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Getting weeds early is key

Tom and Charm Arnott have been growing cotton on ‘Fairfield’ at Boggabilla for 24 years. Speaking to their CottonInfo Regional Extension Officer, Tom Arnott outlined how they are managing the threat of resistant weeds. They encounter a wide range of weeds in their farming operations, including peachvine, barnyard grass, chinese lantern, feathertop Rhodes grass, fleabane, sesbania, climbing bellvine, pigweed, milkthistle, turnip and native vetch. Tom finds climbing bellvine a particular challenge in cotton, because once it is in the crop it is difficult to control, wrapping around the cotton and causing issues at harvest. Tony Taylor, Taylor Ag Consultancy and Tom Arnott “Fairfield” Boggabilla Tom is working with consultant Tony Taylor to implement an integrated weeds management strategy. “Resistance in weeds is already impacting on our business. We have seen how quick it can get away and it can be hard to get back. There’s also a cost associated with trying to get back,” Tom said. “As a result, Tony and I are mapping out a strategy to combat resistance. It’s our first year, so it’s very much a work in progress. To date, I have relied on an over the top glyphosate application and a light cultivation for weed control. We’ve learnt that spraying when the plants are too big doesn’t work – you have to get in when they’re small. “We are now implementing a residual program, which will involve using selective pre-emergents at planting to target hard-to-kill weeds on a field-by-field basis. “We will then use a mix of glyphosate in a double- knock approach, and conduct a more aggressive cultivation with discs and knives to cultivate closer to the plant line. “We’ll also apply a broadleaf ‘layby’ (a residual herbicide used to control weeds in-crop) to all fields to control late weeds coming through. “We also chip weeds: particularly in the school holidays, with the whole family doing their bit. I always have a hoe in the ute!” Tom found the recent CRDC, CottonInfo and ICAN weed management workshops useful in learning strategies to control glyphosate-resistant weeds. “There was plenty of information, and a lot of experience among the growers in the group. It was good to kick around ideas and talk to the agronomists,” Tom said. Growers Tom & Charm Arnott Cropping area Total hectares: 1400 ha. Cotton: 1400 ha irrigated Soil type Black clay Vertosol Rotations Two-year rotation: cotton (summer); double crop winter cereal or chickpeas (winter); long fallow (summer and winter); cotton (summer). Source: CottonInfo Weed Control case studies Further information: CottonInfo weed management page
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Diverse approach to feathertop Rhodes grass control

As an early adopter of zero tillage and controlled traffic farming in Central Queensland, Brendan Swaffer is fully convinced of the benefits, and is well aware of the potential impact of weeds like feathertop Rhodes grass. Since taking over the family farm near Clermont in 2007, Brendan and his wife Jody have been building a robust cropping program with wheat and chickpea in winter and, if soil moisture permits, dryland cotton and sorghum in summer across their 4000 ha of cultivation. Brendan and Jody Swaffer, Clermont have reintroduced tillage to their zero till controlled traffic farming system to manage weedy patches, primarily feathertop Rhodes grass. Dryland cotton has also been a useful addition to the rotation and provides another opportunity to manage FTR. “In the summer fallow our main weeds are summer grass, Johnson grass and fleabane but we are most concerned with the small patches of feathertop Rhodes grass that are appearing,” says Brendan. “We are using a mechanical and chemical double knock to manage these patches of FTR and it has been very effective for us in preventing its spread.” Early in summer Brendon targets any patches of persistent weeds – mostly feathertop Rhodes that has survived under the winter crop. Starting with cultivation of the affected areas, Brendan then follows up a few days later with an application of metolachlor (Group K) to provide short-term residual control of any new germinations that are triggered by the cultivation. “We might spend two days ploughing but only cultivate 150 ha in total,” he says. “For the rest of the year we carry a hoe in every vehicle and stop to chip out small areas of weeds when we see them. We have been enjoying the enormous benefits of zero till and controlled traffic since the 1990s – there is no going back to full cultivation, but it is a useful management tool to target weedy patches before they get out of hand.” Preventing seed set for a couple of consecutive seasons is known to rapidly rundown FTR seedbank as the seed on the surface or even slightly buried only persists for 12 to 18 months. Adding dryland cotton to their rotation has also helped minimise the spread of FTR. The Swaffers produced cotton in four of the five summers from 2010–11 to 2014–15, which enabled the application of Roundup Ready Plantshield to keep pressure on FTR and reduce seed set. Brendan has built in several non-glyphosate weed control measures including cultivation, along with other knock-down and residual herbicides, to take the pressure off glyphosate in their farming system. “Feathertop Rhodes grass is not a problem in conventional systems but the more area farmed the more difficult it is to keep clean,” he says. “It also seems to prefer scrub soils that are a bit lighter textured than the open downs country and alluvial soils we have on this property, giving us a slight advantage.” The fallow starts with spraying out sorghum in June with glyphosate to kill the crop, make harvest easier and kill the weeds. During summer, Brendan applies glyphosate, 2,4D-amine and small amount of metsulfuron (Group B) as a tank mix to target weeds when they are small and actively growing after a rainfall event. The metsulfuron is targeting parthenium and can also provide an additive effect on glyphosate when applied in a tank mix. After each spray application Brendan looks for, and manages any survivors or areas where the sprayer has missed, to minimise the number of weeds that escape and set seed later in the season. In recent years he has moved to more robust rates to ensure efficient weed control and to avoid the need to go over a paddock a second time. With the variable rainfall experienced in Central Queensland, chickpeas are now the Swaffer’s most reliable crop, using moisture seeking planting techniques. “We can plant in April or early May on rain received in February by planting the chickpea seed up to 18 cm deep,” says Brendan. “Chickpea is the only crop that has a long coleoptile that allows emergence from such depth.” Planting chickpea on 50 cm rows using moisture seeking techniques has established chickpea as the Swaffer’s most reliable crop. Brendan has found that a post-plant pre-emergence application of Terbyne (Group C) controls weeds up to canopy closure and no other in-crop herbicide is needed until the crop is desiccated prior to harvest. “Emergence can take three weeks, but we can establish a crop on stored moisture and have it up and away before in-crop rain initiates a fresh flush of weed germination, giving the crop a distinct competitive advantage.” The timing of a moisture seeking planting needs to factor in the frost risk in the district to avoid having the chickpea crop flowering when there is a high chance of frost. In some years there is moisture higher in the profile, allowing both chickpea and wheat to be planted about 10 cm deep. Wheat is also planted a little later in the Clermont district than in other areas of CQ, to avoid frost. Most growers prefer to accept the small yield penalty for planting later rather than risking a crop failure. “Strzelecki wheat is a slow maturing spring wheat of semi dwarf habit that is popular in CQ due mainly to its longer coleoptile length that allows us to plant to a depth of 10 cm,” he says. “But this variety is about to be re-classified to Hard 2 instead of Prime Hard and so many growers will be looking for alternative wheat for the future,” he says. Strzelecki wheat has been a mainstay variety in the Clermont district because of its ability to emerge from a depth of 10 cm. A change in classification of this wheat will most likely drive growers to look for a replacement variety suited to the conditions. Higher levels of crop competition can be achieved in the winter crops compared to the summer crops, with chickpea and wheat both sown on 50 cm rows. Brendan plants chickpea in his cleanest paddocks and uses a post-plant pre-emergence application of Terbyne (Group C) to control weeds up to canopy closure. No other in-crop herbicide is applied except for desiccation for harvest management. Brendon avoids using Balance due to the long plant-back period and the need for a lot of rain to breakdown the residual. Sorghum crops are sown on single skip metre rows, with cotton planted in double skip configuration of 2 in and 2 out to optimise yield and quality. Brendan previously planted sorghum in solid 1 m single rows but has changed to planting a single skip – 2 in and 1 out – and increased intra-row plant density. The soil on the Swaffer’s property requires about 200 mm of steady soaking rain to fill the profile and initiate a summer crop planting. Last season there was no summer crop planted due to a lack of soil moisture however the outlook year is looking more promising for sorghum but they have not planted cotton this season. “We are concentrating on achieving even intra-row spacing using a double disc precision planter to increase weed competition within the row,” he says. “This also promotes even maturity and reduces tillering. The combined effect encourages a shorter flowering period and makes grub and midge control easier, along with reducing the risk of ergot infection.” Sorghum is planted in January and early February following an application of glyphosate, Dual Gold and 2,4D, provided there is no cotton planted nearby. Brendan also applies atrazine and fluroxypyr to provide in-crop weed control. Metolachlor applied in the fallow ahead of cotton provides some residual weed control but the main in-crop weed control strategy is RR Plantshield. Brendan puts far greater emphasis on timeliness of weed control than on specific rates and products. At harvest, Brendan uses perforated screens in the header to remove as much Mexican poppy, and turnip weed seed and soil as possible out of the chickpea grain sample. He also keeps about 100 t of both chickpea and wheat seed that has been graded hard to ensure the cleanest possible seed goes back in the ground the following season. Brendon does all his own spraying with a John Deere 4030R self-propelled sprayer and likes to keep their spray technology up to date. He considers the sprayer to be their main tractor now and changes the sprayer unit every 5 years or so to always have new gear that works well and minimal downtime. “Our groundwater is quite hard so we use ammonium sulfate, especially when spraying out sorghum with glyphosate,” says Brendan. “Although we now have more access to rainwater, storing water is very costly so we have been assessing the difference between rain water and groundwater this year in terms of cost and efficacy on weeds. We expect to invest more in rainwater storage in the future.” Being in full control of the spray program means Brendan can ensure his neighbours are always informed regarding cotton plantings and he only sprays when conditions are suitable. “When sensitive crops are nearby it is all about working in the right conditions and being careful about product selection,” he says. Other resources Mark Congreve explains the key features of FTR, considerations when developing a control strategy, fallow herbicide options and fallow application recommendations in a new series of Grains Research and Development Corporation (GRDC) Know More videos.
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Planned approach to rotations helps manage weeds

Ross, Ingrid, David and Margot Uebergang have been growing cotton for 27 years at Miles on the Darling Downs. Speaking to their CottonInfo Regional Extension Officer, Ross Uebergang outlined how they are managing the threat of resistant weeds. They combat a series of weeds each year, in both their cotton and winter crops, including fleabane, feathertop Rhodes grass, barnyard grass, liverseed grass, bladder ketmia, black pigweed, caustic creeper, caltrop, volunteer cotton, milk thistle, fireweed, black oats and phalaris. Bellvine is an emerging problem on the farm, one Ross Uebergang suspects may become a larger problem down the track. Ross Uebergang, Jess Mickelborough and Tim Richards The Uebergangs are yet to do any resistance testing – something Ross hopes to implement this season – but suspect they may have resistant grass weeds. As a result, they have implemented a whole-of-farm approach to integrated weed management, involving multiple weed-control tactics. “If you keep relying on one tactic no matter what it is, a problem is going to arise,” said Ross. “We are trying to manage resistance and also the buildup of problem weed seeds. If we don’t, resistant or hard-to-kill weeds will bring the whole farming system unstuck.” “For us, grasses are the main problem. We have barnyard grass and feathertop Rhodes grass and we’re unsure if they’re resistant or just hard to kill,” he said. Ross doesn’t rely on glyphosate: his approach includes pre-plant residuals, pre-emergent knock downs, and ‘laybys’ (residual herbicides used to control weeds in- crop), plus non-herbicide tactics including cultivations and spot chipping. “Our current strategy is to apply a residual six-weeks prior to cotton planting and then to pre-irrigate to allow the volunteers and other hard-to-kill weeds to emerge. “We follow this with pre- and post-planting knockdowns, which include gramoxone (Group L). In crop, we apply two Group M (glyphosate) sprays and a Group A spray to target feathertop Rhodes grass and will also apply in-crop residual chemicals with shield spray in problem fields. “After picking, we mulch and rootcut and then do heavy tillage passes to remove ratoon cotton and compaction and then the system starts again. For fields going into fallow, a layby is applied immediately post winter harvest, keeping fields clean for first flush of spring grasses,” said Ross. “We review our practices every year. Pre-season and post-season we have a meeting with our consultant, Tim Richards of MCA, to review our strategy. “This is where we work out our rotations and fields, highlight problem areas and develop our residual program. We have a whole farm approach, but treat fields separately due to different weed spectrum and soil types. “This is our third season of implementing this weed control program and it has really streamlined the whole operation of growing the crop, resulting in greater timeliness of operations which equates to better yields,” he said. Tim Richards of MCA says a successful integrated weed management system means taking a long-term approach. “If a grower is looking further ahead than just this season and is willing to commit to a rotation, then it is easy to implement an integrated weed management system like this one. The spin-off benefit of such a system is superior operational timeliness, as we have – and are adhering to – a plan,” Tim said. Growers Ross and Ingrid Uebergang, David and Margot Uebergang, Uebergang Agriculture Cropping area Total hectares: 1100 ha. Cotton: 400 ha irrigated Soil type Clay loam, brigalow belah, deep cracking self-mulching clays Rotations Three-year rotation: cotton (summer); covercrop back into cotton (winter, then summer); barley or wheat (winter); fallow (summer and winter); and cotton (summer) Source: CottonInfo Weed Control case studies Further information: CottonInfo weed management page
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Are you going spraying or killing weeds?

Spray drift is of great concern for sensitive crops and environments, along with the fact that if the spray doesn’t hit the intended target, you do your dough and your weeds live. Bill Gordon, spray application consultant with Nufarm Australia says the focus of spraying herbicide needs to be on doing the job right so the weeds receive the correct dose and die, and this includes reducing the air borne fraction to a bare minimum. Bill Gordon, Nufarm spray application consultant says most growers are implementing best spray practice when it comes to boom height and nozzle selection but the temptation to spray at higher speeds and into the night can over-ride common sense at times. “In many cases this means not spraying at night if the wind speed is too low,” he says. “Many product labels prohibit night spraying due mostly to the risk of spray drift. Our studies have shown that with a coarse spray quality drift may travel up to 300 to 400 metres during the day after any inversion has broken, but spraying at night can leave up to five times as much chemical in the air using the same products, nozzles and ground speed. This can result in spray drifting 10 to 20 kilometres or more at night, and this is unacceptable for other farmers, the community and the environment.” Mr Gordon says most growers are implementing best spray practice when it comes to boom height and nozzle selection but the temptation to spray at higher speeds and into the night can over-ride common sense at times. “The flip side of this is that it is becoming more evident that using Delta-T as the main determinant of safe day-time spraying conditions may not be the best approach,” he says. “What really matters most is the wind speed and whether the weeds are stressed or not.” “If the weeds are not stressed on a hot day, due to ample soil moisture, then spraying at a higher Delta-T may still be effective and safe, with course droplets surviving quite well and not becoming air-borne.” This can essentially increase the number of daytime hours available to growers to get the job done without spraying at night or early in the morning when the risk of spray drift is the highest. “Getting onto paddocks as soon as possible after rain and using up the daytime hours to target priority paddocks will maximise weed control and minimise spray drift risk,” says Mr Gordon. “Spraying can continue into the evening in summer if the soil remains warm and the wind speed stays above 12 km/hr. If the wind drops off, then spraying should cease, usually by about 10 pm through to a few hours after sunrise.” The bottom line is that it is very difficult to determine a safe night-time spraying conditions. When environmental conditions are borderline in terms of wind turbulence, the safe spray window can be extended slightly through the use of coarser sprayer quality where the proportion of droplets less than 150 microns is 10 per cent or less, keeping drift to a minimum. The trade-off, however, is reduced efficacy when using very coarse droplet size, particularly when the target is small, vertical or hard to wet. “When buying new nozzles, check them against the new standard, which shows spray quality with adjuvants rather than water only,” says Mr Gordon. “The GRDC has recently updated and published the 2017 Nozzle Selection Chart for growers to use as a reference. Using the correct nozzle and adjuvant combination can have a positive impact in reducing spray drift and maintaining efficacy.” [A new factsheet provides advice to help growers meet the new 2,4-D application requirements] “Reducing ground speed by just 5 km/hr can also make a big difference to spray coverage and efficacy of weed control, particularly if there is a high stubble load present,” he says. “Water sensitive paper, in combination with apps such as ‘SnapCard’, is a good way to test the coverage, penetration and spray pattern achieved under different conditions, such as different ground speeds.” Mr Gordon’s rule of thumb for effective weed control when applying fully translocated products (e.g. glyphosate and Group I) is a minimum of 6–8 per cent coverage, while coverage of 10–12 per cent or more is required for contact herbicides. “Pre-emergent herbicides are the most difficult to judge due to the number of variables involved in their effective application, but as a rule of thumb I generally look for coverage of at least 15–20 per cent,” he says. Getting onto paddocks as soon as possible after rain and using up the daytime hours to target priority paddocks will maximise weed control and minimise spray drift risk. Spraying can continue into the evening in summer if the soil remains warm and the wind speed stays above 12 km/hr. If the wind drops off, then spraying should cease, usually by about 10 pm through to a few hours after sunrise. If you are going out killing weeds, you need to get everything right. Bill Gordon’s 10 Tips for Reducing Spray Drift Choose all products in the tank mix carefully. Understand the product mode of action and coverage requirements. Select (and check) the coarsest spray quality that will provide effective control. Expect that surface temperature inversions will form as sunset approaches and will likely persist overnight and even beyond sunrise on many occasions. DO NOT SPRAY. Use weather forecasts to inform your spray decisions. Only start spraying when the sun is about 20 degrees above the horizon and when the wind speed has been above 4–5 km/hr for more than 20–30 minutes, and clearly blowing away from any adjacent sensitive crops or areas. Set the boom height to achieve a double overlap of the spray patterns. Avoid higher spraying speeds. Leave buffers unsprayed if necessary and come back. Continue to monitor conditions, particularly wind speed, at the site during the spray operation. https://www.weedsmart.org.au/webinars/spray-wisely-well-maximise-efficacy-bill-gordon/ Watch what happens in this demonstration of fine particle movement under surface temperature inversion conditions. Other resources: ‘Spray wisely and well’ Webinar – Bill Gordon Ask an expert May 2017 – Bill Gordon Maintaining efficacy with larger droplets – New 2,4-D application requirements SnapCard App GRDC Nozzle Selection Guide 2017 Cotton Field Awareness Map (CottonMap) Nufarm Spray Wise Decisions Spray Application GrowNotes
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Giving summer legumes the competitive edge

Fifty years ago, many farmers and researchers expected herbicides to be the panacea for weed control. The reality has been that no weed species has been eradicated through the use of herbicides alone, and in fact, many weeds have increased in population in the presence of herbicide application in farming systems. This is what motivates researcher Dr Bhagirath Chauhan, Principal Research Fellow with the Queensland Alliance for Agriculture and Food Innovation (QAAFI) to study how crops can do their own weed control through the application of cultural practices. Dr Bhagirath Chauhan says narrower row spacing in summer legumes such as mungbean and soybean will take the pressure off in-crop herbicide applications, provided the crop is sown into clean paddocks and weeds are controlled for at least three weeks after planting. He says that his agronomic trials in summer legume (mungbean and soybean) crops are consistently showing that early canopy closure results in lower weed biomass and higher crop yield. “We have demonstrated that narrower row spacing in summer legumes such as mungbean and soybean will take the pressure off in-crop herbicide applications, provided the crop is sown into clean paddocks and weeds are controlled for at least three weeks after planting,” he says. “Increased yield is a significant benefit and will support growers’ decisions to set up their planting gear to suit farming on narrower row spacings.” In the 2015 and 2016 mungbean seasons, 30 kg/ha of Jade-AU was grown at 25, 50, and 75 cm row spacing and Rhodes grass was sown to provide a known weed density in all plots. There were four levels of weed infestation applied 1. Weeds sown at planting, 2. Weeds sown 3 weeks after planting, 3. Weeds sown 6 weeks after planting, 4. Weed-free throughout the growing season. Rhodes grass was spread at 300 seeds per m2 to create even competition across the site, which is generally not possible if researchers rely on the natural weed seed bank of the experimental site providing the competition. Agronomic trials in summer legume (mungbean and soybean) crops are consistently showing that early canopy closure results in lower weed biomass and higher crop yield. “In plots where the mungbean crop and the weed emerged together, it didn’t matter which row spacing was used – the weed biomass was high and the grain yield was low, less than 360 kg/ha,” says Dr Chauhan. “If the 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. We know from other studies that weed biomass correlates well with weed seed production, so reducing biomass can be expected to also reduce seed production in the weed.” In both seasons, 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. Even in a completely weed-free growing environment the two narrower spacings generated higher yield than the 75 cm rows. “This trial demonstrates the value of reducing row spacing to 50 cm in mungbeans and keeping crops weed-free for the first six weeks after planting,” says Dr Chauhan. “After this point the crop has the competitive edge and any later germinating weeds struggle to get established.” Dr Chauhan has also conducted trials to determine weed densities that will cause a 50 per cent reduction in mungbean yield. These weed densities can provide a guide to growers and agronomists about the level of infestation that will affect yield and allow them to determine an economic response, keeping in mind that any weeds that set seed are building up in the weed seed bank for following seasons. A 50 per cent yield reduction in mungbean can be expected in the face of 31 bladder ketmia plants/m2, 22 feathertop Rhodes grass plants/m2, 33 windmill grass plants/m2, 21 liverseed grass plants/m2 or 23 button grass plants/m2. In a similar row spacing trial in soybeans, Dr Chauhan saw similar results to those of the mungbean trial. He also confirmed that row spacing, not plant population, is the key driver to reducing weed growth. “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,” says Dr Chauhan. “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. Mungbean crop density has a direct effect on the morphology of weeds such as barnyard grass where the weed is quite prostrate when there is no crop competition, and has a more upright habit when there is more crop competition. This may have implications for weed control strategies such as harvest weed seed control.
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How does mixing herbicide MOAs buy more shots?

When a herbicide is released on the market it has a fairly predictable number of uses or ‘shots’ before resistance to that mode of action begins to be evident in the weed population. For example, in-field experience and computer modelling both show that repeated use of glyphosate on a weed population will evolve full-blown glyphosate resistance in approximately 15 years. This effective lifespan ranges from around four years to over 20 years for the most commonly used herbicides, before resistance is evident. Rick Rundell-Gordon, consultant agronomist with Grounded Agronomy, Swan Hill, says the widely-promoted and well-adopted practice of rotating between herbicide modes of action has the beneficial effect of ‘buying time’ because if a MOA is used once every two years the lifespan of the herbicide effectively doubles. Rick Rundell-Gordon, Grounded Agronomy speaking at WeedSmart Week 2017 in Wagga Wagga about the science behind the ‘mix and rotate’ tactic to target multiple resistance mutations in weed populations. “This means the herbicide remains a viable option for weed control for longer and the more diversity in herbicide MOAs applied, the longer the effective use is for all the herbicides in the program,” he says. “If a nil-tolerance approach is taken to weeds that survive a herbicide application then herbicide resistance is much less likely to evolve.” “We now know that mixing two or more compatible herbicides with different modes of action can also increase the number of times an individual herbicide can be used within the herbicide program,” says Rick. “Mixing works by targeting different mutations within the weed population with the one spray application.” For example, mixing trifluralin with another pre-emergent herbicide, both at full label rates, can increase the number of ‘shots’ of both herbicides across the cropping rotation. An important proviso is that the weed population must still have some susceptibility to all of the tank mix partners. ‘Mix and rotate MOA’ is so important it is one of the ‘Big 6’ WeedSmart strategies to manage herbicide resistance. What evidence is there that mixing herbicide MOAs is effective in delaying herbicide resistance? Short answer: Glyphosate resistance in waterhemp in the USA was less likely to occur when farmers used tank mixes. Longer answer: Researchers from the University of Illinois, the USDA-ARS Global Change and Photosynthesis Research Unit, and the State University, New Mexico used spray records from a local spray contractor to compare 50 fields with glyphosate resistant waterhemp and 50 fields without. They looked at a total of 61 management and environmental variables and found that mixing herbicides was the single management strategy that made the most difference to whether or not glyphosate resistant waterhemp became a problem in any field. In a review of herbicide application records from 2004 to 2006 and glyphosate resistance tests in 2010, the researchers found that adding more products to the tank at full rates for a single application causes the probability of resistance in these fields to decline sharply. Peter Newman, AHRI says the evidence is mounting that ‘mixing and rotating herbicide MOAs buys you time and shots’. When mixing herbicide modes of action, always use full label rates and ensure all products are compatible. Is there any research to suggest that mixing pre-emergent herbicides could be effective? Short answer: Computer modelling has demonstrated that the onset of herbicide resistance can be delayed when a mix and rotate strategy is used with pre-emergent herbicides to control annual ryegrass. Longer answer: Based on research from the Australian Herbicide Resistance Initiative, the best advice to growers and agronomists is to rotate between these three groups of pre-emergent herbicides – 1. trifluralin, 2. Sakura, Boxer Gold and triallate and 3. propyzamide. Full label rates must be applied. Assuming four herbicides available (trifluralin, prosulfocarb, pyroxasulfone and propyzamide) AHRI researcher Dr Roberto Busi has also simulated three different scenarios 1. use the same herbicide continuously (trifluralin or any other herbicide if the crop rotation permits), 2. follow a simple herbicide rotation pattern or 3. mix and rotate using two herbicides in each mix. The results show that mixtures are more effective than just rotating MOA in delaying resistance as mixes generally achieve a greater kill rate. Rotate between the boxes, and avoid rotation between the blue boxes from year to year if possible. Mixing is also a good idea. Is mixing and rotating herbicides all I need to do? Short answer: No. Mixing and rotating herbicide modes of action can effectively lengthen the ‘life’ of a herbicide MOA on your farm but it will not prevent resistance on its own. Longer answer: In addition to carefully selecting and managing herbicides it is necessary to also implement as many cultural (non-herbicide) tactics into your weed control program as possible. The overall aim of a sustainable weed management program is to use as many tactics as possible to keep weed numbers low, prevent weed seed set and remove all survivors. Other resources: Increase pre-em efficacy through a mix and rotate strategy Using tank mixes to extend herbicide ‘life’
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SwarmFarm: Targeting small weeds all year

Just five years ago Central Queensland grain farmer Andrew Bate was in a tractor, spraying a wheat crop, and thinking about ways to farm better and more efficiently. His idea to create a ‘swarm’ of small, lightweight machines that could work autonomously and cooperatively, is now a commercial reality. SwarmFarm operations manager and leader of field development, Will McCarthy, says the robots are the ultimate weed scouts, tracking down escapes and eliminating them before they have a chance to set seed. Along with his wife Jocie, Andrew is founding director of SwarmFarm Robotics. The headquarters of their agricultural technology company is their farm ‘Bendee’ at Gindie, south of Emerald, where their team of seven software and mechatronics engineers and technicians is building and testing world-first robotic technology specifically for agricultural applications. “There are currently seven SwarmFarm robots working on grain farms, turf farms and in an environmentally-sensitive area on a mine site,” says Andrew. “Our commercial release of 50 robots setup for spraying weeds using the WeedIT optical sprayer technology is now underway.” Weed control provides an excellent opportunity for robotics to shine. A time-consuming but ‘simple’ task that robots can do very effectively at a slower pace, ensuring every weed in the paddock is accurately and effectively controlled while still at a small size. Weighing just 2 t fully loaded, each robot is only 10 per cent of the weight of a conventional sprayer and they fit in perfectly with zero till and controlled traffic farming systems. The cost benefit of robots applying herbicide lies in the frequency of treatment, accuracy and ability to safely operate any time of the day or night. While a grower may hesitate to go spraying, concerned that there might be another rain event and subsequent germination, the robots can ‘go now and go later’, always targeting small weeds at their most susceptible growth stage. Weighing just 2 t fully loaded, each robot is only 10 per cent of the weight of a conventional sprayer and they fit in perfectly with zero till and controlled traffic farming systems. The SwarmFarm robots optimise the use of existing optical sprayer technology to identify and target small weeds in a green-on-brown situation (i.e. in fallow) by enabling more frequent applications that are slower and more accurate. The ability to go over the same paddock every few weeks is the standout difference that robotics can bring to the management of herbicide resistance. SwarmFarm operations manager and leader of field development, Will McCarthy, says the prescription spraying used on ‘Bendee’ involves the robots passing over the fallow paddocks once every two weeks. “This way, no weed will get bigger than the 50 cent piece size that is optimal for effective control,” he says. “We can apply a wider range of herbicide modes of action, more robust rates for chemicals registered for this use pattern and potentially reintroduce products and brews that may have had reduced efficacy as broadacre sprays in the past.” “The robots are the ultimate weed scouts, tracking down escapes and eliminating them before they have a chance to set seed. Constantly targeting small weeds and preventing seed set is the only way to keep weed numbers low and avoid herbicide resistance.” The SwarmFarm robots enable the optical sprayer technology to really come into its own because the robots can operate slower, the cameras and sprayers can be closer together and the robots can go over the paddock repeatedly so there is no concern about getting the timing right. Every weed can be treated at an early growth stage for the herbicide to have maximum effect, tackling herbicide resistance at the source by applying constant downward pressure on the weed seed bank. The SwarmFarm concept is ideal for new technology developments, as it allows easy integration of third party products as they are being developed, such as green-on-green technology. Will says the robots would then be able to distinguish between a weed and a crop plant and even between weed species. This will allow the removal of volunteer crop plants and even target broadleaf weeds like sowthistle in a broadleaf crop such as chickpea. Although the current focus is on herbicide application, there is great potential to use the same platform to implement non-herbicide tactics such as targeted tillage or robotic chipping, steam or any other non-herbicide tactic found to be effective. “Using the robot concept, microwave technology becomes a realistic option because the robots can stop at every weed and apply the necessary microwave blast to kill each weed, something that is simply not feasible for a tractor operator,” says Will. WeedIT cameras capture data from a 1 m wide band on the ground using NIR and IR light to detect green weeds in a ‘brown’ paddock. The SwarmFarm concept allows easy integration of third party products as they are being developed, such as green-on-green technology or non-herbicide tactics such as targeted tillage or robotic chipping, steam or any other tactic found to be effective. “Aside from weed management, the robots will enable direct management of a crop’s plant population to maximise yield potential for the available soil moisture,” he says. “There is no reason why the SwarmFarm platform can’t be utilised for planting and applying fertiliser precisely and economically, controlling insect pests and even harvesting the crop. The system is in place to support any application really and all that is needed is the planter, cultivator or harvester to be engineered and bolted on.” Andrew reckons that a 10 000 ha property like ‘Bendee’ would only need two SwarmFarm robots to take care of all their weed control operations. SwarmFarm robot features Working through the features of the SwarmFarm robots highlights their simple and robust construction and numerous safety features. Will says the team has worked hard to make diagnosis as simple as possible and the modular components have minimal opportunity for failure. “If there is a problem, the replacement parts can be easily fitted on-farm without specialist technicians and the maintenance is straightforward and well within the capability of any farmer,” he says. Multiple safety features built into the robots, which make them safer than a person operating a spray rig or tractor, include: obstacle detection sensors (can determine if the terrain ahead is suitable to traverse and also stopping if there is something in its path e.g. a vehicle or person), paddock definition (it maps the paddock to show boundaries, fencelines, trees, troughs, dams etc. then uses software to generate A–B lines. The robot then drives itself around these fixed obstacles), remote control using an iPad (allows the operator to stop and restart the robot when within the local farm network), a bumper sensor to turn off the machine as a back-up to the obstacle detection sensors (slow operating speed means any damage would be minimal if this was activated), a geo-fence that turns off the machine if it crosses the line. Each robot has an 8 m boom fitted with eight WeedIT optical cameras, 40 nozzles and a 600 L spray tank. Depending on weed density across the paddock this could last all day or an hour. The robot monitors the volume of spray in the tank and makes a decision whether it can reach the end of a run or not before running out of spray. It then returns to a docking station for refilling. At the moment, a person is required to refill the spray tank but plans are in place to fully automate the refilling operation within the next 8–12 months. The 60 L diesel fuel tank on board gives the machine an operating time of 18 hours between refueling. WeedIT cameras capture data from a 1 m wide band on the ground using NIR and IR light to detect green weeds in a ‘brown’ paddock. There are five individual sprayer solenoids per camera span, giving one spray nozzle every 20 cm. The cameras are set to turn on three nozzles over a weed to ensure good coverage, which is particularly important if there is a breeze blowing. The genius of the SwarmFarm system lies in the ‘smarts’ of the SwarmHive base station computer. Located in the grower’s office the SwarmHive takes care of the robots’ activity and decision making and coordinates the workflow of all the robots operating in the paddock. “If one machine is going slower due to higher weed numbers then the SwarmHive will reallocate the other robots to cover the extra area so that the whole paddock operation is completed at about the same time and all the robots come back to the docking station together,” says Will. “It is updating in real time and making decisions about the weather conditions, mapping weed density, ensuring the robots are operating efficiently and sending alerts if any problems arise, such as a pump malfunction or an obstacle detected.” An on-site automatic weather station located at the docking station monitors key parameters such as Delta-T, wind speed and direction and ensures the robots only operate within the label directions. The SwarmHive automatically turns off the robots and then restarts them when the conditions are within the acceptable range. Integration with an on-site, automatic weather station also provides a reliable record of spray activities and the real-time environmental conditions during the spray operation, such as wind speed and direction. The grower also has ‘on-the-go’ access via an iPad app to monitor and control the robots if necessary, when within the local farm network. Other resources Andrew Bate SwarmFarm Robotics podcast
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News

Beating multi-resistant weeds in the Northern region

Dryland cotton and grains farmer Paul Slack is battling weeds that have high levels of resistance to several important herbicide modes of action. Managing 4850 ha of cropping land within 30 km radius of his home farm at Gurley, east of Moree, NSW Paul is using summer and winter cropping, strategic tillage and a long fallow spray program to get on top of resistant annual ryegrass and black oats populations. Tony Lockrey (AMPS Agribusiness agronomist), Paul Slack (Moree farmer) and Caleb Torrance (AMPS trainee agronomist) inspecting Paul’s corn crop, which is adding diversity to his cropping and herbicide program. A few years ago Paul was faced with a blow-out situation of 90–100 annual ryegrass plants per square metre in a Clearfield canola crop, along with some black oats and barley grass. The ryegrass present was tested for resistance, revealing an alarming profile of resistance to five herbicide mode of action groups. Groups A, B, M and two others, where the lowest level of resistance was to mesosulfuron-methyl (Atlantis, Group B) at 15 per cent. The annual ryegrass present was tested, revealing resistance to five herbicide mode of action groups. A dedicated program aimed at preventing seed set has seen a huge reduction in weed numbers with annual ryegrass now confined to a few isolated patches near waterways. With stubble cover required for the fallow ahead of a dryland cotton crop, Paul and his agronomist Tony Lockrey, AMPS Moree decided to run down the weed seed bank, starting with a double knock application to treat the first germination in autumn. Residual herbicides were incorporated using a Kelly chain through the canola stubble prior to sowing a short season wheat crop. “Sakura + Avadex Xtra provided upwards of 80 per cent control of ryegrass, but it must be used wisely in the rotation — we would try not to use this combination more than twice every four years,” said Tony. “In our experience, Group K herbicide Sakura is more robust in a variety of conditions, proving more stable than other residuals in dry conditions following planting, which often occurs in this region.” An in-crop application of the selective herbicide (Group B Atlantis) in wheat followed by a long fallow and a dryland cotton crop resulted in a huge reduction in weed numbers. Paul said annual ryegrass is now confined to a few isolated patches near waterways. “Using the Kelly chains in canola stubble represented some challenges but it was much easier than in other crop stubbles,” said Paul. “Now that the chain is worn-in I think it could be used in a chickpea crop to incorporate pre-emergent herbicides without damaging the crop. Mostly though we use it to chop chickpea stubble and to control weeds on the headlands.” Having had success with this regime to control multi-resistant annual ryegrass Paul decided to use a similar program to rein in Group A resistant black oats that had spread over about 100 ha. Black oats has been a problem for the last 15 years or so after gaining Group A resistance from the short wheat / chickpea / wheat rotation commonly used at the time, where there was heavy use of Group A products such as Verdict and Topik. Black oats pressure is clearly seen in this area where the crop was not sown. The addition of dim chemistry (Group A) in the chickpeas has helped extend the life of Group A chemistry, even though there is 50 to 60 per cent resistance to Verdict (a Group A ‘fop’) in the black oats population. Paul has used a long fallow period to regain control of resistant black oats, bringing the problem back to a very small area. “We did a long fallow after wheat then back to cotton followed by chickpea and then a short fallow and back to wheat,” he said. “This meant we could apply glyphosate in the fallow and two fop + dim mixes in the following chickpea crop. The addition of dim chemistry (Group A) in the chickpeas has helped extend the life of Group A chemistry, even though there is 50 to 60 per cent resistance to Verdict (a Group A ‘fop’) in the black oats population.” “We might repeat this clean-up program to really run down the black oats seed bank before returning to our normal program, which now features both summer and winter crops and a broader range of herbicide tactics,” said Paul. Black oats blow-outs are most likely in wheat crops and Paul is considering cutting weedy crops to make round bale silage. However, without a strong nearby market for the fodder and the large nutrient loss involved in baling, this decision will be a hard one to make. Milk thistle is looming as another challenging glyphosate-resistant weed that will require a different non-herbicide solution, possibly a mechanical innovation. “We know that zero-tillage farming led to a 30 per cent yield improvement in this environment,” says Paul. “We can’t afford to be forced back to a full tillage system to control weeds.” “There is potential to cut the crops lower in problem areas to expose the summer weeds to knock-down control and to improve herbicide-soil contact and efficacy with residuals,” he says. “In doing so we then also need to find ways to better spread the increased volume of crop residue out the back of the header, right across the 12 m to maximise fallow moisture efficiency. Using a chaff deck system to gather weed seeds at harvest and place the chaff on the wheel tracks is also something we are considering.” The current rotation of corn and cotton in the summer and wheat and chickpea in winter has helped bring all resistant weeds back to a manageable level. Bringing Group B chemistry into the herbicide program has been an effective tool in reducing the number of multi-resistant grass weeds and adding a Clearfield wheat into the rotation is another option for the future.
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News

Taking the competition to the weeds

Competitive crops are the ultimate weapon against herbicide resistant weeds as a non-herbicide tactic that suppresses weed germination and boosts crop yield. When stubble retention and harvest weed seed control are also enlisted in the tactical war on weeds then productivity and profitability become the clear winners. Greg Condon (right) is working with the Fox family at Marrar to build an integrated weed management system that also promotes productivity. Greg Condon, Grassroots Agronomy says growers can consider putting together several components that enable narrower row spacing, which is known to generate a one per cent increase in grain yield for every inch reduction in row spacing. “It is important to remember that this benefit can be gained without going to ultra-narrow rows,” he says. “I’d suggest growers go as narrow as they can within the constraints of their existing equipment and farming system to gain as much yield benefit and weed suppression as possible. Then, when it’s time to buy new equipment growers could look at what’s available that would enable more competitive configurations.” Green crops provide the best possible shading effect to suppress weed growth with a competitive crop having shading power equivalent to 10 t/ha retained stubble. This varies considerably with crop architecture where erect cereals provide less shading of weeds than varieties with a prostrate plant structure. Narrowing the row spacing increases the competition while also contributing to crop yield. One system that some of Greg’s clients are using combines stubble management and narrow rows using a disc seeder at planting and a stripper front at harvest. “The real advantages of stubble retention are seen in improved water holding capacity in the soil, which enables earlier sowing,” says Greg. “One year of retained stubble is generally not a problem for any of the modern seeders but we are seeing disc seeders do a better job handling stubble accumulated over a few years and in various stages of decay.” Front loss from a stripper front can be 1–2 per cent but in some cases this can be compensated by reduced harvest cost and header depreciation as stripper fronts harvest faster. Correct harvester and front setup is essential to minimise harvest losses. Including canola and pulses in the crop rotation also plays an important part in managing the quantity and decomposition of crop residue, particularly in a narrow row configuration. Pulses and canola crops assist in stubble management across the rotation. “Using a stripper front at harvest greatly reduces the amount of crop residue that is cut, chopped and spread out the back of the harvester,” says Greg. “The rearwards rotating rotor and stripper fingers strip the grain off the heads and leave the bulk of the crop residue standing in situ. About 85 per cent of the threshing occurs at the front end of the harvester, enabling double the harvest capacity of a draper, using 60–70 per cent less engine power and 60 per cent less fuel.” Grower experience suggests that stripper fronts work well in lodged crops and still allow the operator to have the front down low to collect any weed seeds, such as annual ryegrass and brome grass, present at harvest. This is particularly effective if the crop is sown on narrow rows, forcing the weed seed heads upwards in the crop canopy. Research into the efficacy of this system for harvest weed seed control is planned for the coming harvest. “The tall stubble left after harvest provides very effective soil shading and protection from drying winds over summer to retain more moisture and enable early sowing, rather than growers needing to wait for breaking rains,” says Greg. “The stubble dries and becomes brittle rather than rotting on the soil surface, making it easier for the disc seeder to operate.” The tall stubble left by the stripper front at harvest has widened their planting window all the way from January to May, giving them incredible flexibility in their cropping program decisions. The chaff line is subject to a high level of shading and higher moisture conditions that suppress germination very effectively. Harvest weed seed control is an additional component that growers like Daniel Fox at Marrar, NSW are adding to the ‘strip and disc’ system. Daniel has moved away from narrow windrow burning and now uses a chafflining chute to deposit the small amount of chaff, along with weed seeds, into a thin band behind the harvester. This contains the weed seeds to a very small portion of the paddock where they either rot away or have to face stiff competition from the following crop. “We are putting much more emphasis on cultural weed control methods now and reducing our reliance on herbicides,” says Daniel. “The tall stubble has really widened our planting window all the way from January to May, which gives us incredible flexibility in our cropping decisions. The system is easier to manage if you start with low weed numbers but we really believe that it can be used to drive down weed numbers after a blow-out too.” In a nut-shell, Daniel and his father David have implemented a controlled traffic farming system based on 16.5 cm row spacing, competitive cultivars, disc seeding, stripper front, chafflining, double-break cropping and sowing east-west where it is practical. On the herbicide front they have a strong pre-emergent program and utilise double-knocks and crop topping to manage in-crop survivors. The Fox family of Marrar, NSW have implemented a controlled traffic farming system based on 16.5 cm row spacing, competitive cultivars, disc seeding, stripper front, chafflining, double-break cropping, and sowing east-west where it is practical. On the herbicide front they have a strong pre-emergent program and utilise double-knocks and crop topping to manage in-crop survivors.
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Case Study

John Stevenson, Lockhart NSW

Orange Park is an 8200 ha corporate dryland cropping operation with eight main blocks, all within a 30 km radius of Lockhart, NSW where John introduced the use of the double break from cereals 10 years ago.   To get the best result possible from OP canola, ‘Orange Park’ manager John Stevenson (left) has their seed professionally graded and only plants seed sized over 2 mm diameter. Karl Grocke (right) has joined the team at Orange Park on their graduate program, making the most of the opportunity to learn from great operators like John. “Our rotation is driven by herbicide resistant weed management,” he says. “A double break, such as hay/canola, pulse/canola, fallow/canola, is implemented once in a 7-year rotation. The rotation is flexible but we do what we can to avoid growing three cereal crops in a row because the result is inevitably a weed blow-out.” The main weeds on Orange Park are annual ryegrass in-crop and fleabane in summer, which has been increasing since 2005, particularly in wet years. Wild oats is a lesser but persistent weed. “We have low level glyphosate resistance and varying levels of Group A resistance to contend with,” says John. “We don’t use much Group B chemistry either, except occasionally in imi-tolerant crops, partly because of decontamination issues with canola, but mainly because of poor efficacy.” The wettest September on record in 2016 saw about 10% of the crop across the Orange Park operation inundated – compromising their weed control and nitrogen management. “Essentially we lost a year of weed control with ryegrass blow outs due to poor crop competition and not being able to do timely herbicide applications,” says John. “We also saw a shift in the weed spectrum with more carryover of weeds that thrive in wet conditions, such as toad rush and lesser loosestrife.” Crop rotation and double break cropping The rotation that is working well on Orange Park since 2008 consists of two cereals followed by canola, then another two cereals and finally a double break before returning to cereals. John incorporates as much diversity within the system as possible to maximise returns and keep pressure on weed numbers. Canola, wheat, barley, pulses (including faba bean, lentils and vetch hay), oaten hay for export, and strategic fallowing to conserve moisture, all feature in the list of options. The diversity in crops enables the rotation of herbicide groups, including pre-emergent herbicides ahead of each crop. Imi-tolerant crops such as Hurricane lentils, IT-canola, possibly barley in the future add to the mix although John often grows hybrid IT-canola conventionally simply for its inherent yield advantage. “The price of lentils is attractive however logistics are difficult, as grain needs to get to Horsham, over 6 hours away,” he says. “Realistically, canola and feed grain for poultry and feedlots are our mainstay crops.” To maximise the competitiveness of canola crops John grows some hybrid crops and also grades OP canola to 2 mm diameter as a cost-effective way to improve crop establishment and early vigour that also suppresses early weed growth. John uses TT canola when weeds become a problem issue and Clearfield canola in low weed population paddocks where he can also apply atrazine on volunteer faba beans. This year John planted 650 ha trial of lentils in a block that would normally have been fallowed. “There was good residual soil moisture from last year’s wet winter and we tried a late planting system to reduce the density of the lentil crop to keep air flowing through canopy, hopefully reducing the incidence of disease,” he says. “Weed control in the Hurricanes XT lentils has been exceptional although the crop has demonstrated the need for better pH amelioration at depth.” “Including lentils will spread the workload and we can target a different weed germination cohort,” he says. “Having a different group of herbicides available will also help add diversity to our control program.” Row spacing, CTF and stubble management John manages Orange Park as eight 1000 ha management units, where a unit may consist of several blocks in close proximity. He is looking at opportunities to implement east–west sowing in suitable blocks to maximise yield and reduce weed pressure. While on a Nuffield Scholarship trip to New Zealand, John saw crops grown on 125 mm (5 inch) row spacing where farmers were able to include ryegrass as a crop in their rotation, without concern over future weed problems. “Historically, our seeding has been on a 300 mm row spacing but we are in the process of investing in a full disc seeding system, which will allow us to narrow the row spacing to 175 mm (7 inches),” says John. The disc seeder will enable John to retain stubble from their 1.7 t/ha pulses, 3.4 t/ha wheat and 4 t/ha barley crops within their 18 m system with 3 m CTF tramlines. Harvest weed seed control John and his team have been narrow windrow burning for three years. Having tried this harvest weed seed control tactic in canola, wheat and barley crops they have found the safest and best results are achieved in canola. “Realistically, narrow windrow burning is not very compatible with the council’s fire regulations so we are looking at alternatives,” says John. “Cereal stubble burns for 4 or 5 hours, and whirlwinds can easily shift burning chaff 300 m into a neighbour’s stubble.” A downside to narrow windrow burning is that more moisture is stored under the narrow windrows, which can cause uneven crop germination the following season. John has been successfully using narrow windrow burning in canola for several years. Twelve days after sowing, this Lancer wheat crop shows the variability in germination where the rows under the narrow windrow have access to more moisture. John is looking into other options for harvest weed seed control and will probably phase out narrow windrow burning over the next few years. Chaff deck systems suit CTF and although John thinks they have merit, there are limitations on the options available when using contract harvesters. Chaff lining seems easier to implement and is likely to feature in the near future. “Narrow rows help push weed seed heads to the top of the canopy,” says John. “Two plants per m2 is too many, especially if the weed is able to adopt a prostrate habit and evade collection at harvest. The big challenge is getting inexperienced header drivers to harvest low, even though we pay the contractor a premium to have this happen.” John uses spray topping in canola, and sometimes wheat and barley, along with hay production to take out late germinating weeds. Fallow management Over summer, John uses a contractor with an optical (camera) sprayer to treat survivors with paraquat following a broadacre spray of glyphosate. He says the optical sprayer is also a valuable tool to help manage cud weed, which is becoming more prevalent. There is no routine cultivation in the system however John does incorporate lime with a speed tiller before planting and a full tillage using a flexicoil is done when there is levelling work required. “When we change over to the disc seeder we will probably need to cultivate to remove the ridges left by the tined system,” he says. “The disc seeders can’t handle too much chaff on the ground either, so burning is still an option for weed control, or when slugs and mice are a problem.” Soil fertility and weeds Across the Orange Park operation John has acidic (pH 4.5) red soil ridges and some sodic vertosols to contend with. He is using variable rate technology (VRT) to apply lime to the red ridges using rates ranging from 1 to 3 t/ha to lift the pH to 5.5. “We saw an immediate response of lower ryegrass population in low pH blocks after lime application due to stronger crop competition,” he says. “Variable rate application and soil testing has been very cost effective for us and has helped reduce weed numbers and improves herbicide efficacy. Fixing soil pH gives the best return on investment through improved nutrient availability, which supports higher yield and better weed control.” John is also using soil sensing and VRT to address constraints in nitrogen and phosphorus. The red soil ridges on ‘Orange Park’ are acidic (pH 4.5) so John is using variable rate lime applications to lift the average pH in these soils to 5.5. In doing so he has observed an immediate reduction in ryegrass numbers due to the improved crop competitiveness.  
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Surveys highlight the cross-resistance to herbicides

John Broster, senior technical officer (herbicide resistance) at Charles Sturt University leads the weed survey project in NSW and has just completed crunching the numbers and finalising the results of the 2016 survey. John Broster, CSU “We gathered samples from the northern NSW and plains regions in 2016, which means we now have survey results from across the major grain growing regions of NSW,” he said. “The target weeds that we collect and test for herbicide resistance are, in order of importance, annual ryegrass, wild oats, sowthistle, barley grass, brome grass, wild radish and Indian hedge mustard.” The weeds that are collected in the surveys are tested for their susceptibility to the major herbicide groups used for their control. “Across NSW the extent of ryegrass resistance to Group A ‘fops’ and Group B ‘SU’ herbicides is by far the highest with about 60 per cent of samples being resistant, and 46 per cent of samples being resistant to Group B ‘Imi’ herbicides. There was less extensive resistance to the Group A ‘dims’ and Group D herbicides at 10 and 11 per cent of samples respectively,” said John. “When we looked at cross-resistance in the ryegrass samples collected in NSW we found that while 24 per cent of samples were susceptible to all five of the major herbicide groups used for ryegrass control, a huge 43 per cent were resistant to three or more of these five herbicide categories.” Speaking at the recent WeedSmart Week forum, John Broster, senior technical officer (herbicide resistance) at Charles Sturt University presented results from the latest weed survey conducted in NSW where 43 per cent of surveyed annual ryegrass plants were resistant to three or more of the five important herbicide categories used to control this weed. These surveys clearly illustrate the level of cross-resistance that exists in cropping paddocks across NSW, and in other states around Australia. At the recent WeedSmart Forum in Wagga Wagga where John presented the latest survey results, 170 growers, agronomists and researchers compared notes and experiences about a whole raft of weed management tools, some largely untested but showing promise in the field. Harvest weed seed control options were of great interest, as were the demonstrated benefits of double-break cropping, utilising livestock in mixed farming enterprises and ways to extend the effective use of herbicides. The ‘Big 6’ WeedSmart tactics known to drive down weed numbers and drastically reduce the impact of herbicide resistance on Australian farms are: Rotate crops and pastures, Mix and rotate herbicides, Increase crop competition, Use the double-knock, Stop weed seed set and Implement harvest weed seed control. Herbicide resistance can’t be beaten with herbicides alone — that’s the take-home message from these surveys. However, even in paddocks where herbicide resistant weeds are almost as common as susceptible ones, this doesn’t mean ‘game over’, as many Western Australian farmers have shown. It does mean that farming systems need more diversity and weed management programs need to include a range of tactics aimed at reducing weed numbers at every opportunity during the year.
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Case Study

Aaron McDonald, Horsham Vic

Farming with his parents, Greg and Leanne, Aaron runs 5500 ewes for wool and prime lamb production, utilising pastures, hay paddocks and crop stubble on their 4050 ha property. The McDonalds are finding a rotation of canola, wheat, canola, wheat, then a double break of canola followed by faba beans or clover hay, is profitable and enables them to keep weed numbers down. In barley crops the straw is also often baled after cutting the crop low, allowing sowing without stubble burning. Aaron does most of their oaten hay production on the poorer soils but also uses oaten hay as an effective means to clean-up paddocks that have a higher infestation of ryegrass. Their clover hay is sold locally, predominantly as cattle feed, while their oaten hay is exported most years. “Annual ryegrass and wild radish are our main problem weeds,” says Aaron. “We test for herbicide resistance every couple of years and so far the results have come back as ‘susceptible’ for most of the major groups. The main challenge we have with wild radish is the fact that it germinates all year round. With ryegrass it’s all about keeping plant numbers low.” Although the testing is not showing herbicide resistance, Aaron is seeing evidence of Select not working as well as it did in the past. To add more mode-of-action diversity to their system the McDonalds are using pre-emergent herbicides Sakura and Boxer Gold in cereals with good success and grow both hybrid (RR and 650TT) and open-pollinated (TT) canola cultivars. “The RR canola enables extra knocks with glyphosate in-crop to clean up paddocks where we are concerned over the efficacy of Select,” says Aaron. “All our other in-crop herbicides are still working well but we are trying to rotate as much as possible with Select and Edge, and using paraquat ahead of canola and glyphosate or paraquat ahead of cereals.” The McDonalds have always sown their crops on fairly narrow rows, 250 mm spacing, and use high sowing rates (wheat and oats sown at 100 kg/ha and canola at 3.6 kg/ha) to provide strong crop competition to help with weed control. The sheep grazing stubbles provides quite good control of summer weeds but some herbicide is always required. Aaron’s main summer weed concerns are melons and self-sown crop. In autumn or pre-sowing he occasionally double-knocks but often there are no survivors so the second knock is not needed. Hay making and harvest weed seed control Aaron has implemented narrow windrow burning for the last 4 or 5 years in their canola crops as a harvest weed seed control tactic to capture late germinating weeds. This is supported with strategic crop topping of the canola to desiccate and then windrowing 80 per cent of the canola area each year. In their cereals, crops are cut low and stubble is burnt on about 75 per cent of the cropped area to allow easier sowing operation, and has the added benefit of destroying some weed seed. In barley crops the straw is often baled after cutting the crop low, allowing sowing without stubble burning. Grazing stubble and burning also helps reduce mice and slug numbers. “Oaten hay production enables us to apply a desiccant over the top prior to cutting for hay,” says Aaron. “This gives us the opportunity to implement a herbicide plus non-herbicide double knock on in-crop herbicide escapes.” Aaron McDonald is using oaten hay and clover hay production as weed management tools within their mixed farming operation south of Horsham. “We graze the cereal stubble and canola narrow windrows after harvest but don’t leave the sheep on the paddocks for long,” he says. “We find that the cereals provide better feed value than the canola windrows but we also put lambs on the canola regrowth for a little extra green pick.” Each year about 5000 lambs move through the on-farm feedlot, where the McDonalds feed out gradings from the barley grain and the straw. “Feeding the grain gradings out in the feed lot also brings weed seeds into the confinement area where we can control them quite easily,” says Aaron. The feedlot adds value to the straw and grain gradings, turning off about 5000 lambs per year. Weed seeds that are brought back to the feedlot are easily managed if they survive being eaten.

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