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Organic farmers are the original integrated weed managers. Now, some of the innovations that are being developed to combat herbicide resistant weeds on conventional farms are proving useful for organic farmers too. Phil and Ashlee Jackson, in partnership with Brad and Jenna Jackson, manage a 400 ha organic farming system at Westmar, southern Queensland, growing wheat, linseed and lablab. Phil Jackson (left) with brothers Matt (centre) and Brad (right). Phil and Brad manage the organic farm at Westmar Queensland. All three brothers work alongside their parents Peter and Janice on their conventionally-farmed land at Gurley NSW. Since 2014 Brad and Phil have been developing valuable weed management tactics, such as camera-guided inter-row cultivator, narrow windrow burning and green manuring, that can be employed in both conventional and organic farming systems. With cultivation being the only real option for summer weed control in organic farming operations Brad and Phil are keen to investigate any options that will help them stay ahead of the weed seed bank. “Not being able to do any in-crop weed control was a big concern for us,” says Brad. “Three years ago we bought a Garford inter-row cultivator from the UK to use it in our wheat and linseed crops.” The cameras on the cultivator guide the alignment of the tynes to follow the plant row with an accuracy of just 10 mm. The 500 mm row spacing enables use of the inter-row cultivator, which can be used when the crop is 100 to 400 mm high. The camera-guided inter-row cultivator allows in-crop weed management until the crop reaches about 400 mm in height. “We use it mainly to control wild radish and wild oats,” says Phil. “It suits our 12 m controlled traffic farming system and there is no reason why we couldn’t also use it strategically in our no-till conventional farming operation at Gurley, NSW.” At harvest, Brad and Phil use narrow windrow burning on as much of the area as possible, to collect and burn weed seed present late in the season. They have found this practice a good way to reduce the weed seed bank most years without burning all the stubble. Narrow windrow burning can be successful in reducing weed pressure in the following seasons, particularly for annual ryegrass. Phil says it can be rewarding when the conditions are favourable, particularly to control annual ryegrass. “We try to burn as early as is safe to clear the way for cultivation for summer weed control,” he says. The Jacksons also utilise green manuring – an age-old weed control tactic in organic farming. They have found the summer legume lablab to be a good option for green manure ahead of a long fallow. Lablab produces a dense and competitive crop that prevents weeds from establishing, while also giving the soil a nitrogen boost. Lablab is a dense, competitive green manure crop that provides excellent ground cover and weed suppression over summer. The tactics employed in this organic operation tick off all the non-herbicide weed control tactics in the WeedSmart Big 6 promoted as a practical system to combat herbicide resistance. In an organic system four of the six tactics can be broadly applied to reduce weed pressure. Rotate crops and pastures – The Jacksons’ rotation is simple but effective. Linseed is grown after wheat to control soil borne root diseases including crown rot, common root rot, yellow leaf spot and spot form of net blotch. It is also resistant to both main species of root lesion nematodes. Linseed yields are higher when grown after AMF host crops that maintain high numbers of the arbuscular mycorrhizae fungi (AMF). High performing crops are one of the best ways to combat weeds. Mix and rotate herbicide MOA – Not applicable on organic farms but very important in systems that use herbicides. Increase crop competition – High performing winter crops combined with a summer legume green manure crop in rotation. Use the double knock to preserve glyphosate – Not applicable on organic farms, however, the idea of monitoring weed control efficacy and removing survivors still applies – more crop, less weeds. Stop weed seed set – Cultivation in the fallow and in-crop (with the guided inter-row cultivator) significantly reduces weed seed set. Implement harvest weed seed control – The Jackson’s currently use narrow windrow burning to capture weed seed at harvest. They are also looking at other options such as chafflining and impact mills. All the current harvest weed seed control tactics are non-chemical tools that are being rapidly adopted on Australian farms. More resources: https://www.youtube.com/watch?v=oYE_k2A7zbIThe Garford guided inter-row cultivator in action (promo video).

If a herbicide resistant weed never sets seed then it won’t be long before the resistance is eradicated. This is easy to say, but has been mighty hard to achieve because it is so time consuming. Enter now the power of robotic weed control. Frequent scouting for, and removal of small weeds, is now a practical reality with a commercial robotic platform available for broadacre cropping operations. Tom Holcombe, SwarmFarm Robotics Field Operations Lead says robotic platforms open up new opportunities in non-chemical weed control. Tom Holcombe, SwarmFarm Robotics Field Operations Lead says the theory has been proven recently in trials in Central Queensland, where weed blow-outs in fallows on two sites were brought under control using repetitive herbicide applications. The two sites were on separate properties in the Springsure district of Central Queensland. One site was 44 ha of fallow at ‘Kilmore’, following dryland sorghum, with weeds managed from August 2017 to March 2018. The other was 28 ha at ‘Denlo Park’, following dryland cotton, with weeds managed from October 2017 to March 2018. “To control weeds present in high numbers at both sites we decided that the robots would spray on a fortnightly basis to regain control,” says Tom. “This regular and repetitive spraying achieved excellent control at each of the sites, avoiding the need to cultivate.” Over a period of eight weeks of routine, fortnightly spraying with knockdown herbicides using a Weedit mounted on the robot, the weed density dropped from the initial 20% of the area, when it was considered out of control, down to approximately 2% of the trial area. Kilmore site – weedy after spray failure. Kilmore site – clean, following intense herbicide application using robotic sprayer. This use pattern would be considered impractical and unadvisable in a conventional herbicide spraying program. The robotic platform made it possible, and it was effective due to the continual knocking of the same weeds until death was achieved and seed set prevented. A commercial robotic platform also brings the opportunity to use optical weed sensing technology in conjunction with non-herbicide weed control tactics such as chipping and microwaving. Both SwarmFarm (with Queensland state government funding) and The University of Western Australia (with GRDC funding) have shown that optical sensing works well with a chipping tyne implement that is activated only when a weed is ‘spotted’. This makes cultivation for weed control site-specific and is compatible with zero-till farming. Another prototype that SwarmFarm developed within the Queensland government’s Strategic Cropping Land Mitigation funded project was a small microwave unit that activates only when a weed is present (as detected using a Weedit sensor). “There has been a lot of interest in the potential of microwave for weed control, but the power and time involved has kept this technology out of reach,” says Tom. “Having several small units teamed with the Weedit sensors and mounted on a robotic platform opens up a whole new set of opportunities.” “Time is no longer a constraint because the robot can stop and apply the necessary treatment without keeping an operator and tractor tied up, and the more often it is used, the smaller the weeds will be – needing less time and power to kill them.” Single-unit microwave weeder prototype using Weedit optical sensor for site-specific weed control. The power constraint is also more realistic than trying to apply a ‘blanket’ microwave treatment across a whole paddock. Since only a few units on a multi-unit bar are likely to be activated at any one time, the power draw is far less and small weeds are much easier to kill than large weeds. “There is also a soil health benefit given that the weeds can be controlled without affecting the soil biota of the whole paddock,” he says. “We are particularly keen on the development of a microwave rig now that we have proven the potential for this technology to be a very effective double-knock to take out weeds that survive a herbicide treatment, and even for its application on organic farms to dramatically reduce the reliance on cultivation,” says Tom. https://youtu.be/kxZWSseIKxoTom Holcombe, SwarmFarm Robotics Field Operations Lead sees optical weed seeking microwave units on a robotic platform as the next big thing in non-chemical weed control. Other links: Microwave effects on weeds and soil Targeting small weeds all year Efficient herbicide use pays off How can I use a mechanical tactic as a second knock

Whether you have a horizontal iHSD impact mill or are looking to get into this technology with the newly-released vertical configuration, you can rest assured that the kill rate of both configurations has been independently proven to be 98 per cent for annual ryegrass. Dr Michael Walsh, Director Weed Research, Faculty of Science, The University of Sydney has been testing the efficacy of impact mills on weed seeds since the early days of development of the Harrington Seed Destructors. Left: Without harvest weed seed control. Right: With iHSD harvest weed seed control. “The vertical configuration of the iHSD mills could change the direction of the chaff flow through the mills and this could affect the processing of the chaff and potentially the efficacy of weed seed destruction,” he says. “Having previously shown that the horizontal iHSD impact mill can achieve at least 98 per cent weed seed kill, we were keen to repeat the test for the vertical mill configuration.” During the 2018 harvest, a wheat crop at Broomehill was used to test the vertical mill. Twelve 20 m strips were marked out in the wheat crop where there was no annual ryegrass present. These plots were used to test the efficacy of the vertical mill at three different harvester speeds – 4, 6 and 8 km/hr. Weed seed destruction was 98% or better at three operating speeds (4, 6 and 8 km/hr). As each plot was harvested, 5000 dyed annual ryegrass seeds were introduced into the chaff stream directly above the inlet to the righthand side mill. The processed chaff from each plot was collected in large, fine-mesh bags attached to the righthand side outlet chute. To determine the weed seed survival rate from each plot, Dr John Broster’s team at Charles Sturt University, Wagga Wagga processed subsamples from each of the 12 bags of chaff. The chaff was thinly spread on trays, covered lightly with potting mix and watered every day for four weeks to stimulate the germination of any surviving annual ryegrass seed. Each day annual ryegrass seedlings present were counted and removed from the trays. “The result of this testing was a weed seed kill rate of at least 98 per cent for the vertical iHSD impact mill, regardless of the harvester operating speed of 4, 6 or 8 km/hr,” says Dr Walsh. “This level of weed seed destruction is equivalent to that of the horizontally mounted mills that we have tested previously.” “From this result we can be confident that provided the harvester is set up to efficiently collect annual ryegrass seed at harvest, growers using either configuration of the iHSD can expect to achieve this very high rate of weed seed destruction.” Peter Newman, Western Extension Agronomist with the Australian Herbicide Resistance Initiative (AHRI) and WeedSmart, says there is keen interest amongst Australian growers in harvester-integrated weed control solutions. “Growers are looking at price and weed seed control efficacy,” he says. “This new configuration of the iHSD provides several new features that will benefit growers, including the ability to easily check for grain loss by opening a rear hatch and disengaging the iHSD belts, the large cavity under the sieves effectively prevents bridging and the stone trap will help to prevent any foreign objects from entering and damaging the mill.” New features include mechanical drive, vertical configuration, rear hatch and stone trap to reduce costs and improve reliability. “The vertical configuration uses the same cage mill for seed destruction as the earlier horizontal version but is mechanically-driven rather than hydraulic, significantly reducing the cost, making the iHSD more attractive to growers.” Following the invention of the HSD by WA grower Ray Harrington and development by UniSA with investment from GRDC, the iHSD has undergone further development by SKF Engineering and DeBruin Engineering, together with national distributor, McIntosh Distribution. McIntosh & Son dealer principal (southern branches) Devon Gilmour says the vertical, mechanical iHSD’s direct-drive system is easy to use and maintain, can be retro-fitted on a wide range of harvester models and is easy fitted on-farm. Impact mills have a proven high weed seed kill rate, making them a very effective, non-herbicide tool in the fight against herbicide resistant weeds. Harvesters fitted with impact mills can spread crop residue more evenly, reducing the loss or redistribution of nutrients, making them an attractive proposition for growers. Other resources: Using your harvester to destroy weed seeds Which harvest weed seed control tool is right for you?

The herbicide-only era is over and the diversity era is here. One example is coupling pre-emergent herbicides with greater crop competition. In a brand new, free online course taught by Dr Chris Preston (University of Adelaide) and Mr Mark Congreve (ICAN), growers and agronomists can gain confidence through understanding how to best use pre-emergent herbicides in both winter and summer cropping systems. Mark Congreve (ICAN), Chris Preston (University of Adelaide) and Peter Newman (AHRI) discuss the ins and outs of pre-emergent herbicide in Australian cropping systems in a new Diversity Era online course. The Diversity Era Pre-emergent Herbicides 101 course includes: free access to 13 educational videos that cover the basics of how pre-emergent herbicides work, plus practical tips to help you use these herbicides on farm in both summer and winter cropping systems straightforward, step-by-step instruction from highly respected and skilled industry professionals with deep knowledge of cropping systems and weed management access to a comprehensive overview of what is currently known about pre-emergent herbicides and how to best use them in your farming system Q&A discussion with Chris and Mark (facilitated by Peter Newman), a resource library with extra information, podcast interviews and a live webinar. In just three hours, find out how pre-emergents can help manage herbicide resistance in crop weeds. There’s videos, audio, PDF downloads, quizzes and a wrap-up webinar to help you get the most out of the Diversity Era Pre-emergent Herbicides 101 course, while working at your own pace. Given that pre-emergent herbicides require more planning and carry some inherent risks, it is important to understand how they work in different soils, how they can be used most effectively through a cropping program, including the fallow, and how to manage any restrictions on future crop choices. Dr Chris Preston says that the renewed interest in adding pre-emergent herbicides to weed control programs is in response to the rapid escalation in herbicide resistance to post-emergent herbicides and the important knockdown herbicide, glyphosate. “Currently, the only widely used herbicide mode of action group in Australian grain production that has no known field populations of herbicide resistant weed species is Group H,” he says. “Pre-emergent herbicides are also prone to herbicide resistance, with the number of resistant populations on the rise, so their judicious use is essential. Incorporating pre-emergent herbicides into the program increases the diversity of herbicide mode of action groups, making it possible to mix and rotate these herbicides to extend their effective life. A well-executed pre-emergent program can also take the pressure off subsequent post-emergent in-crop herbicide applications.” “Knowing how to maximise efficacy and stack these products with other tactics, such as crop competition, harvest weed seed control and stopping weed seed set, needs to be part of the crop management package on every farm, every year.” Having presented innumerable pre-emergent herbicide use workshops around Australia and co-authored practical information resources for agronomic advisors, Mark Congreve is keen to see all growers and advisors familiar with the soil behaviour of pre-emergent herbicides. “Understanding the risks and benefits associated with these herbicides is very important,” he says. “This course is a great refresher and a resource that growers and agronomists can refer back to over and over again as they integrate pre-emergents into their weed management program to suit each season and crop sequence in both winter and summer cropping situations.” The Diversity Era Pre-emergent Herbicides 101 course opened for registration on 20 March 2019, with the release of the first five modules – ‘Understanding Pre-em Basics’ with Chris Preston and a podcast with Chris and AHRI’s Peter Newman. Modules 6–8 ‘Using Pre-ems in a Winter Cropping System’ with Chris will go live on Wednesday 27 March and Modules 9–11 ‘Using Pre-ems in a Summer Cropping System’ with Mark Congreve will be available the next week on 3 April, along with two bonus materials modules and another podcast, this time with Mark and Peter. The final element will be a live webinar on April 10 with Peter Newman, Mark Congreve and Chris Preston. Register now: www.diversityera.com/courses/pre-emergent-herbicides-101 Initiatives like our latest Diversity Era course ‘Pre-emergent Herbicides 101’ (which is free!) are made possible through the support of our stakeholders. Please watch the above video highlighting stakeholder engagement to learn more.

High residue farming with a stripper front and a disc seeder efficiently captures and stores soil moisture, and growers are finding the system can be tweaked to also improve weed management. An increasing number of growers in the northern region are seeing early confirmation that the system works and there is building scientific evidence that they are on the right track with the adoption of narrow row sowing with single disc planters, combined with a stripper front and either a chaff deck or chaff line at harvest. Peter and Kylie Bach, Kurilda Ag, Pittsworth use a Shelbourne harvester front and Emar chaff deck to conserve stubble and put weeds in their place. AHRI and WeedSmart agronomist Greg Condon says this system is providing growers in the northern grains region with opportunities to plant and grow crops that would otherwise not be possible. “Harvest weed seed control is a useful tactic against many of the key weed species in the northern region,” he says. “We now have scientific data to show that, with correct harvester set-up, stripper fronts and drapers can be equally effective at collecting weed seeds at harvest. The advantage of the stripper front is that the vast majority of the crop residue remains as standing stubble in the paddock. This means the harvester does not have to deal with enormous amounts of plant material and there is so little straw going through the machine that choppers and spreaders have much less work to do.” “When a chaff deck or chaff line chute is attached to the harvester, the weed seed is separated from the grain with a small amount of chaff, and deposited either on the controlled traffic wheeltracks or in a narrow band behind the harvester. These weeds can then be subjected to targeted control tactics applied to a very small percentage of the paddock area.” A chaff deck attached to the harvester separates the weed seed from the grain, along with a small amount of chaff, which is deposited on the controlled traffic wheeltracks. For some growers, like Peter and Kylie Bach farming at Pittsworth on the Darling Downs of Queensland, using the stripper front and chaff deck combination in their cereal crops has gone a long way toward solving their problems with volunteer crop plants from previous seasons. “The standing stubble has given us planting opportunities for summer crops that would not have been possible after a conventional harvest,” says Peter. “Barley stubble provides an excellent environment for planting mungbeans and when the mungbeans are harvested, the paddock has much better ground cover with the previously-standing cereal stubble being retained on the soil surface.” The stripper front leaves most of the stubble standing in-situ, meaning much less material needs to be processed in the harvester. Peter and Kylie find that the barley stubble can persist for a few seasons after the growing season, providing soil moisture conservation benefits in their summer cropping program. The ‘strip and disc’ system ticks off three of the WeedSmart Big 6 tactics for managing herbicide resistance – crop competition, harvest weed seed control and diverse rotations. “When weed control is integrated into an agronomic package it is possible to achieve some real synergies in the system – achieving more than just the cumulative benefits associated with each of the parts,” says Greg. “After a few years, there is a combination of standing and residual stubble in the field and stubble load is managed through the sequencing of different crops, without ever leaving the soil bare.” The ground cover benefits of cooler, moist soil opens up the possibility of sowing early and growing longer season crops, and even double cropping is some environments. There is also better nutrient cycling and improved soil biota activity. Tall stubble left after the stripper front harvests the crop and a line of chaff left behind the harvester concentrates any weed seed collected during harvest in this narrow and well-shaded band. While the stripper front has several benefits and efficiencies over the conventional draper, these benefits are not likely to support a change-over until existing machinery is due for replacement, according to an economic study by John Francis, Holmes and Sackett. A draper can achieve many of the same standing stubble benefits and harvest efficiencies as the stripper front if the harvest height is set at 40 to 60 cm. For both options to be effective for weed seed collection the crop competition must be strong to force weeds to set seed high in the canopy. Without strong crop competition, harvest weed seed control generally relies on cutting as low as possible at harvest. Grower experience suggests that stripper fronts have a distinct advantage when it comes to picking up fallen or lodged crops and weeds.

Weed identification is a valuable skill and most farmers can identify the common and important weeds on their farms. For most non-botanists, identification is easiest when the plant is mature and flowering – but to be effective, weed control decisions need to be made well before flowering. With the increasing prevalence of herbicide resistance across all farming regions, accurate identification at early growth stages is essential to ensure the best control strategies are implemented when the weeds are at their most susceptible growth stage. Using just the cotyledon shape as the only diagnostic selection, the 50 possible species can be rapidly narrowed down to less than eight possibilities in most cases. Early identification gives growers the opportunity to apply the best weed control program to treat the species present. Dr David Thornby, Innokas Intellectual Services says the resistance profiles, even for closely related species, can be quite different, especially at the seedling stage. “As part of a Cotton Research and Development Corporation project we have developed a new weed identification mobile app called ‘Weeds of Australian Cotton’ that provides a key to the characteristics of 50 weed species in cotton,” he says. “Clearly, the app will also have value for use in managing weeds in other crops grown in the same regions as cotton.” The app allows users to make selections based on the observed characteristics of the plant, stem, leaves, flowers and seeds, the fleshiness or succulence of the plant and the presence of milky sap or latex. For grasses, users can key in specific details about the inflorescence, spikelet, floret and ligule features. As each detail is added the number of possible species reduces, until a few or just one remains as the best fit for the characteristics selected. “Once there are just a few remaining options, the user can look at the photo gallery and choose the best-fit identification,” says Dr Thornby. “The feature that really sets this app apart from other weed identification apps is that ‘Weeds of Australian Cotton’ includes a ‘cotyledon shape’ characteristic selection.” “There are nine different cotyledon shapes to choose from. Using this feature of the app alone, users can quickly narrow down the most likely identification, and make decisions early regarding the best mix of weed control strategies to implement.” Using the cotyledon shape as the only diagnostic selection, the 50 possible species can be rapidly narrowed down to less than eight possibilities in most cases. When cotyledons are present on very small plants found in the field, accurate identification can give growers a head start on planning a spray application. The timing of herbicide application is product-specific but the general recommendation is for weeds to be ‘small and actively growing’. As a rule of thumb, ‘small’ would include pre-tillering for most grass species, less than 5 cm diameter for most rosette-forming species, and up to about 5 true leaves for other types of broadleaf species. As for ‘actively growing’, this is simply the absence of visible signs of moisture stress. “Coverage is probably the most important factor to consider if weeds were sprayed at cotyledon stage,” says Dr Thornby. “Where feasible, increasing the water rate is the usual response, but it can be hard to hit such genuinely small targets. At this very small size good control could be expected, but they would have to come in contact with the chemical and so it is often practical to compromise by waiting until a couple of true leaves are present.” “It is essential that label instructions are followed regarding weed size, product rate and application method as they apply to each product and weed species to achieve the best weed control result.” It is best not to make too many assumptions about the weed spectrum present based on what was observed in the previous year. Dr Thornby emphasises the need for accurate identification and highlighted the fact that the app does not include every possible plant that could be growing on a cotton farm. A new weed identification mobile app called ‘Weeds of Australian Cotton’ provides a key to the characteristics of 50 weed species in cotton. The app will also have value for use in managing weeds in other crops grown in the same regions as cotton. “The app only includes the 50 species that the development team identified as the key species affecting cotton production,” he says. “Misidentification is certainly possible, so if the options remaining at the end of your selections do not clearly match the plant you are looking at in the field, it is necessary to confirm identification with an expert, especially if the weed is proving hard to kill.” Download ‘Weeds of Australian Cotton’ app on the Apple App Store for iOS mobile devices or Google Play for Android mobile devices or visit www.cottoninfo.com.au

‘Diversity’ is one of those ‘how much is good enough’ things. It is often recommended that farmers use ‘as much diversity as possible’ in their weed management program to keep a lid on herbicide resistance, but it is difficult to quantify how much diversity will achieve adequate control. Computer models, like the new ‘Diversity’ model, have proven to give reliable predictions of the real-world outcomes likely to result from the implementation of different weed management programs. The new Diversity computer model has enabled researchers to test the effect of different weed control programs and scenarios on herbicide resistance in three key weed species, with the aim of prolonging the effective life of the triple-stack herbicide gene technology in irrigated cotton systems. The Diversity model tracks the simultaneous evolution of resistance to multiple herbicides, using multiple genetic pathways, in several weed species at once. With triple-stacked herbicide tolerance traits in genetically modified cotton expected to be available to Australian growers within the next five years, the Australian Cotton Research and Development Corporation has invested in research to determine how much diversity in control tactics is required to protect the effective life of this technology. The model suggests that using more diverse strategies in weed control can add 20 years to the effective ‘life’ of this new herbicide tolerance technology. Modelling repeatedly shows that new technologies must be supported with several other herbicide and non-herbicide tactics and survivor management given the highest priority. Bayer’s XtendFlex™ technology confers tolerance to glyphosate, dicamba and glufosinate in cotton and was approved for commercial release by The Office of the Gene Technology Regulator in December 2016. Prior to commercial release, extensive work is underway to understand the system’s fit in the unique Australian environment and to ensure growers will get the most from the technology. XtendFlex™ cotton varieties are stacked with the Bollgard® 3 insect resistance technology, and are expected to provide growers with a robust pest and weed management tool. The concern for weed scientists like Dr David Thornby, Innokas Intellectual Services, is that the triple-stack of herbicide tolerance is already compromised, with glyphosate resistance well-established in several weed species on many cotton farms. To-date, the problem is greatest in dryland cotton farming systems, but is also quite prevalent in non-crop areas of irrigated farms, such as along irrigation channel banks. Dr David Thornby suggests that growers should not put off implementing the 2+2&0 strategy in the hope that XtendFlex cotton varieties will fix their weed problems when the new technology is released in Australia in a few years. Having previously used computer modelling to assist in the development of the cotton industry 2+2&0 weed control strategy, Dr Thornby has led a team to develop a model to test how many tactics growers will need to implement to achieve effective control of three key weed species – sowthistle, flaxleaf fleabane and awnless barnyard grass – once the XtendFlex technology is adopted. “Real-life experience aligns with the predictions made using the DAF Glyphosate Resistance computer model, with glyphosate resistance being evident in awnless barnyard grass within 13 years of commencing zero tillage, if glyphosate is the only product used for summer weed control and survivors are not controlled,” he said. “We also predicted that common sowthistle populations would exhibit resistance within 15 years if glyphosate was the only product, or 20 years if a few other tactics were implemented.” “We managed to predict that sowthistle would lag behind barnyard grass by a few years, under current and historical management strategies, and that has been borne out in the real world. This suggests that the computer models do provide reliable predictions of the speed at which herbicide resistance develops in weed populations, so we have built on this earlier work to develop the ‘Diversity’ computer model.” Using this new model has enabled researchers to test the effect of different weed control programs and scenarios on herbicide resistance in these three key species, with the aim of prolonging the effective life of the triple-stack herbicide gene technology in irrigated cotton systems. “Using the model we can show that just using the three over-the-top herbicides in triple-stacked cotton crops will lead to a failure of the technology to control awnless barnyard grass within 10 years,” he said. “This is because of the already wide-spread incidence of glyphosate resistance in this species, and the fact that glufosinate is only marginally effective on this species and dicamba is not effective at all.” “If a grower also implements the 2+2&0 best practice of two other practices – cultural or different herbicide modes of action – in both the crop and fallow, and zero tolerance of survivors, we can extend the effective life of the technology to control awnless barnyard grass and sowthistle to 30 years,” he said. “For example, the use of the triple stack partners in a double knock tactic at least some of the time, including a pre-emergent herbicide and chipping survivors is a practical and effective control program to support the over-the-top herbicide options available with XtendFlex.” “Of the three key species studied so far, flaxleaf fleabane is expected to be an on-going problem for cotton growers,” said Dr Thornby. “Glyphosate resistant fleabane can be hard to control with the XtendFlex herbicide options and the model suggests that at least two additional tactics would need to be applied every year to keep numbers low. Gaining control is challenging and given the amount of seed produced on these plants, even achieving a kill rate of 95 per cent is not sufficient to manage the seed bank.” Flaxleaf fleabane can germinate over a wide portion of the year, putting strong pressure on pre-emergent herbicides as well. To-date, the Diversity model has only been used to test scenarios in irrigated cotton systems but plans are in place to test-run dryland cotton scenarios ahead of the release of XtendFlex cotton varieties in Australia. The model also has the capability to investigate the effect of including other crops in the rotation to assist with weed control. The bottom line is that the triple-stack herbicide tolerance gene technology will be a useful tool for cotton growers but it is not a stand-alone weed control program. It must be supported with several other herbicide and non-herbicide tactics and survivor management given the highest priority. Dr Thornby said growers should not put off implementing the 2+2&0 strategy in the hope that XtendFlex will fix their weed problems. It is possible to use intensive patch management to reduce the numbers of glyphosate resistant weeds, particularly awnless barnyard grass, and doing so will give growers a better starting point to maximise the effectiveness of the triple-stack herbicide technology when it is released.

Weeds that are allowed to germinate with summer crops significantly reduce yields and can set a vast amount of seed. Conversely, crops that get away to a clean start for the first three to six weeks can often maintain most of their yield potential. Competitive crops, grown on narrow row spacing, can reduce the number of weeds that germinate later in the crop and although these weeds may have minimal impact on yield, any survivors will add to the weed seed bank and must be controlled with other tactics. In sorghum and maize crops, weeds like barnyard grass, liverseed grass and fleabane can be hard to kill once they emerge, and they have the potential to reduce yields by 30 per cent or more if left untreated. In mungbean, University of Queensland researchers found a 50 per cent crop yield reduction can be expected as a result of weed populations as low as 20–35 plants/m2 of bladder ketmia, feathertop Rhodes grass, windmill grass, liverseed grass or button grass. Many growers are looking for opportunities to safely include residual herbicides into their summer cropping weed control program to complement pre-plant knock-down herbicide applications. Mark Congreve, ICAN senior consultant said pre-emergent herbicides can provide a six to eight week weed-free environment for crop establishment and their inclusion increases the diversity of herbicide modes of action used in the farming system – a useful delaying strategy for herbicide resistance. Mark Congreve, ICAN senior consultant says pre-emergent herbicides can provide a six to eight week weed-free environment for summer crop establishment. Starting the summer crop clean usually involves an effective knock-down herbicide applied prior to sowing to treat weeds germinating on the planting rain, followed by an effective pre-emergent. “It is generally easier to target grass weeds in a broadleaf crop and vice versa. For example, if grass weeds are the main problem in a paddock then grain sorghum may not be a good crop choice,” he said. “There are no effective in-crop post-emergent herbicides for control of emerged grass weeds in sorghum, so any weeds that escape the pre-emergent herbicide treatment are likely to set seed and replenish the seedbank.” Broadleaf crops such as cotton, mungbeans, soybeans and sunflowers have more pre-emergent and in-crop herbicide options to treat grass weeds, potentially making these crops a better choice where grasses are the main problem. Crop competition and pre-emergent herbicides are complementary tactics, with their combined effect reducing weed seed numbers and supporting crop yield. Once the crop has been selected and the pre-emergent program chosen, implement all practices that promote vigorous crop growth and early canopy closure. An over-reliance on pre-emergent herbicide use will select for herbicide resistance, just as it has for post-emergent herbicides. To minimise this, it is important to use a diverse range of weed management tactics, including non-herbicide tactics such as inter-row cultivation or chipping, to remove survivor weeds before they set seed. Where possible, rotate pre-emergent herbicide modes of action between years. “Most growers find that there are one or two weed species that are really driving their decision making, so having a dedicated program to drive down numbers of these key weeds to ensure the summer crop is clean at harvest, will make future weed control easier and allow greater flexibility in crop choice.” Resources How can summer crops help drive down weed seed numbers? Creating stiff competition against summer weeds Why diversity is so important in the battle with herbicide resistant weeds

With soil moisture at a premium, there is nothing spare to waste on summer growing weeds. With four of the most difficult to control summer weeds, feathertop Rhodes grass (FTR), awnless barnyard grass, common sowthistle and flaxleaf fleabane, now with confirmed cases of glyphosate resistance, the pressure is on to find effective non-herbicide control tactics. These weeds can produce 40,000, 42,000, 25,000 and 110,000 seeds per plant respectively. Other studies have found these numbers could be even higher, so every effort to reduce seed production is worthwhile. Dr Michael Widderick, is the lead DAF researcher in the mungbean and sorghum crop trials to better understand the agronomic factors that increase the crop’s competitive advantage over feathertop Rhodes grass and awnless barnyard grass. Various trials in mungbean, soybean and sorghum crops have consistently found that planting these summer crops in competitive configurations can reduce weed biomass and seed production while maintaining or increasing crop yield. The change in row configuration may involve set up costs to modify planting equipment but does not require an increase in seeding rate as the effect has been demonstrated using the same established populations for mungbean and soybean. For sorghum, the competitive edge comes through increased plant population rather than narrower rows. Along with narrowing the row spacing in mungbean and soybean, there are also benefits in early weed control. Keeping crops weed-free for the first three to six weeks seems to be a valuable rule of thumb to give crops the head start required to drive down weed numbers. Weeds that germinate in-crop after the 3–6 week mark are fewer in number and individual plants also produce less seed. As a non-herbicide control tactic, crop competition is very important in any integrated weed management program. With investment from the GRDC, researchers from NSW Department of Primary Industries, University of Sydney and Queensland Department of Agriculture and Fisheries are conducting trials to identify ways to increase the competitiveness of sorghum and summer pulses. In the 2017–18 summer sorghum was sown in trials using three row spacings (50, 75, 100 cm) and two crop densities (5 and 10 plants per m2). In a separate trial, mungbean plots were established using three row spacings (25, 50 and 75 cm) and two crop densities (20 and 35 plants per m2). Seed of feathertop Rhodes grass and awnless barnyard grass was spread at planting and the plots were irrigated to ensure optimal crop and weed emergence. With only one year of data from this trial so far it is difficult to make recommendations. Average seed head production in non-crop treatments was 1745 heads/m2 for feathertop Rhodes and 1525 heads/m2 for awnless barnyard grass. Growing either crop more than halved the number of weed seed heads produced, even in the least competitive configuration for the two crops. Row spacing in mungbean had a clear impact on weed seedhead production for both weed species. This effect has been demonstrated numerous times in a range of agronomic trials with mungbean. Narrowing row spacing to 25 cm reduced feathertop Rhodes grass seed heads to 32 plants/m2. For awnless barnyard grass, narrowing row spacing to 50 cm or less reduced seed heads to less than 10 per m2. Note: this represents one year of data only. In these plots, mungbean sown on row spacing 25 cm at low crop density (20 plants/m2) competed strongly with awnless barnyard grass (left) and feathertop Rhodes grass (right). In these plots, mungbean was sown on row spacing 75 cm at low crop density (20 plants/m2). The plot on the left was kept weed free while the centre plot shows limited suppression of feathertop Rhodes grass. Being a low growing weed, the level of infestation of awnless barnyard grass (right) is difficult to see in this photo. For sorghum it seems increased plant population had the best effect, significantly reducing weed seed head numbers for both weed species. Unlike mungbeans and soybeans, sorghum yields were reduced in plots with narrower row spacing configurations. At each row spacing, the higher plant density (10 plants/m2) treatment yielded more than the lower density plant population. In a separate trial, University of Queensland researchers confirmed that row spacing, not plant population, is the key driver to reducing weed growth in soybean crops. In soybeans, weed biomass was reduced by 89 per cent under narrow rows (25 cm) and 75 per cent under wider rows (75 cm) when the crop was kept weed-free for the first three weeks after planting. If weeds were controlled for the first six weeks, then weed biomass was reduced by 98 per cent under narrow rows and 88 per cent under wider rows. In weed-free plots there was a 20 per cent yield benefit in changing from 75 cm row spacing to 25 cm. This yield difference was 65 per cent in plots where weeds were introduced 6 weeks after planting and a huge 121 per cent higher when the weed infestation occurred three weeks after planting. Similarly, if a mungbean crop is kept weed-free for the first 3 weeks after planting, then the narrower row spacings of 25 and 50 cm saw a reduction in weed biomass. In both the 2015 and 2016 summers, the combination of keeping the crop weed-free for at least the first 3 weeks and planting on the narrower rows (25 or 50 cm rather than 75 cm) generated a yield increase of 159–197 per cent in 2015 and 198–223 per cent in 2016. Summer crops are an integral part of many farming systems and play an important role in an integrated weed management program. Many summer weeds only remain viable on the soil surface for a period of around 12 months so if a competitive summer crop is followed with a competitive winter crop and harvest weed seed control, there are more opportunities to drive down weed numbers in the soil seed bank. More resources: Giving summer pulses the competitive edge How can summer crops help drive down weed numbers?

The Australian cotton industry has benefited enormously through widespread adoption of Roundup Ready technology, with close to 100 per cent adoption since 2010/11. A downside of the uptake of this technology has been the shift in the weed spectrum found in cotton fields. Department of Agriculture and Fisheries (DAF) researcher Dr Jeff Werth says growers have achieved better control of Cyperus sp. (nutgrass and other sedges), but surface germinating and glyphosate tolerant species, along with reduced control of vines and legumes have found the new cropping system favourable. Jeff Werth (DAF) collecting data at the patch eradication trial at Hermitage Research Facility, Warwick. The dense patches of awnless barnyard grass seen in this image are the glyphosate-only treatments. “This shift has taken years to occur and now we are seeing weedy patches establishing in cotton crops,” he said. “We have used crop modelling to show that managing these patches is effective in awnless barnyard grass and now we have field experimental results demonstrating that the industry’s best management practice weed control strategy works.” Dr Werth and the DAF weed research team designed an experiment to field-test the 2+2&0 (2 non-glyphosate tactics in crop plus 2 non-glyphosate tactics in fallow and no survivors) strategy in a dryland cotton system. They chose a dryland cotton field with a dense population of glyphosate-susceptible awnless barnyard grass (ABG) and used a low rate of glyphosate (250 g/ha Roundup Ready®) to simulate glyphosate-resistance with approximately 70% control of the barnyard grass each time glyphosate was used. The treatments applied were designed to compare ‘glyphosate only’ with the ‘2+2&0 strategy’ to see the effect on ABG emergence and seed bank. They also tested a few ‘eradication’ tactics, which were applied at three different times in the cropping season – 1. Early (Oct to mid-Dec), 2. Mid (mid-Dec to mid-Feb) and 3. Late (mid-Feb to March). The experiment ran for a four-year cotton-fallow-fallow-cotton rotation. Table 1.  Example of control tactics used on Awnless barnyard grass comparing glyphosate only, to BMP and additional eradication treatments. Phase Treatment 1. Early season 2. Mid-season 3. Late season Glyphosate only Glyphosate (PRE) Glyphosate (OTT) Nil Glyphosate (OTT) Glyphosate (OTT) Best Management Practices (BMP or 2+2) Paraquat + Pendimethalin (PPPE) Diuron (Layby) Nil (Treatments 2-9) (Treatments 2-9) Additional Eradication tactics (Erad) Metolachlor (PRE) Metolachlor (PRE) Hand-hoeing (Treatments 3, 6, 7 and 9) (Treatments 3, 6, 7 and 9) (Treatments 5, 7, 8 and 9) “When glyphosate was used without applying any other weed control tactics, weed emergences were almost always higher than where multiple tactics were used,” said Jeff. “The most consistent tactic for reducing barnyard grass emergences was metolachlor applied six weeks prior to planting in the ‘Eradication phase 1’ treatments.” Pendimethalin applied at planting seemed to have little effect on the major flush of weed germination that usually occurs in spring, but did have some effect on later germinations. “Including residual herbicides in the weed control program can really reduce the number of weeds that emerge, and as a result, there is less pressure on post-emergence herbicides applied later in the crop,” he said. This simulation experiment also demonstrated that the 2+2&0 strategy was effective in driving down the weed seed bank, which is the ultimate goal of any integrated weed management program. Jeff said that it took three years to really see the differences between the two main treatments, so persistence is required if you don’t see immediate changes in weed numbers. Eradication treatments applied early in the crop season were also the most effective in driving down the weed seed bank. Table 2.  Total Awnless barnyard grass emergence in each year of the experiment.  Means with the same letters are not significantly different. Treatment Year 1 Year 2 Year 3 Year 4 Cotton* Fallow* Fallow Cotton* (plants m-2) 1.  Glyphosate only 1118  d 316  b 87  b 118  d 2.  BMP 176  bc 45  a 39  a 88  cd 3.  BMP + Erad (phase 1) 116  ab 56  a 18  a 23  ab 4.  BMP + Erad (phase 2) 257  c 27  a 34  a 26  ab 5.  BMP + Erad (phase 3) 324  c 44  a 40  a 60  bcd 6.  BMP + Erad (phase 1 and 2) 81  a 42  a 9  a 29  ab 7.  BMP + Erad (phase 1 and 3) 129  ab 54  a 6  a 32  abc 8.  BMP + Erad (phase 2 and 3) 191  bc 26  a 17  a 16  a 9.  BMP + Erad (phase 1,2 and 3) 108  ab 43  a 8  a 11  a P-value <0.001 0.014 0.005 0.004 *Means back-transformed from Log(x+1) The time taken to see a decline in weed populations is related to the longevity of the seed of different weed species. In a cotton farming system small seeded species such as feathertop Rhodes grass, windmill grass, fleabane and sowthistle generally last in the soil for 2–3 years; larger seeded species such as awnless barnyard grass and liverseed grass last about 4–6 years and harder seeded species like bladder ketmia and peachvine last 6–10 years. Awnless barnyard grass produces a large quantity of seed if it escapes weed control tactics, resulting in patches of potentially resistant weeds in cotton fields. “It is reasonable to expect that the longer the 2+2&0 strategy is applied, along with early season eradication tactics, the greater the difference there would be compared to a glyphosate-only approach,” he said. “In years with multiple rainfall events across the summer, there would be increased benefit from employing early eradication tactics to avoid a potential build-up of the weed population. It is critical to ensure that survivors are controlled to prevent potentially resistant seed re-entering the soil.” The 2+2&0 strategy forms the basis of the Cotton Herbicide Resistance Management Strategy and is best applied in all cases to minimise the risks of resistance development. If a problem is detected early, the 2+2&0 can form the baseline response, and extra tactics can be incorporated to limit potential spread of the patch in the field, and drive down the seed bank.

Collecting and destroying weed seeds as part of the harvest operation is recognised as the most efficient and effective way to implement harvest weed seed control (HWSC) within an integrated weed management system. Acknowledged as the ‘holy grail’ of the WeedSmart Big 6 tactics to manage herbicide resistance, HWSC was implemented on over 40 per cent of Australian grain farms in 2014 and adoption is expected to increase to 80 per cent by 2020. Chaff impact mill machines render the weed seed unviable, causing the destruction of over 95 per cent of the weed seed that enters the mills. There are currently six HWSC methods being used in Australia, all of which have been invented, adapted and adopted by Australian farmers. When choosing between these methods growers must consider the set-up cost, nutrient removal costs and labour requirements. Most agree that the ultimate HWSC tool would complete the weed seed control in one pass at harvest, retain all stubble and nutrients and not require any follow-up work such as marketing hay or burning chaff. There are currently two machines that meet these requirements – the iHSD (Integrated Harrington Seed Destructor) and the Seed Terminator. These two chaff impact mill machines render the weed seed unviable, causing the destruction of over 95 per cent of the weed seed that enters the mills. In 2017 harvest, both the iHSD and Seed Terminator machines were in commercial operation on farms around Australia and both experienced the teething problems that can be expected for new technology moving into the real-world. They have since been in field trials overseas – the Seed Terminator in Canada and the iHSD in France – where both machines completed around 200 hrs work without a hitch. Kondinin Group Manager of Research and Development, Ben White interviewed 20 growers using either the iHSD or Seed Terminator during the 2017 harvest and reported that their observations suggested both brands were achieving over 95 per cent reduction in seed viability. “Both types of impact mills ran into the same real-world problems of handling high flow rates of chaff, choking on green crop or weed matter and significant damage to the mills from any sand or soil that is picked up by the harvester,” he said. “Both machines also caused a reduction in harvester capacity of between 12 and 20 per cent in wheat, even though the harvesters had been remapped. This is a significant cost that growers must allow for through machine depreciation and base hourly operating costs, as more hours are needed to harvest the same area of crop.” Over 70 per cent of the growers that the Kondinin Group engineers visited had remapped their harvesters to improve the harvest capacity. Operators should note that chaff impact mill technology pulverises the entire chaff fraction, which generates significant levels of dust during the harvest operation. This means that more frequent machine clean-down may be required to minimise fire risk, as well as increased frequency of filter cleaning or replacement. “Although the problems outlined here are important, they are all likely to be resolved as this technology matures in the commercial world,” said Ben. “There is enormous interest in this method of harvest weed seed control and this will ensure that the problems are solved.” Seed Terminator, WA. Australian Herbicide Resistance Initiative’s cost comparison of HWSC methods suggests that the chaff impact mills cost $16-17/ha compared to $22/ha for narrow windrow burning and $6-7/ha for chaff tramlining and chaff lining, depending on crop yield and area. In addition to the weed control benefits achieved through the use of any HWSC method, the chaff impact mill option also reduces crop volunteers. Research into the efficacy of impact mills is an ongoing process, particularly while the two types of machines are undergoing rapid developmental changes. Recent research by Michael Walsh (AHRI and Sydney University) with help from John Broster at Charles Sturt University (CSU), shows that despite the problems that have been experienced with the new machines, iHSD mills are passing the research tests with flying colours. Their research concluded that: The iHSD achieved 96–99% destruction of the seeds of 11 weed species when processed in wheat chaff. Weed seed destruction varied by about 10% depending on crop chaff type – ryegrass seed kill was greatest in lupin (98%) > wheat (92%) > canola (90%) > barley (88%). Weed seed kill dropped by about 4% when chaff moisture increased above 12%. Weed seed kill increases with mill speed and 3000 rpm is the accepted optimal speed for the iHSD. SAGIT funded research conducted by Trengove Consulting in 2017 found similar results for the Seed Terminator: Ryegrass weed seed kill was 93% at 2250 rpm and increased to 98% or greater at normal operating speeds (2500–3000 rpm). Greater than 99% control of several other species including wild radish, brome grass, wild oat, bifora, bedstraw and tares. Increasing chaff flow rate (harvest rate) did not reduce control of these species. Samples analysed in 2018 by the Weed Science Research Group, at The University of Adelaide showed that the Seed Terminator could consistently kill 96% of weed seeds when operated at 2750 rpm. These kill rates refer only to the weed seed that enters the impact mills. To achieve high level of weed control it is essential that all efforts are made to ensure the weed seed enters the front of the header and is then separated and directed into the mills. iHSD, WA. Timing, cutting height, operating speed, weed and crop type and harvester set-up all play a part in achieving maximum harvest weed seed control. As is recommended for all HWSC methods that treat the chaff fraction, separation of the chaff and straw through the harvester often requires the addition and fine-tuning of a baffle plate to achieve greater efficiency. Setting up and operating harvesters to achieve the best weed control outcomes often involves some modification and compromise. By taking the time to get things right, growers usually find that they end up with more grain in the bin and a better sample, making the extra effort worthwhile. WeedSmart has secured the rights to distribute an electronic version of Kondinin Group’s Research Report: Residue Management at Harvest, which is available in the Resources section of www.weedsmart.org.au. WeedSmart encourages growers and advisors to support Kondinin Group’s independent research through subscription to Farming Ahead.

For weeds that have a natural tolerance to glyphosate, the double-knock has provided growers with an excellent tool to take two swipes at weeds like fleabane, sowthistle and feathertop Rhodes grass and achieve a greater level of control. NSW Department of Primary Industries weeds researcher, Dr Md Asaduzzaman (Asad) has uncovered disturbing evidence of double-knock resistance in tall fleabane (Conyza sumatrensis) samples collected during weed surveys funded by the Cotton Research and Development Corporation (CRDC). NSW Department of Primary Industries weeds researcher, Dr Md Asaduzzaman (Asad) has uncovered disturbing evidence of double-knock resistance in tall fleabane (Conyza sumatrensis) samples collected during weed surveys funded by the Cotton Research and Development Corporation (CRDC). “Our surveys in 2016 and 2017 showed that cotton fields were generally weed-free but herbicide resistance is building in weeds along farm roadsides, drains and channels and around infrastructure,” he said. “We identified two tall fleabane biotypes that have resistance to glyphosate, paraquat and the double-knock tactic of an initial glyphosate application followed with an application of paraquat 7 days later.” The rate response analysis showed that one of these biotypes is 4.9 times more resistant than the susceptible biotype, requiring 2.5 L/ha Paraquat-250 to kill 50 per cent of the plants from the resistant population compared to just 0.5 L/ha to achieve the same result in the susceptible population (see Table 1). While this level of resistance is generally considered ‘moderate’ it is clear that resistance is building and must be taken very seriously given the importance of the double-knock tactic in most cotton and grain production systems in Australia. Table 1 Resistance levels of tall fleabane screened against paraquat, glyphosate and glyphosate + paraquat (R-resistant > 50% survival; DR-developing resistance < 50% and > 20% survival and S-susceptible < 20% survival)   Tall fleabane biotype   % Plant survived under Paraquat-250 @ 2 L/ha Glyphosate-540 @ 1.2 L/ha Glyphosate followed by Paraquat (Double-knock) TFB01 >75 100 75 TFB02 75 75 75 TFb-Suscept 0 0 0 These two populations, collected near Nandi, Queensland and Coleambally, NSW, are the first paraquat-resistant tall fleabane to be identified in Australia. Resistance to paraquat in this species has previously been recorded in Japan, Sri Lanka and Taiwan. Location of confirmed cases of double knock resistance in tall fleabane. “Although the tall fleabane plants from these two populations showed signs of herbicide damage, such as narrowing of leaves and slow growth, when the double-knock was applied, they were able to survive and produce seed,” said Dr Asad. “This species produces a large quantity of seed, germinates quickly and the seed can travel over 10 km in the wind so dispersal of paraquat / glyphosate resistance traits will be impossible to contain.” Tall fleabane seedlings 28 days after the double knock (glyphosate + paraquat) tactic was applied. This discovery makes tall fleabane the second species in Australia to have confirmed resistance to both glyphosate (Group M) and paraquat (Group L), the first being a population of annual ryegrass identified in Western Australia in 2013. Having demonstrated resistance to the dual application of these herbicides in the otherwise effective double-knock tactic is cause for great concern. Weed populations take longer to evolve resistance to paraquat and glyphosate compared to some other modes of action, but it will happen after years of regular applications without survivor control. Like other fleabane species, tall fleabane is susceptible to crop competition but flourishes in poorly competitive, wide-row crops such as dryland cotton. Combatting herbicide resistance and keeping weed numbers low will require the implementation of a wider range of weed control tactics rather than relying heavily on the double knock tactic. “Growing more competitive crops and using a wider range of pre- and post-emergence herbicides and strategic tillage will help manage this weed,” said Dr Asad. “Above all is the need to monitor and remove any survivor weeds in line with the cotton industry’s weed control strategy of ‘2 + 2 and 0’ that recommends two non-glyphosate tactics in-crop plus two non-glyphosate tactics in the fallow and zero survivors.” In other research Dr Asad is testing the opportunities for cotton growers to use cover crops to create additional opportunities for herbicide rotations, run down the seed bank and delay the adaption of weed populations by reducing the frequency of single modes of action herbicide use. Paraquat resistance has previously been confirmed in 10 species in Australia, including flaxleaf fleabane (Conyza bonariensis). Other resources Resistance risk to knock-down herbicides on irrigated cotton farms Protecting knock-down herbicide options What are the herbicide options for the summer fallow

On water-repellent soils, such as the Mallee sands of South Australia and Victoria, stronger crop competition has been shown to have an immense impact on brome seed production. In a difficult environment, where crop establishment is often patchy, researchers have demonstrated that water and nutrient harvesting within the crop furrow can result in better establishment when crops are sown on or near last year’s row. Results from four years of trials on non-wetting sands at the Mallee Farming Systems (MSF) trial site at Karoonda, SA consistently show that the increased surface soil moisture, crop establishment, crop biomass and crop / brome competition effects achieved through edge-row sowing can reduce brome grass seed set. Blue dye shows the higher moisture that can be found beneath last year’s row (left) and crop sown using edge row placement into last year’s crop stubble. Photos: Bill Davoren CSIRO Dr Rick Llewellyn, research group leader (agricultural systems) with CSIRO says that brome grass is the most costly weed for Mallee farmers to manage, even though herbicide resistance in brome grass is currently low in the region. “A series of trials have investigated the effect of different herbicide use, particularly pre-emergence herbicides, and row placement on crop yield and brome grass seed production,” he says. “To successfully manage brome grass it is necessary to keep weed seed numbers low and avoid blow-out situations. Our aim was to find the best options for reducing seed set.” When this year’s crop can make use of the resources in last year’s furrow there is more reliable crop germination and it can allow earlier sowing in years with marginal rainfall. On non-wetting sands, the practice of edge-row sowing has led to reductions in brome seed set of at least 55 per cent, and as high as 75 per cent, over the past four seasons. “Using edge-row seeding to achieve stronger establishment and crop competition on these difficult but widespread sands has resulted in a large and relatively reliable impact on brome grass seed production,” says Dr Llewellyn. “Growers will need to weigh this benefit against any potential disease risk and any stubble management issues in parts of a paddock that are not non-wetting sands, before changing their seeding set-up for edge-row sowing.” One important observation was the extent of brome grass germination in the crop row at the time of applying the pre-seeding knockdown. With seven times more brome grass seedlings emerging on the row, a successful knockdown is very important and a great opportunity to give the pre-emergence herbicide the best chance of success. Pre-emergent herbicides have the potential to achieve up to 75 per cent control of brome grass under optimal conditions but these products are notoriously variable from season to season. Trifluralin (1.5 L/ha) was commonly the least effective pre-emergent herbicide option while Sakura mixed with Avadex consistently achieved the greatest reduction in brome grass seed set. “In the 2015 trials at Karoonda, Sakura alone resulted in 55 per cent less brome panicles than trifluralin alone, and Sakura + Avadex resulted in 72 per cent less brome panicles than trifluralin alone,” says Dr Llewellyn. “Reducing seed production is the most important component of effective weed management. In some seasons, while the trifluralin and metribuzin treatments halved early brome grass density, they did not result in significant seed set reduction.” “Unfortunately, the more reliable Sakura plus Avadex treatment, with its extended period of activity is too costly for common use in low input regions. This leaves growers to get the most from lower cost but less reliable pre-emergence herbicide options and increases the need to include non-herbicide tools, such as improved crop competition through tactics like edge-row sowing.” Brome grass is a weed that demands an integrated approach to keeping the seedbank low, especially where growers are wanting to reduce their reliance on Group B tolerant crops. More resources Crop row placement (MSFP) Crop Row Placement – 10 things to consider Take a look at edge-row sowing submitted by one of our MSF members. Travelling at 9km/hr and sowing with a John Deere Conserva Pak, and StarFire guidance system giving 2cm accuracy. The dry start meant there was very little moisture mid row but moisture was found in the previous year's crop row. Sowing as close to the moisture band helps to get a better germination in dry conditions. However, the practicalities of edge-row sowing are still being worked through. It can be hard to manage stubble and keep it standing when sowing so close to last year's row. In this situation it has worked with accurate guidance systems that allow you to sow on the same row year after year and always in the same direction. Thanks to the GRDC Stubble project you can learn more about crop row placement in stubble retained systems specific to the Mallee at the link belowhttp://www.msfp.org.au/farmtalk-crop-row-placement Posted by Mallee Sustainable Farming on Friday, 22 June 2018

As a whole, the northern grains region has had a very tough start to the 2018 winter cropping season. With a few showers around there are hopes of some reprieve from a long, dry spell. Unfortunately, weeds will most likely be the first to respond to rainfall and growers will need to make some difficult decisions surrounding their cropping program, pre-emergent herbicide applications and maximising the competitiveness of any crops that get established. Brad Jackson, Gurley, will speak at the WeedSmart Week 2018 forum and host a bus tour of his family’s property, outlining his experience with pre-emergent herbicides, optical weed detection, narrow windrow burning and using a diverse cropping program to stay ahead of herbicide resistance. By August the dice will have rolled on the season and growers and agronomists are invited to attend the 2018 WeedSmart Week event in the Narrabri and Moree districts. The 3-day program consists of a 1-day forum at Lochabar Station near Narrabri on 20 August. The following two days will be filled with bus tours to farms around Narrabri and Moree where growers have but in place integrated weed management programs to minimise the impact of herbicide resistance on their businesses. The theme for the event is ‘Diversify and Conquer – manage weeds using the BIG 6’. At the forum and on the bus trips growers, agronomists and researchers will have all the options and ideas on the table for discussion. https://www.facebook.com/WeedSmartAU/videos/925458154287495/ Three growers from the region who attended the 2017 WeedSmart Week in Wagga Wagga will be making presentations over the three days, outlining ways they have tackled herbicide resistance head on. Farming north-west of Moree, Jason Rogers drops a GPS marker on any suspect weed patches he finds so he can treat them with spot spraying, chipping or strategic tillage. In recent years he has moved into applying residual herbicides soon after harvest and is also mixing and rotating fallow sprays to extend the efficacy of all available modes of action. He says barley and Clearfield canola provide early canopy closure and the strongest crop competition for winter weeds. Byron Birch is implementing a 5-year rotation of cereals, pulses and dryland cotton on a 4500 ha lease block on ‘Morven’, north-west of Narrabri. He is contending with annual ryegrass that was delivered in the 2016 flood and appears to have some tolerance to both Group A and B chemistry, and there are some small patches of glyphosate-resistant barnyard grass emerging. Byron has used dryland cotton to provide strong competition for moisture over summer to suppress the expansion of weedy patches on the farm. Brad Jackson farms with his father Peter and brothers Phil and Matt at Gurley where they usually have a robust winter cropping program featuring wheat, barley, chickpea, canola and linseed. Following 2017 WeedSmart Week they have reintroduced the use of pre-emergent herbicides to their herbicide program and are taking every opportunity to mix and rotate herbicide modes of action. The Jackson’s WeedIT optical sprayer has revolutionised their herbicide program, allowing them to spray low weed density paddocks more frequently and target small, fresh seedlings. Brad and Phil are also developing valuable weed management tactics, such as camera-guided inter-row cultivator and green manuring, that can be employed in an organic farming system at Westmar. WeedSmart Week attendees will have several opportunities to see and discuss cutting-edge technologies such as optical sprayers, autonomous tractors and emerging ‘green-on-green’ spray sensors. Beefwood Farms’ manager, Glenn Coughran has used optical sprayers as the foundation of a rejuvenated weed control program over the last 12 years and seen the benefits of combining this technology with autonomous tractors over the last three years. Glenn is keen to see ‘green-on-green’ optical weed detection become a reality and is working closely with AgriFac to have this technology integrated into their spraying equipment. In a region where mixed farming is far less common now than it was a few decades ago, Tom Lampe uses livestock to deal with weeds that are hard-to-kill with herbicide. Using three 250 ha paddocks, each with a 5 ha ‘cooler’, Tom sprays the paddocks soon after harvest and then allows the sheep to graze the wheat, barley, chickpea and sorghum stubble, providing additional feed for the stock through the year. These are some of the growers ready to host bus tours, even though the weather may prevent them doing what they normally would to manage their cropping program. These experienced and thoughtful farmers have implemented weed management programs that ‘Diversify and Conquer – manage weeds using the BIG 6’ in all seasons. The growers, agronomists and researchers that will speak and participate 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 northern cropping region. There’s one thing for sure – doing nothing is not an option. Register for this important 3-day event for the single ticket price of $95, guaranteeing a seat on both the bus tour days as well as the forum, all fully catered, at https://www.weedsmart.org.au/northern-weedsmart-week-august-2018/

Chris Davey, partner and director of YP AG at Kadina has worked with growers on the Yorke Peninsula of SA for over 20 years, assisting them to devise weed control programs that reduce the impact of herbicide resistance. His group of 20 clients farm between Port Broughton and Arthurton with annual rainfall ranging from 300 to 500 mm and very diverse soil types. Chris initiated the Northern Sustainable Soils farmer group in 2007 to provide growers with the opportunity to research farming system tactics and discuss their ‘fit’ for the highly variable soils found on the Peninsula. YP-AG partner and director, Chris Davey works with his grower clients including Gary Bruce (left), to plan integrated weed management programs that include as many of the WeedSmart Big 6 tactics as possible. “The soils here range from shallow sheetrock and limestone to grey calcareous loams, dune and swale systems to heavy red fertile clay,” he says. “This variability drives many management decisions and has a direct relationship with many of our weed problems.” Chris has used resistance testing services to keep track of herbicide resistance in the main weeds, with growers managing resistance in annual ryegrass, brome grass and wild radish for some time and more recently finding milk thistle, Indian hedge mustard and prickly lettuce increasingly problematic. Annual ryegrass and brome grass on the Peninsula are known to have resistance to herbicides in Groups A (fop and dim), B, D and M and wild radish is resistant to Groups B, F and I. “This area was the home of ryegrass resistance and growers are trying hard to avoid the same blow-out situation with brome grass,” says Chris. “Growers are well aware of the potential consequences if resistant brome grass gets out of hand so most are using some form of patch management and even chemical fallow in blocks where the brome grass has out-competed the crop.” In response to increasing herbicide resistance, 85 per cent of Chris’ clients have adopted some form of harvest weed seed control within their weed management program. “Sixty per cent of my clients are using narrow windrow burning and 25 per cent are using either a chaff cart or chaff lining chute,” he says. “In the 2017 harvest there was also one iHSD and one Seed Terminator operating here.” Chris is a strong supporter of all the tactics in the WeedSmart Big 6 and actively promotes the inclusion of all tactics in his clients’ integrated weed control programs. 1. Crop and pasture rotation The close lentil – wheat rotation that has dominated farming systems on the northern Yorke Peninsula in recent years is acknowledged as a weak link in terms of weed control. This rotation has led to an increase in broadleaf weeds such as milk thistle and prickly lettuce, with bifora, tares and medic also exploding in the lentil phase in some years, leaving a high weed seed bank for the following year as well as increasing the risk of herbicide resistance evolution. Chris says the economic drivers for the rotation can make weed control decisions difficult and there is a need for other profitable rotation options that can assist in reducing weed pressure. The main problem with the short rotation is that weeds are exposed to the same herbicide modes of action every two years. Although imi-tolerant (Clearfield) varieties have been very useful, particularly PBA Hurricane lentils, allowing the use of Group B herbicides in the crop or in previous seasons, the alkaline soils on the Peninsula have expedited the more rapid evolution of Group B resistance in wild radish, mustard, milk thistle and ryegrass. Lentils have provided several economic and weed control benefit to farming systems on the Yorke Peninsula but the short lentil / wheat rotation is a definite weakness when it comes to managing herbicide resistance.   2. Double knock to protect glyphosate Glyphosate resistant ryegrass is widespread on the Yorke Peninsula, primarily along fencelines but as fences are removed to form larger paddocks, there is a significant risk that the resistance gene will be spread by headers. In 2013, the Peninsula had the dubious honour of having the first confirmed case of glyphosate resistant brome grass on a farm near Maitland, and this season, glyphosate resistance in barley grass was observed for the first time on northern Yorke Peninsula. An annual double knock application before seeding is considered very important to help protect the efficacy of glyphosate and is widely practiced on the Peninsula. Sowing earlier to achieve a yield advantage and dry sowing can impact on the use of double knock. Chris advises his clients to avoid early or dry sowing in weedy paddocks and to hold off sowing until the double knock has been implemented, even though there could be a yield penalty. Under dry, dusty conditions most growers will choose two contact herbicides such as paraquat or paraquat / diquat rather than glyphosate / paraquat for the double knock. 3. Mix and rotate herbicide groups There is a heavy reliance on pre-emergent herbicides on the Yorke Peninsula and in weedy paddocks growers need to use additional shots to drive down weed numbers to preserve yield. In cereals, the Boxer Gold and Sakura applications are often spiked with triallate to strengthen the pre-emergent efficacy because there are no in-crop herbicide options in wheat and barley crops. Pre-emergent herbicides are also very important in lentils as the main break crop to reduce ryegrass numbers so there is less pressure on the clethodim / Factor mix in crop. Trifluralin susceptibility in ryegrass has been very low since the late 1990s and so is not a tank mix option, unless targeting broadleaf weeds like wireweed or three corner jack. 4. Stop weed seed set Chris says Yorke Peninsula growers generally use their late fungicide application in August or September to scout for weed escapes in crop. Taking a nil tolerance approach, growers might hand pull small areas, or spot spray. Using paraquat or paraquat / diquat, growers can avoid using glyphosate on potentially resistant individuals when chemically fallowing areas of their crop. The permit for Weedmaster DST use to crop-top in barley provides a useful control tactic for radish and ryegrass at the end of the season, but is often too late for brome grass, which has usually already set seed by this stage of the crop. In blow-out situations Chris often advocates for the ‘short-term pain for long-term gain’ of a chemical fallow using paraquat or Spray.Seed. Chris suggests that the chemical fallow is the best tool to use if brome numbers are building up in a paddock. In his experience, the performance of the following crop usually makes up for the one-year sacrifice due to increased nutrients and moisture availability. He says some growers plan for the inclusion of a small portion of the rotation to be sown as a chemical fallow, while a larger number would use chemical fallow only in a failed crop or for a weedy portion of a paddock as a patch management option. 5. Crop competition Where the soil type allows, Yorke Peninsula growers have readily adopted east west sowing having seen the benefits of this row orientation promoted through AHRI and WeedSmart. Some soil types, such as the sand swales around Port Broughton, dictate sowing direction but it is an option in other areas. Barley is the most competitive crop grown across the Peninsula and growers usually consider choosing the most competitive cultivars available. This is coupled with high sowing rates and narrower row spacing of 22–30 cm (9–12″) spacing, although there is local research that suggests there could be benefits of even narrower row spacing. 6. Harvest Weed Seed Control (HWSC) Chris’ trial work with HWSC shows the importance of getting the weed seed into the header. He says brome grass can be difficult as its flexible stem doesn’t always get cut and can flick back up once the harvester has passed. Wild radish generally stands up well with 70–80% of seed entering the header. Even with a 50 to 60% capture of brome grass, depending on the season and how early harvest occurs, HSWC is still an important part of any weed management program. Capture of ryegrass seed is seasonal with the ryegrass lodging in some years and not picked up by the header, while it will stand up well and achieve 80% capture in other years. Once weed seed is in the header, Chris’ research has shown that it doesn’t matter what HWSC method is used – all are effective. Chaff carts and narrow windrow burning have been widely adopted for many years but Chris expects that chaff lining and chaff decks is likely to increase while NWB will decrease in use. Chaff lining was widely adopted in 2017 harvest as an economical and easy way to manage weed-laden chaff. He also expects some growers with larger areas and some contractors to purchase iHSD and Seed Terminator modules, with one each of these operating in 2017 harvest on the Peninsula. Chris Davey’s trial work with various harvest weed seed control methods has shown that the amount of weed seed entering the header can vary, but once in the header all methods are equally effective at reducing the weed seed bank for the next season.