every ryegrass germination. “Generally there are two double knock applications in the fallow,” he said. “The timing of the operations is determined by the weed size and the extent of the germination.”

“The staggered germination pattern of ryegrass can make it difficult to know when to spray,” he said. “It is also tempting to not do the second knock when the first spray appears to have worked well, but we have seen the benefits when a strip has been left un-sprayed and it is clear that the second application is essential.”

To round off their integrated weed management strategy Mr Bunny has also implemented narrow windrow burning of canola chaff as a non-chemical harvest weed seed control measure.

This year is the third year of narrow windrow burning on the property and Mr Bunny is convinced of its effectiveness in reducing the weed seed bank. “The only real problem with narrow windrow burning is the chance of the windrows getting wet before you are allowed to burn,” he said. “We try to start burning as soon as permits are available. So far we have had successful burns in 2 out of the 3 years.”

A hot fire is the key to effective narrow windrow burning to kill weed seeds.

A hot fire is the key to effective narrow windrow burning to kill weed seeds.

Mr Bunny had previously used stubble burning as a weed control measure but had found that burning the whole paddock was ineffective and there was the associated loss of stubble.

“Burning the narrow windrows is a much safer operation and for negligible cost it is possible to modify the header and introduce another weapon against resistant weeds.”

The canola chaff easily generates the required 400 degrees Celsius required to kill ryegrass seed. The next challenge for Mr Bunny is to implement the strategy in harvested wheat paddocks. The main difficulty with taking this step is the need to cut the wheat lower than usual and the timing of harvest compared to when the ryegrass seed begins to fall.

“We will be working on lowering the header, aiming for ‘beer can height’, and adjusting the chute to make the windrows as narrow as possible without causing blockages,” he said.

Being able to effectively burn chaff in every paddock, every year is the aim and Mr Bunny is determined to solve any problems that stand in the way.

Mr Bunny said two people can easily burn 400 ha of narrow windrows in one afternoon. Each windrow is lit every 400 metres or so, starting soon after midday. The windrows burn quite quickly and most are burnt out by late afternoon. Mr Bunny checks the paddocks again late in the afternoon and extinguishes any that are still alight.

“With the wheat we anticipate the need to burn off smaller areas at a time and that there will be more risk of the fires spreading across the paddock,” he said.

Summer rains can cause problems with the wet windrows tending to only burn along the top where the chaff has dried off. Mr Bunny has found that even in years where the effectiveness of the burn is reduced there is still a benefit in concentrating the weed seed into narrow bands in the paddock where germinations can be more easily and cost-effectively targeted.

Growth Farms Australia recently hosted researcher Michael Walsh from the Australian Herbicide Resistance Initiative and a group of growers from Western Australia with extensive experience with herbicide resistant weeds, including annual ryegrass. Growers from the Young district were invited to meet the visiting experts and to see narrow windrow burning demonstrated.

Delta Agribusiness consultant David Crowley and GRDC funded, Charles Sturt University researcher John Broster arranged field days at Young, Griffith and Lockhart to give local growers an opportunity to meet the West Australian expert panel to discuss their experience with harvest weed seed control methods, including the Harrington Weed Destructor, chaff carts and narrow windrow burning.

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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. 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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 Adjuvants 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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