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Can multi-species planting provide effective weed control?

Crop competition is one of the most effective weed control tools available to growers, but some crops simply don’t have a competitive edge.
Dr Andrew Fletcher, a farming systems scientist with CSIRO, says companion planting and intercropping is an option that growers can consider to bolster the competitiveness of an otherwise uncompetitive but valuable crop in the rotation. International research suggests that it can!
Andrew Fletcher, CSIRO farming systems researcher sees potential for multi-species plantings to compete with weeds. Photo: GRDC
“When two or more species are grown together they can occupy ecological niches that might otherwise be taken up by weeds,” he says. “Multi-species plantings have several potential benefits including increased crop yield and improved soil health, but the right combination can also reduce weed biomass by over 50 per cent.”
Multi-species plantings can be quite challenging to integrate into a grain cropping rotation but are more easily used in mixed grain and livestock operations and in intensive pastures for dairy cattle. International research suggests there is a significant untapped opportunity to increase the use of these systems in Australian grain production systems. However, relevant Australian data is scarce and more research is required to understand this untapped potential in Australian systems.    
A mixed-species cover crop can provide multiple soil health benefits, grazing and fodder for livestock and weed control through crop competition and stopping weed seed set.
“Crop competition is a non-herbicide pillar in the WeedSmart Big 6, with the potential to do some serious heavy lifting in terms of weed control,” says Andrew. “Intercropping and companion planting offers a means to bolster the competitiveness of some crops and to keep them in the rotation without risking a weed blow-out.”
What is intercropping, companion planting and mixed-species planting?
In brief: These systems all involve planting two or more crop species together. The combinations are almost limitless.
The details: Intercropping involves planting two or more species together and harvesting the grain of multiple crops. This generally relies on the grain species having different size seed and compatible harvest times.
Companion planting involves two or more species planted together with the intention to harvest grain from one species only after grazing or terminating the other species before seed set.
Sowing a low-growing species like clover between the rows of cereal can compete with weeds in the inter-row area, fix nitrogen and provide the basis of a pasture after the cereal grain is harvested. This is one example of companion planting.
Mixed-species planting is used to describe plantings of several species grown together primarily for the soil health benefits, and that may have potential for grazing and or forage conservation.
How do these systems suppress weed growth?
In brief: These multi-species systems are designed to take up the ecological space that might otherwise present and opportunity for weeds to fill.
The details: Intercropping and companion planting provide additional weed control in situations where one of the species is a relatively poor competitor as a sole crop. By maximising competition, weed growth is suppressed by up to 58 per cent compared to the least competitive species grown on its own. If a competitive crop such as barley is sown in the most competitive configuration possible, there is little additional benefit from adding a second species.
The downside of using this multi-species strategy for weed control is that in-crop herbicide options the choice of herbicides is limited. This is mainly due to the common combinations being a grass crop with a legume or brassica, meaning grass and broadleaf herbicide options can’t be used, except for when one species is terminated. This needs to be factored into decisions around intercropping and companion cropping.  
What are the best-bet combinations for enhanced weed control?
In brief: It depends on the farming system and the other reasons for considering a multi-species planting.
The details: If the aim is to produce grain, the species selected should have easily separated seed. A well-known example is peaola (field pea plus canola). A recent review of historical trials showed that the median yield increase was 31 per cent compared to sole crops of peas and canola, but the weed control effects of peaola in Australia are unquantified.
An effective companion planting combination is wheat undersown with tillage radish and a legume. The broadleaf companions are sprayed out at stem elongation, leaving the cereal to mature through to harvest.
If there is livestock in the farming system, dual purpose combinations such as grazing canola plus vetch and oats can provide excellent weed suppression. This mix could be grazed and then terminated as hay or silage at stem elongation.
Multi-species plantings add a layer of complexity to the farming system, but many growers have taken on the challenge and are reaping the rewards in crop yield, soil health and weed suppression.

Article
News

Investigate adverse experiences when using herbicides

A shuttle of glyphosate applied over the top of a Roundup Ready cotton crop was recently shown to also contain a damaging level of 2,4-D impurity, resulting in significant crop injury and yield loss.
The grower involved did not accept the suggestion that the crop damage was due to poor sprayer decontamination or spray drift from a fallow application of 2,4-D, and he was able to prove the problem was due to product impurity.
2,4-D herbicide injury in cotton after the crop was sprayed with glyphosate product contaminated with 2,4-D.
Other shuttles of the same batch may have been applied to fallow weeds where the residual 2,4-D in the glyphosate would have gone unnoticed. Full rate 2,4-D in glyphosate is known to compromise glyphosate efficacy, but studies of low-rate 2,4-D impurity in glyphosate could not be found.
Where can impurities come from?
While the agricultural chemical manufacture and supply chain in Australia is considered first-class and is highly regulated, there is an acceptance that the nil-impurity requirement for the manufacture of agricultural chemicals is unattainable in facilities that use multi-purpose equipment for synthesis, formulation and packaging of products.
Companies therefore apply their own quality assurance standards before releasing products for distribution and sale. If the level of risk posed by certain residual impurities in a product is underestimated, there is potential for instances of crop injury, pesticide residue in produce or poor performance of the product on the intended target weed, fungus or pest.
Mistakes can and do happen within the manufacturing process and chemical supply and distribution chain. To ensure that risks of contamination are minimised and that quality assurance protocols are followed carefully, it is important that any breaches or errors are identified quickly, reported and investigated.
Keep good records of each spray event, including batch numbers of applied product, to help identify the cause of adverse experiences with herbicides.
There are two important things to note: firstly, the current regulations specify that crop protection products must contain nil impurities (other than manufacturing impurities listed in the APVMA standard); and secondly, companies are required to recall product batches when contamination issues are identified. The Australian Pesticide and Veterinary Medicines Authority (APVMA) oversees a highly regulated system of registration, compliance and enforcement on crop protection products.
Assess potential application issues
When misapplication (wrong product applied, incorrect mixing, contaminated product etc) occurs, symptoms of affected plants are usually uniform throughout the treated area. It is often suggested that poor application technique or poor sprayer decontamination is the reason for crop injury or poor weed control results – suggesting a grower ‘own-goal’. Such potential errors must be considered, but if best practice spray techniques and spray rig decontamination procedures have been followed, product impurity should also be considered and investigated.
The chemistry of the product will determine the risk of residues being held within the tank and spray lines of the application rig. This is why there are differences in the sprayer hygiene requirements after using particular products.
Most modern spray rigs have impervious rubber and plastic, or stainless steel components, drastically reducing the risk of chemical absorption and subsequent extraction. Residues on the rubber surfaces are the main concern, and all registered cleaners will physically remove residues when used as directed, but cracked rubber components can present a contamination risk. All filters/strainers must be cleaned and all actuators and taps musts be cycled as the cleaner is run through the spray boom and tank loading system, agitators and tank.
Crop injury or poor weed control that is associated with just one sprayer tank load would suggest sprayer contamination. Effects from contaminated tanks are usually worse at the beginning of the spray run, with damage diminishing with spraying and tank reloading. The field pattern can provide clues to the sprayer filling routine in the field where the crop damage occurred.
The other major reason commonly cited for crop injury in spray drift. Although there is always some small amount of drift when agricultural chemicals are sprayed from a ground rig, the amount is down to ‘virtually safe’ levels within a few tens of metres. If the conditions are very windy, or the boom is too high, or the droplet size too small, spray could drift a few hundred metres from the application ground rig.
Spray droplets may travel a few feet to several kilometres from the targeted area, depending on weather conditions and spray application; but the potential for drift damage decreases with distance because droplets are deposited or become diluted in the atmosphere. The pattern of injury is normally seen most prominently on the section of the field closest to the sprayer that generated the spray drift, and decreases across the field.
During inversion conditions, a similar amount of product is subject to drift, but the drifting product will not dilute as much in the air, so concentrations at specific locations can be higher than expected in non-inversion conditions.
What to do if your crop is damaged or weeds don’t die as expected?
Along with several other possible causes, unintended application of contaminated product should be considered as a potential explanation for crop injury or poor weed control.
Keep in mind that if product impurity is the problem, it is most likely due to a low-dose effect that may be difficult to diagnose or may take longer to express in the target weeds or susceptible crops.
Finding the cause of an ‘adverse experience’ with herbicide is one of the most important reasons to keep accurate and detailed spray records.
If a problem occurs:

Take detailed, time-stamped photographs of the crop or weeds and record everything you know about the crop or fallow management, weather conditions in the weeks prior to the damage being seen, spray history of the field etc. If possible, geotag the photos so they can be easily associated with the correct field.
Record the relevant batch numbers of the chemicals used, which can be checked against the retention samples at the factory if necessary. Collect samples from drums of product used prior to the injury being observed (up to 14 days prior to symptoms being obvious). When you take samples, make sure there are witnesses who can vouch for the voracity of the evidence you have collected. Testing for one impurity (e.g. 2,4-D in glyphosate) costs less than $500 per sample.
Document the injury over time. For example, injury in cotton from low rates of 2,4-D will grow out in two weeks, but injury from higher rates, could last three to four weeks and are the most likely to result in yield loss. Similarly with weeds although the impact may be more difficult to document.
Mark out the affected area in the field to help assess crop yield loss at the end of the season. Note the pattern and intensity of the problem across the field.
Eliminate as many possible causes as you can. Re-assess the application technique and equipment, consider the pattern of damage in the field, look at the weather conditions for the relevant period of time and so on.
Test for herbicide resistance in weeds.
Report the crop damage or poor weed control. The APVMA administers the Adverse Experience Reporting Program, which allows anyone to report a problem with an agricultural chemical, including crop and plant damage, for example, plant death, severe stunting or significant yield loss. This is also the way to report poor weed control outcomes.

The APVMA acknowledges there is likely under-reporting of adverse experiences. The magnitude of under-reporting is unknown and provides limitations in quantifying product risk.
Investigations of spray drift are conducted by the relevant state government body, for example: NSW EPA (call Environment Line: 131-555), Biosecurity Queensland (call 132-523) and Chemical Standards Officer (Victoria) (call 03 5430 4463). Industry organisations will also support growers impacted by chemical damage to crops.
If the damage is due to factors other than spray drift, the affected party will need to take legal action and seek compensation themselves.
Related resources
Is poor weed control due to herbicide resistance?

Article
Case Study

Jamie and Susie Grant, Jimbour Qld

Jamie and Susie Grant are always on the front foot when it comes to storing soil moisture to maximise yield in their dryland cotton crops on ‘Kielli’ near Jimbour on Queensland’s Darling Downs.
Over the years they have adopted controlled traffic, minimum tillage, cover cropping and vigilant weed management as key strategies to maximise water infiltration and minimise losses to run-off, evaporation and wasted evapotranspiration throughout the year.
The Grants have implemented an integrated weed management system that incorporates several of the WeedSmart Big 6 strategies, with an emphasis on preventing weed seed set.
Cover cropping provides crop competition
Jamie says they have not grown a winter crop for over 20 years and have phased out other summer crops, such as sorghum, in preference for dryland cotton.
“For the last 15 years we have grown French millet as a summer cover crop on half the cropped area. And this year we are moving to a new configuration where we will have the whole farm sown to millet and cotton in alternate bays,” says Jamie.
Cotton sown into French millet cover crop stubble.
The plan is to plant cotton on 3 m row spacing across the whole cropped area (instead of on rows 1.5 m apart on half the farm). Between the cotton rows will be a 1.5 m swath of millet on 380 mm rows, leaving 750 mm between the edge of the millet and the adjacent cotton row. The following year the cotton rows will be planted through the centre of the millet swath.
Jamie expects this system to increase infiltration and storage of moisture across the farm and to support a higher yielding cotton crop.
“During summer, the soil will be better protected from erosion with ground cover spread over the whole farm, and in a good rainfall season the soil reserves should be refilled and available for use in a subsequent drier year,” he says. “We have done a small, 9 m wide trial of the new configuration and the difference in cotton yield was phenomenal.”
Summer weed management begins with a double knock prior to planting both millet and cotton to ensure the crops can establish in a weed-free environment. Millet is planted in October then sprayed out when the stalks have reached maximum cellulose level but before the plants set seed. The cellulose-rich stalks reach about a metre in height within about six weeks of planting.
When the crop is sprayed out, the stalks collapse to produce a 100 per cent mulch cover that protects the soil surface from evaporation and erosion, while allowing rapid infiltration of rainfall and suppressing weed germination, especially over summer. Volunteer cotton is controlled if necessary in the millet.
The Grants follow industry best practice for the in-crop management of weeds in their Round-Up Ready cotton.
Preventing weed seed set in winter fallow and in-crop
Over 15 years ago Jamie and Susie invested in optical spray technology to better manage their fallow weeds, but it was never the full solution. The problem of treating weeds of varying size and maturity meant that weeds were an ongoing drain on their precious soil moisture stores.
“When we bought one of the first WeedSeekers into Australia we knew we would reduce our herbicide use in the fallow, but the time taken to treat weeds using the optical weed detection technology was a limiting factor,”says Jamie. “Before long we had moved to a wider WeedSeeker boom just to get across the country quick enough. Then we added a broadacre spray behind the WeedSeeker to pick up the smaller weeds – the whole system just wasn’t working well enough due to labour and timeliness factors.”
When Jamie heard about the development of the SwarmFarm robots he was keen to be part of the early testing phase and was the first grower to deploy a SwarmBot – named November – under commercial conditions.
“I knew from the start that the robotic platform would solve our weed control problems and could see the potential for this technology to revolutionise the way we farm,” he says. “We have since leased a second robot – Victor – practically eliminating the need for a broadacre sprayer. The next modification will be to give the robots higher clearance so we can conduct in-crop weed control right up to canopy closure in the cotton.”
Robotic spot spraying in cotton inter-rows.
Jamie and Susie were controlled traffic pioneers, so the move to lightweight machines for all their field operations, other than harvesting, is the ultimate aim. Jamie expects the robots to be able to undertake all the spraying, ground preparation, planting and fertilising operations and wheeltrack renovation within the next few years. This relies on the fine-tuning of the SwarmBot auto-refilling capability.
The current use of the two robots, each fitted with a 9 m WEED-IT boom and 1000 L tank, for fallow weed spraying has halved the Grant’s herbicide use compared to the 27 m wide WeedSeeker boom.
“The difference in herbicide use has come through more proactive use of the optical weed detection technology, rather than reacting once we saw weeds growing in the field,” says Jamie. “We are continuously spraying and treating smaller and smaller weeds, with very, very few misses. We are always on the front foot with weeds now, so we can take advantage of any planting opportunities that arise, without having to wait to spray weeds ahead of the planter.”
The robots also earned their place on the farm during the drought by preventing the establishment of weedy patches. Jamie can justify the use of different chemical groups in fallows that might otherwise be considered too expensive, and herbicide resistance has all but disappeared.
The robots have prevented the establishment of weedy patches and allowed the use of a wider range of herbicide groups in the fallow.
The robots work at a slow, steady pace, providing a more stable platform for the boom than the much wider WeedSeeker rig, and enabling the sensors to detect very small weeds – down to just 5 mm in diameter. The operation is repeated every two weeks, so weeds never have the opportunity to mature or set seed.
The WeedSeeker typically sprayed between 5 and 7 per cent of the paddock area compared to the WEED-IT on the robots spraying just 2 to 3 per cent of the paddock due to the small size of weeds and the accurate spray pattern.
The glyphosate is very effective on small weeds and any misses or hard to kill weeds are captured with an application of Starane (Group 4 [I]) or Biffo (Group 10 [N]) – using hardly any product doing an excellent job on the few remaining weeds. After planting cotton Jamie applies paraquat to be on the safe side when it comes to minimising the risk of glyphosate resistance.
 “After planting we expected to park the robots until the cotton crop was finished, but in fact we are finding more and more jobs for them to do,” says Jamie. “We are already using them to apply foliar fertiliser and early in-crop weed control. We are working toward eliminating the need for the high clearance Spra-Coupe for in-crop spraying.”
Using the robots, the Grants have reduced the amount of herbicide used in-crop by at least 50 per cent, and most likely close to 70 per cent, by only spraying the inter-row area and not the cotton plants. Achieving this has been as simple as blanking off three nozzles over each cotton row.
“Although the sensors on the WEED-IT respond to some of the cotton leaves in the inter-row, there is still a large reduction in the amount of herbicide used compared to the blanket spray using the Coupe,” says Jamie.
After rain, 28 per cent weed cover is the highest weed density that the Grants have sprayed using the robots. At this density they would have previously chosen to use the broadacre sprayer rather than the WeedSeeker boom. Jamie says the robots had no problem taking care of the situation, but they did require several refills. He hopes to get to the point where the robots only require checking and filling once a day, and he is ‘in on the ground floor’ assisting SwarmFarm with the auto-refilling trials.
Jamie says automatic refilling of the robots will be the next big step up for spraying efficiency.
Ultimately, Jamie would like to have enough robots to keep one staff member occupied full time. Even now, having Victor and November taking care of the farm’s weed control program allows skilled farm staff to spend their time doing more interesting work with their trade or other skills, rather than the boring job of operating a spray rig in fallow.
Along with the many other benefits, Jamie considers Victor and November to be the safest spray ‘operators’ in the business because they start and stop spraying in response to the weather conditions as detected by the on-board weather station.
“The robots will not deviate from the set weather parameters,” he says. “A weather app is being developed and will soon be available to monitor and record the whole spray operation and weather conditions at the time of spraying.”

Article
Case Study

Peter and Kylie Bach, Pittsworth Qld

Their 1000 ha farming operation, Kurilda Ag, is based near Pittsworth on the Darling Downs in Queensland, an area known for its reliable rainfall and deep self-mulching black clay soils. Peter says the recent long string of dry years has clearly demonstrated the value of stubble cover in their zero till, controlled traffic system.

“We are using crops to compete with weeds for as much of the year as possible,” he says. “We double crop whenever there is sufficient soil moisture to plant and having only short fallow periods most years reduces the opportunity for weeds to take hold.”
Peter and Kylie have been farming for 15 years, with a focus on summer crops, mainly sorghum and mungbean. Barley is grown in winter, predominantly for stubble cover to conserve moisture.
About five years ago they bought a Shelbourne stripper header and an Emar chaff deck for their harvester to achieve the dual purpose of conserving standing stubble and implementing harvest weed seed control. Their weed management program includes most of the WeedSmart Big 6 tactics that minimise the impact of weeds on their business.
Shellbourne stripper front is used in barley to conserve more standing stubble.
“Our main aim at the time was to deal with a large population of Johnson grass on a farm we had recently bought,”says Peter. “Although it is relatively easy to control Johnson grass with herbicide, we wanted to try a non-herbicide method to reduce the weed seed bank as quickly as possible.”
Across the farm, Johnson grass is now under control and feathertop Rhodes (FTR) grass, sowthistle and fleabane are the main problem weeds.
“Generally, when we keep on top of feathertop Rhodes that also manages the fleabane,” says Peter. “Sowthistle is getting harder to kill and we suspect glyphosate resistance is increasing. We also know of a few small areas of resistant ryegrass.”
The transition from barley to mungbeans, or barley to sorghum, provides the opportunity to use a different suite of chemicals. The Baches generally stay away from Roundup Ready (RR) crops and are using more soil residual herbicide in their program than they did previously.
Peter says there are more options available now, particularly with soil residual chemistry, to enable increased chemical diversity with the crops they grow.
“The residuals are chosen specifically with the next crop in mind,” he says. “With inconsistent rainfall patterns it can increase the risk of crop injury if there is insufficient rainfall to break down the chemical before the next planting.”
Metolachlor (Group 15 [K]), such as Dual Gold, plus glyphosate (Group 9 [M]) is applied at the end of July or early August in preparation for grain sorghum. After the sorghum crop is harvested, Peter prepares to plant barley. After the barley crop he then applies a residual herbicide like imazethapyr (Group 2 [B]), such as Spinnaker, ahead of mungbean crop emergence.
They have an optical boom sprayer but are finding it gets less use these days with less area being fallow managed.
Peter says that crop competition through frequent cropping maintains pressure on weed numbers, but to sustain this intensive cropping program they need to maximise the soil moisture levels throughout the year with ground cover and standing stubble.
Peter Bach says the ability to keep growing crops throughout the year keeps the pressure on weeds.
“Retaining stubble has been our standard practice for years but the lack of stubble produced by mungbeans was a weak link in the system,” he says. “We were interested in the stripper front for use in barley, and a grower in the Riverina gave us the confidence to give it a go.”
The mungbean crop benefits from the tall barley stubble and responds with higher yield. After the mungbean crop is harvested, the barley stubble tends to lay over, giving excellent ground cover that also benefits the following crop. The stripper front essentially maximises the benefit of the barley crop for the whole rotation, and has counteracted the effect of drier seasons.
“Soon after we bought the stripper front and chaff deck the rain stopped and a long series of dry years set in,” says Peter. “The tall stubble from that first barley harvest made it possible for us to keep growing crops for at least two years on very minimal rainfall. Since then it has helped make the most of every rainfall event and is a key part of our farming system.”
The standing barley stubble benefits the following mungbean crop and continues to provide good ground cover after the mungbeans are harvested.
They currently use XL spearpoints on CR600 units on their tyne planter, which does an excellent job planting barley on 38 cm (15 inch) row spacing, but the Baches plan to reduce the row spacing in barley to 25 cm (10 inch) and will most likely change from the tynes to a disc system.
An NDF disc opener planter is used for summer crops, which are planted on 76 cm (30 inch) rows. All crops are sown using moisture seeking techniques, which Peter says is more important than precision planting when it comes to achieving even crop establishment.
“Although we have had a few failures with deep planting, it has generally been a good strategy for us,” he says. “The key is to plant deep but not put too much soil back over the seed. In drier years we also reduce the seeding rate to ensure even germination. Early summer planting dates seem to be the best-bet option for our district.”
The aim is to plant mungbeans between the rows of fresh barley stubble that is standing up well, but if the planter gets off line it can be hard to achieve proper seed-to-soil contact with the high level of stubble present. Ultimately, it would be good to have GPS steering on planter bar to ensure the planter tracks exactly between the rows of stubble.
In the lead-up to harvest both mungbean and sorghum crops are desiccated but this operation is too late to stop seed set on late germinated weeds. To prevent weed seed set in these in-crop escapes Peter is working on system that can be used to spray weeds in the inter-row just before the sorghum starts to flower.
At harvest the Emar chaff deck is used in all crops, every year. In the last five years this harvest weed seed control tool has had a massive impact by reining in large populations of Johnston grass.
“The chaff deck applied consistent downward pressure on the Johnson grass seed bank every year and also helps us manage feathertop Rhodes grass,” says Peter. “Of course, the benefit is most noticeable when populations start high, but it is also good to know that it is also effective in keeping numbers low across the farm.”
He has also noticed that the chaff deck is very effective in controlling volunteer crop plants. Having all the weed seed and any grain that was thrown out the back of the harvester placed on the wheeltracks makes control much easier and more effective.
“When we do fallow sprays, we run larger nozzles over the wheeltracks to make sure any weeds that germinate are controlled before they can set seed,” he says. “In some instances, the only weeds present in-crop are along the wheeltracks so we can just turn on the six nozzles running over the three sets of wheeltracks.”
The combination of the stripper front and the chaff deck has resulted in more crop and less weeds at ‘Kurilda’, even through a series of very dry years.

Podcasts

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Audio
Podcast

162: Regional Update – Bernie Quade, Agronomist, Wyalkatchem, WA

Bernie talks to us about how frost has affected his region and provides some tips on Summer weed control.
This is our last Western Region Update for the year! Thanks to Bernie for coming on and having a chat with us!  Give Bernie a follow on Twitter here.

Audio
Podcast

161: Getting residual herbicides right after harvest

We hear from ICAN’s Mark Congreve on this (pictured above).
Northern Grower Alliance CEO Richard Daniel also joins us to talk about summer weed control how using an optical spray can maximise your use of residual herbicides.
We also hear from Frankland based Agronomist, Tim Trezise, who had a query on the challenges around crop topping weeds at the dough stage and whether you still get good control by using higher rates of paraquat or glyphosate. Pete answers this question in the podcast!
Links

Podcast: Why crop topping is a great tool to prevent weed seed set
Podcast: Richard Daniel explains results from Northern Grower Alliance survey on optical spraying
GRDC: Consider Consider plant back implications after herbicide use
Webinar: Register for our webinar “Metolachlor usage in the northern region” 

Audio
Podcast

160: Regional Update – Jana Dixon, WeedSmart HRZ Extension Agronomist, Clare, SA

This is our last Southern Regional Update for the year! Our WeedSmart High Rainfall Zone Agronomist, Jana Dixon, joins us to provide a regional update on Clare, South Australia and surrounds.

We also chat about what growers need to think about when it comes to planning around potential chemical shortages.

Case Studies

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Article
Case Study

Jamie and Susie Grant, Jimbour Qld

Jamie and Susie Grant are always on the front foot when it comes to storing soil moisture to maximise yield in their dryland cotton crops on ‘Kielli’ near Jimbour on Queensland’s Darling Downs.
Over the years they have adopted controlled traffic, minimum tillage, cover cropping and vigilant weed management as key strategies to maximise water infiltration and minimise losses to run-off, evaporation and wasted evapotranspiration throughout the year.
The Grants have implemented an integrated weed management system that incorporates several of the WeedSmart Big 6 strategies, with an emphasis on preventing weed seed set.
Cover cropping provides crop competition
Jamie says they have not grown a winter crop for over 20 years and have phased out other summer crops, such as sorghum, in preference for dryland cotton.
“For the last 15 years we have grown French millet as a summer cover crop on half the cropped area. And this year we are moving to a new configuration where we will have the whole farm sown to millet and cotton in alternate bays,” says Jamie.
Cotton sown into French millet cover crop stubble.
The plan is to plant cotton on 3 m row spacing across the whole cropped area (instead of on rows 1.5 m apart on half the farm). Between the cotton rows will be a 1.5 m swath of millet on 380 mm rows, leaving 750 mm between the edge of the millet and the adjacent cotton row. The following year the cotton rows will be planted through the centre of the millet swath.
Jamie expects this system to increase infiltration and storage of moisture across the farm and to support a higher yielding cotton crop.
“During summer, the soil will be better protected from erosion with ground cover spread over the whole farm, and in a good rainfall season the soil reserves should be refilled and available for use in a subsequent drier year,” he says. “We have done a small, 9 m wide trial of the new configuration and the difference in cotton yield was phenomenal.”
Summer weed management begins with a double knock prior to planting both millet and cotton to ensure the crops can establish in a weed-free environment. Millet is planted in October then sprayed out when the stalks have reached maximum cellulose level but before the plants set seed. The cellulose-rich stalks reach about a metre in height within about six weeks of planting.
When the crop is sprayed out, the stalks collapse to produce a 100 per cent mulch cover that protects the soil surface from evaporation and erosion, while allowing rapid infiltration of rainfall and suppressing weed germination, especially over summer. Volunteer cotton is controlled if necessary in the millet.
The Grants follow industry best practice for the in-crop management of weeds in their Round-Up Ready cotton.
Preventing weed seed set in winter fallow and in-crop
Over 15 years ago Jamie and Susie invested in optical spray technology to better manage their fallow weeds, but it was never the full solution. The problem of treating weeds of varying size and maturity meant that weeds were an ongoing drain on their precious soil moisture stores.
“When we bought one of the first WeedSeekers into Australia we knew we would reduce our herbicide use in the fallow, but the time taken to treat weeds using the optical weed detection technology was a limiting factor,”says Jamie. “Before long we had moved to a wider WeedSeeker boom just to get across the country quick enough. Then we added a broadacre spray behind the WeedSeeker to pick up the smaller weeds – the whole system just wasn’t working well enough due to labour and timeliness factors.”
When Jamie heard about the development of the SwarmFarm robots he was keen to be part of the early testing phase and was the first grower to deploy a SwarmBot – named November – under commercial conditions.
“I knew from the start that the robotic platform would solve our weed control problems and could see the potential for this technology to revolutionise the way we farm,” he says. “We have since leased a second robot – Victor – practically eliminating the need for a broadacre sprayer. The next modification will be to give the robots higher clearance so we can conduct in-crop weed control right up to canopy closure in the cotton.”
Robotic spot spraying in cotton inter-rows.
Jamie and Susie were controlled traffic pioneers, so the move to lightweight machines for all their field operations, other than harvesting, is the ultimate aim. Jamie expects the robots to be able to undertake all the spraying, ground preparation, planting and fertilising operations and wheeltrack renovation within the next few years. This relies on the fine-tuning of the SwarmBot auto-refilling capability.
The current use of the two robots, each fitted with a 9 m WEED-IT boom and 1000 L tank, for fallow weed spraying has halved the Grant’s herbicide use compared to the 27 m wide WeedSeeker boom.
“The difference in herbicide use has come through more proactive use of the optical weed detection technology, rather than reacting once we saw weeds growing in the field,” says Jamie. “We are continuously spraying and treating smaller and smaller weeds, with very, very few misses. We are always on the front foot with weeds now, so we can take advantage of any planting opportunities that arise, without having to wait to spray weeds ahead of the planter.”
The robots also earned their place on the farm during the drought by preventing the establishment of weedy patches. Jamie can justify the use of different chemical groups in fallows that might otherwise be considered too expensive, and herbicide resistance has all but disappeared.
The robots have prevented the establishment of weedy patches and allowed the use of a wider range of herbicide groups in the fallow.
The robots work at a slow, steady pace, providing a more stable platform for the boom than the much wider WeedSeeker rig, and enabling the sensors to detect very small weeds – down to just 5 mm in diameter. The operation is repeated every two weeks, so weeds never have the opportunity to mature or set seed.
The WeedSeeker typically sprayed between 5 and 7 per cent of the paddock area compared to the WEED-IT on the robots spraying just 2 to 3 per cent of the paddock due to the small size of weeds and the accurate spray pattern.
The glyphosate is very effective on small weeds and any misses or hard to kill weeds are captured with an application of Starane (Group 4 [I]) or Biffo (Group 10 [N]) – using hardly any product doing an excellent job on the few remaining weeds. After planting cotton Jamie applies paraquat to be on the safe side when it comes to minimising the risk of glyphosate resistance.
 “After planting we expected to park the robots until the cotton crop was finished, but in fact we are finding more and more jobs for them to do,” says Jamie. “We are already using them to apply foliar fertiliser and early in-crop weed control. We are working toward eliminating the need for the high clearance Spra-Coupe for in-crop spraying.”
Using the robots, the Grants have reduced the amount of herbicide used in-crop by at least 50 per cent, and most likely close to 70 per cent, by only spraying the inter-row area and not the cotton plants. Achieving this has been as simple as blanking off three nozzles over each cotton row.
“Although the sensors on the WEED-IT respond to some of the cotton leaves in the inter-row, there is still a large reduction in the amount of herbicide used compared to the blanket spray using the Coupe,” says Jamie.
After rain, 28 per cent weed cover is the highest weed density that the Grants have sprayed using the robots. At this density they would have previously chosen to use the broadacre sprayer rather than the WeedSeeker boom. Jamie says the robots had no problem taking care of the situation, but they did require several refills. He hopes to get to the point where the robots only require checking and filling once a day, and he is ‘in on the ground floor’ assisting SwarmFarm with the auto-refilling trials.
Jamie says automatic refilling of the robots will be the next big step up for spraying efficiency.
Ultimately, Jamie would like to have enough robots to keep one staff member occupied full time. Even now, having Victor and November taking care of the farm’s weed control program allows skilled farm staff to spend their time doing more interesting work with their trade or other skills, rather than the boring job of operating a spray rig in fallow.
Along with the many other benefits, Jamie considers Victor and November to be the safest spray ‘operators’ in the business because they start and stop spraying in response to the weather conditions as detected by the on-board weather station.
“The robots will not deviate from the set weather parameters,” he says. “A weather app is being developed and will soon be available to monitor and record the whole spray operation and weather conditions at the time of spraying.”

Article
Case Study

Peter and Kylie Bach, Pittsworth Qld

Their 1000 ha farming operation, Kurilda Ag, is based near Pittsworth on the Darling Downs in Queensland, an area known for its reliable rainfall and deep self-mulching black clay soils. Peter says the recent long string of dry years has clearly demonstrated the value of stubble cover in their zero till, controlled traffic system.

“We are using crops to compete with weeds for as much of the year as possible,” he says. “We double crop whenever there is sufficient soil moisture to plant and having only short fallow periods most years reduces the opportunity for weeds to take hold.”
Peter and Kylie have been farming for 15 years, with a focus on summer crops, mainly sorghum and mungbean. Barley is grown in winter, predominantly for stubble cover to conserve moisture.
About five years ago they bought a Shelbourne stripper header and an Emar chaff deck for their harvester to achieve the dual purpose of conserving standing stubble and implementing harvest weed seed control. Their weed management program includes most of the WeedSmart Big 6 tactics that minimise the impact of weeds on their business.
Shellbourne stripper front is used in barley to conserve more standing stubble.
“Our main aim at the time was to deal with a large population of Johnson grass on a farm we had recently bought,”says Peter. “Although it is relatively easy to control Johnson grass with herbicide, we wanted to try a non-herbicide method to reduce the weed seed bank as quickly as possible.”
Across the farm, Johnson grass is now under control and feathertop Rhodes (FTR) grass, sowthistle and fleabane are the main problem weeds.
“Generally, when we keep on top of feathertop Rhodes that also manages the fleabane,” says Peter. “Sowthistle is getting harder to kill and we suspect glyphosate resistance is increasing. We also know of a few small areas of resistant ryegrass.”
The transition from barley to mungbeans, or barley to sorghum, provides the opportunity to use a different suite of chemicals. The Baches generally stay away from Roundup Ready (RR) crops and are using more soil residual herbicide in their program than they did previously.
Peter says there are more options available now, particularly with soil residual chemistry, to enable increased chemical diversity with the crops they grow.
“The residuals are chosen specifically with the next crop in mind,” he says. “With inconsistent rainfall patterns it can increase the risk of crop injury if there is insufficient rainfall to break down the chemical before the next planting.”
Metolachlor (Group 15 [K]), such as Dual Gold, plus glyphosate (Group 9 [M]) is applied at the end of July or early August in preparation for grain sorghum. After the sorghum crop is harvested, Peter prepares to plant barley. After the barley crop he then applies a residual herbicide like imazethapyr (Group 2 [B]), such as Spinnaker, ahead of mungbean crop emergence.
They have an optical boom sprayer but are finding it gets less use these days with less area being fallow managed.
Peter says that crop competition through frequent cropping maintains pressure on weed numbers, but to sustain this intensive cropping program they need to maximise the soil moisture levels throughout the year with ground cover and standing stubble.
Peter Bach says the ability to keep growing crops throughout the year keeps the pressure on weeds.
“Retaining stubble has been our standard practice for years but the lack of stubble produced by mungbeans was a weak link in the system,” he says. “We were interested in the stripper front for use in barley, and a grower in the Riverina gave us the confidence to give it a go.”
The mungbean crop benefits from the tall barley stubble and responds with higher yield. After the mungbean crop is harvested, the barley stubble tends to lay over, giving excellent ground cover that also benefits the following crop. The stripper front essentially maximises the benefit of the barley crop for the whole rotation, and has counteracted the effect of drier seasons.
“Soon after we bought the stripper front and chaff deck the rain stopped and a long series of dry years set in,” says Peter. “The tall stubble from that first barley harvest made it possible for us to keep growing crops for at least two years on very minimal rainfall. Since then it has helped make the most of every rainfall event and is a key part of our farming system.”
The standing barley stubble benefits the following mungbean crop and continues to provide good ground cover after the mungbeans are harvested.
They currently use XL spearpoints on CR600 units on their tyne planter, which does an excellent job planting barley on 38 cm (15 inch) row spacing, but the Baches plan to reduce the row spacing in barley to 25 cm (10 inch) and will most likely change from the tynes to a disc system.
An NDF disc opener planter is used for summer crops, which are planted on 76 cm (30 inch) rows. All crops are sown using moisture seeking techniques, which Peter says is more important than precision planting when it comes to achieving even crop establishment.
“Although we have had a few failures with deep planting, it has generally been a good strategy for us,” he says. “The key is to plant deep but not put too much soil back over the seed. In drier years we also reduce the seeding rate to ensure even germination. Early summer planting dates seem to be the best-bet option for our district.”
The aim is to plant mungbeans between the rows of fresh barley stubble that is standing up well, but if the planter gets off line it can be hard to achieve proper seed-to-soil contact with the high level of stubble present. Ultimately, it would be good to have GPS steering on planter bar to ensure the planter tracks exactly between the rows of stubble.
In the lead-up to harvest both mungbean and sorghum crops are desiccated but this operation is too late to stop seed set on late germinated weeds. To prevent weed seed set in these in-crop escapes Peter is working on system that can be used to spray weeds in the inter-row just before the sorghum starts to flower.
At harvest the Emar chaff deck is used in all crops, every year. In the last five years this harvest weed seed control tool has had a massive impact by reining in large populations of Johnston grass.
“The chaff deck applied consistent downward pressure on the Johnson grass seed bank every year and also helps us manage feathertop Rhodes grass,” says Peter. “Of course, the benefit is most noticeable when populations start high, but it is also good to know that it is also effective in keeping numbers low across the farm.”
He has also noticed that the chaff deck is very effective in controlling volunteer crop plants. Having all the weed seed and any grain that was thrown out the back of the harvester placed on the wheeltracks makes control much easier and more effective.
“When we do fallow sprays, we run larger nozzles over the wheeltracks to make sure any weeds that germinate are controlled before they can set seed,” he says. “In some instances, the only weeds present in-crop are along the wheeltracks so we can just turn on the six nozzles running over the three sets of wheeltracks.”
The combination of the stripper front and the chaff deck has resulted in more crop and less weeds at ‘Kurilda’, even through a series of very dry years.

Article
Case Study

Elton and Pam Petersen, Moonie Qld

A SwarmFarm robot, ‘Oscar’, has added another dimension to Elton and Pam Petersen’s integrated weed management program, which features the majority of the WeedSmart Big 6 tactics.
In two summer fallows the Petersens have regained control of glyphosate resistant feathertop Rhodes grass (FTR) and awnless barnyard grass (BYG) that was threatening their 2000 ha dryland cropping operation at Moonie, on the Western Downs.
Elton and Pam Petersen, ‘Traighli’ near Moonie on the western Darling Downs.
The Petersens have achieved this remarkable feat after deploying ‘Oscar’ with a 12 m weedIT boom attachment. In the 20 months that Oscar has been spraying weeds in the summer fallow, ‘he’ has clocked up over 3000 hrs and passed over more than 25,000 ha.
Elton and Pam purchased ‘Traighli’, a 2370 ha grain and cattle property 5 km north of Moonie, on the western Darling Downs, in 2015. Previously they had farmed on the Fraser Coast growing sugarcane, soybeans and pineapples, and running cattle.
At the time of purchase, weeds that adapt well to conservation cropping systems had established populations that were impacting on the profitability of grain production. Elton’s initial plan was to use cultivation and blanket spraying to regain the upper hand, particularly of the herbicide resistant summer-growing grass weeds.
“Cultivation certainly helped reduce weed numbers, but was never intended to be a long-term, sustainable solution to manage these weeds. It was also too costly to use the blanket sprayer frequently enough to prevent seed set,” said Elton. “We were interested in optical spot spraying technology and everyone we spoke to who used this technology gave very positive feedback – except that it was still not practical to spray as frequently as is required to target small weeds.”
After further investigation the Petersens decided to invest in technology that would maximise the efficacy of the optical spot sprayer in their weed control program.
“Our choice was between a 36 m tow-behind weedIT boom and a 12 m weedIT boom mounted on a SwarmFarm robot,” said Elton. “We saw the robotic platform as a way for us to really hit our grass weed problem hard and to drive down the weed seed back as quickly as possible, with minimal operator input.”
The Petersens with SwarmFarm founders Andrew and Jocie Bate and SwarmFarm team members Tom Holcombe and Jarrod Jackson.
“In such a short space of time we have dramatically reduced the seed bank to the point where Oscar can work for up to 40 hours scouting and spraying weeds without the spray tank needing to be refilled,” said Elton. “This fact alone is incredibly important. It gives us much more freedom without compromising the weed management program.”
Elton has also experienced a significant mind-set change to weed management as a result of deploying Oscar. Applying constant pressure to small, fresh weed seedlings has seen the weed seed bank dwindle as no new seed has been produced for two summers.
When blanket spraying, Elton knew he was compromising on water and chemical rates in the interests of saving money and time. He said the focus was always on trying to make the spray operation more efficient and this often resulted in some weeds being larger than ideal when the herbicide was applied.
“With a tow-behind optical boom we would have improved our chemical and water application rates but not solved the frequency and consistency problem we had with the blanket spray system,” he said. “Automation brings the consistency. If Oscar goes out spraying and finds only a few weeds it only costs us $0.50/ha in diesel, and we are paying for the machine whether we use it or not.”
In the 2020/21 summer fallow, chemical costs totalled just $12.80 per ha for all the summer weed control and the pre-plant knockdown spray. Elton says this is equivalent to the cost of a single blanket spray in the past.
“In our old system we were never on top of resistant weeds and although the new system probably has similar costs, we are achieving a much better result,” said Elton. “We have essentially invested in technology that does a better job with less chemical – the long-term benefits have been realised more quickly than we dared to hope. The saving in chemical cost is even greater than I expected.”
Summer fallow spray program
In the 2020-21 summer fallow Oscar completed seven passes of the whole farm between mid-November 2020 and May 2021. For the 25-week fallow period, the property received around 650 mm of rainfall (more than the annual average for the property), with the longest stretch without rain being just 10 days. Being able to send Oscar out spraying almost immediately after rain has allowed the Petersens to treat each new germination of weeds while still very small. Elton also has Oscar set to only spray when the conditions are cool, to maximise herbicide uptake.
BYG sets seed very quickly, even quicker than FTR, so there is no opportunity to stop seed set other than killing the seedling before it seeds. Elton believes he is on track to eradicate both of these grass weeds within the next few years and will be able to reduce or eliminate the use of Group A herbicide in the summer fallow.
He says they are currently applying Group A herbicide in three passes, but each round is only using one drum of Group A product, across the 2000 ha cropped area.
The other fallow sprays are glyphosate immediately after harvest and after the first rain (for crop volunteers) and then the pre-seeding knockdown.
“This property is heavy grey cracking clay soil and melon hole country, so we have really noticed a difference in being able to access the paddocks with such a light machine much sooner after rain than is possible with a tractor,” said Elton. “Everything is centred on hitting weeds when they are very small and at their most susceptible to herbicide. This has resulted in a large reduction in the amount of chemical used.”
Another feature that Elton uses to enhance the efficacy of the pre-plant herbicide treatment is to slow Oscar down and increase the sensitivity of the optical detection to ensure that the very smallest of weeds are ‘seen’ and sprayed. This essentially saves them the cost of a pre-plant blanket knockdown.
Very clean fallow in the background compared to two passes that were missed due to an error in the robot’s instructions.
Winter weed control tactics
The Petersen’s winter cropping program is limited to growing chickpea, wheat and barley, so although they rotate the available chemistry, their options are restricted. When the opportunity arises they plant a summer crop followed by a winter fallow to target black oats and phalaris.
“We do one in-crop spray in wheat to target these grass weeds and are aware of the risk of Group A resistance in black oats, and a second in-crop spray is to control broadleaf winter weeds,” says Elton. “We use robust rates and ensure there are no survivors. A targeted winter fallow program would also go a long way to reducing the impact of herbicide resistance in black oats.”
Chickpea crops are now sown on the same 375 mm (15 inch) row spacing as the cereals, which is proving beneficial in both higher yield and weed suppression compared to the 760 mm (30 inch) spacing used previously in chickpea. Pre-emergent herbicide is applied ahead of chickpeas and in summer crops.
“We set our planting date to avoid frost risk and want to get the crop in as quickly as possible and have the option to use moisture seeking techniques in dry years,” says Elton. “You can’t overestimate the effect of canopy closure on weeds and evaporation.”
Resources

SwarmFarm: Targeting small weeds all year

Article
Case Study

Single family, Coonamble NSW

Tony and Sharon Single farm with Tony’s parents John and Mary, south east of Coonamble in northern NSW with views of the Warrumbungle Range.
Across the 4500 ha cropping area at ‘Narratigah’, the weed numbers are low as a result of the Single’s ‘farming moisture’ philosophy, which involves planting whenever there is sufficient subsoil moisture to establish a competitive crop on their heavy clay soils. Their location allows a mix of summer and winter cropping, so if there is an opportunity for a summer crop they take it, even if that might result in missing the winter crop.
Tony (left) and John Single use their Single Shot weed detecting drone to scout for and map weeds to create a prescription map for their tractor mounted boomspray.
“Farming moisture is our risk management strategy and it has paid off time and time again,” says Tony. “We are really farming with probability and by reducing our risk we have been able to maximise profits. If there is insufficient subsoil moisture we just don’t plant. This means we have very few failed crops and we take advantage of the intermittent winter fallows to run down the seedbank, particularly for winter-active grass weeds.”
Tony says the area has a slightly summer dominant rainfall pattern but rainfall is very variable. The main crops grown are wheat, chickpea and sorghum, along with any other crop that might fit a certain planting opportunity.
While their cropping decisions are very water responsive, there can be situations where the need for ground cover outweighs other considerations. This can occur after a chickpea crop and if they feel it is necessary, Tony and John will plant a crop just to produce stubble, knowing that the yield will most likely be low.
“Generally, if it is too dry to plant we will choose to fallow to build up the soil moisture profile knowing that this is the least-risk strategy and gives the best result in the long term,” says Tony. “We can effectively gain good weed control for the full 12 months through the use of cropping and fallowing in both winter and summer.”

Resistance status
Herbicide resistance is considered the biggest threat to their business even though they currently have resistant weeds well under control. Glyphosate resistance was first confirmed at ‘Narratigah’ in 2005 in annual ryegrass, and Tony and John are also aware of some small areas of glyphosate resistant barnyard grass.
“These are our most important weeds and keeping a lid on resistance is crucial to prevent them becoming limiting factors in our cropping choices,” says Tony. “We also have other weeds including milk thistle, fleabane, blow-away grass and feathertop Rhodes grass – the full suite of northern region weeds really.”
Tony says their efforts to consistently drive down the weed seed bank, and having regular winter fallows, minimises the impact of herbicide resistance on their business.
“Our weed seed bank is low and weeds do not dictate our cropping decisions,” he says. “Ryegrass has a relatively long growing season so we have ample opportunity to stop seed set through a winter fallow. There are also several chemical options for use with our spot spraying technology and new pre-emergent herbicide options too, along with cultural controls such as chipping.”
“We are more concerned about the implications of resistant barnyard grass, which washed in from up-stream. Barnyard grass has the ability to germinate and very quickly set seed, making it more difficult to contain.”
To avert the risk of more seed being deposited by overland flow, the Singles have constructed a number of diversion banks on the up-stream side of their cropping area to divert water.
Tony is also noticing ‘rate creep’ as weeds like milk thistle that are slow to metabolise herbicide, become harder to control. He says they are needing to use a higher rate of paraquat in the double-knock applications. The Singles are managing this through regular double-knocking in fallow and strategically using saflufenacil with paraquat to enhance control.
Black oats currently has a low resistance profile due to the use of winter fallows and fop chemistry is still effective in many paddocks.
The Singles use their proprietary drone weed mapping system ‘Single Shot’ to scout for and map weeds, helping them to better plan for and implement each herbicide application.
Their integrated weed management system is an excellent example of the WeedSmart Big 6 in practice.
#1 – Diversity in cropping
The combination of winter cereals, winter pulses and summer cereals provides many opportunities for controlling weeds pre-season and in-crop.
“The decision to plant sorghum is driven by weed and disease pressure in winter crops,” says Tony. “In a paddock that is becoming difficult to manage, we would rather change to sorghum than turn to a heavy reliance on pre-emergent herbicides and in-crop spraying of winter weeds in winter crops. Swapping to a summer crop gives us the opportunity to target problematic weeds using a winter fallow phase.”
This practice, plus the persistent drought in recent years, has resulted in more fallow area and allowed them to drive down the weed seed bank of annual ryegrass and black oats. It is now very rare for them to target grass weeds in-crop in winter cereals.
Using their drone and sensor to scout for and map weeds in the fallow periods has been a powerful tool to attack the weed seed bank in both summer and winter. Decoupling the weed detection and spraying operations opens up opportunities for more diverse weed control.
Tony and John can use the drone to map the presence of weeds just before, or soon after, significant rainfall events. Once they are able to get on the paddocks with the sprayer they can target previously existing weeds with spot spraying an effective herbicide mixture while applying a blanket rate to the new germination of weeds following the rain.
Knowing exactly what is in the paddock before they start spraying means they can consider a wider range of potential chemical options or techniques. Once the plan is made, they know how much product they will need and the cost. Knowing that they will only be treating say 5 ha in a paddock, they can afford to use chemicals that they would never consider for a blanket spray application.
#2 – Mixing and rotating MOA
Tony and John use some preemergent chemistry strategically in fallows to maximise weed control diversity while keeping their options open for cropping.
They aim to use a preemergent application to control key broadleaf and grass weeds after harvest, which takes the pressure off glyphosate without compromising planting opportunities the following autumn.
A combination of soil residual herbicides such as picloram, Balance and Flame has given good results early in the summer fallow, followed with a pre-sowing double knock of glyphosate and paraquat, giving a total of five chemical groups targeting fallow weeds. When it suits the program, they use chemistry mixes such as Sharpen + paraquat in the double knock, increasing the modes of action and increasing the efficacy of the treatment on the weed spectrum.
In addition to the use of preemergent chemistry, winter grass weeds are also targeted in broadleaf crops, usually with clethodim (Group A, Group 1), but the Singles are aware of the resistance risk and are looking to introduce Clearfield canola as alternative means of grass control in break crops, and to bring more diversity to their system.
Using their drone mapping technology, Tony and John can merge multiple flights of a paddock during the year into one map to show the location of all the weeds detected. This map can then be used to apply a site-specific soil residual herbicide for the next season to say 15 to 20 per cent of the paddock. In treating smaller areas, they can afford to consider chemistry that might otherwise be too expensive, add more diversity to chemicals used and reduce their plant-back risks.
#3 – Crop competition
The Singles consider crop competition to be their #1 weed control tactic, simply because it is the only one that provides season-long in-crop weed control.
“We do everything we can to maximise the crop’s ability to suppress weeds,” says Tony. “This starts at planting, where we have invested in planting gear with moisture seeking capability so we can plant crops on time and ensure good establishment. We take great care to ensure there are no gaps for weeds to exploit, and always square-off the headlands.”
Planting at 330 mm row spacing allows for inter-row sowing and stubble retention, and planting rates are chosen to maximise yield – with long-season wheat sown at 40 to 60 plants/m2, and later plant wheat sown at 80 to 100 plants/m2. The slope of each paddock dictates the tramline direction to be perpendicular to the overland flow, which results in most paddocks being sown north south.
For all crops Tony aims to achieve 100% knockdown prior to planting with a double knock treatment, followed with a well-established, vigorous crop.

#4 – Double knock
The Singles started using the double knock tactic twenty years ago in their winter fallows, and introduced it to summer fallows about ten years ago.
“The double-knock strategy hasn’t added significantly to our overall weed control costs,” he says. “When we first started using the double-knock we counted it as a direct cost to the system, but we now see the second knock with paraquat as a preemptive strike on future weeds – an investment in lowering the weed seed bank, and we are picking up savings with lower volumes of chemical required in subsequent weed control applications.”
The double knock tactic is now embedded in their weed management strategy and they have invested in spray gear to allow them to cover their area within the recommended 7 to 8 day window. Tony says the high level of control they achieve with the double knock means there are fewer and fewer weeds each year and this reduces the cost of the operation, particularly now they have the capacity to spot spray weeds with highly consistent weed detection.
“This tactic puts a significant dent in the weed seed bank and reduces the number of large and potentially stressed plants being sprayed,” says Tony. “This makes it a very effective resistance tool, particularly for our hard to kill weeds.”
#5 – Stopping seed set
The Singles are aiming for 100 per cent weed control in fallow, particularly for annual ryegrass and BYG, by managing paddocks in a site specific way at a square metre level using their drone scouting technology.
“The drone can effectively scout for weeds at a rate of 200 ha/hr, which makes it very quick and easy to scout a paddock and then go out and chip the five or so plants that might be left growing in a paddock,” says Tony. “This moves us closer to achieving 100 percent weed control. We have really driven down our weed numbers and significantly reduced the impact of herbicide resistance in our operation.”
Occasionally, Tony will drive along the tramlines in the side-by-side and chip out any grass weeds in chickpeas that have either escaped control or germinated late in-crop. Then prior to harvest, Tony and John look for any patches of weeds that have escaped control and take action to prevent seed set.
“If we find there is a patch of weeds getting away from us we don’t hesitate to sacrifice small areas of the crop to prevent seed set,” says Tony. “In 2020 we had a three or four hectare patch of ryegrass and decided to use a small slasher to mow the crop and weeds then sprayed the area with paraquat. That way we made sure the weeds did not set seed and prevented the spread of resistant weed seed at harvest.”
The Singles do not spray any selective herbicides outside their cropped area and prior to harvest they slash a 2 m width of crop along fencelines to stop the header bringing weeds into the paddock from the fenceline.
#6 – Harvest weed seed control
Several years ago, the Singles trialed narrow windrow burning for harvest weed seed control but decided that the negative effects outweighed the weed control benefits.
“For us, ground cover is supremely important for erosion control, reducing evaporation and increasing infiltration through the heavy clay soils,” says Tony. “We are watching the developments in impact mill technology and will most likely go down that path if we feel harvest weed seed control is needed in the future.”

Videos

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Video
Webinar

S-Metolachlor usage in the northern region

In this WeedSmart webinar, we talk to WeedSmart northern extension agronomist Paul McIntosh and Syngenta’s Field Biology Manager Rob Battaglia about how S-Metolachlor (Dual Gold) works, its efficacy, and what potential resistance problems might be around the corner. They explain what tactics growers should adopt to reduce potential resistance problems on this key grass weed herbicide, referring to the WeedSmart Big 6.
Topics covered include:

Application considerations for maximum efficacy
Incorporation
Effect of stubble
Herbicide solubility
Herbicide binding characteristics
Herbicide safener “EPIVIO-C”

Video
Video

Detect, then spray

For the past few years John Single and his son Tony have been using the air-borne weed sensor, Single Shot, developed by John’s other son Ben, to rapidly detect and map weeds on their dryland cropping property, Narratigah, near Coonamble, NSW. Read more here.

Video
Video

Optical spray has a good fit in CQ

CQ grain grower Kurt Mayne bought a weedIT boom in 2019 and has been impressed with the benefits that have come with the addition of an optical sprayer to their weed control program. Find out more here.

Fact Sheets

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Fact Sheet

Changes to herbicide Mode of Action (MoA) names

The global MoA classification system is based on numerical codes which provides infinite capacity to accommodate new herbicide MoA coming to market, unlike the alphabetical codes currently used in Australia.
Farming is becoming increasingly global. Farmers, agronomists and academics around the world are now, more than ever, sharing and accessing information to assist them to grow crops, while managing sustainability issues such as herbicide resistant weeds. It’s important then that the herbicide MoA classification system utilised in Australia be aligned with the global classification system. This will ensure more efficient farming systems into the future and allow Australian farmers and advisors to access the most up-to-date information relating to managing herbicide resistance.
CropLife Australia is working with key herbicide resistance management experts, advisors and the APVMA to ensure farmers and agronomists are aware of the planned changes.
The numerical classification system should be fully implemented by the end of 2024.
You can find further information by reading the factsheet and visiting the CropLife website here.

Fact Sheet

Sustainable glyphosate use in winter grain cropping systems in southern Australia

The number of glyphosate resistant weed species present in winter grain crops, along fencelines and in irrigation channels in Australia.

You can reduce the risk of glyphosate resistance in weeds if you follow the recommended practices in this factsheet.

Fact Sheet

Sustainable glyphosate use in Australian vegetable production

The number of glyphosate resistant weed species present in Australian vegetable production systems is increasing.

You can reduce the risk of glyphosate resistance in weeds if you follow the recommended practices in this factsheet.

Fact Sheet

Sustainable glyphosate use on roadsides, railways, public utilities and parks

The number of glyphosate resistant weed species present on Australian roadsides and railway lines is increasing.

You can reduce the risk of glyphosate resistance in weeds if you follow the recommended practices in this factsheet.

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