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This has been the key message of weed management experts in Australia ever since 1996, when Australia’s worst weed, annual ryegrass, was found to be resistant to our most useful herbicide, glyphosate.  
A few years later, the Australian Glyphosate Sustainability Working Group (AGSWG) was set up under the CRC for Australian Weed Management (Weeds CRC) to bring together commercial and research expertise from around the country with a determination to ‘keep glyphosate resistance rare’.
With investment from the Grains Research and Development Corporation, AGSWG established a database of confirmed cases of glyphosate resistance in Australia and developed information products for all users of this important weed control tool.
After guiding growers and agronomists through a critical 15 years of managing glyphosate resistance in Australia the AGSWG has been disbanded, however the work of advising farmers and other weed managers will continue.
Keep weed numbers low and do everything you can to prevent resistant weeds from setting seed.
Australian Herbicide Resistance Initiative (AHRI) director, Professor Hugh Beckie, says glyphosate means so much more than weed control to Australian farmers, particularly for dryland cropping.
“This herbicide has been the means of achieving incredible productivity increases in dryland crop production, initially providing an alternative to tillage for fallow weed control and thus conserving soil moisture over summer,” he said. “It is also now used as a broad spectrum knockdown pre-seeding and post-harvest in many crops and in RoundUp Ready cotton and canola.”
“As predicted, the incidence of glyphosate resistance is ramping up, having been heavily relied on for weed control since its introduction to Australia in 1976,” said Prof Beckie. “It is important to understand that glyphosate is not only used extensively on farms but also along roadways, fence lines, railway lines, in public parks and in home gardens. This means that resistance can, and does, evolve in many different settings and can move across the landscape in weed seeds and pollen.”
According to the International Herbicide-Resistant Weed Database there are currently 20 species and thousands of populations known to have evolved resistance to glyphosate in Australia.   
While this is a serious situation, and glyphosate resistance can no longer be considered ‘rare’, it is still possible to regain control of weed populations that have evolved resistance.
One of the useful products that AGSWG published was a series of factsheets outlining the practices that should be followed and those that should be avoided. These factsheets have recently been updated and published on the WeedSmart website.
There is a factsheet for each of the main glyphosate user groups – grain producers, cotton growers, horticulturalists, orchardists and vinegrowers, irrigators and managers of public lands and utilities. While the principles remain the same for all industries, there are some practical variations in implementation.
Using a diverse weed control program and taking care to apply glyphosate in the optimal way can tip the scales in the grower’s favour and keep this valuable product as an option well into the future.
Download glyphosate factsheets

Northern grains and cotton factsheet
Winter grains and irrigation factsheet
Orchards and vineyards factsheet
Roadside and railways factsheet
Vegetable production factsheet

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GRDC Grower Relations Manager – North, Richard Holzknecht, says while it is important that growers control fallow weeds early to maximise efficacy, it’s equally important spraying is only undertaken when weather conditions are right. Spray equipment also needs to be set up and operated appropriately.
“While spraying at night and in the morning is not restricted, product labels state that chemicals should not be applied when hazardous inversions are present,” Mr Holzknecht said.
He warned off-target damage could occur from physical drift and inversion drift, which posed a significant risk during summer spraying as day/night fluctuations in temperature often result in inversions forming overnight and or early in the morning.
“Wind speed, in particular, should be monitored at least every 15 to 20 minutes and if the wind drops, spraying should stop,” he said.
The main factors influencing drift potential were weather conditions at the time of spraying and how spray machinery was operated in terms of spray quality, speed and boom height. Photo GRDC
“So, planning and being proactive is extra important. Growers need to talk with their neighbours to determine the location of any sensitive crops, such as cotton, and ensure they understand label recommendations and permit regulations, particularly those governing the use of 2,4-D.”
Mr Holzknecht said the main factors influencing drift potential were weather conditions at the time of spraying and how spray machinery was operated in terms of spray quality, speed and boom height.
In an inversion, chemical droplets can remain suspended in concentrated form and be carried significant distances.
“It is important growers understand the weather conditions that indicate an inversion is present and avoid spraying during these times.
“Surface temperature inversions are often associated with calm, low wind conditions, dust remaining suspended, fog or mist forming in low areas and sounds travelling long distances. All these signs indicate the risk of inversion drift is significantly high.”
Mr Holzknecht advised growers and spray contractors to closely monitor weather conditions.
The Grains Research and Development Corporation (GRDC) is actively investing in spray application research and training to assist industry in implementing best-practice spray systems, and it recently released a new video explaining the key factors affecting spray drift.

Source article: Spray safely to reduce drift risk this summer
Spray drift in-depth resources

GRDC Spray drift hub
Stop the drift webinar
Are you going spraying, or killing weeds?
How do you manage summer weeds without spraying at night?
Spray wisely and well webinar
Effect of formulation and environment on dicamba volatility webinar
Spray well – correct nozzles, adjuvants and water rates

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Livestock containment areas allow the Eagles to rest their pastures and fodder crops, efficiently use a variety of feeds and restrict the spread of weed seeds. On top of this they have also seen benefits in growth rates and lambing percentages.
Sam says the six or seven hectares they have available for containment was not expensive to build and has made it much easier to manage their livestock and cropping enterprises.

“I’d definitely recommend building containment areas for sheep,” he says. “It is such a simple concept that has so many benefits. They really help to manage ground cover on your pastures and cropping paddocks, and in dry times they make feeding out much less stressful. In the last drought we had up to 6500 sheep in containment, including lambs, and I could feed them all in less than three hours, and didn’t have to feed every day.”
Sam and Emily use the containment areas for several purposes throughout the year. Although they generally keep their pasture and cropping paddocks separate, the sheep play an important role in weed management across the whole farm.
Horsham producer Sam Eagle uses every opportunity to maximise the synergies within a mixed farming operation.
“The containment areas allow us to bring in feed from outside if necessary and feed out screenings from our own grain, being confident that any weed seeds that come with that feed won’t be spread around the farm,” says Sam. “It is easy to manage any weeds that germinate in such a defined and small area of the farm.
“When we buy in sheep we shear them as soon as they arrive to remove any risk of them introducing weeds like Bathurst burr,” he says. “We use the containment areas to avoid overgrazing pastures so the sheep eat the weeds like barley grass as well as the more palatable species. They also provide an effective double knock effect for weeds that have herbicide resistance.”
Livestock containment paddocks boost productivity while stopping the spread of herbicide resistant weed seeds.
The Eagles cut weedy paddocks for hay or silage and feed it out in the containment areas where they can control any weeds that germinate. Sam says above-ground pit silage has been very cost effective at around $10 a cubic meter to cut the silage and store it under a tarp before feeding out in the containment paddocks.
“Silage is a very good weed control tactic,” he says. “You cut it early, so you are stopping weed seed set, and after three days of good weather you can spray out the paddock for a spray fallow.”
The Eagles prefer to either graze a crop fully or grow it for grain, having found that the ‘grain and graze’ tactic for dual purpose crops had an unacceptable yield penalty and opened up the canopy to allow weeds to grow through and compete in the grain phase.
Grazing cover crops and failed grain crops generates cash flow and helps manage weeds. Sam keeps an ungrazed reference area in dual purpose crops so he can remove grazing pressure at the right time if he wants to let the crop go through to grain.
They have found Moby barley plus clover to be the best cover crop to graze and then spray out. Oats and pasture are both cut either for hay or silage to conserve fodder and remove weed seeds.
“In the cropping paddocks sheep will eat most of the weeds that evolve herbicide resistance, like wild radish, annual ryegrass, fleabane and whip thistle. They also generate cash flow from cover crops and from grain crops that don’t go through to harvest due to drought, flood, weeds or frost,” says Sam. “Over summer the sheep reduce our herbicide costs and reduce the stubble load, which makes sowing easier. Once the feed supply runs out, we put the sheep into containment until they start to lamb. This allows the pastures and crops to get ahead and gives us good feed to put the ewes into for lambing.”
“The sheep can make inter-row sowing more difficult in our CTF system so we have to be careful to cut the stubble 300 mm or less above ground level so the stalks don’t lodge across the inter-row as the sheep graze the stubbles,” he says. 
Having used narrow windrow burning as their harvest weed seed control tactic for six years, Sam and Emily used a contract harvester with an impact mill for their harvester for the 2018 season. They were pleased with the job the mill did and are looking to purchase one of their own once the technology matures a little more. They use crop-topping in pulses and windrowing in canola to stop weed seed set and also spray herbicide under the cutter bar in canola.
“We test weeds for herbicide resistance so we know what still works and plan out a diverse herbicide program with multiple chemical groups used in a broad crop rotation,” says Sam.
Other than the grazing and weed management benefits, Sam and Emily have also found numerous productivity benefits for their 2500-strong merino flock. Using the containment yards for joining has seen increased conception rates and after preg-testing their ewes, Sam and Emily make separate mobs for the twins and singles so they can better manage the ewe’s nutrition while in containment. Once the lambs are weaned and are brought into containment their growth and feed utilisation rates are higher than when paddock grazed, meaning the returns on feed inputs are higher and the Eagles are able to either turn off hoggets earlier or at a higher weight.
Building and using containment areas
Size and design – they can be any size, provided an allowance is made for 2 to 5 m2 per sheep (2000 to 5000 sheep per ha). At the right stocking density the containment yards compact well and do not generate dust or strong odour. Place the food and water sources as far away from each other as possible in each containment yard – this helps keep the water troughs clean.
Water – sheep require 6 litres of water each per day and more in very hot weather. Flow is more important than pressure, so use thicker pipe (e.g. 30 to 50 mm) to supply the troughs.
Feeders – feed can be placed in self-feeders, feed troughs or on the ground.
Place the water and feed sources at opposite ends of each containment yard to keep the water clean for longer, and provide as much shade as possible.
Shade – think about shade when designing the containment areas and look for ways to provide as much shade as possible. Protect any established trees.
Feedstuffs – utilise a variety of feeds such as screenings, canola, hay, purchased grain and silage. Match the nutrient value of the feed with the class of animal you are feeding and supply any necessary mineral supplements. Get advice if you don’t have a good knowledge of animal nutrition.
Stock health – give sheep 6-in-1 vaccines and drench before putting a mob into containment.
Key benefits

Less feed wastage means feed costs are reduced and productivity is higher with more lambs produced (higher conception rate) and faster weight gain compared to paddock grazing.
The containment paddocks can have a variety of uses including being a fire break, lamb feedlot, shearing holding yard and joining paddock. Move sheep out once lambing commences.
Holding sheep in the containment paddocks allows the pastures and fodder crops to create a green wedge of feed before being grazed. They also provide a suitable place to hold sheep once the pastures and fodder crops have run out in summer, maintaining groundcover levels across the farm.
Good for your mental health in drought conditions as you don’t have to drive around dry paddocks every day, feeding doesn’t take as long each day, ground cover is preserved across the farm and the sheep can be kept in good condition.

More information

Eagle family case study
Sheep confinement area fact sheet

Unfortunately, glyphosate resistance seems to confer no such disadvantage on awnless barnyard grass.
In a recent random survey of summer-growing weeds in the northern grains region, 36 per cent of awnless barnyard grass (Echinochloa colona) populations proved resistant to glyphosate.

Awnless barnyard grass response to no crop competition – glyphosate resistant (GR) ABG with 0 mungbean plants/pot (left) and glyphosate susceptible (GS) ABG with 0 mungbean plants/pot (right).
Through a focused effort to better understand this problematic weed, GRDC invested in a series of studies on various aspects of its ecology. This work was done by QAAFI weed researchers, led by Dr Bhagirath Chauhan at the University of Queensland, Gatton.< “Awnless barnyard grass is one of the top three most problematic weeds of summer crops and fallows in Australia,” says Dr Chauhan.
“Our studies looked at environmental and cultural effects on germination, the impact of crop competition and early weed control, seed retention at harvest and the effect of low rates of glyphosate.”
These studies confirmed that awnless barnyard grass can emerge in spring, summer and autumn in Queensland, with temperature being the main driver of seed germination.“Germination is rapid for seed exposed to the light on the soil surface, as in no-till summer fallows,” he says. “As the temperature increases, seed buried up to 8 cm below the surface can also germinate. Covering the soil with crop residue suppressed germination by about 20 per cent, from 70 per cent without cover down to 47 per cent with sorghum trash.”
To run down the seedbank of awnless barnyard grass, whether glyphosate resistant or not, requires two to three years of no recruitment through ‘seed rain’. Strategic tillage is only useful if the seed bank is buried to a depth of more than 8 cm and then not disturbed again for many years as the seed will persist for longer than two years once buried.
“The best way to reduce seed production in this weed is to grow competitive crops in summer and to focus on controlling weeds for the first two weeks after crop emergence,” says Dr Chauhan.
“Both mungbean and sorghum crops can significantly suppress awnless barnyard grass growth and reduce the quantity of seed set over the warmer months.”
“Compared with weed plants grown alone, mungbean interference of four and eight plants per pot reduced weed seed production by 85 to 95 per cent. These reductions were similar for both glyphosate resistant and susceptible biotypes.”
Mungbean crop competition suppresses awnless barnyard grass (crop plants removed to show the effect on weed growth and habit. From left to right: GR ABG with 4 mungbean plants/pot; GS ABG with 4 mungbean plants/pot; GR ABG with 8 mungbean plants/pot; GS ABG with 8 mungbean plants/pot.
Likewise, even a sorghum crop at one metre row spacing, suppressed weed growth and seed production. Awnless barnyard grass produces 4000 seeds per plant when emergence is with the crop, 1000 seeds per plant when emergence is two weeks later and less than 100 seeds per plant when emergence is four and six weeks after crop emergence.
“This shows the importance of early weed control – even in widely-spaced sorghum,” says Dr Chauhan. “Plants that do emerge with the sorghum crop or within the first two weeks retain about 45 per cent of their seed at harvest.
Although larger plants produce more seed than smaller ones, plant size did not predict the level of seed retention at sorghum harvest.”
Awnless barnyard grass response to early weed control in wide-row (1 m) sorghum – BYG emerging with the crop (left) vs emerging after the crop (right).
While harvest weed seed control might be less practical in sorghum than other summer crops, removing almost half of the seed produced in-crop would be a valuable contribution to reducing the seed bank.
The random weed survey indicated that all populations, whether resistant to glyphosate or not, were susceptible to propaquizafop, clethodim and imazapic, providing some herbicide options for growers to achieve early weed control.n terms of pure plant ecology, there were few surprises – some awnless barnyard grass biotypes are more invasive than others, but growth and seed production of this weed at all moisture levels and environmental conditions ensures survival of the species and contributes to its weedy nature.
“In a study of ten awnless barnyard grass populations we saw large variations in many traits, but growth behavior and seed production potential in these populations did not help predict the likelihood of glyphosate resistance evolving,” he says. “Soil moisture is the main driver of weed growth and seed production.
However, when this weed is well-watered even the glyphosate-resistant populations were three times more susceptible to the herbicide than when the weed is water-stressed.”

In both resistant and susceptible biotypes, very low rates of glyphosate were shown to stimulate growth. This is known as the ‘hormesis phenomenon’, where a stress can stimulate a positive response.
Plants treated with glyphosate at active ingredient rates of 2.5 to 40 g/ha grew taller and produced more leaves, tillers, inflorescences and seeds than the control treatment. These rates are far lower than label rates for awnless barnyard grass and demonstrate the importance of accurate mixing and application of herbicides to ensure lethal rates are applied.

These weed ecology studies have demonstrated that glyphosate resistance in awnless barnyard grass does not confer any advantage or disadvantage over susceptible biotypes. The recommendation then is to treat all populations as resistant to glyphosate and to stack as many of the WeedSmart Big 6 tactics against it as possible, even if each tactic only provides a relatively small control benefit.

More resources

Webinar – Weed biology insight to improve the management of feathertop Rhodes grass and barnyard grass (the barnyard grass segment starts at the 30 min mark)  

The extent of herbicide resistance in summer grasses revealed 
Getting on top of barnyard grass in summer crops and fallow
Creating stiff competition against summer weeds

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Barley grass has a number of tactics up its sleeve to help evade both herbicide and non-herbicide weed control methods. This has made it a weed of interest for the University of Adelaide’s Weed Science Group, led by Associate Professor Gurjeet Gill, who are investigating the ecology of emerging weeds in the low rainfall zones of southern Australia
University of Adelaide researchers Dr Gurjeet Gill and Ben Fleet say that understanding weed ecology and undertaking herbicide screening will help find ways to manage increasing resistance in barley grass.
With investment from the GRDC, Dr Gill and his team analysed the dormancy traits and herbicide resistance status of 146 random samples of barley grass collected by agronomists in WA, SA, Victoria and NSW in 2018.
Of the 146 random samples collected, five per cent of populations showed resistance to Group A herbicides and 21 per cent showed resistance to Group B herbicides. There was no evidence of resistance to glyphosate or paraquat.
There were also large differences between the populations in the level of seed dormancy as seen by the timing of seedling emergence in autumn. Barley grass populations from the Eyre Peninsula in particular were much slower to establish than those from other low rainfall regions. Late emerging weeds can escape weed control with knockdown herbicides.
In a later study, growers from the Eyre Peninsula Agricultural Research Foundation (EPARF) collected samples of barley grass seed in 2019 from paddocks where growers had experienced difficulty in controlling barley grass with herbicides. These samples were tested for resistance screening in 2020.
Resistance screening of barley grass from suspect paddocks on the Eyre Peninsula, SA.
“The expectation was that most populations from the targeted survey in 2019 would be resistant to Group A herbicides,” says Dr Gill. “Resistance to the Group A herbicides was confirmed in 17 of the 22 populations from EP, or 77 per cent. Within this Group, resistance to quizalofop was 100 per cent for the suspect populations while there remains some useful activity from clethodim and butroxydim, which will help the growers in the short term.”
Herbicide resistant barley grass shows no response to a high rate of the commonly-used Group A herbicide, quizalofop (right) compared to a plant from a susceptible population (left).
The same populations were also tested with Group B imidazolinone chemistry, which offers some activity against Group A resistant barley grass, although one of the EP populations was completely resistant to the IMI herbicide. The good news is all of these populations remain susceptible to glyphosate and paraquat.
Dr Gill says that research and field observation confirm there is significant variability in barley grass populations’ ecology and herbicide resistance status.
“Understanding how different barley grass populations behave is key to their management,” he says. “The seed dormancy and seed shedding traits of a population have important implications in terms of management options. Barley grass often evades pre-emergent herbicides through delayed emergence and at the other end of the season barley grass often sheds its seed before crop maturity, so harvest weed seed control is rendered ineffective in many circumstances.”
Barley grass is susceptible to strong crop competition, and on mixed farms Dr Gill says some farmers have had success using pyroxasulfone herbicide in wheat ahead of a pasture phase, where good grazing management can limit seed production in barley grass.
Applying the WeedSmart Big 6 integrated weed management strategy to barley grass will keep herbicides working for longer and maximise the impact of cultural control tactics.

Chris Davey has been advocating planned and sustainable weed control programs with growers on the Yorke Peninsula for many years and has been a great supporter of the WeedSmart message in his patch and beyond.
In August Chris accepted an offer to join the WeedSmart team as the new Southern Extension Agronomist. He joins Peter Newman in the Western region, Greg and Kirrily Condon in the East and Paul McIntosh in the North.
Chris Davey, YP-AG has joined the WeedSmart team of extension agronomists and played a key role in coordinating the 2020 WeedSmart Week in Clare, SA.
Chris has hit the ground running with his first responsibility being to coordinate the 2020 WeedSmart Week event in extraordinary circumstances.
The annual 3-day event went off without a hitch around Clare in early September, with growers and agronomists from across South Australia hearing from experts in herbicide resistance management and visiting farms where growers have implemented a range of strategies to keep weed numbers low.
“WeedSmart Week is a terrific way to share ideas and information surrounding integrated weed management,” says Chris. “We are all challenged with the task of using herbicides strategically within a management program that also includes many non-chemical tactics. There is solid science behind the recommendations and experience in the field shows that WeedSmart’s Big 6 approach is practical and effective.”
Justin Harris, Davon Pastoral Co, Thomas Plain (second from left) was one of the six host farmers for WeedSmart Week 2020, Clare SA.
In welcoming Chris to the WeedSmart team, program manager Lisa Mayer says having an extension agronomist of Chris’ calibre dedicated to sharing the WeedSmart message with growers in southern Australia offers many opportunities to ramp up the pressure on herbicide resistant weeds in the region.
“Southern growers are facing some serious issues with herbicide resistance impacting on their farming decisions,” she says. “Chris and the other extension agronomists in the WeedSmart team have a wealth of experience and knowledge, particularly in their own regions, and this underpins their work in adapting the Big 6 principles to suit the conditions in each farming system.”
“We are thrilled to have been able to successfully deliver WeedSmart Week in South Australia this year amid great uncertainty,” says Ms Mayer. “The forum and field tours came together very successfully due to the local support from Chris and the YP-AG team, along with our collaborators – Pinion Advisory agronomist, Jana Dixon, and the Hart Field Site Group.”
WeedSmart program manager Lisa Mayer and GRDC Manager Weeds, Jason Emms at the 2019 WeedSmart Week in Emerald, Qld.
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.
WeedSmart Southern Extenion agronomist Chris Davey discussing the pros and cons of different harvest weed seed control systems with growers Gary Bruce (left) and Jarrad Cock (right) at the WeedSmart Week machinery site.

As farmers get their hands on fast and accurate weed mapping technology, the frequency of blanket herbicide spraying can be greatly reduced. With an accurate digital map that shows where the weeds are right now, most boomspray rigs can become low-cost spot sprayers.
For the past two 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.
 
John Single with a drone carrying the Single Shot weed sensor. By separating the weed mapping and weed spraying tasks the Singles can take a planned approach to their weed management throughout the year.

Ben saw the benefits of separating the weed detection and weed spraying tasks and set about building the platform and working with Robotic Systems to bring the idea to reality.

“The main aim is to stay ahead of herbicide resistance,” says John. “Ten years ago we started work on developing drone-mounted sensors that could take over the task of detecting weeds in a green-on-brown situation. Many sprayers, particularly later models, do not require any modifications and there are many benefits in having the weed mapping done separately rather than on-the-go.”

Weed maps enable growers to take a planned approach to their weed management throughout the year and to build a historical record of weeds in a paddock. The Single Shot sensor maps green-on-brown but are not limited to fallow situations. The sensors can be used in newly sown crops to map weeds that emerged on the planting rain or were missed in a previous application.

These patches, or individual weeds, can be treated in-crop or a pre-emergent can be applied to the patches at the end of the season. The sensor can also be used in-crop to identify high biomass areas within a paddock where high weed density requires more drastic action, such as cutting for hay, and in wide-row crops where the canopy does not fully close and weeds can be detected between the rows.
Screen shot of the Trimble guidance screen in operation with a Single Shot spray map.

The Singles have used the Single Shot technology in several different management scenarios already and the possibilities seem endless. John says they have used the sensor to identify survivor marshmallow and milk thistle plants in fallow and then spot spray them with a high rate of Starane to prevent seed set. They have mapped feathertop Rhodes grass in wheat to generate a map for applying pre-emergent herbicide post-harvest and have filtered data to segregate weeds based on size, giving them the option to apply a blanket spray on smaller weeds and a herbicide spike to treat larger weeds, or to use a second boom to apply two different products or rates. Where pre-emergent herbicides are used, a perimeter determined by the user can be added to cover the seed distribution area of the mother plant.

Another important role for Single Shot at Narratigah is to scout for survivor weeds after herbicide applications. The Singles crop 4500 ha and can map the farm at a rate of up to 300 ha per hour. This is one of the most important tasks in a herbicide program and yet it is generally not done effectively due to the time required. Having ‘eyes in the sky’ makes routine and accurate scouting practical after every spray treatment.

The sensor is capable of covering 300 ha/hr under continuous flight or targeting weeds greater than 5 cm diameter. Under normal operating conditions, and including battery changes, the Singles achieve a work rate of around 200 ha/hour. Critically, data processing can be done in the field, if the internet is available at the site, and is done at a speed 1.7 times faster than flight time.

Once a weed map has been created, the drone can be sent out again to take high resolution imagery of plants in specific locations in the paddock for identification purposes, allowing John and Tony to plan a herbicide program with their agronomist, based on exactly what’s in the paddock.

When it comes to spraying, having the weeds mapped before the spray operator gets in the cab means that the job can be done when conditions are suitable, including at night.

The real power of the Single Shot system is the ability to run simulations and to re-process the data to fine-tune a herbicide program based on weed size or density. The sensor requires just a 1 cm ‘brown’ perimeter around a weed to be able to detect the weed size.

The weed maps are built from images that are ten thousand times higher resolution than satellite images, giving a 1 cm sampling size. Every part of the paddock is photographed twice so obstacles such as stubble occlusion can be significantly reduced. The drone flies at a height of 75 m, following a pre-determined path, and can also be flown lower and or slower if necessary to collect specific data. The sensor also accurately identifies stressed weeds.

“Information is power and this has really put us back in control of our weed management,” says John. “We know how much chemical to buy to do the job at hand, we know the costs and can alter the chemistry to suit a budget if necessary, we can choose to blanket spray or spot spray, and our ability to apply the double knock tactic is greatly improved.”

Ready for unmanned aerial vehicle (UAV) spraying
In a bid to be one step ahead of the game, the Single Shot software will also calculate the shortest path for the sprayer, which is most useful when doing spot spraying on an ATV, or in the future, to deliver herbicide via a drone-mounted sprayer (UAV) or autonomous vehicles.

“We ran a scenario for treating about two thousand survivor weeds in a 125 ha paddock using a spray drone,” says Ben. “To apply a blanket spray to the paddock, the spray drone would need to travel about 310 km. Using the Single Shot software we determined the shortest path to reach all the weeds, which cut down the time required to do the job to just two and a half hours. The sprayer would only be applying herbicide for 16 km of the 54 km flight, and just 5 per cent of the paddock would have herbicide applied.”
Left: Actual weed coverage in a 125 ha paddock (blue line is the boundary, and purple is weed). Right: The path that the UAV would travel using the shortest route computation.

Weed mapping using tools and systems like Single Shot are putting growers back in the driving seat to cost-effectively and consistently implement the WeedSmart Big 6 tactics that underpin sustainable herbicide use and maintain productivity gains through no-till farming systems.

Low weed seed banks underpin all profitable farming enterprises. Keeping weed numbers low and quickly regaining control of blow-outs is the sole purpose of the WeedSmart program.
Each year growers and agronomists are invited to attend WeedSmart Week, somewhere in Australia. This year the 3-day event will begin with a 1-day forum at Clare Golf Club on Tuesday 1 September. The following two days will be spent touring farms in the Clare region to see how growers are implementing the WeedSmart Big 6 tactics to minimise the impact of herbicide resistance on their businesses. The WeedSmart Week theme ‘Diversify and Disrupt – Use the BIG 6 to beat crop weeds’ says it all!
YP AG senior agronomist Chris Davey (right) is encouraging growers from South Australia and beyond to attend WeedSmart Week in September as a good opportunity to formulate a plan to manage weeds throughout the year and through the rotation using the WeedSmart Big 6.
This flagship event of the WeedSmart program is supported by GRDC as the major sponsor and a wide range of herbicide and machinery companies that have skin in the weed control game. This year’s event will be co-hosted by Pinion Advisory, YP AG and the Hart Field Site Group and will be the sixth WeedSmart Week event.
WeedSmart program leader, Lisa Mayer says the event in Clare is the first of its kind for South Australia, giving growers and agronomists access to practical research and implementation of tactics that are known to effectively manage the risk of herbicide resistance in weeds.
“Weeds have gained the upper hand on some farms and have too much influence over farming system decisions,” she said. “The herbicide and non-herbicide tactics that form the WeedSmart Big 6 have been researched and demonstrated in the field – we know they work! Growers and agronomists in each region and on each farm can adapt the Big 6 principles to bring more diversity to their farming system and bamboozle weeds.”
“WeedSmart is committed to exploring and promoting farming systems and technologies that produce ‘more yield, fewer weeds’ every year.”
WeedSmart Week brings together a wealth of knowledge and experience from local and inter-state growers, researchers, advisors and technology experts – putting the spotlight on herbicide resistance and weed management. Growers can see what is and isn’t working first-hand and consider how key principles can be applied directly to their own farming operation.
At the forum and on the bus trip growers, agronomists and researchers put all the options and ideas on the table for discussion. In August last year, leading agronomist from YP AG, Chris Davey attended the Horsham event along with Pinion Advisory agronomist, Jana Dixon, and growers Jarred Tilley and Adam Cook.
Chris says it was a very valuable experience that gave him the opportunity to interact with growers and industry people involved in weed management in a range of environments.
The machinery displays and demonstrations at WeedSmart Week events are a great opportunity to see some of the newest weed management technology and grower innovations.
“The interaction between attendees was excellent as growers and agronomists swapped experiences and things they had learned about tackling certain weeds or modifying equipment,” said Chris. “Having WeedSmart week in Clare this year is a fantastic opportunity, particularly for South Australian growers, to get together and discuss new ideas and learn how different tactics are working for other growers.”
There will be a focus on both herbicide and non-herbicide tools and plenty of chances to see how mechanical tactics like harvest weed seed control can fit into a variety of farming systems to drive down weed numbers.
Jarred Tilley, a mixed farmer at Kapunda, will be one of the host farmers for the WeedSmart Week farm tour. Jarred is tackling glyphosate resistant ryegrass and has recently added a chaff cart to their weed management strategy. He has had good success with baling the chaff and using it to improve the profitability of their livestock enterprise.
The growers, agronomists and researchers speaking and participating in expert panels at the Day 1 forum will spark important discussions about herbicide resistance and how the Big 6 tactics can be used to target the weed species and farming systems in the southern cropping region. There’s one thing for sure – doing nothing is not an option.
Day 2 and 3 will be bus tours to farms in the Northern Yorke Peninsula and the Mid to Lower North regions around Clare. Attendees will have several opportunities to see and discuss cutting-edge technologies such as the latest sprayer technology and a range of harvest weed seed control implements, including impact mills and chaff decks, and will find out how other growers in the region are implementing the Big 6 weed management tactics in a variety of farming systems and environments.
Register for this important 3-day event for the ‘early bird’ single ticket price of $165 (GST incl), guaranteeing a seat on both the bus tour days as well as the forum, all fully catered here!
WeedSmart is committed to the health, safety and well-being of everyone working in, and in support of, the Australian grains industry. WeedSmart Week may be postponed in response to the current coronavirus outbreak, and in accordance with Australian Government advice in relation to social distancing.

Wheat and canola crops offer growers some really practical options to improve crop competition against weeds, particularly grasses, and vastly reduce weed seed set.
Researchers at the University of Adelaide, led by Dr Chris Preston and with GRDC investment, conducted an extensive study to identify the agronomic factors that promote strong early crop growth.

They found that simple strategies of growing hybrid canola and sowing wheat early, can couple with pre-emergent herbicides to achieve a very effective double-knock. The result is more yield, less weed seed produced and less selection pressure on the herbicides.
“In the canola trial we used a range of pre-emergent herbicides and compared open pollinated and hybrid canola,” says Chris. “The bottom line of our trial is that if you grow a hybrid canola with pre-emergent herbicides and do nothing else different, you’re going to reduce your grass weed seed set by 50 per cent.”
If you grow a hybrid canola with pre-emergent herbicides (left) and do nothing else different, you’re going to reduce your grass weed seed set by 50 per cent (right, conventional canola and no pre-emergent herbicide).
This level of non-herbicide weed control was also measured in an Australian-first study that looked at the competitive ability of 16 canola genotypes against annual ryegrass and volunteer wheat over two contrasting seasons, led by Professor Deirdre Lemerle at Charles Sturt University.
In a separate trial conducted by Rohan Brill, former research and development agronomist, NSW DPI based in Wagga Wagga, and colleagues at Trangie and Tamworth, a rule of thumb was established that seed size had a greater effect on early biomass production in canola than did cultivar type (hybrid vs OP). This gave rise to the recommendation that all farmer-retained OP canola seed be cleaned and graded to collect planting seed that is 2 mm in diameter or larger.
Their study showed that sowing large canola seed, regardless of the cultivar, is key to strong early crop growth and the crop’s ability to compete with weeds.
Having observed that later planted wheat often hosts more weeds, the Adelaide University team looked at the effect of planting wheat as early as possible.
“Our previous idea for managing weedy paddocks was to delay sowing, apply another knockdown treatment to control more weeds and then put the crop in,” says Chris. “In this trial we found that even in weedy paddocks you can put the wheat in early with a robust pre-emergent herbicide package, and the result is more wheat yield and less ryegrass seed at the end of the season.”
Dr Chris Preston, University of Adelaide, says if you sow the right wheat variety early and apply the right pre-emergent herbicide package, you can halve your grass weed numbers, just from competition in the middle part of the season, and you don’t have to change anything else.
“If you sow the right variety early and apply the right pre-emergent herbicide package, again you can halve your grass weed numbers, just from competition in the middle part of the season and you don’t have to change anything else.”
There are a few practicalities to consider when looking to sow wheat earlier. Firstly, you need to choose a variety that will still flower in the right flowering window for your location. If you are sowing several weeks earlier than normal you need a longer season variety to manage frost and heat risk at the end of the season.
Crop competition trial site at Roseworthy, SA.
Secondly, if you are sowing completely dry, then most of the pre-emergent herbicide options are open to you. If there is some soil moisture, but not enough for crop germination, some of the pre-emergent herbicides will not perform well. You need to give careful consideration to your choice of herbicide to suit the environmental conditions of each season.
These findings underpin WeedSmart’s aim, to promote farming systems that produce ‘more yield and less weeds’.
More resources:

Best seed, best establishment and fewer weeds
Choose highly competitive canola

WeedSmart Scientific Partner

Barley is known as a fairly competitive crop, but not all genotypes are equal when it comes to weed suppression and weed tolerance.
To un-pick the complex mechanisms behind competitive ability in barley, QAAFI weed researchers Gulshan Mahajan and Bhagirath Chauhan, and cereal plant breeder Lee Hickey, teamed up to quantify the effect of weed interference on commercial and elite-line barley genotypes.

Their two-year field trial compared the competitive ability of eight barley genotypes against a mimic weed (oats) by measuring weed biomass, weed seed production and barley yield.

Weeds can cause huge yield losses in barley – between 43 and 78 per cent difference between weedy and weed-free growing conditions for the eight genotypes tested.
There is considerable variation in the weed competitive ability of current and elite breeding lines of barley in Australia.
The most weed suppressive variety, Westminster, reduced weed seed production by 73%, compared with that of LaTrobe. Similarly, weed biomass of Westminster reduced by 55%, compared with that of LaTrobe.
There is scope for the development of high-yielding weed-competitive barley genotypes through additional screening of elite lines in weedy conditions.
Higher panicle production in barley appears to be a strong indicator of a genotype’s competitive ability.

When it comes to using a crop to compete with weeds there are two discreet mechanisms –

weed suppression, where the growth and seed production of weed plants is reduced and
weed tolerance, where crop yield is maintained, even in weedy conditions.

The most competitive genotypes will use both of these mechanisms and knowing which mechanisms are at play is valuable information when planning an integrated weed control program. Competitive genotypes are a powerful non-herbicide weed control tactic and growers will gain significant benefits if they can plant a strong weed-suppressive crop into a weedy situation, particularly if they do not have to sacrifice yield.
While yield and malt quality have driven the barley breeding program to date in Australia, this research suggests that there is great advantage in understanding the response of the variety to weed pressure.

Observations on the competitive ability of the four commercial varieties tested:

Commander barley is both weed suppressive and weed tolerant. If sown with an effective pre-emergent herbicide, Commander is probably the best choice to maintain low weed numbers.
Westminster is the most weed suppressive and might be a better choice if weed numbers are starting to increase, or for use in low input and organic production systems. Westminster is not weed tolerant, so a significant yield penalty should be expected in weedy situations.
Although Compass is tall and has a droopy architecture (like Commander and Westminster) it is not weed suppressive or weed tolerant, and should only be chosen for weed-free situations.
LaTrobe is the least weed seed suppressive but is weed tolerant, maintaining a reasonable yield in the presence of weeds.

The competitive ability of a particular genotype may vary in different locations, seasons and management systems, and in the presence of different weed species.
Experimental design features
The experiments were conducted in 2017 and 2018 at the University of Queensland research station at Gatton. The crops were sown at a depth of 5 cm in rows 35 cm apart on 17 May 2017 and 23 May 2018. The crops were irrigated to maintain field capacity and were harvested on 4 November 2017 and 28 October 2018.
There were eight barley genotypes, weedy and weed-free treatments and three replicates.
Four of the barley genotypes are commercial varieties and four are elite breeding lines being assessed prior to commercial release. Like most other plant breeding programs, Australian barley varieties are usually screened in a weed-free environment with a focus on yield and malting qualities.
In this experiment, each genotype was sown at the recommended seeding rate (125 kg/ha) in a weedy and weed-free environment. Oats was used as a mimic for wild oats, a serious weed in barley. Wild oats could not be used because it has non-uniform germination and sheds its seed before barley harvest.
The plot size was 8 by 1.4 m. The weedy plots were sown with a commercial oat variety at a target density of 40 plants/m2.
There was no significant seasonal effects so data from the two seasons could be analysed together.
Weed infestation and genotype influenced the number of panicles produced per metre row length of the barley crop and crop yield. Only genotype influenced crop plant height.
While genotype had a significant impact on weed biomass, weed seed yield, weed-tolerance ability and weed-suppressive ability, phenotypic traits are not always a reliable indicator of a genotype’s weed suppressive ability or weed tolerance ability.

 
In this experiment, panicle number was a good indicator of both weed suppressive ability and weed tolerance ability, but plant height and architecture were not reliable indicators.
Left: Weed seed yield in weedy treatment for each barley genotype.Right: Effect of barley genotype and weed treatment on barley grain yield.
Other factors, such as lodging and harvest index, will also need to be considered in a variety selection process but were not measured in this experiment.
Some genotypes possess both mechanisms for competing successfully with weeds while others possess one but not the other, and some have poor suppression and tolerance.
Table: Plant attributes and mean values for the weed-tolerance ability and weed-suppressive ability of the eight tested barley genotypes.
This research suggests that screening barley varieties in a weedy situation may provide valuable information to growers seeking to choose varieties that will provide the greatest weed suppression and or weed tolerance in weedy paddocks. It is not possible to screen for competitive ability in a weed-free environment and there is clearly scope for the development of high-yielding weed-competitive barley varieties in Australia.

In the face of increasing herbicide resistance in key weed species, the value of non-herbicide weed control tactics increases considerably.
The real value of crop competition (narrow rows, high seeding rate, weed-competitive genotypes) comes to the fore a few weeks after planting and through the main growing season to suppress late emerging weeds. Herbicides will remain the main tool for weed control in preparation for planting and to provide a weed-free environment for the crop to establish and rapidly achieve canopy closure.
This research was conducted and funded by the University of Queensland, a WeedSmart scientific partner.
Related resources:

Read the published paper
QAAFI – a WeedSmart research partner
WeedSmart Big 6 – Grow a competitive crop

This winter, researchers are recommending that growers and agronomists consider collecting live plant samples for herbicide resistance testing as a first step to identify and manage herbicide resistance in crop.
The first multi-species herbicide resistance survey conducted in the Northern grain growing regions of NSW and Queensland has shown that testing for herbicide susceptibility is well worthwhile as there are likely to be products that are still effective on weeds that are resistant to other modes of action.
Dr John Broster, Charles Sturt University recommends growers conduct regular herbicide resistance testing to better inform their herbicide program decisions.
Results from the ‘Quick Test’, offered by Plant Science Consulting, will usually provide a guide for herbicide strategies to use in the current season to stymie the effects of herbicide resistance. If weeds escape herbicide applications early in the season they will add large quantities of seed to the weed seed bank for next year, but if these plants can be killed this season their impact will be greatly reduced.
Testing weed seed at the end of the season is also a valuable tool to make more informed decisions for next season’s herbicide program, particularly for pre-emergent herbicides, which cannot be assessed using the Quick Test. There are three weed seed testing services in Australia, including Charles Sturt University.
The implementation of a variety of WeedSmart tactics, such as the double knock, mixing and rotating herbicides, stopping seed set and harvest weed seed control will also have a lasting impact on weed numbers.
With GRDC investment, Dr John Broster, Charles Sturt University NSW and Dr Michael Widderick, Queensland Department of Agriculture and Fisheries, Queensland led their respective teams through the process of testing samples and analysing the results for weed seed collected throughout the Northern cropping region in 2016 and 2017.
Weed seed samples were collected from 440 paddocks across northern NSW (244) and Queensland (196). The seeds were sown in controlled conditions and when the plants reached the three to five leaf stage they were tested for resistance to a range of herbicides. While collecting weed seed samples the researchers also assessed the weed density in each surveyed paddock.
The winter-growing weed species collected across the northern region and screened at CSU included annual ryegrass, wild oats, barley grass, brome grass, wild radish, Indian mustard, turnip weed and African turnip weed.
For NSW, this survey adds weight to other weed surveys conducted over recent years. Dr Broster says around 1000 paddocks in NSW and Queensland have now been surveyed between 2014 and 2018.
Wild oats is widespread across NSW and Queensland, having been found in just over half the paddocks surveyed. Annual ryegrass was also very abundant but so far only found in NSW, where it was present in almost 70 per cent of paddocks surveyed.
Barley grass, brome grass, Indian mustard weed and turnip weed were found only in NSW while wild radish and African turnip weed were mainly found in Queensland.
“The stand-out finding from our broader testing in NSW is that approximately 60 per cent of collected annual ryegrass populations were resistant to diclofop, sulfometuron and imazamox/imazapyr,” says Dr Broster. “Resistance to other commonly used herbicides for ryegrass control is relatively lower, but must be noted if these herbicides are to remain options for future herbicide programs. We measured resistance to clethodim (6%), trifluralin (7%) and glyphosate (6%) herbicides in the collected ryegrass populations sampled across the NSW regions.”
“Glyphosate resistance in ryegrass is more prevalent in the northern NSW regions than other parts of the state. Resistance to selective herbicides is lower in the northern NSW region than other parts of the state.”
2016 northern NSW and Queensland survey results summary for winter weed species

All results quoted below are the % of surveyed populations where resistance was detected.
Ryegrass only found in NSW – 94 populations tested. Resistance was found to diclofop (Hoegrass, 44%), imazamox/imazapyr (Intervix, 33%), sulfometuron (Oust, 29%), glyphosate (Roundup, 10%) and clethodim (Select, 2%). The sampled populations were susceptible to prosulfocarb + s-metolachlor (Boxer Gold) and pyroxasulfone (Sakura). All but one population was susceptible to trifluralin (Treflan, 1% developing resistance).

Glyphosate resistant annual ryegrass, 2016 Northern Region weed survey. Map courtesy of Dr John Broster, Charles Sturt University NSW.

Wild oats – 193 populations tested across Queensland (71) and northern NSW (122). Resistance was found to clodinafop (Topik, 38%) and Hussar (idosulfuron, 4%). These populations were fully susceptible to clethodim (Select), glyphosate (Roundup) and triallate (Avadex Xtra).
Barley grass – 17 populations, all in NSW. All susceptible to quizalofop-p-ethyl (Targa), clethodim (Select), mesosulfuron-methyl (Atlantis) and paraquat (Gramoxone).
Brome grass – 13 populations, all in NSW. Resistance found to mesosulfuron-methyl (Atlantis, 36%) only with all populations susceptible to quizalofop-p-ethyl (Targa), clethodim (Select), imazamox/imazapyr (Intervix) and glyphosate (Roundup).
Wild radish – 12 populations from Queensland and northern NSW. Resistance found to chlorsulfuron (Glean, 8%), diflufenican (Brodal, 80%) and 2,4D Amine, 77%. All populations were susceptible to glyphosate (Roundup), imazamox/imazapyr (Intervix) and Atrazine.
Indian hedge mustard – 7 populations found only in NSW. Resistance was found to chlorsulfuron (Glean, 17%) and diflufenican (Brodal, 43%). All populations were susceptible to glyphosate (Roundup), imazamox/imazapyr (Intervix), Atrazine and 2,4D Amine.
Turnip weed – 32 populations found in Queensland and northern NSW. Resistance was found to chlorsulfuron (Glean, 19%) and imazamox/imazapyr (Intervix, 11%). All populations susceptible to glyphosate (Roundup), Atrazine, diflufenican (Brodal) and 2,4D Amine.
African turnip weed – 17 populations found in Queensland and northern NSW. Resistance found to 2,4D Amine while all populations were susceptible to glyphosate (Roundup), chlorsulfuron (Glean), imazamox/imazapyr (Intervix) and Atrazine.

Related links:

Testing for herbicide resistance and susceptibility
Correct preparation of Quick test samples video below

The wettest April in 60 years is likely to cause growers in Tasmania’s high rainfall zone some unique challenges when it comes to controlling annual ryegrass, the Australian grain industry’s #1 weed.
Blow-outs are mostly in wet years and in paddocks with other underlying issues where ryegrass can take advantage of any gaps or areas of lower crop vigour. Many growers are finding that ryegrass is particularly difficult to manage in winter cereal and canola crops where the long cool season allows multiple germinations of ryegrass and the wet conditions reduce the residual benefits of pre-emergent herbicides.
WeedSmart southern agronomist Greg Condon says creative farmers and agronomists are addressing the problem head on and finding ways to implement the WeedSmart Big 6 weed management tools to stop seed set and drive down weed numbers.
“Farmers need to operate in a low-weed environment so they have more options in their crop and livestock decisions,” says Greg. “The principles of crop diversity, crop competition and mixing and rotating herbicide modes of action are central to keeping farming systems profitable.”
Diversity in cropping and livestock operations needs to result in diverse weed control tactics.
“The creativity comes in with the problem-solving process needed to apply these principles in challenging environments. The practices that have been developed in other high rainfall zones do not always apply directly to the Tasmanian farming systems.”
Growers and agronomists can use the WeedSmart Big 6 to keep ryegrass numbers under control while maintaining maximum flexibility in their cropping program. Greg says all the tactics will work in the Tasmanian high rainfall zone, with the exception of harvest weed seed control.
“Growers in the region have a distinct advantage when it comes to diversity in their farming system and this needs to drive the use of different weed control methods to keep the weeds guessing – using both herbicide and non-herbicide tools,” he says.
“Unfortunately, harvest weed seed control is far less effective in the Tasmanian cropping zones than it is in other high rainfall zones,” he says. “This is because a large percentage of the ryegrass that germinates in the crop will shed its seed before harvest. Some growers may still find value in this tactic to collect the seed from the later cohorts of the weed but it just isn’t as cost-effective as it is in other areas.”
Even without harvest weed seed control as a mainstay option, growers can still implement a three or four year ‘war on weeds’ program to drive down the ryegrass seed bank.
“To start with, tactics such as spring cropping, fodder crops and triple break crops can be used to maximise the efficacy of available herbicides and reduce ryegrass germinations,” says Greg.
“When it comes to herbicides it is critical that a plan is put in place to mix and rotate herbicides across the whole crop sequence,” he says. “In-crop herbicides are scarce and products like clethodim are registered for use in many crops so it is easy to keep using it, but we know that quickly leads to resistance problems.”
Having diversity of crops in the system only helps with weed control if it is used as a way to rotate chemistry. Testing the weeds for their susceptibility to single products and mixes of herbicides allows growers to plan ahead with more confidence. Double knocking each herbicide application preserves the available chemistry, particularly glyphosate.
Growers can also take advantage of ryegrass’ poor competitive ability. When placed in a competitive environment, ryegrass sets less seed, reducing the pressure of this weed on farming system decisions.
“Crop agronomy has a major impact on competitiveness,” says Greg. “The choice of crop, solid plant establishment, sowing early with a robust pre-emergent herbicide and attending to any soil constraints all swing the advantage toward the crop and away from the weeds.”
The final tactic that growers can implement is stopping weed seed set using hay and silage, crop-topping in canola or spraying under the cutter bar when swathing, or using camera-guided shielded sprayer technology to target weeds growing in the inter-row.
Cutting weedy areas of the crop for hay is a highly effective tactic that can reduce the impact of a weed blow-out.
Ian Herbert, Southern Farming Systems’ Tasmanian Projects and Trials Manager says fodder crops and livestock play a critical role in managing ryegrass on many Tasmanian farms.
“Growers can plant fodder crops directly after grain harvest, graze these fodder crops through winter, while allowing multiple germinations of ryegrass to occur, and then remove these plants using broad spectrum herbicides and or cultivation prior to planting a grain crop in spring,” he says. “This tactic reduces the pressure on selective herbicides and changes the timing of when ryegrass is controlled, compared to years where the paddock is in a cereal production phase. Cultivation is often needed to remove the deep pugging from livestock, which often occurs during our wet winters.”
Livestock can play an important role in weed management and there are many options available to growers.
Michael Chilvers is one grower who is embracing an integrated approach to managing ryegrass on his 1200 ha farm south of Launceston, where he runs a diverse cropping enterprise of around 300 ha of grain production along with intensive lucerne hay, potato and hybrid seed production.
Michael says the exceptionally wet autumn across much of the high rainfall zone, and particularly in their region, is going to put heavy pressure on the pre-emergent herbicides applied at planting.
“Incorporation of pre-em herbicides is critical and often not easy to achieve,” he says. “Unfortunately, the newly released pre-em products are probably not going to be an option for us in very wet seasons so we need to focus on getting the most out of the existing products.”
Michael is also very aware of the heavy reliance on Group A herbicides such as clethodim across his farming system and is doing what he can to rotate away from this key mode of action at every opportunity.
“Not only do we use it frequently, we also know that its efficacy can be compromised in our environment through a long cool growing season, which means we are running a real risk of losing it if we don’t adopt a more diverse approach to managing ryegrass,” he says.

In-crop weed control is particularly difficult in some years. Even after you have done all you possibly can to get your crop off to a competitive start the growing season can throw up some major challenges.
In this article we explore key principles that impact on the efficacy of in-crop ‘selective’ herbicides. You will most likely have to make some compromises and it is almost impossible to implement every tactic perfectly every time.
Herbicide mixes help to preserve the effectiveness of each mode of action by avoiding unnecessary usage.
Over the last few years WeedSmart has collected and promoted great advice from seasoned agronomists, wise researchers and crafty farmers on all aspects of weed control. To save you some time we have collected the resources that we think can be of assistance as you make the hard decisions about what to apply, when to apply and how to apply the herbicide and non-herbicide weed control tools at your disposal.
Post-emergent herbicides have been widely used in Australian crops because they are generally highly effective and easy to use. Unfortunately, their popularity has led to widespread resistance and most farms will have at least one weed species that is resistant to at least one post-emergent herbicide mode of action.
Despite recent increases in resistance, post-emergent herbicides remain an integral component of weed control strategies in many production systems.
Key messages:

Avoid the routine use of any weed control tactic – mix, rotate and keep changing.
Know what modes of action still work – test for susceptibility.
Have a plan for dealing with a weed blow-out.
Right Product, Right Time, Right Application.

Planning your in-crop herbicide use
Widespread and increasing herbicide resistance demands a planned approach to herbicide use throughout the crop sequence. If you have been using a particular herbicide or group of herbicides routinely, it is probably because they work well. To ensure these effective products remain an option into the future, it is necessary to use them less often!
Testing weeds for their susceptibility to a range of herbicides is cheap compared to applying a herbicide that has limited or no effect. Resistance to one or more herbicide does not mean you have no options.
We now know that mixing and rotating herbicides is an effective strategy to prolong the effective life of each mode of action. But even these mixes and rotations need to be change.
There are currently very few in-crop herbicides available for grass control. There are more options for broadleaf control. Plan a herbicide use program that spans your crop sequence so you can ‘save’ particular herbicides for use in crops where there might be limited alternatives, while using a range of other modes of action in other crops.
All herbicides applied in crop will have some impact on crop safety. Herbicides must be applied according to the correct crop growth stage for each herbicide.
Shielded spraying opens up the possibility of using other chemistry in-crop that would otherwise not be an option. Some growers are also looking for ways to include non-herbicide in-crop tactics such as inter-row cultivation or scuffling in wider-row cropping situations.<

CLICK IMAGE TO DOWNLOAD FILE
For planning herbicide use through the season and the crop sequence the NSW DPI Weed Control in Winter Crops booklet is full of useful tables of selective herbicides for each crop type. Click to download a copy.

CLICK IMAGE TO DOWNLOAD FILE
If you don’t have a copy of Mark Congreve and John Cameron’s ‘Understanding Post-emergent Herbicide Weed Control in Australian Farming Systems’ GRDC technical manual, you really need to download this resource.

CLICK IMAGE TO DOWNLOAD FILE
The GRDC Integrated Weed Management in Australian Cropping Systems manual provides a comprehensive guide to IWM, including the use of in-crop herbicides.

CLICK IMAGE TO DOWNLOAD FILE
This table shows the in-crop herbicides and their application timing for cereals. It is an extract from the NSW DPI Weed Control in Winter Crops booklet. You can download a copy here.

 
WeedSmart resources:

What are the ‘mix and rotate’ options for in-crop herbicides?
Testing for susceptibility and resistance
How can I implement the mix and rotate strategy to combat herbicide resistance?
How can I avoid getting stuck in an imi herbicide cycle?
Can we grow broadleaf crops without clethodim?
What can be done to regain control of herbicide resistant sowthistle?
Grower case study: Tim Rethus, Horsham Vic
Grower case study: Leigh Bryan, Swan Hill Vic
Grower case study: Phil and Brad Jackson, Westmar Qld

– Achieving maximum impact
Herbicide application decisions are complex and it is almost impossible to have all the important factors in place every time. Start with the product label and follow the instructions on rate, nozzle use, boom height, speed, adjuvants, optimal environmental conditions and so on.
When mixing, the order is important to avoid precipitation in the tank but it is also important to ensure that the tank mix partners each retain their efficacy. Some mixes are antagonistic and should be avoided because this will likely result in a significant reduction (up to 50% in some products) in efficacy. Adding an adjuvant can reduce herbicide selectivity and thereby increase crop damage.
The GRDC GrowNote Spray Application manual provides detailed information on:

Planning your spray operations – things to think about
Preparing for spraying – checks, accuracy and efficiency
Spraying system – major components and set-up considerations
Selecting a spraying system options available and operational considerations
Review and planning for future needs

CLICK IMAGE TO DOWNLOAD INTRODUCTION MODULE
The manual comprises 23 modules and a ‘water flush for residuals’ calculator. Each module includes a series of videos (see playlist below).

The video playlist is a great place to start:

 
WeedSmart resources:

Getting mixing right to avoid glugs and efficacy issues
Don’t start mixing until the water quality is right
Spray well: correct nozzles, adjuvants and water rates
Are you going spraying or killing weeds?
Never cut the rate

 
Right time – Manage multiple germinations
Timing is one of the hardest things to get right. Large spray programs and wet weather can make it very difficult to apply herbicides at the optimal time in every paddock for every weed.
The guiding principle is to always target small weeds, even if this means multiple applications. In wet years, multiple germinations will occur and waiting for the next germination invariably means the first flush will be much more difficult to kill and more likely to generate lots of seed for next year.
All herbicides applied in crop will have some impact on crop safety. Herbicides must be applied according to the correct crop growth stage for each herbicide. Also consider the effect of environmental conditions, particularly frost, on crop safety.
Environmental conditions at the time of spraying can make a huge difference to herbicide update in weeds. Look for the directions on the label for optimal conditions as spraying outside these parameters will result in less effective weed control.
avoiding chemical residues in grain.
WeedSmart resources:

Spray small multi-resistant radish twice
Does ambient temperature really affect herbicide performance?

Be ready for weed blow-outs
Wet years are the classic weed blow-out situation. Pre-emergent herbicides breakdown faster, spray applications can’t be applied on time and weeds will take advantage of any gaps that might develop in the crop.
Monitoring the weed pressure and having a plan to limit the potential damage might help.
The aim is to stop a massive seed set event using tactics such as – crop topping, hay or patching out. And be ready to implement harvest weed seed control – all the methods work well.
WeedSmart resources:

Grower case study: Trevor Syme, Bolgart WA
Grower case study: Mark Branson, Stockport SA
Grower case study: Day Family, Lockhart, NSW

The first multi-species herbicide resistance survey conducted in the Northern grain growing regions of NSW and Queensland has shown that while resistance to key herbicides is prevalent, growers are keeping weed numbers low, for now.
Rising resistance to glyphosate has been clearly demonstrated but this key herbicide can continue to be a highly effective tool for weed control, provided growers and agronomists implement a variety of tactics, such as the double knock, mixing and rotating herbicides and seed bank management, as a matter of urgency.
Dr Adam Jalaludin (DAF) collecting weed seed to be screened for herbicide resistance in the first multi-species weed survey in the northern grains region.
With GRDC investment, Dr Adam Jalaludin, Department of Agriculture and Fisheries, Queensland and Dr John Broster, Charles Sturt University NSW led their respective teams through the process of testing samples and analysing the results for weed seed collected throughout the Northern cropping region in 2016 and 2017. This survey was part of a wider GRDC investment in ‘Innovation in Crop Weed Control’ project across the northern region.
Weed seed samples were collected from 440 paddocks across northern NSW (244) and Queensland (196). The seeds were sown in controlled conditions and when the plants reached the three to five leaf stage they were tested for resistance to a range of herbicides. While collecting weed seed samples the researchers also assessed the weed density in each surveyed paddock.
The summer weed species collected across the northern region and screened in Queensland included sowthistle, fleabane, awnless barnyard grass, feathertop Rhodes grass, windmill grass and liverseed grass.
Of these predominantly summer-active species, only sowthistle, awnless barnyard grass and liverseed grass are listed on the label as being controlled by glyphosate alone. There is no label claim that the other three species – fleabane, feathertop Rhodes grass and windmill grass, will be controlled at the registered label rates of glyphosate (729 g active ingredient per ha). 
“Not surprisingly, all fleabane populations collected failed the glyphosate test,” says Dr Jalaludin. “Interestingly, 32 per cent of the feathertop Rhodes grass populations and 42 per cent of the windmill grass populations were actually susceptible to glyphosate.”
“Of concern was that 36 per cent of awnless barnyard grass populations and 14 per cent of the sowthistle populations were resistant to glyphosate.”
Dr Adam Jalaludin (DAF) recommends herbicide susceptibility testing as the first step in addressing patches of resistant weeds.
“In this survey we detected evolved resistance to haloxyfop in feathertop Rhodes grass and to imazapic in windmill grass, albeit at a low frequency.”
Glyphosate resistance is certainly entrenched in the northern region, and for sowthistle is much worse than in other areas of Australia. The good news is that weed density is relatively low and there is susceptibility to other herbicides.
“It is essential that an integrated approach is taken to manage these key weeds in summer crops and fallow,” said Dr Jalaludin. “An increasing number of weeds from a range of species are surviving glyphosate treatment, giving a clear indication that over-reliance on this herbicide is unsustainable.”
“Herbicide testing is a good place to start to identify which herbicides provide the best control. Herbicide applications should be supported with as many other WeedSmart tactics as possible and any survivors removed.”
Summary of results
The populations of viable sowthistle seed were screened with glyphosate, 2,4-D amine, Velocity and chlorsulfuron. Glyphosate and cholsulfuron provided poor control while all populations were susceptible to 2,4-D amine and Velocity.
Fleabane populations 1 week after spraying with glyphosate. Susceptible control population (right) and a resistant population (left) collected during the northern region herbicide resistance survey.
Fleabane populations across the Northern region were screened with glyphosate and 2, 4-D amine. All fleabane populations tested survived treatment with glyphosate while no sample survived the application of 2,4-D amine.
Screening of the feathertop Rhodes grass populations revealed 68 per cent were not controlled by glyphosate. One population survived treatment with haloxyfop, while all populations were controlled with clethodim.
Thirty-six per cent of the awnless barnyard grass populations collected across the Northern region were resistant to glyphosate. Fortunately, all populations were susceptible to propaquizafop, clethodim and imazapic.
Most of the windmill grass populations sampled in the survey were found in NSW. Screening showed that more than half (58%) of the populations were not controlled with glyphosate. Similarly, 40 per cent of the populations survived imazapic treatment. All populations were totally controlled by propaquizafop and clethodim.
The screening of the few viable liverseed grass populations collected across the Northern region did not reveal any evolved herbicide resistance.
Weeds collected in this survey were screened against several herbicides for which there are no label claims for some species. In field conditions, these weeds are often subject to exposure to a range of herbicides, which may be observed to have some activity. It is illegal to apply herbicides in any way contrary to the label and the results from this research are not a recommendation of use.

When it comes to harvest weed seed control methods there is good evidence that all the available options achieve a similar end result in terms of weed seed bank decline. But there is a wide variation in initial outlay, in associated activities and in nutrient removal or concentration.
Then there is the on-going problem of using average costs compared to using your own costs when doing the calculations.
WeedSmart western extension agronomist, Peter Newman has developed a spreadsheet growers can use to do calculations for their own farm to compare the cost of different HWSC options.
To assist, WeedSmart western extension agronomist Peter Newman has developed an interactive spreadsheet tool that growers and advisors can use to compare the costs of the available harvest weed seed control (HWSC) tools, using data and costings from their own farm situation.
“We have good data to suggest that harvest weed seed control costs are $7 to $19 per hectare and there are only minor differences in the cost between the available tools when compared using the same farm data,” says Peter. “But because every farm is different and small differences in costs per hectare can make a big difference at the whole farm scale, it is important for growers to have confidence that they can afford and justify the expenses incurred.”
Some HWSC tactics involve the purchase of substantial machinery – such as an impact mill, chaff cart or chaff deck – but the operational and labour costs might be lower than methods such as narrow windrow burning, which involves low set-up costs but higher nutrient losses and labour costs associated with burning. Invariably narrow windrow burning is the most expensive option in the long-run due to the high nutrient removal cost.
There is good data to suggest that harvest weed seed control costs are $7 to $19 per hectare and there are only minor differences in the cost between the available tools when compared using the same farm data. A chaff cart (pictured) is a particularly good fit on mixed farms.
“As a general rule, the cost of HWSC is lower per hectare on larger farms with lower yields,” says Peter. “This is because the capital cost is spread over a larger area, less nutrients are removed because the yields are lower and the low biomass crops allow low harvest heights without slowing down the harvester or using extra fuel. The converse is generally true for smaller farms with higher yields.”
“By imputing your own figures into the HWSC costing tool you can quickly evaluate the financial impact of the available options,” says Peter.
Another important factor to consider is that some of the technology is relatively new to market and there are unknowns such as the expected life of components when operating in commercial field conditions. As time goes by the manufacturers will be able to provide more concrete advice on service and repair costs, and any component failures will be overcome.
The easy-to-use spreadsheet takes into account capital cost, nutrient spread/loss, cost of ownership, harvest cost, reduction in harvest capacity, fuel use and replacement of wearing parts. Users also input data about their farm size and crop yields.

Peter Newman joined us for a webinar to discuss the HWSC cost estimate tool, you can watch the full recording below.