No water, just weeds? Managing weeds in irrigation channels
Are your channels a source of weeds on your farm? Irrigation channels require regular monitoring as they are often a source for new weed incursions. Weed seeds can enter farms from irrigation water and any new weeds emerging need to be removed prior to seed set. Retaining irrigation water on farm can help to limit any potential spread. Weeds in irrigation channels are an important source of weeds. What do we know? Channels are a source of seeds that can move into cotton fields adding to the weed seed bank. Weeds in channels are a potential host for disease and insect pests. They can interrupt water delivery reducing irrigation efficiency. Large weed infestations can provide habitat for feral pests. Larger weeds can also undermine the integrity and stability of the channel bank. What are the options? In addition to knockdown and residual herbicides always include mechanical removal as part of an integrated approach to weed management. Valor (Group G) herbicide contains flumioxazin and is registered for knockdown and residual control of broadleaf and grass weeds on irrigation channel banks. It has low volatility and binds strongly to the soil so the risk of movement is very low. Valor binds tightly to the soil after 25mm of rain, if that doesn’t occur within 3 weeks after application the channel will require flushing and the waste water retained on farm. It is not degraded by solar radiation even if exposed for weeks prior to water or rainfall. Pendimethalin (Group D) is a herbicide which provides residual control predominantly of grass weed species. Pendimethalin is very tightly bound to soil particles and has very low solubility; meaning it stays where it is applied. Pendimethalin should be applied to the bank after grading or reshaping and if rainfall does not occur for 14 days the channel should be filled with water and then waste retained for pre-irrigation of cotton fields. Diuron (Group C) is a herbicide which provides residual control of a range of grass and broadleaf weeds. Diuron has limited mobility binding tightly to the soil, extremely low volatility and has a relatively low solubility rating. Application needs to be onto moist bare soil and prior to rainfall to fix the herbicide to the soil. If rainfall does not occur fill the channel, let stand for 72 hours and then drain the water into waste. Glyphosate (Group M) is a knockdown herbicide with activity on a large number of weeds common to irrigation channels. The overuse of glyphosate for weed control in non-field areas is a contributing factor to the development of herbicide resistance; thus its use around channels, road sides and non-field areas should be restricted. Any survivors from glyphosate application need to be removed to prevent weed seeds topping up the soil seedbank with a potentially resistant population. Amitrole-T (Group Q) is a knockdown herbicide that controls a range of seedling grasses and young broadleaf weeds. Using Amitrole-T as a substitute for glyphosate will help to reduce the likelihood of glyphosate resistance developing. The importance of pre-emergent and residual herbicides Getting the best out of any herbicide is important, none more so than glyphosate. By incorporating pre-emergent herbicides into our planting program we reduce the emergence of weeds in crop allowing growers to target a small population of weeds reducing the risk of herbicide resistance developing. Running the weed seed bank down and targeting small weed numbers is a robust strategy for ensuring complete weed control. It’s a numbers game, low weed numbers means there is less likelihood of resistant individuals within the population, and large weed numbers increases the risk of resistant individuals present in the population. Demonstration trials at Wee Waa and Whitton in 2018-19 highlighted this clearly. In addition to the risk of resistance from spraying large weed numbers the yield penalties from these early weedy treatments were significant. A 3.5b/ha difference between the weedy control and those treatments with pendithethalin or diuron reinforces the clear message of diverse weed control options. Learn more in this short video from CottonInfo’s weed tech lead Eric Koetz: Source: CottonInfo Further information: CottonInfo weed management page
Spring into action with fallow residuals
While frost on winter crops is often growers’ main concern in August and September, this is also the time when some summer weeds start germinating if conditions are favourable. A spring rainfall event, followed by a week or two of warmer weather, can quickly kick off the season for summer weeds. Mark Congreve, Consultant with Independent Consultants Australia Network, says fleabane, sowthistle and feathertop Rhodes can all start germinating as early as August in northern regions when temperatures are suitable. Mark Congreve, consultant with Independent Consultants Australia Network, says summer growing weeds that establish in late winter and early spring may result in plants that are large and very difficult to control with knockdowns if control is left until after the busy harvest period. “Establishment at this time of year may result in plants that are large and very difficult to control with knockdowns if control is left until after the busy harvest period,” he says. “Once this happens the only options for control are a robust double-knock herbicide strategy, or tillage.” The full canopy cover in a dense winter crop generally prevents most germinations within the crop, but these weeds can establish in open crops, in missed rows or wide guess rows, around crop edges or in winter fallows. Mark suggests that pre-emergent herbicides applied in late winter or early spring fallow, before the first spring storms, can play an important role in managing these early germinations of ‘summer’ weeds, helping create a weed-free winter-spring fallows until it is time to sow a summer crop. “This is easiest when a paddock has been ear-marked for a specific summer crop,” he says. “Rotation planning is really important – where you know what you will be planting, there are normally one or more options with acceptable plant-back periods for most crop choices. Where you are unsure about what crop will be planted into the paddock, then decisions are more difficult.” Pre-emergent herbicides applied in late winter or early spring fallow, before the first spring storms, can play an important role in managing these early germinations of ‘summer’ weeds, helping to create a weed-free winter-spring fallow until it is time to sow a summer crop. Photo: Ben Fleet To ‘keep the options open’ growers are restricted to using products with shorter plant-back periods, and therefore less residual control. If using a product with potentially damaging residual activity on subsequent crops, growers are reliant on further rainfall to breakdown the herbicide in the soil prior to summer crop planting. “In some situations, it may be possible to plant the summer crop any time after the residual is applied in spring,” says Mark. “A good example of this is using Dual®Gold for feathertop Rhodes grass control in paddocks going to sorghum.” For other combinations of residual herbicides and summer crops a plant-back period may be required. Mark said it is very important to use the label information to determine the level of risk involved in applying a particular product andjudge whether it is safe to plant the summer crop or not. “Where plant-back periods exist, the breakdown of these herbicides needs a combination of time and soil moisture over the warmer months, so it is important to look at how the rain has fallen, as well as the totals,” he says. “Having the soil surface wet for a few weeks from regular rainfall events during these warmer months will support more microbial breakdown of the herbicide than one storm event that delivered the same quantity of rainfall, followed by weeks of dry weather.” Ideally, a well-timed spring residual herbicide will keep the fallow clean until the summer crop planting window opens. Assuming the appropriate plant-backs have been met, an effective knock-down herbicide may be needed to remove weeds germinating on the planting rain, should the spring residual herbicide be running out. The decision around the choice of additional pre-emergent applied at planting will depend upon the length of residual expected from the spring application, the known weed pressure in the field, the availability of inter-row cultivation or post-emergent in-crop herbicide options and the predicted rainfall outlook. Growers and agronomists interested in learning more about the benefits and risks of pre-emergent herbicides can access a free online course at www.diversityera.com, presented by Mr Congreve and Dr Chris Preston. Related pages Early weed control benefits summer crops
CQ grain growers endorse WeedSmart Big 6
Weed management moves to a whole new level when you add the word ‘integrated’. This is the driving force behind the WeedSmart Big 6 approach, which suggests that growers implement as many of these six key tactics as possible into their crop management programs. Herbicide resistant weeds might not be widespread in Central Queensland yet, but all the indications are that the problem is flying just under the radar. Following the discovery of the world’s first population of glyphosate resistant sweet summer grass near Emerald, random weed surveys have since confirmed glyphosate resistance in both feathertop Rhodes grass and fleabane samples collected in the region. Members of the Central Queensland Grower Solutions Group have been working hard to build an integrated weed management system that suits their farms. In doing so they are ticking off many of the ‘Big 6’ tactics each season. These tactics are summarised as: Crop and pasture rotation Double knock to protect glyphosate Mix and rotate herbicide groups Stop weed seed set Crop competition Harvest weed seed control In August last year, twelve Central Queensland growers attended the 2018 WeedSmart Week in Narrabri as part of a 6-day fact-finding tour through southern Queensland and northern NSW, delivered by the CQ Grower Solutions Group. Kurt Mayne and Scott Becker were among the group, and this year they are backing WeedSmart Week in their own backyard of Emerald, Queensland. This practical and thought-provoking event also has the solid backing of the CQ Grower Solutions Group, a joint initiative of GRDC and Queensland Department of Agriculture and Fisheries (DAF). Rolleston grain grower, Kurt Mayne returned from the study tour with a realistic view of the risk of herbicide resistance and a firm commitment to getting himself on the front foot before it starts to impact on the profitability of his business. “One of the stand-out tools that we saw being used very effectively was optical sprayer technology,” said Kurt. “When I returned from the tour last year, I purchased a WeedIT sprayer to prolong the effective life of the chemistry that we currently have available.” CQ grain grower, Kurt Mayne is impressed with the benefits that have come with the addition of an optical sprayer to his weed control program. Kurt will be part of an expert panel at WeedSmart Week in Emerald to discuss the pros and cons of this technology. “In our farming system it is hard to incorporate pre-emergent herbicides in the fallow because that can restrict our opportunity cropping options. 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.” With WeedSmart Week being held for the first time in Central Queensland, Kurt is looking forward to the opportunity to hear how other growers are contending with herbicide resistance in weeds and how different ideas and technologies could be implemented in the region. Kurt will be part of the spray technology discussion panel at the forum on 13 August. Farming near Moura, Scott and Kelly Becker are keen to trial harvest weed seed control as a possible addition to their weed management program. Being fully aware of the impact herbicide resistance could have on their family farming business, the Beckers have been proactive with chipping out small patches of feathertop Rhodes grass in sorghum. “We are planning our cropping program four or five years ahead, mainly to manage stubble cover and to rotate herbicide modes of action,” said Scott. “We have incorporated most of the WeedSmart Big 6 tactics to keep weed numbers low and think that chaff lining could be a useful way to contain any weed seeds produced in-crop.” Keeping weed numbers low is high priority for Scott Becker, Moura, who is keen to find a practical harvest weed seed control option suited to CQ farming systems and weed spectrum. “It’s a numbers game when it comes to weed management and the only way we can win is to be doing everything possible to keep numbers low and prevent seed set where possible,” he said. Hayley Eames, Department of Agriculture and Fisheries development extension officer said the CQ Grower Solutions project has been delivering a range of extension activities aimed at addressing production constraints around five key themes, including integrated management of hard to control weed species, since 2015. “Herbicide resistance is ever increasing in Central Queensland and although individual weed control tactics are quite well understood in the region there needs to be more integration of control measures,” she said. “Growers have relied on rotation from summer to winter crops and from cereals to pulses and this has worked well for a long time. There is scope to include other strategies though, such as strategic use of pre-emergent herbicides and harvest weed seed control.” DAF is supporting WeedSmart Week in Emerald as a rare opportunity for local grain and cotton growers to focus on managing the looming threat of herbicide resistance in weeds. The 2.5-day program will begin with a 1-day forum at the McIndoe Function Centre, Emerald on 13 August. The following day will be filled with a bus tour to farms around Emerald where growers have put in place integrated weed management programs to minimise the impact of herbicide resistance on their businesses. The final part of the program is a half-day tour of the SwarmFarm Robotics base at Gindie on Thursday 15 August to see and discuss cutting-edge technologies such as optical weed sensing for spraying and chipping, robots and emerging ‘green-on-green’ spray sensors. Register for this important 3-day event before 31 July for the ‘early bird’ single ticket price of $130, guaranteeing a seat on both the bus tour days as well as the forum, all fully catered, at https://www.weedsmart.org.au/weedsmart-week-emerald/
Birchip grain growers endorse WeedSmart Big 6
Weed management moves to a whole new level when you add the word ‘integrated’. This is the driving force behind the WeedSmart Big 6 approach, which suggests that growers implement as many of these six key tactics as possible into their crop management programs. Farming in the Wimmera, the Rethus and Ruwoldt families have been working hard to build an integrated weed management system that suits their farms. In doing so they are ticking off many of the ‘Big 6’ tactics each season. Wimmera grower Tim Rethus, with the planter the family has developed to reduce weed germination at sowing. Photo: Stock and Land In 2018 Tim Rethus and Ian Ruwoldt attended WeedSmart Week in Narrabri and this year they are backing WeedSmart Week in their own backyard of Horsham, Victoria. This practical and thought-provoking event also has the solid backing of the Birchip Cropping Group. Tim and his brother Luke farm with their father Geoff and long-time worker Glenn in the central and southern Wimmera, where they are contending with Wimmera annual ryegrass, brome, wild oats, vetch, bifora, sow thistle and prickly lettuce. “Our approach to weed control centres on keeping weed germination levels low and using diverse farming practices,” said Tim. “Dad was an early adoptor of minimum tillage back in the early 1980s and we have progressively moved to farming systems that involve less and less disturbance. One of the major benefits is that we are leaving the weed seeds on the soil surface where they are exposed to the weather and don’t have the soil contact they need, and this really reduces weed seed germination.” Register for this important 3-day event for the ‘early bird’ single ticket price of $130, guaranteeing a seat on both the bus tour days as well as at the forum, all fully catered, at https://www.weedsmart.org.au/weedsmart-week-horsham/ A key element to the Rethus’ success is their determination to achieve near-zero disturbance at planting. When they adopting a 40-foot CTF system in 2008 their min-till single disc seeder did a good job and reduced soil throw but ten years on, the soil in the cropping beds has responded to the removal of machinery traffic, and the single discs were often stalling in the softer soil and the depth control was no longer adequate. This led the Rethus’ to invest in a zero-till precision planter to provide more precision at planting, including inter-row sowing for lentils, and to make best use of the newest chemistry available. “This precision seeder was a good unit but it was complex and didn’t suit all our crops,” said Tim. “So, we decided to combine the precision row units with twin-disc openers on a new 80-foot NDF frame but use an air-seeder to deliver the seed.” To further reduce soil throw, residue managers are not used. Instead ‘PTT Sabre-tooth’ discs are used to cut through the residue and reduce pinning. The two discs are slightly different in size, so they rotate at slightly different speeds, providing a cutting action to keep residue out of the seeding furrow. “Adding side-shifting rams to the toolbar means we can also inter-row sow our lentils and we have a seeder that meets all our requirements, especially in terms of maintaining low weed seed germination at seeding while still sowing at 15-inch row spacing.” Zero disturbance planting in CTF beds is working a treat to minimise weed seed germination. The Rethus family practice a diverse crop rotation of wheat, barley, durum, canola, lentils, beans and oats, and use shielded spraying, hay production, brown manuring, spray topping and diverse herbicide strategies to minimise weed seed set. Tim said the reality of herbicide resistance means non-chemical tools are very important to maintain low weed numbers and this is one of the driving forces behind their efforts to fully integrate hay production into their CTF system. Tim is keen to share his thoughts and experiences in precision farming and weed management with other growers at the Horsham WeedSmart week from 27 to 29 August, and has been instrumental in organising a practical session centred on setting up harvesters to make harvest weed seed control as effective as possible. Farming at Kewell, Ian Ruwoldt and his brother Greg also have several strategies in place to manage ryegrass, bedstraw, marshmallow, vetch and bifora. Ian found the WeedSmart event in Narrabri to be very comprehensive and a good opportunity to think through the tactics that could help solve their weed problems. “We currently use oaten hay, chemical rotation, imidazolinone (imi) chemistry with canola and a chaff deck on the harvester to keep weed numbers low,” said Ian. “Thinking about the WeedSmart Big 6 helps to formulate a plan to manage weeds through the year and through the rotation.” Kewell farmer Ian Ruwoldt is encouraging other Wimmera growers to attend WeedSmart Week in August as a good opportunity to formulate a plan to manage weeds through the year and through the rotation using the WeedSmart Big 6. “The forum covers a lot of topics and the discussions are very practical and very relevant to the region, so this year’s event will focus on the weed issues facing Wimmera and Mallee farmers.” Attendees will have several opportunities to see and discuss cutting-edge technologies such as optical sprayers, robots and emerging ‘green-on-green’ spray sensors, and will find out how other growers in the region are implementing the Big 6 weed management tactics. The growers, agronomists and researchers speaking and participating in expert panels at the Day 1 forum will spark important discussions about herbicide resistance and how the Big 6 tactics can be used to target the weed species and farming systems in the southern cropping region. There’s one thing for sure – doing nothing is not an option. Register for this important 3-day event for the ‘early bird’ single ticket price of $130, guaranteeing a seat on both the bus tour days as well as at the forum, all fully catered, at https://www.weedsmart.org.au/weedsmart-week-horsham/
Never cut the herbicide application rate
Scientific studies have demonstrated that resistance can rapidly evolve in weeds subjected to low doses of herbicide. Some weeds can develop resistance within a few generations. Full rates when mixing herbicides too! When mixing herbicides it is important that each product is still applied at the full label rate to ensure high mortality. Applying different chemicals in one mix can provide an additive advantage. It is important to understand the mode of action of each herbicide on the plant when preparing a herbicide mix. This is just as important for pre-emergent grass weed mixes as it is for post-emergent mixes aimed at broadleaf weed control. ALWAYS READ THE LABEL. Surrounding weed seeds with a combination of pre-emergent herbicides with different modes of action can give a high level of control and help extend the useful life of all the chemicals used. The high level of control must be supported with additional control measures for all survivors. All products with different modes of action must be applied at full label rates for this to be an effective strategy. Mixing two chemicals with the same mode of action can achieve some additional efficacy, however, the mix should deliver the combined full rate to ensure a lethal dose. The amount of stubble present and crop safety are all important considerations when mixing chemicals. For example, when using a tank mix of Avadex® and trifluralin to control ryegrass in wheat, the rates used will vary depending on the sowing system and level of stubble retention. Be sure to get good advice. Many herbicides on the market are a combination of two or more modes of action within the one product. These products must be applied at the full label rate to be effective. Having dual action does not negate the need to change herbicide products and rotate modes of action. Repeated use of any single strategy will reduce the effectiveness of that strategy over time.
Spray well – correct nozzles, adjuvants and water rates
Spray application is a technical field and growers need to make sure their equipment and application techniques are spot-on. The GRDC Spray Application GrowNote provides detailed information and about 80 videos to demonstrate key skills. Prevent spray-drift 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’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 High water rates don’t have to slow you down Some growers are concerned that increasing the water rate when applying herbicide will slow down their spray operation and cost them money. However, the biggest financial loss during spraying usually comes from a failed spray job. To keep your spray operation as time efficient as possible when using more effective and reliable application volumes, you can: Use nurse tanks around the farm to reduce the time spent travelling back to a central re-fill point. Use a larger pump, e.g. 2.5 inch, to make re-filling quicker. Pre-mix the batch while the sprayer is operating. Many mixes can be held in the mixing tank for up to 6 hours. However, wettable granules and suspension concentrates will need agitation to keep them in solution. For pre-emergent herbicides in high stubble situations, carrier volume has a large effect on the level of control achieved. Across four trial sites Dr Borger’s research demonstrated that ryegrass control with trifluralin or Sakura® increased from 53% control when the carrier volume was 30 L/ha to 78% control when the carrier volume was increased to 150 L water/ha in high Water quality and mixing order Water quality is often overlooked as a possible contributor to herbicide failure and can lead to confusion over the herbicide resistance status of weeds on a property. Water should be considered as one of the chemicals in any mix, given that water quality varies markedly depending on its source. Getting the mixing order right is essential for effective spray results. Don’t start mixing until the water quality is right Podcast – Mixing herbicides Adjuvants Sometimes adding an adjuvant is beneficial and sometimes it is detrimental; and there is an art to knowing how to best deploy these additives. When weeds are susceptible to the applied herbicides, the effectiveness of adjuvants generally goes un-noticed. Correctly applied adjuvants can reduce the impact of low level herbicide resistance by helping to maximise the amount of herbicide taken up by the plant.
Paired-rows give entry level crop competition
Higher crop yield and less weeds naturally flow from increased crop competition, but the costs involved in changing machinery and farming systems can be a barrier to achieving these benefits. Narrowing row spacing, while maintaining the same seeding rate, is generally accepted as the simplest way to increase crop competition, but growers who are not ready to change over their machinery can gain much of the weed suppression benefit using paired-row sowing systems. If this is coupled with east-west sowing the benefits are even greater. Peter Aikman, Annuello, Victoria has used a paired-row system to maintain crop competition to suppress weeds while gaining seeding efficiencies through slightly wider row spacing. This crop of Compass barley was dry sown in April 2018 and germinated on 12 mm rainfall on 4 May. Peter Newman, WeedSmart western extension agronomist says paired-row systems such as the Stiletto Boot, which is popular in West Australian sandy soils, are a cheap way to increase crop density and achieve earlier canopy closure. “Generally, there is not a yield response over single row seeding but yield is maintained in weedy situations, taking some pressure off in-crop herbicides without adding significantly to the weed seed bank,” he said. “Paired-row systems reduce the ‘auto allelopathy’ effect that suppresses plant growth when the seeds of crops like wheat are planted very close along the row. Spreading the seed out, essentially in a slightly wider band, gives each crop seed more room to germinate and grow without impacting on the growth of neighbouring crop plants.” In southern Australian farming systems there has been steady adoption of paired-row systems, such as Rootboot and Groundhog, to improve seedbed utilisation (SBU), which is a measure of the seed and fertiliser spread relative to the row spacing. Southern WeedSmart extension agronomist Greg Condon says the paired-row systems help avoid the problems with fertiliser toxicity that can occur in single wide row systems. “Older paired-row setups moved too much soil and left the seedbed very rough,” he says. “They also had poor stubble handling capacity, used more fuel, achieved poor seed-soil contact and growers had problems with pre-emergent herbicide safety in some situations.” “Most of these constraints have been fixed with the newer configurations now available on the market. Growers who might have had bad experiences before will probably find that paired-row boots now move less soil, have narrower openers and fit better with a wider press-wheel setup.” Greg says that although paired-row systems are a good interim option, the best long-term solution is to change to narrow single-row spacing, no wider than 250 mm for tynes or 190 mm for disc planters. Good establishment in paired-row sown canola. Paired-row system technology options Dr Jack Desbiolles, senior agricultural research engineer at University of SA has undertaken extensive trials investigating the benefits of increasing the space between seeds in the seedbed. Paired-row sowing is one way to effectively achieve this and can deliver both increased yield and useful suppression of weeds. “When it comes to paired-row seeding systems, the technology can be categorised into either split or integrated designs,” said Dr Desbiolles. “The split designs use a Y-splitter tail located further behind the opener, which delivers seeds into a furrow backfill. While seed spread can be more limited, seed placement can be accurate, but seed is often exposed to diluted furrow moisture and contamination from residue and pre-emergence herbicide, all of which can reduce the rate of crop establishment.” Dr Jack Desbiolles says when it comes to paired-row seeding systems, the technology can be categorised into either split or integrated designs. While these Y-splitter design solutions represent easy and low-cost upgrades for compatible single row seeding systems, the newer, integrated paired-row designs are becoming more mainstream. “The integrated designs are compact and streamlined, sitting closely behind the opener and are designed to deliver seeds onto an undisturbed ledge on each side of the trench that the opener creates,” he said. “The accuracy of seed placement depends mostly on the primary furrow shape not affecting the integrity of side ledges. These paired-row configurations are more expensive but often achieve good seed-soil contact without diluting soil moisture or allowing residue or herbicide contamination.” One grower’s experience Farming at Annuello in the north-west of Victoria, Peter Aikman (pictured at the top) started using a Rootboot paired-row system in 2014 as part of their strategy to increase sowing efficiency after buying additional land and doubling their cropped area. Peter’s Horwood Bagshaw seeder had been set up on 30 cm, single row spacing for cropping wheat, barley and legumes in rotation. To cover more area per day at seeding Peter changed to 35 cm row spacing but did not want to lose the crop competition benefits that he had seen at 30 cm spacing. “Widening the tine spacing allowed us to increase sowing speed and add two more tynes to increase the seeder width. Together these changes increased our seeding efficiency from 12 ha/h to 16 ha/h, which means we save seven days at seeding time and can finish planting the whole area on time,” he said. “To keep the crop competition benefits we turned the row direction to east-west where practical, and use the Rootboot opener to seed 10 cm paired-rows on 35 cm tyne spacing.” Peter has found that this paired-row system moves some soil around, but in some instances this can be a good thing as it helps to fix any small areas left bare after a legume crop or slightly eroded after using the self-propelled sprayer on sand hills. “Brome grass is one of our major weeds and we are trying to reduce its germination and seed set by using the combination of the paired-row system and east-west sowing, together with other strategies such as robust crop and herbicide rotation, monitoring for weeds, acting early to prevent weed blow-outs and using harvest weed seed control.” More resources Quantifying the effect of paired-row systems on crop competition and yield Podcast with Annuello grower Peter Aikman Colin McAlpine grower case study Hughes/Raszky grower case study Ben Webb grower case study Trevor Syme grower case study
Quantifying the effect of paired-row systems on weeds and crop
In 2005 Dr Jack Desbiolles, senior agricultural research engineer at University of SA led research into the effects of seedbed utilisation and seed rate on weed competition and wheat yields on a shallow grey Mallee loam near Minlaton in South Australia. The SAGIT funded research, in collaboration with the Southern Yorke Peninsula Alkaline Soils Group, centred on investigating the impact of seedbed utilisation (SBU), which quantifies the extent of the row spacing occupied by the crop. Low SBU seeding typically makes a uniform seeding job easier to achieve but there is an increased risk for fertiliser toxicity to reduce seedling emergence, and inter-plant competition can significantly limit the yield potential in higher potential seasons. Dr Jack Desbiolles’ research favours the adoption of paired-row seeding systems as a practical way to benefit from higher seedbed utilisation. Photo: Birchip Cropping Group (BCG) Two wheat crop seeding rates were tested – ‘Standard’ seeding rate of 88 kg/ha to establish 180 to 190 plants/m2and ‘High’ seeding rate of 125 kg/ha to establish 250 to 260 plants/m2. Three levels of seedbed utilisation (SBU) were trialled and Marloo oats was broadcast at 40 kg/ha (105 seeds/m2) and incorporated using a prickle chain on the ‘weedy’ plots to simulate weed competition. A knife blade plus double-shoot rubber seed boot on 25 cm row spacing gave low (15 per cent) SBU. The intermediate treatment was 45 per cent SBU using a double shoot narrow ribbon Anderson opener, also on 25 cm row spacing. Full (100 per cent) SBU was applied using a 20 cm wide share with a 20 cm reach plus Morris spreader boot set on 20 cm row spacing, effectively sowing seed across the full bed area and leaving no inter-row space. While crop seeding rate had little effect initially, the 100 per cent SBU had a significant effect on early weed vigour. This treatment reduced weed biomass by 16 to 20 per cent, and reduced weed tillering by 25 to 30 per cent in the early stages of growth. Increasing seedbed utilisation from a common 15 per cent (left) to 100 per cent (right), especially when combined with higher seed rate, effectively suppressed weed biomass and seed production while significantly increasing crop yield. SBU also had an impact on later weed growth where greater SBU proportionally reduced weed biomass by 11 to 14 per cent (in the 45% SBU system) and 29 to 32 per cent (in the 100% SBU system). A 43 per cent reduction in weed growth was achieved using a high seeding rate combined with 100% SBU. Weed seed production followed similar trends, with the best results being a 38 per cent reduction in seed weight per weed plant using full SBU and the higher seeding rate. Following a 289 mm rainfall growing season, the full SBU seeding combined with high seed rate increased wheat grain yield by 0.43 t/ha (in a weed-free environment) and 0.83 t/ha (in a weedy environment), relative to the low SBU, low seed rate control. This research confirmed the principles of crop competition and showed that paired-row systems were a practical option to help achieve greater weed competition and higher yield potential through greater seedbed utilisation. More recently, Dr Desbiolles conducted research on different soil types in the Murrayville district (Vic) in collaboration with Mallee Sustainable Farming Inc, and with DAFF funding, comparing paired-row systems to a commonly-used single row knife point system. In this trial, the paired-row systems gave the highest and most consistent crop establishment across a swale-dune Mallee sandy soil system, with good moisture conditions at seeding and sufficient in-crop rainfall. The plant establishment benefits ranged from +15 per cent on the mid-slope and sand hill, to +20 per cent on the sandy stony flats, relative to a district system control, and after a dry season finish, achieved up to 0.15 t/ha gain in wheat grain yield. “These results correlate well with the earlier work done in Minlaton which measured crop yield and weed suppression benefits through increased seedbed utilisation,” he said. “Improving crop establishment and gaining the crop competitive advantages relies on correct seeder set-up.” In a review of seeder set-up for the GRDC Stubble Management project, Dr Desbiolles highlighted the following considerations when it comes to using paired-row systems in different situations: Recommended for use in marginal soil moisture conditions when seeds can be placed onto undisturbed soil moisture. Recommended for effective incorporation of pre-emergent herbicides (IBS) application. Crop safety is best secured using paired-row attachments closely integrated behind the opener. Possible use in stony soils if compatible with shallow operating depth. Possible use in non-wetting poor fertility soils, where seeding is at furrow tilling depth. Possible use under rhizoctonia pressure if coupled with best practice disease management. Possible use in high residue situations when coupled with good residue management strategies. Other resources: Paired-rows give entry-level crop competition Peter Newman (AHRI/WeedSmart) and Peter Horwood (Mingenew, WA grower) discuss paired-rows Selecting a seeding system for your soil
Clean borders – avoid evolving resistance on the fence line
About one-quarter of glyphosate-resistant populations within broadacre cropping situations across Australia come from fencelines and other non-cropping areas of the farm. Along paddock borders, where there is no crop competition, weeds can flourish and, if not controlled, set lots of seed. The traditional approach has been to treat these weeds with glyphosate to keep borders clean but after 20-odd years this option is now failing and paddock borders are becoming a significant source of glyphosate-resistant weed seed. Weed researcher Eric Koetz said the limited options for managing weeds along irrigation infrastructure and other non-crop areas is a problem and is putting additional pressure on knock-down herbicides in irrigated systems. In some situations, cultivation can be used to kill the weeds and provide a firebreak, but on light soils this may pose an erosion risk and mowing or slashing may be safer options. Another possible tactic is to continue using herbicides but to ensure that a clean-up operation is carried out before any survivors can set seed. Some growers are choosing to increase the heat on weeds along the borders by planting the crop right to the fence and then baling the outside lap and spraying with a knockdown herbicide to kill any weeds and provide a firebreak. Another good option in some situations is to maintain a healthy border of vegetation using non-invasive grasses. In Queensland, buffel grass is a good example of a grass that can outcompete other weeds while not invading crop lands. If only herbicides are used on fencelines, resistance is inevitable. Surviving weeds on fencelines have no competition and access to plenty of soil moisture, so they set a lot of seed and resistance can easily flow into neighbouring paddocks. Other resources It’s time for a glyphosate intervention Farm hygiene cottons on – Cleave Rogan, St George What’s new in management of herbicide resistant weeds on fencelines? Keeping the farm clean – Graham Clapham, Norwin Don’t jeopardise glyphosate for clean fencelines Keeping fencelines clean Resistance risk to knock-down herbicides on irrigated cotton farms
Clean seed – don’t seed resistant weeds
This can potentially reduce crop yield and almost certainly means that the weeds will set abundant seed and most likely shed that seed before the crop is harvested, increasing the weed pressure in future years. The best way to ensure clean crop seed is to buy certified weed-free seed each year. But many growers prefer to retain some grain on-farm for planting the next year. For best results growers usually harvest seed from their cleanest paddocks and conduct some form of seed cleaning either on or off-farm. However, research shows that there is a tendency to underestimate weed seed contamination in seed retained for planting. An AHRI study on 74 farms across the Western Australian grainbelt showed 73% of cleaned crop seed samples had some level of weed seed contamination. The up-side is that 25% of cleaned samples were weed-free, so it can be done! This means that many unknowingly introduce significant levels of weed and volunteer crop seeds into the farming system at seeding time, even when crop seed has been cleaned. More alarmingly, many of these weed seed populations are resistant to a range of commonly used post-emergent herbicides. Uncleaned crop seed samples can have almost 25 times more contamination than cleaned crop seed. It is important to remember that resistance will evolve faster from introducing resistant weed seeds into a paddock, compared to resistance evolving independently in that paddock. The cleaning method used strongly influences contamination levels – a ‘gravity table’ is the most effective, followed by other methods such as rotary screens and sieves. Contamination levels of each cleaning method for all contaminants. Crop type also has a significant effect on the amount of contamination, with wheat containing much higher annual ryegrass seed numbers than barley, possibly because barley was more likely to out-compete weeds during the growing season. Another advantage of having seed professionally cleaned and graded is that larger crop seeds can be retained, promoting stronger seedling vigour and higher germination rates. Systems promoting farm hygiene such as meticulous seed cleaning and sanitising tillage, sowing and harvesting equipment between paddocks will help prevent the introduction of new weed species, noxious weeds and herbicide resistance.
Growers set to ‘Diversify and Disrupt’ weeds in the Wimmera
This August, Birchip Cropping Group (BCG) is co-hosting the first WeedSmart Week to be held in Victoria. Growers and agronomists are invited to attend the 3-day event, beginning with a 1-day forum at Horsham Town Hall on 27 August. The following two days will be spent touring farms around the Horsham area to see how growers are implementing the WeedSmart Big 6 tactics to minimise the impact of herbicide resistance on their businesses. The WeedSmart Week theme ‘Diversify and Disrupt – Conquer weeds with the Big 6’ says it all! Kewell farmer Ian Ruwoldt is encouraging other Wimmera growers to attend WeedSmart Week in August as a good opportunity to formulate a plan to manage weeds through the year and through the rotation using the WeedSmart Big 6. GRDC is the major sponsor of WeedSmart and Senior Regional Manager – South, Craig Ruchs, encourages growers from the Wimmera and beyond to make the most of the opportunity to be part of the focussed and interactive couple of days. “Weeds frequently drive systems decisions, having the potential to affect flexibility, choice and ultimately profit. Taking a strategic and planned long-term approach, implementing the WeedSmart Big 6 principles, can help put growers back in control,” he said. “Pulses are a particularly important element of crop rotations for many growers in the Wimmera and the production of these crops presents both unique opportunities and challenges for weed control.” “Bringing greater diversity in weed control tactics is critical in the ongoing battle against weeds and WeedSmart Week provides a highly effective platform to share research outcomes and on-farm innovation in a very practical and applied way.” WeedSmart Week brings together a wealth of knowledge and experience from local and inter-state growers, researchers, advisors and technology experts – putting the spotlight on herbicide resistance and weed management. Growers can see what is and isn’t working first-hand and consider how key principles can be applied directly to their own farming operation. GRDC Senior Regional Manager – South, Craig Ruchs (Photo: GRDC) At the forum and on the bus trip growers, agronomists and researchers put all the options and ideas on the table for discussion. In August last year, three members of the Birchip Cropping Group, Ian Ruwoldt, Tim Rethus and Sam Eastwood, attended the 2018 WeedSmart Week in Narrabri, NSW. Farming at Kewell, Ian Ruwoldt and his brother Greg have several strategies in place to manage ryegrass, bedstraw, marshmallow, vetch and bifora. Ian found the WeedSmart event in Narrabri to be very comprehensive and a good opportunity to think through the tactics that could help solve their weed problems. “We currently use oaten hay, chemical rotation, imidazolinone (imi) chemistry with canola and a chaff deck on the harvester to keep weed numbers low,” said Ian. “Thinking about the WeedSmart Big 6 helps to formulate a plan to manage weeds through the year and through the rotation.” “The forum covers a lot of topics and the discussions are very practical and very relevant to the region, so this year’s event will focus on the weed issues facing Wimmera and Mallee farmers.” Attendees will have several opportunities to see and discuss cutting-edge technologies such as optical sprayers, robots and emerging ‘green-on-green’ spray sensors, and will find out how other growers in the region are implementing the Big 6 weed management tactics. The growers, agronomists and researchers speaking and participating in expert panels at the Day 1 forum will spark important discussions about herbicide resistance and how the Big 6 tactics can be used to target the weed species and farming systems in the southern cropping region. There’s one thing for sure – doing nothing is not an option. Register for this important 3-day event for the ‘early bird’ single ticket price of $130, guaranteeing a seat on both the bus tour days as well as the forum, all fully catered, at https://www.weedsmart.org.au/weedsmart-week-horsham/
Testing for herbicide susceptibility and resistance
There are several reasons why weeds might survive a herbicide treatment but it is increasingly common for herbicide resistance to be the culprit. Testing weeds for herbicide susceptibility and resistance can save growers thousands of dollars, making the investment of a few hundred in testing very worthwhile. There are two main tests – The Quick Test and The Seed Test The Quick Test is done using weed plant samples collected in-crop and provides the results within a few weeks. The Seed Test is done on weed seed samples, usually collected around harvest time and the results take a few months. The Quick Test uses plant samples collected on-farm and sent to the laboratory. The plants are revived and planted into pots, then tested against the required herbicides. The Seed Test requires the collection of ripe seed, which is planted out at the laboratory. After dormancy has been broken and the seedlings have started to grow they are tested for their response to herbicides. Both tests are equally accurate. The Quick Test can not test for resistance to some pre-emergent herbicides, such as trifluralin. The value of the Quick Test is that you can find out what herbicides still work on the weeds collected and this gives you the option to use a different herbicide to treat the weed patch within the same season and before the plants set seed. Gathering samples for the Quick Test collect from the middle of the patch of weeds that are suspected to be resistant if the weeds are large, collect 20 plants if the weeds are small, collect 50 plants shake off the loose dirt and place the sampled weeds in a zip-lock plastic bag do not add water to the bag keep the sample cool if possible, collect and send samples on a Monday or Tuesday sample from different patches in the paddock, note the location/s and keep samples from different patches separate send by express post to Plant Science Consulting Check the website for details about the services offered, costs and specific instructions before submitting samples. Gathering samples for the Seed Test Collecting weed seed before or at harvest is the most common method used. The collected seed must be mature, from green to when the seed changes colour. Before harvest, collect 30 to 40 ryegrass seedheads or several handfuls of wild oats seed. After harvest, it is common to find seedheads still in the paddock or samples of contaminated grain can be sent for analysis. Keep samples from different locations separate and details noted on the bag. Only use paper bags (double layer) to collect and send seed samples. Ensure bags are sealed so that the samples don’t mix during transit. There are three weed seed testing services in Australia: Plant Science Consulting CSU Herbicide Resistance Testing UWA Herbicide Resistance Testing Visit the website/s for details about the services offered, costs and specific instructions before submitting samples. How to collect samples for the Quick Test How the Seed Test works Podcast In the podcast below, Dr Peter Boutsalis provides practical tips on collecting weed seeds for herbicide resistance testing. You can also see visual examples of weed seeds ready for collection on the podcast page here. Related information Testing for herbicide resistance with Dr Peter Boutsalis Testing for herbicide susceptibility pays off What herbicides still work