Resources

Tony and Sharon Single farm with Tony’s parents John and Mary, south east of Coonamble in northern NSW with views of the Warrumbungle Range. Across the 4500 ha cropping area at ‘Narratigah’, the weed numbers are low as a result of the Single’s ‘farming moisture’ philosophy, which involves planting whenever there is sufficient subsoil moisture to establish a competitive crop on their heavy clay soils. Their location allows a mix of summer and winter cropping, so if there is an opportunity for a summer crop they take it, even if that might result in missing the winter crop. Tony (left) and John Single use their Single Shot weed detecting drone to scout for and map weeds to create a prescription map for their tractor mounted boomspray. “Farming moisture is our risk management strategy and it has paid off time and time again,” says Tony. “We are really farming with probability and by reducing our risk we have been able to maximise profits. If there is insufficient subsoil moisture we just don’t plant. This means we have very few failed crops and we take advantage of the intermittent winter fallows to run down the seedbank, particularly for winter-active grass weeds.” Tony says the area has a slightly summer dominant rainfall pattern but rainfall is very variable. The main crops grown are wheat, chickpea and sorghum, along with any other crop that might fit a certain planting opportunity. While their cropping decisions are very water responsive, there can be situations where the need for ground cover outweighs other considerations. This can occur after a chickpea crop and if they feel it is necessary, Tony and John will plant a crop just to produce stubble, knowing that the yield will most likely be low. “Generally, if it is too dry to plant we will choose to fallow to build up the soil moisture profile knowing that this is the least-risk strategy and gives the best result in the long term,” says Tony. “We can effectively gain good weed control for the full 12 months through the use of cropping and fallowing in both winter and summer.” Resistance status Herbicide resistance is considered the biggest threat to their business even though they currently have resistant weeds well under control. Glyphosate resistance was first confirmed at ‘Narratigah’ in 2005 in annual ryegrass, and Tony and John are also aware of some small areas of glyphosate resistant barnyard grass. “These are our most important weeds and keeping a lid on resistance is crucial to prevent them becoming limiting factors in our cropping choices,” says Tony. “We also have other weeds including milk thistle, fleabane, blow-away grass and feathertop Rhodes grass – the full suite of northern region weeds really.” Tony says their efforts to consistently drive down the weed seed bank, and having regular winter fallows, minimises the impact of herbicide resistance on their business. “Our weed seed bank is low and weeds do not dictate our cropping decisions,” he says. “Ryegrass has a relatively long growing season so we have ample opportunity to stop seed set through a winter fallow. There are also several chemical options for use with our spot spraying technology and new pre-emergent herbicide options too, along with cultural controls such as chipping.” “We are more concerned about the implications of resistant barnyard grass, which washed in from up-stream. Barnyard grass has the ability to germinate and very quickly set seed, making it more difficult to contain.” To avert the risk of more seed being deposited by overland flow, the Singles have constructed a number of diversion banks on the up-stream side of their cropping area to divert water. Tony is also noticing ‘rate creep’ as weeds like milk thistle that are slow to metabolise herbicide, become harder to control. He says they are needing to use a higher rate of paraquat in the double-knock applications. The Singles are managing this through regular double-knocking in fallow and strategically using saflufenacil with paraquat to enhance control. Black oats currently has a low resistance profile due to the use of winter fallows and fop chemistry is still effective in many paddocks. The Singles use their proprietary drone weed mapping system ‘Single Shot’ to scout for and map weeds, helping them to better plan for and implement each herbicide application. Their integrated weed management system is an excellent example of the WeedSmart Big 6 in practice. #1 – Diversity in cropping The combination of winter cereals, winter pulses and summer cereals provides many opportunities for controlling weeds pre-season and in-crop. “The decision to plant sorghum is driven by weed and disease pressure in winter crops,” says Tony. “In a paddock that is becoming difficult to manage, we would rather change to sorghum than turn to a heavy reliance on pre-emergent herbicides and in-crop spraying of winter weeds in winter crops. Swapping to a summer crop gives us the opportunity to target problematic weeds using a winter fallow phase.” This practice, plus the persistent drought in recent years, has resulted in more fallow area and allowed them to drive down the weed seed bank of annual ryegrass and black oats. It is now very rare for them to target grass weeds in-crop in winter cereals. Using their drone and sensor to scout for and map weeds in the fallow periods has been a powerful tool to attack the weed seed bank in both summer and winter. Decoupling the weed detection and spraying operations opens up opportunities for more diverse weed control. Tony and John can use the drone to map the presence of weeds just before, or soon after, significant rainfall events. Once they are able to get on the paddocks with the sprayer they can target previously existing weeds with spot spraying an effective herbicide mixture while applying a blanket rate to the new germination of weeds following the rain. Knowing exactly what is in the paddock before they start spraying means they can consider a wider range of potential chemical options or techniques. Once the plan is made, they know how much product they will need and the cost. Knowing that they will only be treating say 5 ha in a paddock, they can afford to use chemicals that they would never consider for a blanket spray application. #2 – Mixing and rotating MOA Tony and John use some preemergent chemistry strategically in fallows to maximise weed control diversity while keeping their options open for cropping. They aim to use a preemergent application to control key broadleaf and grass weeds after harvest, which takes the pressure off glyphosate without compromising planting opportunities the following autumn. A combination of soil residual herbicides such as picloram, Balance and Flame has given good results early in the summer fallow, followed with a pre-sowing double knock of glyphosate and paraquat, giving a total of five chemical groups targeting fallow weeds. When it suits the program, they use chemistry mixes such as Sharpen + paraquat in the double knock, increasing the modes of action and increasing the efficacy of the treatment on the weed spectrum. In addition to the use of preemergent chemistry, winter grass weeds are also targeted in broadleaf crops, usually with clethodim (Group A, Group 1), but the Singles are aware of the resistance risk and are looking to introduce Clearfield canola as alternative means of grass control in break crops, and to bring more diversity to their system. Using their drone mapping technology, Tony and John can merge multiple flights of a paddock during the year into one map to show the location of all the weeds detected. This map can then be used to apply a site-specific soil residual herbicide for the next season to say 15 to 20 per cent of the paddock. In treating smaller areas, they can afford to consider chemistry that might otherwise be too expensive, add more diversity to chemicals used and reduce their plant-back risks. #3 – Crop competition The Singles consider crop competition to be their #1 weed control tactic, simply because it is the only one that provides season-long in-crop weed control. “We do everything we can to maximise the crop’s ability to suppress weeds,” says Tony. “This starts at planting, where we have invested in planting gear with moisture seeking capability so we can plant crops on time and ensure good establishment. We take great care to ensure there are no gaps for weeds to exploit, and always square-off the headlands.” Planting at 330 mm row spacing allows for inter-row sowing and stubble retention, and planting rates are chosen to maximise yield – with long-season wheat sown at 40 to 60 plants/m2, and later plant wheat sown at 80 to 100 plants/m2. The slope of each paddock dictates the tramline direction to be perpendicular to the overland flow, which results in most paddocks being sown north south. For all crops Tony aims to achieve 100% knockdown prior to planting with a double knock treatment, followed with a well-established, vigorous crop. #4 – Double knock The Singles started using the double knock tactic twenty years ago in their winter fallows, and introduced it to summer fallows about ten years ago. “The double-knock strategy hasn’t added significantly to our overall weed control costs,” he says. “When we first started using the double-knock we counted it as a direct cost to the system, but we now see the second knock with paraquat as a preemptive strike on future weeds – an investment in lowering the weed seed bank, and we are picking up savings with lower volumes of chemical required in subsequent weed control applications.” The double knock tactic is now embedded in their weed management strategy and they have invested in spray gear to allow them to cover their area within the recommended 7 to 8 day window. Tony says the high level of control they achieve with the double knock means there are fewer and fewer weeds each year and this reduces the cost of the operation, particularly now they have the capacity to spot spray weeds with highly consistent weed detection. “This tactic puts a significant dent in the weed seed bank and reduces the number of large and potentially stressed plants being sprayed,” says Tony. “This makes it a very effective resistance tool, particularly for our hard to kill weeds.” #5 – Stopping seed set The Singles are aiming for 100 per cent weed control in fallow, particularly for annual ryegrass and BYG, by managing paddocks in a site specific way at a square metre level using their drone scouting technology. “The drone can effectively scout for weeds at a rate of 200 ha/hr, which makes it very quick and easy to scout a paddock and then go out and chip the five or so plants that might be left growing in a paddock,” says Tony. “This moves us closer to achieving 100 percent weed control. We have really driven down our weed numbers and significantly reduced the impact of herbicide resistance in our operation.” Occasionally, Tony will drive along the tramlines in the side-by-side and chip out any grass weeds in chickpeas that have either escaped control or germinated late in-crop. Then prior to harvest, Tony and John look for any patches of weeds that have escaped control and take action to prevent seed set. “If we find there is a patch of weeds getting away from us we don’t hesitate to sacrifice small areas of the crop to prevent seed set,” says Tony. “In 2020 we had a three or four hectare patch of ryegrass and decided to use a small slasher to mow the crop and weeds then sprayed the area with paraquat. That way we made sure the weeds did not set seed and prevented the spread of resistant weed seed at harvest.” The Singles do not spray any selective herbicides outside their cropped area and prior to harvest they slash a 2 m width of crop along fencelines to stop the header bringing weeds into the paddock from the fenceline. #6 – Harvest weed seed control Several years ago, the Singles trialed narrow windrow burning for harvest weed seed control but decided that the negative effects outweighed the weed control benefits. “For us, ground cover is supremely important for erosion control, reducing evaporation and increasing infiltration through the heavy clay soils,” says Tony. “We are watching the developments in impact mill technology and will most likely go down that path if we feel harvest weed seed control is needed in the future.”

The pressure for growers to get across a large area in a short period of time has led to an increased use of complex tank mixes – but the efficiency gains of this practice can easily become unstuck if taking short-cuts results in not being able to spray the brew out. Stephen Pettenon, FMC technical services specialist. FMC technical services specialist, Stephen Pettenon, says if there are many products in a tank mix, it becomes increasingly difficult to prevent adverse chemical reactions from occurring in the ‘brew’. “If operators follow a few guiding principles it is possible to safely mix a complex combination of herbicides, insecticides and even crop nutrients,” he says. “But it is also quite easy to end up with a tank of sludge that can not be sprayed out, if you don’t take the time to get it right.” With several new products, such as FMC’s Overwatch, Syngenta’s Reflex and Callisto and Bayer’s Sakura Flow, being released as suspension concentrates (SC), it is important to recognise that there is no guarantee that a desired combination can be mixed and sprayed out effectively. “The first consideration is whether the tank mix is safe and if there are any biological antagonisms likely to arise,” says Stephen. “This is where one product impairs the efficacy of a tank mix partner or increases the risk of crop damage. These antagonisms are relatively rare in pre-emergent situations, but where they occur they can also have implications for the evolution of herbicide resistance.” “The second, and more common, problem in tank mixes is the potential for the mix partners to be chemically incompatible,” he says. “This can result in the formation of irreversible precipitate reactions or some components settling out of suspension and potentially causing blockages.” Tank mixing involves many products and so potential crop safety losses must also be a consideration. The WeedSmart Big 6 tactics for reducing the impact of herbicide resistant weeds on farming systems also promotes the importance of applying herbicides in the most effective and safe manner. *Always read the label and check with your agronomist for compatibility before mixing and applying agricultural chemicals. What are the top tips for complex mixes? In brief: The number one tip is to take your time. Rushing is the most common cause of tank mix failures. The details: Products that are SC or water dispersable granules (WDG) need time to properly disperse. They also need sufficient solvent – that is water. Start by filling the tank to at least 70 per cent of its capacity with good quality water before adding any products. Each chemical must be added and dispersed fully before the next chemical is introduced to the tank. Keep water rates above 80 L/ha and ensure the agitation system is working well to improve the likelihood of keeping a complex mix in suspension. Simplify the mix if you can. Keeping two or three products in a compatible mix is generally less challenging than achieving the same for a six or seven-way mix. Be realistic about what can be achieved in a single tank mix. Courtesy of FMC. Do I need to be careful when choosing between formulations? In brief: Yes, not all products are created equal. The details: Some products are only available as a powder formulation (suspension  concentrate – SC) and it is not possible for them to be produced as a more soluble, emulsifiable concentrate (EC). For example, Rustler 900 WG is a formulation that requires plenty of time to absorb water and swell the granules and then to disperse into the tank water. Allow at least 5 to 10 minutes, with agitation, before adding the next product. Suspension concentrates also require significant amounts of time. Some formulations of the same active can behave vastly differently in tank mixes. A well-known example is that potassium (K salt) loaded glyphosates are often less compatible in a tank mix than isopropylamine (IPA) and monoethanolamine (MEA) loaded glyphosate products. K salt formulations have never been good mixers because the potassium ion has a high ionic charge and small molecular mass, so it has a high affinity to bind with other molecules. K salt formulations are known to cause flocculation issues if mixed with SC and WDG products and such combinations should be avoided. There are some brands of potassium glyphosate formulations with complex surfactant systems that are mixing-friendly, provided agitation is maintained. Mixing order is crucial. Start with correctly conditioned water and then add the least soluble formulation first, allowing time for each product to disperse before adding the next component. If you are unsure of the compatibility of the desired products for the mix, conduct a jar test or ask for technical advice. The major chemical companies are involved in ongoing compatibility testing of the products that may be useful tank mix partners. Are there things I can do with the sprayer set up to minimise potential problems? In brief: Avoid over-filtering and be careful when using transfer systems. The details: It is common for spray rigs to use filtration that is too fine for the nozzle size being used. Using the correct in-line and secondary filter for the selected nozzle can greatly reduce the chance of blockages. For example, the standard 100 mesh filters on most spray rigs may not be the best choice for handling the mix. If using a single orifice nozzle that is 02 or greater in size, then using a 100 mesh filter (when a 50 mesh is adequate), will greatly reduce the area of passage and potentially increase the chance of blockages. If transfer systems are used it is important that the small tank contains only one of the spray mix components. Pre-mixing some or all the products in a transfer system or nursery tank can have some advantages in time efficiency for refilling the sprayer. Problems can arise if the full mixture of chemical is added to a small nurse tank. For example, if the full load of components is added to a 1000 L nurse tank destined for a 5000 L spray rig re-fill, there is unlikely to be sufficient water in the nurse tank to allow for complete dispersion of the product. If transfer systems are used it is important that the small tank contains only one of the spray mix components. Other resources Agricultural pesticides formulations (SmartTrain course notes)

Preserving the option for opportunity cropping is critical for Rolleston grain grower Kurt Mayne, but this means he needs to be careful with pre-emergent herbicides in his fallow weed control program. Kurt and his family operate a 6000 ha mixed farming operation of dryland grain production and backgrounding steers for feedlots at ‘Broken Plains’, 13 km east of Rolleston in Central Queensland. They grow chickpea and wheat every winter and summer crops when the opportunity presents on the 1400 ha of farmed country previously used for finishing cattle on leucaena (AKA tagasaste). Kurt Mayne bought a secondhand 36 m weedIT in early 2019 and can now spot spray their entire cropping area within two days. Wanting to keep one step ahead of herbicide resistance, Kurt took the opportunity to join a GRDC Grower Solutions study tour that included attending the 3-day WeedSmart Week event in Narrabri in 2018. He returned from the tour convinced that he needed to take extra steps to minimise the risk of herbicide resistance before it began to impact on his crop choices and profitability. “Optical spraying technology was the tactic that really stood out for me on the study tour,” says Kurt. “We bought a weedIT boom soon after I returned from the trip and I have been impressed with the benefits that have come with the addition of an optical sprayer to our weed control program.” “In our farming system it is hard to incorporate pre-emergent herbicides in the fallow because that can restrict our options for opportunity cropping over summer,” he says. “The optical sprayer makes fallow weed management much more effective, and when that’s combined with pulses in the rotation we are able to keep on top of grass weeds like feathertop Rhodes grass, which was getting increasingly difficult to manage.” The main weeds at ‘Broken Plains’ are feathertop Rhodes grass (FTR), milkthistle and fleabane – all notoriously hard to kill in fallow situations. Kurt bought a secondhand 36 m weedIT in early 2019 and can now spot spray their entire cropping area within two days. He also uses a tow-behind sprayer for their broadacre spray applications. Kurt says the pressure from FTR had led to an increasing need for cultivation to stop seed set and he saw that optical spray technology would mean he could reduce the amount and frequency of cultivation. “We use the weedIT to spot spray weeds with a double knock of glyphosate plus a Group I [Group 18], followed with paraquat; targeting these hard to kill weeds when they are small,” says Kurt. “No residuals are used in fallow because they can limit our options for summer cropping particularly.” “The aim is to keep the fallows weed-free so we have low weed numbers at planting,” he says. “Once a crop is planted we do use residuals to give it the best chance to grow ahead of any weeds that might emerge on the planting rains.” The weedIT has markedly reduced the amount of chemical applied in the fallow and reduced the time needed to do an application across the cropped area. Kurt is finding it much easier to apply the double knock tactic for glyphosate within the optimal timeframe. “Being able to get a proper double knock done when you need to, means you can get on with other jobs, knowing that you have done the best control treatment possible on the weeds,” says Kurt. Crops and varieties are chosen to maximise yield potential and this also means there is maximum suppression on weeds. Their crops are sown on 50 cm row spacing in a 12 m controlled traffic system, except for sorghum, which is grown on 1.5 m spacing. “We are basically farming moisture here, so if there is suitable rainfall we want to be in a position to take that opportunity to plant,” he says. “Sorghum and mungbean are the usual summer crop options, and we aim to be cropping for 10 months of the year if conditions allow.” In drier years the winter crops are sown deep, about 15 cm, to access available moisture. Chickpeas are particularly well suited to moisture seeking planting techniques. Kurt grades his own chickpea and wheat seed to remove weed seeds and ensure that the largest and most vigorous seeds are planted. He buys in mungbean and sorghum seed each season to maximise seedling vigour and establishment, and ensure the seed is weed-free. Chickpeas are particularly well suited to moisture seeking planting techniques. Kurt grades his own chickpea and wheat seed to remove weed seeds and ensure that the largest and most vigorous seeds are planted. Kurt uses a tyned planter and a single disc for nitrogen application. He has recently embarked on a program to apply ‘deep P’ across the cropped area. The phosphorus is applied about three months before planting at a rate of 250 kg/ha MAP at a depth of about 30-45 cm using a dozer. He has been very impressed with the crop response to the phosphorus application, which has clearly demonstrated that low phosphorus levels have been a constraint on production. The Maynes are seriously considering adding harvest weed seed control to their weed management program. Kurt sees real benefits in the chaff deck system that delivers the chaff onto the tram lines – both as a weed control tactic and a means of reducing the frequency of tram line renovation. On the cattle side of their business the Maynes buy in about 1600 feeder steers and run them for less than 12 months on 2800 ha of buffel and leucaena pasture.

Glyphosate has been the go-to product for keeping weeds in these areas under control for a long time but unfortunately it is often the only product used and the weeds are commonly quite large when they are sprayed. The result is that glyphosate resistance can, and does, quietly build up in these zones in a wide variety of weed species. Fencelines will always be a potential source of weed seed but there are ways to ensure that the seed from these areas is not already resistant to the herbicides when it blows into the production areas. Farmanco agronomist, Brent Pritchard, collected the suspect capeweed samples on a farm near Borden in Western Australia. The capeweed had evolved resistance to glyphosate in an un-cropped drainage area, where it had routinely been sprayed with glyphosate, and had then invaded the adjacent field. The cropped area had been managed with a diverse rotation of wheat, TT canola, pasture and fallow over a 17-year period. The capeweed samples also showed signs of resistance to metosulam (Eclipse®) and diflufenican (Brodal®), but were susceptible to a range of other herbicides including clopyralid, MCPA, bromoxynil, diuron, metribuzin, simazine, Spray.Seed® and Velocity®. Dr Yaseen Khalil, a researcher in the agronomy team at the Australian Herbicide Resistance Initiative (AHRI), conducted the resistance screening and confirmed the resistance status of the capeweed population. AHRI’s Dr Yaseen Khalil confirmed the resistance status of the capeweed samples and is urging growers to take a more diverse approach to weed management in non-cropped areas around the farm “There is no doubt that an integrated approach to weed management needs to be applied to non-production areas such as fencelines, around buildings, along tracks and roads and around irrigation infrastructure,” says Dr Khalil. “Probably the first step is to stop using glyphosate alone in these areas unless you are able to reliably apply a double knock to every application. Evolving resistance to this useful herbicide in non-productive zones is counter productive at the least.” Wherever possible, apply glyphosate in a mix with other herbicides effective on the target weeds, then follow with a second knock. The main problem on fencelines is the lack of competition to weeds. If pastures are part of the crop rotation it may be possible to establish the pasture species along the fenceline and leave them in place when the paddock returns to the cropping phase. Similarly, the crop can often be sown right up to the fence and the first round or two mown or baled for hay prior to harvest. If there are livestock in the production system they can be used to graze the perimeter in the fallow or in suitable crops. Mowing or baling the perimeter of the crop can halt the incursion of weeds into the crop area. Establishing cover using desirable perennial species and eliminating fenceline spraying could be a long-term solution to stop fencelines being a source of herbicide resistant weeds. If this is not practical, or if the non-crop area must be kept bare for other reasons, such as managing insect pests, close attention must be paid to using alternative herbicides, double knocking, mixing and rotating herbicides and eliminating survivors. Applying the WeedSmart Big 6 tactics to non-crop areas is a pre-emptive strike on ‘home-grown’ herbicide resistance. More resources: AHRI Insight – World-first: glyphosate resistant capeweed Management of herbicide resistant weeds on fencelines Don’t jeopardise glyphosate for clean fencelines