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How can I be certain that herbicide residues in the soil have fully degraded at planting?

In the course of a chemical fallow there are often several applications of herbicide and some residues may still be present on or near the soil surface when it is time to plant the next crop. In particularly dry years, residues may even carryover from the crop prior to the fallow. NSW Department of Primary Industries soil scientist, Dr Mick Rose, says there has been concern in recent years about the effect these residues may have on soil microbial activity and on the establishment and growth of crops following the fallow, even after the plant back period. Dr Mick Rose, DPI NSW soils researcher, is developing tests and predictive models to support growers in their decisions about crop choice after using residual herbicides. (Photo: GRDC). “Glyphosate has been the most commonly used knockdown herbicide in northern fallows for several decades and more recently growers have been looking to use more diverse programs that include chemicals with residual activity on weeds,” he says. “The increased use of imazapic and diuron have been of most concern to growers when choosing the next crop, particularly after a low rainfall fallow period.” With investment from GRDC, Mick has been working on a project led by Dr Michael Widderick from the Department of Agriculture and Fisheries, Queensland to develop a soil test for imazapic and diuron residues that will indicate damaging residue levels and help growers to decide which crops would be safe to plant in a paddock. “We are determining the threshold levels of residues of these two herbicides at which crop damage is likely for six crops, both winter and summer growing, in a range of soil types,” he says. In earlier work he also looked at the level of glyphosate residue in soils around the country at planting time and the impact these residues have on soil biological processes. “We found that residues of glyphosate were commonly detected in the soil at planting but there was no indication that the herbicide was adversely affecting soil biological activity,” says Mick. “This suggests that the label recommendations are suitable and the proper application of glyphosate in Australia is not posing a threat to soil health.” “For growers to be able to keep using glyphosate they need to implement the WeedSmart Big 6 strategy, including using diverse chemistry in fallows,” he says. “Residual herbicides are a useful tool for growers but there are some gaps in our knowledge about how these herbicides break down in different soils and under different seasonal conditions.” Why not just follow the plant back recommendations on the label? In brief: The label provides the minimum plant back period provided certain environmental conditions are met. There is a possibility of crop injury even though plant back periods are observed. The details: Many factors affect the bioavailability of a herbicide in the soil. For example, even though a clay soil and a sandy soil might have similar residue levels, more herbicide will be available for uptake in the sandy soil. More rain will increase the rate of breakdown, but it is not known exactly how much rain will ensure the specific soil is ‘safe’ to plant into. Another important factor is that many things can contribute to a germination failure. In some situations, residual herbicide may be suspected as the culprit, but can be difficult to either rule it in or out with certainty when diagnosing the reason for a problem at planting. If herbicide residues in the plant tissue can be shown to be phytotoxic, then another, less susceptible crop could be sown into the paddock. Dr Annie Ruttledge, DAF Qld weeds researcher, inspecting chickpea plants growing in soils containing different levels of imazapic and diuron herbicide residue. What effects can herbicide residues have on emerging crops? In brief: The herbicide itself can inhibit germination and growth, or it can exacerbate other factors, such as root disease. The details: At different levels of bioavailability, herbicide residues will have different effects on crop plants. If the herbicide is readily available to the plant, then susceptible crops will take it up from the soil and it can have phytotoxic effects ranging from suppressed vigour to yellowing and potentially plant death. Testing the plant tissue of a struggling crop can show if the leaves contain sufficient herbicide to have caused the observed symptoms. Some herbicide residues in soil can also ‘prune’ plant roots, particularly the fine roots that help access moisture and nutrients. Obviously, if the young plants are struggling to access resources then they will be less vigorous and possibly die. Damaged roots are also more susceptible to water stress, disease and poor nodulation in legumes, making it difficult to determine the initial cause of the problem in the field. If herbicide residues are shown to be the problem then a more tolerant crop can be sown, speeding up the breakdown of the residue and there will be more rainfall events before the next cropping season comes around. Seedling emergence and establishment is being measured for six crops (winter and summer) in the presence of different levels of herbicide. What pre-planting soil tests are being developed to give growers confidence to plant? In brief: The current project is establishing phytotoxicity thresholds for six summer and winter crops in a range of soil types, for two herbicides – imazapic and diuron. The details: By mid-2021 the aim is to have established the thresholds so that soil could be tested pre-plant to determine what crops would be safe to plant. This will give growers confidence to use these herbicides in a diverse strategy to manage weeds like feathertop Rhodes grass in the fallow, while avoiding germination or establishment failures in the following crop. Spray records play an important role in the management of these herbicides and mistakes can easily be made if the spray history for the past several years is not taken into account. In time, growers and their agronomists will gain a better understanding of how these herbicide residues behave in the soils on a particular property and will be able to make herbicide application and crop rotation decisions with more confidence. In another project with the Soil CRC, Mick is developing a predictive model for herbicide breakdown for a wider range of herbicides used in southern and western cropping systems. Until these tests and models become available, the use of an in-field or pot bioassay with a susceptible crop can be helpful in determining potential plant back issues.   Related resources Herbicide residues in soil – the scale and significance (GRDC Update paper) Herbicide residues in soil (GRDC Podcast)
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Case Study

Andrew Kenny, Badgingarra WA

Andrew and Gina Kenny farm at Badgingarra, in WA’s west midlands using an integrated program of crop rotation, mouldboard ploughing, grazing and chaff lining to keep their weed numbers very low. Andrew’s parents, Mike and Sara, arrived in the Badgingarra district to farm in 1959 and started clearing the land for cropping, at about the same time cropping land was also being developed around Esperance. Badgingarra farmer, Andrew Kenny has used TT, and more recently RR, canola to take advantage of different chemistry and weed control tactics. “There is a fault line that runs through the property with distinct soil types on either side,” says Andrew. “On one side of the line is our best cropping soil – clay through to pea gravel; on the other side is white sand with very limited water holding capacity, which we use mainly for grazing.”   Grazing to maximise productivity About 60 per cent of the 4150 ha property is used for continuous cropping and the rest for grazing sheep. The Kennys grow some hay for their own use and the sheep also graze the crops – mainly barley, and sometimes wheat and canola – from mid-June to mid-August. For over ten years the Kennys have run 5500 ewes in two flocks – a 4000-ewe self-replacing merino flock and 1500 Prime SAMM ewes mated to Poll Dorset terminal sires. Producing both wool and meat, the sheep are an important component in the business. SAMM are a dual-purpose sheep that was later further developed to produce a heavy slaughter lamb at a young age, as well as good quality wool. “We grow mainly Bass and Planet barley, which we will graze two or three times with 2500 hoggets before allowing it to finish for grain,” he says. “These varieties both tiller well and respond quickly after grazing to the first node stage.” Sheep utilise 40 per cent of the farm where the sandy soils do not retain sufficient moisture for cropping. The Kennys retain lupin seed, make hay, graze crops, chaff lines and stubbles and use the sheep to provide a double knock effect. Low weed numbers allows dry sowing Once the season breaks, the Badgingarra area can generally rely on good rainfall through the growing season. In 2018 there was a late break, resulting in Andrew taking a risk and sowing 75 per cent of their crop dry. That year he saw the benefits of earlier sowing and is confident that their weed numbers are now low enough to make dry sowing a safe practice. “On the heavier soils we grow canola, wheat and barley. Sandier soils that are lower in the landscape have better nutrient levels than those at the top of the landscape, and are suitable for cropping lupin, wheat and barley.” Barley has been a consistently strong performer in recent years so the area has increased. Lupins provide a good break from cereals and provide a high protein feed that is easy to store on farm and kept primarily as a drought reserve. The Kennys introduced canola to their cropping program in the 1990s and have used TT canola, swathing and spraying under the swather with glyphosate as key tools in their weed control program. They also crop top Barlock lupins to stop seed set. Andrew rotates herbicide modes of action through the crop cycle, particularly with the pre-emergent chemistry – using propyzamide in lupin, trifluralin in canola, Sakura in wheat and trifluralin + metribuzin in barley. He also targets weeds ahead of seeding with a double knock of glyphosate then paraquat, or uses Spray.Seed®(paraquat/diquat) on its own. In weedy paddocks Andrew avoids growing two barley crops in a row, choosing instead to switch to canola or lupins to utilise other herbicide MOA, but in paddocks with very low weed numbers he will occasionally grow barley on barley to boost profitability. With few in-crop options for ryegrass control, Andrew relies on having clean paddocks at seeding and robust pre-emergents. To ensure the crops get off to a good start, Andrew buys in hybrid canola seed and uses a mobile contract seed cleaner to clean farm-retained cereal and lupin seed. He has increased crop competition using a paired row boot on a 30 cm spaced tyne bar to give an effective row spacing of 7.5 cm. “The tynes are custom built and we use them for sowing all our crops,” he says. “They probably work best in the cereals, but we don’t have any problems in the other crops either. The aim is to do everything we can to increase crop germination, which gives us more crop and less weeds for the same amount of effort.”   Burying glyphosate resistance Andrew says annual ryegrass and wild radish continue to be their most challenging weeds and he has recently added RR Truflex canola hybrid to the rotation to give more options to use glyphosate. “I am very conscious of the risk of accelerating glyphosate resistance and so we also use mouldboard ploughing to bury glyphosate resistant weed seeds and improve the wettability of the sandy soils,” he says. “Mouldboard ploughing has fixed non-wetting issues wherever we have used it and this improves crop germination, but on the very sandy soil fixing the non-wetting is not enough to sustain cropping, so these poorer soils remain under pasture.” The benefits of mouldboard ploughing for weed control varies according to soil type. Andrew has seen it most effective on their sandy soils but found it difficult to achieve full inversion on the gravel country.   Chaff lining suits sheep Ten years ago Andrew began narrow windrow burning for harvest weed seed control, mainly in cereals and only in weedy paddocks. They had good results in weedy paddocks but after eight years Andrew was looking for an alternative that would have less impact on nutrients and require less labour. “We graze the stubbles over summer and the sheep would make tracks through the narrow windrows, which increased the number of places the windrows needed to be lit,” he says. “In 2017 we decided to give chaff lining a go.” Although the farm is not set up for controlled traffic, Andrew does run the harvester on the same lines each year, allowing him to place the weed seed in the same place each season. With the chaff lining chute as a semi-permanent modification to the harvester, Andrew is now able to implement HWSC in all crops and all paddocks. With the chaff lining chute as a semi-permanent modification to the harvester, Andrew is now able to implement HWSC in all crops and all paddocks – he can just forget that it’s there! “The chute, baffle and spreader chopper were fabricated and fitted for around $6000,” he says. In addition to concentrating the weed seed, chaff lining also concentrates any crop seed losses out the back of the harvester. This means the sheep can make use of any lost grain and Andrew expects the productivity gains from chaff lining would be similar to that measured for chaff dumps. “In 2018 we had a high level of weed germination in the chaff lines but we did not treat them differently to the rest of the paddock,” says Andrew. “The chaff chute left clumps in the paddock and I thought this might lead to seeding blockages, but in reality, the tyne seeder easily worked through the fine chaff material.” Andrew expects there would be some rotting of the chaff and weed seeds in years with wetter summers, but this has not yet been put to the test. What is evident though is the impact of higher soil moisture retention under the chaff lines. Sheep graze the stubbles and do a good job of stopping seed set on any green ryegrass that escaped capture at harvest. The sheep also reduce the overall stubble load and trample the chaff lines, making sowing easier.   Other resources Podcast – Mouldboarding + Chafflining + Grazing
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Case Study

Mat Freeman, Walkaway WA

Mat Freeman farms an aggregation of cropping properties at Mullewa and Walkaway in the Geraldton Port Zone of WA. Across the aggregation he has been systematically mouldboard ploughing since 2011 to tackle the non-wetting sands, and deep ripping has been practiced for around 30 years to alleviate compaction. While fixing the constraints associated with non-wetting sands is the primary reason for mouldboard ploughing, there is also a weed control benefit. Mat Freeman, Walkaway WA has used mouldboard ploughing to fix non-wetting sands and bury weed seeds. “Having effectively buried the weed seed bank with the mouldboard ploughing, the plan is to leave the subsoil undisturbed for as long as possible,” he says. “Hard-seeded weeds such as wild radish can remain viable in the soil for several years and can germinate if they are brought back up to near the soil surface.” Inverting the profile buries weed seed and brings some clay up from depth. Annual ryegrass and wild radish are the main weed species on the farm and Mat is making the most of the re-set value of mouldboard ploughing to keep weed numbers low going forward. Effective amelioration operation To achieve full inversion of the soil profile, the soil needs to be moist. The amelioration program also involves the removal of obstacles, applying limesand and then ploughing to a depth of about 35 cm. This is usually done after a lupin crop where there is the least amount of crop residue on the soil surface. The following year Mat spreads more limesand to treat the acidic subsoil that is brought to the surface. “Starting with a pH of around 5 on the surface and 4 in the subsoil, we are aiming for a pH around 5.5 on the surface and 5 at depth,” he says. “To achieve this requires about 4 t/ha limesand applied over the two years to treat both the topsoil and subsoil.” “Mouldboard ploughing needs to be done well, in wet soil and with not too much crop residue on surface,” he says. “We are close to completing the ploughing program across the whole farm and expect a long-term productivity benefit from the liming and mouldboard ploughing operation as a result of improved pH.” After using contractors for the first few years Mat now has his own mouldboard plough, and has committed to a program of ploughing 500 ha each year ever since 2011, along with regular deep ripping. When he first started deep ripping, Mat used a ripper that worked to a depth of about 35 cm but he now has a ripper that works to a depth of around 70 cm. To avoid bringing the weed seed back near the surface he uses straight, rather than C-shaped, shanks to shatter the compaction at depth without bringing weeds or clay to the surface. Harvest weed seed control decisions “The weed program here is about attacking them from all angles,” says Mat. “We do what we can to avoid letting weeds set seed. We have been running a Seed Terminator impact mill for a couple of harvests, having previously used narrow windrow burning for harvest weed seed control.” Mat has replaced narrow windrow burning with an impact mill for harvest weed seed control. Although narrow windrow burning worked well, Mat found there was a big risk of burning everything after a big cereal crop followed by lupins or canola, and it was hard to get the right weather conditions for burning. He was also concerned about the cost and long-term impact of lost nutrients. The farm is full CTF for harvest so Mat considered chaff lining as a possibility using RTK to ensure the chaff lines went on top of each other to then be burnt. With the soils being generally low in moisture Mat thought it was unlikely that the chaff would rot and was concerned that he might ‘have the chaff lines forever’. He also considered a chaff deck but decided it was not the best option for the farm and chose instead to invest in impact mill technology. Crop-topping in lupins has been part of Mat’s weed control program for a long time and he sees value in continuing with this tactic even though he now has the impact mill on the header. Rotation weed control tools “There is often 20 per cent of the farm sown to lupins and crop-topping is a good way to control any lodged or fallen grass weeds,” he says. “The outside laps in each paddock often have more weeds because it is harder to plough and the weed seeds are not always buried as well as they are in the main paddock area. Crop-topping is an effective way to help minimise weed seed set in these areas, in addition to the destruction of the weed seeds that go through the impact mill.” Crop topping in lupins is particularly useful for stopping seed set in lodged ryegrass that might not be picked up by the harvester. In canola Mat has previously used swathing and spraying under the cutter bar but is finding that direct heading works just as well. Crop rotation varies slightly on different farm units but generally follows a wheat, lupin, wheat, canola sequence. Some of the very light and fragile sands have not previously been suitable for canola but Mat has been able to introduce canola on these soils following liming and mouldboard ploughing. Pre-emergent herbicides are used for all crops – except straight after ploughing where the low organic matter levels can lead to more severe crop damage. After mouldboard ploughing and liming Mat follows a crop rotation of wheat, lupins, wheat, canola. He is planning to reduce the row spacing from 12 inch to 10 inch with his next planter to increase crop competition. Mat uses a tyned seeder with 12 inch row spacing but plans to change to a 10 inch row spacing with the next seeder to go the next step in crop competition for weed control. Cereals are sown on the CTF lines but Mat prefers to sow canola and lupins at 30 degrees to achieve better establishment in these sandy soils. This angle gives him the option to change direction back and forth each year and is not as rough as sowing on a 45 degree angle. Factors other than crop competition tend to influence variety choice but Mat looks to maximise crop competition through improved establishment, better soil fertility, better access to moisture and is looking to narrow the row spacing in the future.   Deep ripping for yield In addition to the mouldboard ploughing to ameliorate non-wetting, Mat also uses deep ripping to improve crop production. Deep ripping is done every second year after lupin and canola crops and has made marginal soils profitable, which has led to a significant increase in overall farm profitability. Deep ripping trials in 2015 confirmed that there were significant benefits in addressing soil compaction and improving water penetration into the profile, particularly in wheat where ripping to a depth of 600 mm generated a yield benefit of almost 1 t/ha.   * Grain price wheat = $270/t and cost shallow ripping = $45/ha and deeper ripping = $75/ha. At Walkaway deeper ripping and topsoil slotting (inclusion plates) was the highest yielding treatment. Visual observations showed more plant roots deeper in the slots than un-ripped and NDVI measurements indicated a higher biomass in the deeper ripping treatments during the season. Source: Deeper deep ripping and water use efficiency, GRDC RCSN Geraldton GER9, by Craig Topham, Agrarian Management and Bindi Isbister, Precision Agriculture “Deep ripping has really boosted yield and we find the crops persist better between rain events and finish better at the end of the season. The crop develops a deeper root system that can access more water at depth and the result is better yield and grain quality,” he says. Although the mouldboard ploughing effect persists for several years, the sandy soils quickly settle and develop a hardpan at depth, even without machinery traffic. Mat aims to rip every second year if there is sufficient soil moisture in autumn, preceding sowing, taking care not to bring weed seeds to the surface. The CTF system is based on 12.2 m centres for the sprayer, planter and harvester and was installed in each paddock after the initial mouldboard ploughing to preserve the benefit of this operation. Using this soil amelioration program, Mat is now bringing land into crop production that was previously only used for grazing.
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Article

Maximising the weed control value of my crop rotation

with Kevin Morthorpe, Trait & Seed Technology Stewardship Manager, Pioneer Seeds A diverse crop rotation is the twine that holds a good farming system together and underpins an effective weed management program.   Kevin Morthorpe, Pioneer Seeds’ Trait & Seed Technology Stewardship Manager says herbicide tolerance traits in crop hybrids can be used to maximise competition against weeds and increase the herbicide options available to growers while optimising yield and profitability of the crop sequence in rotations. Kevin Morthorpe (left) – Pioneer Seeds’ Trait & Seed Technology Stewardship Manager, with Dr Ray Cowley – Canola Research Scientist, Corteva Agriscience and Pioneer Seeds’ Rob Wilson – Strategic Customer & Market Development Manager and Clint Rogers – Western Regional Sales Manager & Canola Product Lead at a canola research trial near Jindera in southern NSW. Plant breeders continue to introduce herbicide tolerance traits in a number of crops in Australia, including corn, canola, pulses, cereals, grain sorghum, summer forages and cotton. “For example, in canola there are several herbicide tolerance traits and they are primarily available in hybrids,” he says. “This means growers get both improved crop performance due to hybrid vigour and more flexibility in herbicide use patterns.” The increased vigour of canola hybrids also generates greater biomass production and early canopy closure that suppresses growth and seed set of weeds that germinate in-crop, complementing the use of pre-emergent herbicides. “Hybrids super-charge crop competition through a strong root system and vigorous growth,” Kevin says. “From an economic angle, hybrids optimise yield in both high input and tough environments. In fact, we see more growers selecting hybrids when producing canola in tough conditions.” Since the release of the first herbicide tolerant canola in 1991, the popularity of herbicide tolerance has seen a 98 per cent adoption of canola varieties with tolerance to imidazolinone (Clearfield), triazine (TT) or glyphosate (RR). In the last 15 years, the area sown to hybrid canola has risen to an impressive 47 per cent in Australia. With glyphosate tolerant canola hybrids entering South Australia in 2021 and new hybrid releases, the hybrid percentage will increase further over coming years. With glyphosate tolerant canola hybrids entering South Australia in 2021 and new hybrid releases, the hybrid percentage will increase further over coming years. Kevin says that Pioneer Seeds have seen increasing demand for Clearfield canola in recent years following a dip in popularity. Through strategic application of herbicide tolerant traits in diverse crop rotations it seems that farmers are overcoming the resistance problems that were prevalent with the Clearfield technology and can now re-introduce these varieties and take advantage of the weed control benefits and high yields they offer, and manage herbicide residues in the soil. “A diverse rotation of crops and pastures is one of the WeedSmart Big 6 tactics, which Pioneer Seeds endorses wholeheartedly to protect the longevity and effectiveness of herbicide tolerance traits,” he says. “Through an effective crop rotation you can tick off all the herbicide and non-herbicide tactics needed to drive down weed numbers.” How do I make the most of a hybrid crop? In brief: Employ best practice agronomy. The details: Grain hybrids are vigorous plants that produce increased biomass and grain yield. To do this, they must be supported with adequate crop nutrition. When properly fed, hybrids will provide increased crop competition and achieve greater water use efficiency compared to their conventional counterparts. Growing a hybrid crop with herbicide tolerance traits does not equate to a full weed control program. These crops must be used within the WeedSmart Big 6 framework, within a diverse crop rotation and using herbicide tactics such as double knocking alongside cultural practices such as harvest weed seed control and crop competition to reduce seed set. They also combine well with pre-emergent herbicides to achieve excellent early weed control and suppress seed set in any late germinating weeds. Can I use hybrid crops with herbicide tolerance to fix a weed blow-out? In brief: No. This technology is not suitable for salvage operations. The details: When Roundup Ready canola varieties were first released there was an expectation that these traits could be used to reverse a weed infestation. This proved not to be the case. Hybrid crops are best used in low weed density situations where they can effectively drive down the weed seedbank. They should be grown in rotations that include an effective double-break, brown manure crop or a pasture phase. Having hybrid crop options for both summer and winter growing seasons increases the opportunities to tackle weeds throughout the year or to use different fallow herbicides while maintaining the ability to safely grow crops in the following season. New glyphosate tolerance traits (Truflex® and Optimum GLY®) and the stacking of herbicide tolerance traits of triazine tolerant and Clearfield® (TT+CL) have expanded the safe window for herbicide application in canola. Are residues in grain a concern when using stacked trait herbicide tolerant hybrids? In brief: Not if the stewardship program is followed. The details: New glyphosate tolerance traits (Truflex® and Optimum GLY®) and the stacking of herbicide tolerance traits of triazine tolerant and Clearfield® (TT+CL) have expanded the safe window for herbicide application in canola. This gives more options, more flexibility and more crop safety through the rotation. The stewardship program for the herbicide tolerant trait hybrids describe herbicide use patterns that growers must follow to confidently avoid the accumulation of herbicide residue in the grain and ensure that Australian maximum residue limits (MRLs) will not be exceeded. [Note that MRLs in other countries may be different to the Australian MRL. Find out more at Grain Trade Australia]  To avoid problems with crop safety within the rotation it is important to maintain accurate paddock records to avoid applying herbicide to the wrong crop variety and ensure susceptible crops are not sown into paddocks with herbicide residues in the soil. On the flip-side, herbicide tolerance in crops increases the options for crop selection within the rotation. Also, keep in mind the importance of controlling any volunteers from a herbicide tolerant crop in the summer fallow or following crop.
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Case Study

Andrew & Jocie Bate, Gindie Qld

The idea of small, lightweight machines replacing heavy tractors was prompted by Andrew’s determination to alleviate soil compaction on the 50 to 150 cm deep black cracking clays at Bendee. Ninety per cent of the area is sown to winter crops, which are grown primarily on soil moisture stored over the previous summer. Andrew and Jocie Bate, farmers first and foremost. A desire to alleviate compaction on their farm at Gindi, Central Queensland is the driving force behind their agtech venture into robotics. “Central Queensland winters are generally dry and we rely on moisture stored during summer storms and retained through zero tillage and stubble cover,” says Andrew. “Wheat provides the best stubble and chickpea is our most profitable crop so we just rotate between these two crops. About one year in five we will have the opportunity to plant a summer crop and we’ll double crop a small area to mungbeans or possibly forage sorghum or dryland cotton.” The Bates also run a cattle enterprise separate from their cropping, except for limited grazing of forage sorghum one in three years in just one paddock. They usually avoid having the cattle on the cropping paddocks due to the compaction and the proliferation of hard to control weeds that can occur. Moisture seeking improves crop reliability Deep, or moisture-seeking, planting has been a valuable tactic for the Bates, particularly in chickpea crops. In years where there is no summer crop in the ground they are able to plant as early as April, without waiting for planting rain. “We plant chickpea seed up to 25 cm deep into moist soil,” says Andrew. “Wheat is more difficult to establish this way but varieties like Mitch that have a strong coleoptile can be planted up to 13 cm deep into moisture. It is still hot here in April and the temperature can reduce coleoptile length, so planter setup is critical to get even emergence from depth. If we can achieve a good even stand, the crops have access to good moisture to sustain vigorous early growth.” Mitch is not a prime hard wheat variety so Andrew only grows it when soil moisture is limiting, knowing that it will push out of the ground even in tough conditions. Wheat stubble is essential for their farming system, so Andrew does everything necessary to ensure a good wheat crop is established. The deep sowing technique has proven almost bullet-proof over the last 20 years with wheat being reliably established in eight years out of ten, and they have had 100 per cent success with chickpeas. In most years Andrew grows their crops on stored moisture plus one inch of early rainfall and hopes for one follow-up rainfall event in-crop. In-crop weed control “We put a lot of emphasis on having clean fallows and achieving strong emergence of the crop,” says Andrew. “This is critical to maintaining our low weed numbers in our winter crops. All our crops are sown on 50 cm row spacing, except sorghum, which is sown in meter rows. In the recent dry summers, we have opted to grow forage sorghum rather than grain sorghum as a risk management strategy due to limited stored moisture in the profile.” Metsulfuron-methyl (e.g. Ally, Group B) and Tordon 242 (Group I) herbicides are providing reliable in-crop control of broadleaf weeds in wheat crops and has a useful level of soil residual activity that reduces the incidence of weeds germinating late in the season. Andrew says the dry conditions in Central Queensland winters results in minimal in-crop weeds, so there is little pressure to adopt harvest weed seed control tactics – their focus is on controlling summer fallow weeds. Wheat provides the essential stubble cover to maximise soil moisture conservation over summer to underpin the following, and most profitable, chickpea crop. In the chickpea and mungbean crops Andrew uses Group A chemistry, mainly haloxyfop (e.g. Verdict), to manage grass weeds. While he avoids residuals as much as possible to maintain flexibility in the rotation, he uses simazine (Group C) across all of his chickpea and isoxaflutole (Group H, e.g. Balance) on about a quarter of the chickpea area to provide long-term residual control of many problem grass and broadleaf weeds, including glyphosate tolerant feathertop Rhodes grass, sowthistle, and fleabane in crop and during the following summer fallow. “We use minimal in-crop herbicide and rotate between chemical groups though the crop rotation,” says Andrew. “But really we rely mainly on our fallow management to have clean paddocks to plant into.” Within the next few years all the weed control and planting at Bendee will be done by the robots. Andrew and Jocie will soon dispense with their self-propelled spray unit and just use their robots supplemented with blanket aircraft applications on less than 10 per cent of the farm area. The weediest paddocks on Bendee still only require herbicide to be applied to 20 per cent or less of the area. The robots can also do broadacre spraying but this will be more practical once the docking and refilling capability is implemented. “We generally have dry harvest conditions so most of the soil compaction is done by the sprayer in wet conditions,” says Andrew. “Right from the start this has been a driving force behind the development of the SwarmBot concept.” There are currently two SwarmBot-5 robots with WEEDit attachments working on Bendee. The two robots cover 24 ha/hr and can work 24 hours a day if conditions permit. With weather stations now onboard, the robots will drop into sleep mode when the weather conditions are outside acceptable parameters and then wake up and resume work when the conditions are good. Robots and the optical WEEDit sprayer have combined to reinvent the fallow weed management system at Bendee Farming. With more passes, there are more opportunities to spray weeds when they are small and easy to kill, and rotate chemical groups more often. Summer weeds are of greatest concern at ‘Bendee’, with sowthistle, fleabane, wild sunflower and feathertop Rhodes grass being the main targets for fallow weed management. These key species are a bigger problem in years with wet summers, where the weeds can get away during the fallow period and then haunt you in the following crop. Andrew is working on setting up the robots to wick-wipe weeds such as milk thistle growing above the canopy in chickpea and stop seed set. Robots and the optical WEEDit sprayer have combined to reinvent the fallow weed management system at Bendee Farming. While Andrew acknowledges that calendar spraying is generally a bad idea with regular spray rigs, it is a really valuable tactic when you have robots at your disposal. “We are doing more frequent passes with the robots applying knockdown herbicides and it works well because we are always spraying fresh, small weeds and minimising seed set, therefore reducing the risk of herbicide resistance,” he says. “We are also better able to control weeds that are considered hard to kill with glyphosate, such as wild sunflower, feathertop Rhodes, sowthistle and fleabane, which are all much more susceptible to glyphosate when they are very small.” “With robots, it’s not about how many acres you can spray in one day – it’s more about how many passes you can do in one season. More passes, gives you more opportunities to kill weeds when they are small and easy to kill and rotate chemical groups more often.” The benefit of the robot and optical sprayer combination is that both operate equally well at night as in the day, and so can be out spraying whenever the conditions are within the optimal range of temperature, wind speed and humidity. Andrew can also use a wider range of knockdown options such as glyphosate (Group M), paraquat (Group L), glufosinate-ammonium (Group N), and proprietary mixes such as amitrole (Group Q) plus paraquat when spot spraying to reduce costs. “Running the robots weekly to hit weeds hard opens up untapped potential in existing herbicides because they are being spot sprayed on small weeds only,” he says. “This avoids the need for residuals in fallow and there’s even the option to add spot cultivation if required.” “With robots you can spot spray a paddock that an agronomist would say was not worth spraying. Having a low weed seed bank means there is less pressure to go spraying straight after rain because there will be fewer weeds germinating.” With 4000 ha of summer fallow to keep clean Andrew is also re-evaluating their double-knock strategies using the robots. He is finding that the proprietary mix Alliance (Group Q + L) is a good double knock for glyphosate and he often puts two compatible modes of action in the same tank mix. “The WEEDit makes double-knocking much more practical, and using the robots means the workforce and family have less exposure to chemical,” says Andrew. “We can afford to double-knock more often.” Where weedy patches have established Andrew employs patch management strategies to prevent seed set. Intensive herbicide treatments or use of the robotic cultivator are now options at Bendee, particularly if the weed escapes are large plants. “Ideally we are working toward the development of microwave technology for the robots rather than targeted tillage,” says Andrew. “Microwave weeding is only practical on a robotic platform and when applied using weed detection there is a big reduction in the energy required. For us, the key advantage is the zero soil disturbance – a lot of weeds thrive in a disturbed or cultivated environment even if the disturbed area is small.” Andrew and Jocie see microwave technology as a good non-herbicide option that is compatible with robots and no-till farming systems. This prototype is proof of concept. Along fencelines and paddock edges Andrew has reduced his use of 2,4-D in the last few years due to the impact 2,4-D has on glyphosate efficacy on key species such as sowthistle and feathertop Rhodes grass. Instead he is now doing more passes with broadleaf herbicides on borders and hand-spraying feathertop Rhodes grass. “Buffel grass provides good competition for weeds along fences,” he says. “It is very important to just use broadleaf selectives and preserve the buffel, otherwise you end up with all sorts of weeds.” Robotic planting The Bates have built a planter that the SwarmBot can tow and in time they expect to have the robots completing the whole planting operation. Previously the SP sprayer was used to apply the blanket spray in front of the tractor with the planter but now the two robots can follow each other, one applying the blanket spray and one towing the planter, with both operating at 10 km/hr. The controlled traffic system at Bendee is based on a 12 m header front, spraying band of 12 m and the 6 m robot planter will make extra wheel tracks but apply far less weight to the paddock than the conventional planter that has wheels every 4 m, with each wheel applying more weight than a whole robot. SwarmBot planter set up for planting cotton. Other resources: SwarmFarm: Target small weeds year round Robotics opens up more non-herbicide options
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Article

Harvest weed seed control in a nutshell

*Note: In Australia we call the whole machine a harvester, not just the cutting front. At harvest time many weeds that have grown in the crop still have seed held in the seed head. These seeds enter the harvester along with the grain and most exit the harvester and are spread across the paddock in the chaff and straw. Collecting these weed seeds at harvest and either destroying them or depositing them in a known location where they can be monitored and controlled later, is an excellent way to stop weeds in their tracks. Brome grass is the most costly weed for Mallee farmers to manage, even though herbicide resistance in brome grass is currently low in the region. If you are considering adding harvest weed seed control (HWSC) to your weed control program there are excellent resources on the WeedSmart website to help guide you through the initial decisions and the implementation of this important weed control tool. Key messages: Decide on which system fits your farm best. Get maximum weed seed into the header. Know how to manage the collected weed seed. Which system is best? HWSC is being rapidly adopted in Australia and other countries around the world. There are six systems currently being used on Australian farms and they have all been developed by farmers. Research has demonstrated that all are very effective weed control tactics, achieving over 80 per cent control and for some nearly 100 per cent. There are six systems currently used to collect and manage weed seed at harvest: chaff carts chaff lining chaff decks (chaff tramlining) impact mills Bale Direct narrow windrow burning While they are all effective, they vary considerably in capital and ownership cost, nutrient removal costs, operational costs and labour costs. Some HWSC tactics involve the purchase of substantial machinery – such as an impact mill, chaff cart or chaff deck – but the operational and labour costs might be lower than methods such as narrow windrow burning, which involves low set-up costs but higher nutrient losses and labour costs associated with burning. Invariably narrow windrow burning is the most expensive option in the long-run due to the high nutrient removal cost. To calculate the cost of each method for your farm you can use a calculator developed by AHRI’s Peter Newman. https://www.weedsmart.org.au/calculating-the-cost-of-hwsc-for-your-farm/ The HWSC tools all involve some modification to the harvester. The simplest modification is for chaff lining and narrow windrow burning, where a simple chute is attached to the rear of the harvester to direct the residue into a band on the ground, running the same direction as the harvester has travelled. These chutes are often constructed and fitted on-farm. All the other systems are commercial modifications that are fitted to the harvester – chaff decks and impact mills – or trail behind the harvester – chaff cart and Bale Direct. WeedSmart resources: Videos from the HWSC course outline the science and practice of HWSC https://www.weedsmart.org.au/resources/hwsc/ Calculating the cost of HWSC https://www.weedsmart.org.au/calculating-the-cost-of-hwsc-for-your-farm/ Stepping into chaff lining https://www.weedsmart.org.au/stepping-into-chaff-lining/ Using your harvester to destroy weed seeds https://www.weedsmart.org.au/using-your-harvester-to-destroy-weed-seeds/ Get the weed seeds into the header Harvest weed seed control only works on weed seed that enters the header. Getting the weed seed into the header relies on the seed being held in the seed head at the time of harvest. The seed head must also be at harvestable height. Consider the weed spectrum and the likelihood of seed capture. Even if some seed has shed, chances are there will be other seed heads that have not yet shed and even this will assist with reducing the amount of seed entering the seed bank. There are four chaff-only systems and two all-residue systems. The chaff-only systems – chaff carts, chaff lining, chaff decks and impact mills – require the harvester to be set up to separate chaff and straw, and to keep the weed seed in the chaff stream. This may require modifications to the harvester rotor and sieves and the installation of a baffle to keep the weed seed in the chaff stream. If you choose the Bale Direct system or narrow windrow burning, all the straw and chaff ends up in the same place, so no other modification to the harvester is needed. WeedSmart resources: Harvester setup for HWSC https://www.weedsmart.org.au/webinars/harvester-set-up-for-harvest-weed-seed-control-hwsc-for-all-header-colours/ Getting weed seed into the chaff stream https://www.weedsmart.org.au/setting-up-harvesters-to-capture-weed-seed-in-the-chaff/ Using HWSC in different weed spectrums https://www.weedsmart.org.au/is-harvest-weed-seed-control-a-real-option-for-managing-northern-region-weeds/ Manage the weed seed after harvest If you choose an impact mill as your HWSC tool then the tactic is completed in one pass at harvest, with nothing extra to do. All the residue is spread in the field and the weed seeds are rendered unviable. All the other HWSC tools involve some action after harvest to remove or destroy the weed seed collected at harvest. Chaff decks deposit the weed seed-laden chaff in one or both harvester tramlines or wheeltracks. Some growers find that the chaff rots and the weed seeds die, but in other environments growers find that it is necessary to control weeds that germinate in the tramlines using herbicide or non-herbicide tactics applied just to the tramlines. Chaff carts can be emptied as they fill in the paddock or emptied at a central point. Many growers use chaff piles as a high nutrient value stockfeed, others burn the piles and others leave them unburned in the paddock and sow through them the following season. Chaff lines are usually left unmanaged with the expectation that the following crop will provide adequate competition to the weeds to minimise weed growth and seed production. The Bale Direct system results in large bales of crop residue that can be sold into suitable markets. Distance to market is usually an important factor in the success of this system for HWSC. Narrow windrow burning uses fire to destroy the weed seed in the Autumn following harvest. There are significant labour costs and safety risks to consider along with the loss nutrients and ground cover. Key resources to learn more: Diversity Era online course – Harvest weed seed control 101 https://www.diversityera.com/courses/harvest-weed-seed-control-101 Kondinin Group Residue Management at Harvest – Weed Seed Options research report https://www.weedsmart.org.au/app/uploads/2018/06/RR_1802_weedsmart.pdf Kondinin Group Harvest Weed Seed Warriors research report https://www.weedsmart.org.au/app/uploads/2020/05/RR_February_2020_Weedsmart.WS_.2020.pdf Grower experiences: Chaff decks and chaff lining in a high rainfall zone https://www.weedsmart.org.au/case-studies/esperance-growers-using-chaff-decks-and-chaff-lining/ Keeping pressure on brome grass with HWSC https://www.weedsmart.org.au/case-studies/bruce-family-alford-sa/    
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Case Study

Beefwood Farms, Moree NSW

The combination allowed for more efficient and targeted use of herbicides through double knocking and more timely and frequent applications to treat weeds at their most susceptible growth phase.   Beefwood Farms manager, Glenn Coughran. With low weed density across the 11,000 ha operation Glenn is able to avoid the use of pre-emergent herbicides, which have limited crop rotation choices in the past, particularly in years where summer rainfall has been low. Glenn is keen to see ‘green-on-green’ optical weed detection become a reality and is working closely with AgriFac to have this technology integrated into their spraying equipment. Located between Goondiwindi and Moree on the western side of Newell Highway, Beefwood Farms is an aggregation of six neighbouring properties, all operated from the central workshop area. Gerrit and Pam Kurstjens, originally from Grubbenvorst, the Netherlands, purchased the aggregation in 2006 and began the transition from livestock to a controlled traffic continuous cropping operation using the latest technologies to achieve greater efficiencies. Beefwood Farms owner, Gerrit Kurstjens (left) with his daughter Marieke and MCA Ag agronomist Stuart Thorn. “Our cropping program has to respond to the weather, and to a lesser extent prices, but normally the sequence is wheat then barley then chickpea or left out for winter and into sorghum in summer,” says Glenn. “We are keen to try dryland cotton but unless we have conditions that result in a full profile of soil moisture it just isn’t a feasible option.” “Each year we fallow about 20 to 25 per cent of the farm in winter in preparation for planting the summer crop,” he says. “If the sorghum is off soon enough these paddocks are usually double cropped back to chickpea the next winter. This tactic gives us two consecutive winters to work on any winter grass weeds, particularly wild oats, using different chemistry.” But with a string of very dry years recently the opportunities to grow summer crops has been limited. They generally avoid using residual chemistry in summer due to concerns over the possibility of insufficient late summer rainfall to breakdown the chemical prior to planting the winter crop. “We have been caught using imazapic in a summer fallow and then we didn’t get the necessary 150 to 200 mm of rainfall needed to break down the residual,” he says. “This meant we had to grow Clearfield barley, which was a good option in the circumstances, but you are restricted to just a few varieties and we don’t want to be limited in our crop choices too often.” The CTF system is based on 3 m machinery wheeltrack centres, 12 m headers, 24 m planters, 48 m self-propelled boom sprayers and 24 m WEEDit optical sprayer. Beefwood operates two NDF disc planters for the winter cropping program – a double bar machine planting on 33 cm row spacing and a newer single bar machine where the closest spacing they could achieve is 37.7 cm. The sorghum crops are sown on 1.5 m row spacing. “We can’t sow the cereals any closer to increase crop competition but we have seen a response to increased seeding rates,” says Glenn. “Also, the whole farm is planted east-west to maximise shading in the inter-row. This helps a little in the sorghum too where increased seeding rates would not create any competition outside the row.” In drier years Glenn will often increase the area sown to barley as it has a greater competitive ability and tends to perform better under marginal soil moisture conditions than wheat. Beefwood Farms’ consulting agronomist is Stuart Thorn, a director of MCA Ag, Goondiwindi. Stuart oversees the herbicide program for the operation, including recommendations for herbicide mixes and rotation of herbicide modes of action. “Bringing in new country into our cropping program usually involves tackling large weed populations such as a recent acquisition where barnyard grass was a big problem and we used residuals to help regain control,” says Glenn. “Residuals have also helped with feathertop Rhodes grass, and then we backed away once the problem was under control, which usually only takes a few years.” In the fallow Glenn uses a double knock of glyphosate applied as a blanket spray and then followed up with paraquat to treat any survivors using the optical sprayer. They also use glyphosate at robust rates through the spot sprayer and no longer mix glyphosate and 2,4-D. To stop weed seed set in-crop Glenn will often implement a late spray of a Group Z grass selective herbicide, flamprop-m-methyl, to patch out weedy areas of wild oats in wheat. Chickpeas are always desiccated to prepare the crop for harvest and this can have some weed control benefit going into the fallow. Picloram applied in cereals to control broadleaf weeds such as sowthistle also provides a residual effect to reduce fleabane germination in July/August. “Maintaining stubble and ground cover is our number one priority so there is no cultivation for weed control or any other purpose,” says Glenn. “Our best chance to grow competitive crops is to have stored soil moisture.” At this stage Glenn has not implemented any harvest weed seed control measures at Beefwood but he is keeping an eye on developments. Due to the loss of stubble involved, they will not adopt narrow windrow burning but other tactics that maintain and spread stubble cover would be considered if the need arose. Automation for spot spraying works well – but is now on hold Having already seen the chemical savings and the weed control benefits of using optical spraying technologies for over 10 years, Gerrit and Glenn were looking for ways to extend the value of the technology to achieve even greater efficiency with chemical use, particularly in fallows. “Gerrit has contacts with the Dutch company, Precision Makers, who had developed software for autonomous lawn mowers, and in about six months they had made the necessary modifications and installed the software on a Fendt 936 Vario tractor that we had on the farm,” says Glenn. “We found the autonomous tractor paired with the optical sprayer was a perfect fit, allowing us to spray 24 hours a day if conditions are right and to spray on the weekends without adding to our labour costs.” After a few years they purchased a John Deere 8345 tractor, also fitted with Precision Maker equipment. Over the last 10 years the optical spray operations have applied herbicide to an average 2 to 8 per cent of the field area, using robust rates, but this is still far more economical than blanket sprays. The now-decommissioned automated tractor towing a WEEDit optical sprayer. “We know it works very well when weed density is low. Now we can use the autonomous tractor to spray more frequently than you would with a driver, we have started pushing the boundaries and using the optical sprayer in paddocks with weed density of 30 per cent, knowing that we can keep coming back,” says Glenn. “Even at a higher herbicide rate this is cheaper than a blanket spray operation. The more often we go back the less large weeds there are and we are spraying smaller weeds that are easier to kill.” In a recent spray job on 3500 ha of fallow the optical sprayer activated spray nozzles on just 0.7 per cent of the area, at a cost of 24c per ha for chemical, without a driver. “Using the autonomous tractor is not about reducing our labour force,” says Glenn. “The person who used to drive the tractor is still looking after the spray job. The other job that is perfect for the autonomous tractor is tram track renovation.” Every three years, usually following chickpeas when there is less crop residue, the tractor operates a TPOS flat track renovator along the 2 to 6 km long CTF wheeltracks – saving someone from a very boring job. Having proven the value of automation to the farming system at Beefwood Farms, they have been forced to put their work in this area on hold after John Deere bought out the automated machinery component of Precision Makers in 2019 and have decided to concentrate on automated mowers for the turf industry. They are currently not servicing the automation software that Beefwood Farms had installed in two tractors. “Unfortunately, until we find a suitable alternative, we have had to go back to fully conventional operations for spraying,” says Glenn. “It is hard to accept when we have seen the benefits of automation for these routine operations.” A few years ago, Beefwood Farms bought a 48 m AgriFac self-propelled sprayer to increase their spraying capacity for blanket sprays and fallow spot spraying. The AgriFac sprayer is twice as wide at the WEEDit boom and can travel at twice the speed of the autonomous tractor, so even though there is a driver they are covering three to four times the area. Green-on-green spraying Beefwood Farms is also on the cutting edge of the latest innovation in weed detection and herbicide application, working with AgriFac and Bilberry in the testing of green-on-green spraying. Since purchasing the AgriFac SP sprayer they have been keenly observing the advances in the artificial intelligence, or machine learning, and assisting with the field testing. Beefwood Farms is working closely with Agrifac and Bilberry to bring green-on-green weed detection and spraying to reality. To work in-crop the software on the sprayer needs to interpret the images from the camera, distinguish a weed from surrounding crop plants and then identify the species and size of weed. Within moments the sprayer needs to respond and deliver the correct herbicide at the right rate to the identified weed. “The expectation is that the sprayer will be able to treat a ‘site’ of 30 cm square with exactly the right product at the right rate,” says Glenn. “This is really exciting technology and once it is fully developed we see no reason why it couldn’t be used autonomously.”
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Case Study

Kwinana East HWSC growers, WA

Having said that, growers in low rainfall areas have successfully implemented HWSC, even in cereal crops yielding 0.5 to 1.5 t/ha. In 2018, GRDC invested in the collection of ten case studies with growers from the Kwinana East port zone around Merredin, WA to discover what modifications and tactics they were using to successfully collect and destroy weed seeds at harvest in this low to mid rainfall zone. The HWSC methods these growers use are narrow windrow burning, chaff lining, chaff decks, chaff carts and impact mills. Former Planfarm agronomist, Dani Whyte, visited the growers who are all running very efficient, low cost operations to generate profits in this environment and seeing the benefits of HWSC in their farming systems. Dani Whye, former Planfarm agronomist, visited ten growers from the Kwinana East port zone around Merridin, WA to discover what modifications and tactics they were using to successfully collect and destroy weed seeds at harvest in this low to mid rainfall zone. “It is difficult to grow highly competitive crops in this region where the average rainfall range is 200 to 350 mm and the scale of operation often does not allow for high seeding rates and narrow row spacing,” she said. “This means that weeds such as ryegrass tend to have a prostrate growth habit and are generally not ‘held up’ by the crop at harvest. This results in a greater proportion of the weed seed being found closer to the ground where they can escape under the cutter bar, compared to what is typically seen in higher biomass crops.” Since having the weed seeds enter the header is the critical first step to successful harvest weed seed control the growers have focussed on reducing harvest height to 10 cm or less above ground level. Because the crop biomass is low this does not impact on harvest costs but it is all the more important to ensure the paddocks are free of rocks and other obstacles. “Along with low harvest height, many of these growers have also made minor modifications to the comb to maximise both grain and weed seed capture,” says Dani. “Sharp knives and lift kits have been shown to help gather the crop and weed seed heads onto the cutter bar in low biomass crops.” Glen Riethmuller from DPIRD, has recommended attaching coreflute to the finger tyne reel to enhance the harvesting of low yielding crops, and this may also benefit weed seed capture. The coreflute sits approximately 25 mm longer than the reel fingers and has a sweeping action to pull grain and weed heads into the header front and prevent them falling backwards off the knife. Farming a total area of around 7500 ha at Southern Cross, WA, brothers Clint and Wayne Della Bosca and their wives Jess and Dianne chose to add a chaff deck to their harvester for the 2016 harvest as part of their move into controlled traffic farming. Knowing where the weeds are has given them confidence to sow earlier and to use different herbicide options. It adds flexibility to the system. Having noticed that some weed seed heads were not entering the header front, even though he was harvesting as low as possible, Clint has fitted corflute to the reel and a narrow knife guard and extendable fingers to the header front to capture more weed seed and grain at harvest. Quick tips for harvest weed seed control in low biomass crops The most common tactics these ten grain growers used to maximise weed seed capture in low yielding or low biomass crops were to increase crop competition, make some simple modifications to the header front, cut the crop low, harvest weedy paddocks first and use their chosen form of HWSC in every paddock, every year. WeedSmart western region agronomist, Peter Newman says growers are using these tactics and seeing benefits in their weed control, but there is limited research done to validate many of these practices. “We do have strong evidence for some things though such as the impact of increasing crop competition any way you can, and cutting crops low to maximise weed seed capture,” he says. “The header front modifications are observed to work well and are generally relatively cheap for growers to trial on their machines and evaluate the benefits themselves.” 1. Crop competition Establish competitive crops by sowing early, increasing seeding rates and east-west sowing where possible. Choose competitive varieties, particularly for weedy paddocks. Reduce row spacing to ‘hold weeds up’ in the crop canopy – a move from 12” to 10” row spacing or adopting paired row sowing can increase yield, reduce weed seed set and aid harvest of both the crop and the weed seed. 2. Header front modifications Extended fingers and a narrow knife guard/ lift kit fitted to header front. Sharp knife. Narrow knife guard with plastic extension fingers to capture and hold heads on the front so they don’t fall forwards. Coreflute attached to the finger tyne reel to pull grain and weed heads into the header front and prevent them falling backwards off the knife. 3. Harvest time Choose a HWSC tactic that suits your farm. They all work well to reduce weed burden but there are differences in cost, additional work, nutrient concentration and stubble management. Number 1 tactic – harvest 10 to 15 cm off the ground. Paddocks must be clear of stumps and rocks. Harvest weedy paddocks first before weeds shed their seed or lodge. Clean down the harvester before shifting paddocks. Chaff decks (pictured), chaff carts, impact mills, chaff lining and narrow windrow burning are all being successfully implemented in the Kwinana East zone. Case study growers Cusack family, Narembeen (narrow windrow burning) Shadbolt family, Mukinbudin (narrow windrow burning) McGinnis family, Merredin (chaff line) Todd family, Dowerin (impact mill) Crane family, Kondinin (impact mill) Metcalf family, Dowerin (chaff cart) Dolton family, Bruce Rock (chaff cart) Turner family, Pingelly and East Corrigin (chaff cart) Kirby family, Beacon and Nyabing (chaff deck) Della Boscar family, Southern Cross (chaff deck) Download whole booklet Other resources Podcast – Farmers share their HWSC experiences with Planfarm agronomist, Dani Whyte AHRI Insight – Behind every successful HWSC approach is crop competition Podcast – Harvest tips, crop topping + trifluralin resistance Narrow row spacing: Is it worth going back? 
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Case Study

Stephen and Michelle Hatty, Matong NSW

The family now crops a total 2100 ha of land within an 11 km radius, on a very flat landscape with soils ranging from red loam to heavy red clay and self-mulching black clay. They adopted reduced tillage practices in the 1990s and now run a 12 m controlled traffic farming (CTF) system.   The Hatty family uses a double break crop sequence strategy of a pulse then canola, followed by wheat then barley to put firm downward pressure on the weed seed bank. The very wet season in 2016 resulted in unavoidable soil compaction and weed escapes, which prompted Stephen and Michelle to upgrade from a tyne seeder on 333 mm rows to an NDF disc seeder on 250 mm rows. The seeder has worked well from the first season onwards with dry sown crops establishing uniformly since 2017. “We had been considering the change for a while as disc seeders work well in heavy clay soils, conserve more moisture and result in much less soil disturbance,” says Stephen. “We had been finding that even though the soil structure is quite good, the tyne seeder tended to bring clods to the surface when the soil is dry at the start of the canola seeding program in April.” “It also gave us the opportunity to further increase crop competition with the narrower rows,” he says. “We also get better seedbed utilisation and can lift our planting rates to maximise yield.” Changing to a disc seeder gave the Hattys the opportunity to further increase crop competition with the narrower rows and lift their planting rates to maximise yield and optimise seedbed utilisation. The Hattys use a double break crop sequence strategy of a pulse then canola, followed by wheat then barley to put firm downward pressure on the weed seed bank. Stephen says the pulse phase of faba beans, lentils or field peas helps improve subsoil moisture and soil nitrogen for the following canola crop. Pulses offer different chemistry options for grass weeds and even brown manuring if weed pressure is high. “For example, trifluralin is normally out for cereals but can be used after a pulse crop like faba beans that doesn’t leave much cover on the paddock,” he says. “We also use water rates of 80 to 100 L/ha to maximise the effectiveness of pre-emergent herbicides in high stubble situations.” The Hattys are keen to host trials on their property where they are able to see first-hand the outcome of different agronomic options or crop performance. In 2017, they hosted NSW DPI trials looking at the competitive ability of Planet and La Trobe barley, with Planet being more prostrate in growth habit and La Trobe being very upright. In 2017, they hosted NSW DPI trials looking at the competitive ability of Planet and La Trobe barley, with Planet being more prostrate in growth habit and La Trobe being very upright. “We sow all our crops early in their optimal sowing windows and try to take advantage of more competitive varieties to suppress weed growth,” says Stephen. “In dry conditions barley is a great option to reduce weeds, produce significantly higher grain yield and return more straw than wheat ahead of sowing a pulse crop.” In 2015 the Hattys added harvest weed seed control to the program. They chose to fit an Emar chaff deck system to their Case 8230 header and have been confining weed seed to the 3 m tramlines ever since. Since adding an Emar chaff deck system to their Case 8230 header in 2015 the Hattys have slowed down the chaff deck conveyors and added a chopper to improve straw spreading. “We have slowed down the chaff deck conveyors and added a chopper to improve straw spreading,” says Stephen. “We had already been harvesting fairly low to suit the tyne seeder so there was no real change to the way we harvest. As time goes on we expect that less and less weed seed will be deposited each harvest resulting in fewer and fewer weeds growing on the tramlines.”
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Case Study

Day family, Lockhart NSW

Mark and Steven Day run Woodlea Ag Enterprises in conjunction with their father Max, with the backing and support of their wives and families in the decision making process. The continuous cropping operation at Lockhart, NSW is based on a zero till, 12 m controlled traffic system on 3 m wheeltracks and using an NDF disc seeder. Returning to the farm in the 2000s after completing their tertiary studies, Mark and Steven have developed a farming system that uses new technologies and capitalises on well-worn rotational farming concepts.   Mark Day, and his brother Steven, run a highly efficient cropping rotation on their family farm at Lockhart, NSW. In 2009 the Days noticed that weed pressure was building and they were concerned that the weed seed bank would soon be unmanageable in their canola-wheat-wheat rotation. “We took the advice of our agronomist and decided to introduce a legume brown manure phase,” said Mark. “Our first choice was field pea because they are the most competitive legume option and provide a good level of ground cover and biomass. In recent years we have also grown vetch, lupins and faba beans to avoid disease build-up in field peas.” Over the last 10 years the Days have settled into a stable double break rotation, which has been a key strategy to keep weed numbers low in their cropping operation, and they have also introduced chaff decks for the last three harvests for weed seed management. Key developments Pre-2009 – CTF, continuous cropping canola, wheat, wheat and variable rate technology (for lime and gypsum prescriptions and P replacement) 2009 – legume brown manure introduced in response to increasing weed pressure 2012 – NDF seeder and full stubble retention 2016 – chaff deck for HWSC across whole farm Grid sampling for pH and replacement phosphorus has led to variable rate lime, gypsum and P applications. Crop rotation “We start with the brown manure legume followed by TT canola, then a double cereal phase of wheat and barley,” he said. “This sequence allows for optimal use of herbicides within the stubble retention system and we can rotate a range of herbicides.” Double break – brown manure legume then TT canola. Double cereal – wheat then barley. “Herbicide rotation and double knocking to protect glyphosate is keeping a wide range of herbicides effective and we take advantage of the differences in stubble load to use each product in the most effective way,” he said. “For example, we apply Sakura when planting wheat following canola crop and the stubble load is not excessive, allowing the Sakura to work well.” The legume brown manure followed by canola gives Mark and Steven the opportunity to use a range of herbicide tactics, including rotating propyzamide, atrazine and clethodim, to drive down grass and broadleaf weed numbers. They also occasionally apply grass selective herbicide over the top before brown manuring if required. The manure crop also helps retain soil moisture and maintain a baseline of nitrogen in their system. Adding stubble retention also contributes to soil moisture and nutrient conservation, but the crop sequence is key to making the NDF disc seeding system work well. “Our rotation is set up so canola is established in a low residue situation after the brown manure, wheat is established into canola stubble and the brown manure pulses are sown into high crop residue situation after the cereals using a deeper disc setting,” said Mark. When it comes to managing weeds through the rotation, the legume is brown manured using a traditional glyphosate paraquat double knock following a roller to achieve better spray coverage of weeds low in the canopy. The double knock is also applied prior to seeding. Tillage is used on about five per cent of the cropped area each year in response to specific situations such as providing a triple knock of the brown manure crop, for restoration of wheeltracks and headlands and to incorporate lime or address nutrient stratification. Strategic cultivation also enables the effective use of trifluralin in the disc seeding system. Cultivation provides the third knock at the end of the legume crop whenever there is a dual purpose for the tillage (e.g. wheeltrack renovation or stubble management). In-crop strategies include increasing seeding rates in weedy or high pressure areas using variable rate technology, spraying under the cutter bar when windrowing canola and crop-topping feed barley at the end of the rotation. Harvest weed seed control – Chaff decks Even though the system was humming along well, the extreme wet conditions in 2016 led to significant weed escapes, prompting the Days to look into harvest weed seed control. Having seen the benefits of the chaff deck system, Mark and Steven bought one for their own harvester and worked with their contractor, Warwick and Di Holding, to have one fitted to the harvester that operates on their property. Chaff decks have proven their worth for harvest weed seed control. “At first we had to convince ourselves that the weeds really were coming off the sieves and we were amazed just how much is collected and deposited on the wheeltracks when the harvester is set up correctly,” said Mark. “The whole farm is now treated with the chaff deck for harvest weed seed control, every year. The weeds are confined to a manageable and defined area. Other benefits include the reduction in dust over summer and we can easily assess harvest losses.” There have also been a few downsides to the chaff deck system that need to be worked around, such as stubble lumps on wheeltracks and the potential for nutrient redistribution to the wheeltracks over time. “We have seen poor establishment in some situations and certainly black oats can evade all harvest weed seed control tactics as the seed has already shed by harvest time,” he said. “Windrowing barley may be a worthwhile method to address this problem.” The Days expect to move to an impact mill for HWSC in time.
Article
Case Study

Mark Branson, Stockport SA

Since 2017, precision agriculture enthusiast Mark Branson has been hunting herbicide resistant weeds using a DJI Phantom drone. Flying at a height of 75 to 90 m across a 46 ha paddock, the drone takes 500 images that are later ‘stitched together’ to give one image of the field. “It is as simple as ‘where you can see the rows, there’s no weeds’ and ‘where you can’t see defined rows, that’s a weedy patch’,” says Mark. “When you add an NRG filter you can clearly see the extra biomass that results from weed growth.” Mark (right) and Sam Branson use their drone to identify and map weedy areas in crop on their mixed farming operation at Stockport, SA. (Photo: Vanessa Binks) Once patches are mapped and ground-truthed to check the species present, Mark then decides on the most appropriate course of action. In the last three years he has cut five patches of about 10 ha each for hay using a cutter bar mounted on the SP sprayer. The main resistant weeds on the farm are annual ryegrass, wild oats and wild radish. Although it is easy to see the wild radish present in wheat crops the grasses are hard to see from the ground, and it is difficult to accurately map weedy patches. The idea of using a drone to scout for weeds was sparked in 2015 when Mark’s son Sam bought a drone with a GoPro camera attached to gather video footage. Mark could see the possible application in precision agriculture and in 2016 he bought DGI Phantom 4 to look down into crops. One of the first ‘jobs’ the drone did was to identify an area of poor urea application in a crop. “The real advantage in identifying the mistake in-crop was that we had the opportunity to take remedial action and fix the problem with an application of liquid nitrogen in the affected area,” says Mark. “Without the drone that mistake would have gone un-noticed and we would have suffered a yield loss in that portion of the paddock.” When it comes to hunting for resistant weeds, Mark first traces the boundary of the paddock in the drone software package and then, with a set flying height and number of images to collect, the drone takes off and takes the required set on images. The advantages of the drone imagery over satellite images include being able to collect and use images collected on cloudy days and having full control over the timing of the data collection. The drone is also better suited to the job than the tractor-mounted biomass sensors that can only collect data from a 40 m swathe at a time. For the drone image capture to be successful it is necessary to have stable light conditions. “It is fine to fly on both clear and cloudy days, provided the conditions don’t change for the duration of the 20 min flight time,” says Mark. “It is best to fly between 9.30 am and 4 pm to reduce the impact of shadows and I generally prefer cloudy days.” One of the few advantages of the tractor-mounted biomass sensors over the drone is the ability to collect data at night. Mark spent a few thousand dollars on his drone but as prices continue to drop, he says a suitable drone can be bought for $1500 or less. He uses a third-party provider, Drone Deploy, to process the images collected into the one seamless image for an annual cost of US990. “The Drone Deploy subscription is expensive but the quality of the image stitching is excellent and the turn-around is fast,” he says. “It only takes 3 or 4 hours for a set of images to be stitched and returned.” Using an NRG filter it is possible to clearly see the extra biomass that results from weed growth in-crop. Mark has three batteries for the drone, each having a flight time of 20 minutes, which means he can easily fly any of his paddocks in a day. He advises any new pilots to be conscious of no-fly zones and to comply with licencing requirements. “The drone has certainly proved its worth as a good tool for scouting and for identifying and mapping suspicious areas that need investigation and diagnosis,” he says. “I am also working to find an index that will reliably show frost damage.” Mark and his son Sam crop 1200 ha of wheat, barley, peas, beans, canola, lentils, oats. In November 2015 the catastrophic Pinery fire severely impacted the Branson’s property, destroying crops, machinery and livestock, and they were very fortunate that the fire leapt over their home, leaving it unscathed. Prior to the fire the Bransons ran a self-replacing merino flock of 1000 ewes, three-quarters of which were lost in the fire. They have now built back up to 850 ewes. Mark was a founding committee member of the Society of Precision Agriculture Australia (SPAA) in 2002 and completed a Nuffield Scholarship in 2005, looking into the economic and environmental impacts of precision agriculture and conservation farming in New Zealand, USA, Canada, UK and France. “I started marrying up wheeltrack widths in 2002, and then bought a tractor with an RTK steer kit in 2004,” says Mark. “The Nuffield Scholarship confirmed a lot of existing knowledge and understanding, and gave me new direction and confidence to apply precision agriculture to our farm operation. Since then we have used variable rate technology particularly for nutrient management – gypsum, lime, N and P – and seeding rate.” The Stockport area has suffered two very dry seasons, receiving just 3 per cent of their average growing season rainfall 2018, a less than 1 percentile year. Conditions were very similar in 2019. Big 6 in action on Branson Farms The Bransons run a winter cropping rotation and sheep are an important part of weed control program, with the pasture phase being key to driving down annual ryegrass numbers. They have implemented a wide range of tactics from the WeedSmart Big 6. 1. Rotate crops and pastures The Bransons run a winter cropping rotation and sheep are an important part of weed control program, with the pasture phase being key to driving down annual ryegrass numbers. The crop sequence Mark uses is pasture, canola, wheat, wheat, barley, grain legume, hard or durum wheat (high protein), wheat, [or canola if weeds are building], wheat, wheat, barley, grain legume and back to pasture. The pasture phase is a minimum of two years and preferably three years to ensure all the ryegrass has germinated before returning to cropping. Within the cropping phase Mark includes a cereal with resistance to cereal cyst nematode (CCN) and no longer uses imi chemistry or imi-tolerant crops due to resistance in ryegrass. TT canola is still a useful strategy for ryegrass control. The pasture or ley phase is based on cereals mixed with either medic (on alkaline soils) or sub-clover (on acidic soils). Mark’s father used the same system, based on soil colour, but now Mark has the two mixes in the seeder box ready for VR application according to the PA maps from pH surveys. Mark also uses the sheep to graze crop stubble at high density for a short time after harvest. The sheep benefit from the stubble and graze any weeds present. Although their hooves compact the surface of the soil the layer is easily broken up at seeding. 2. Mix and rotate herbicides Mark is very aware of herbicide resistance and the need to rotate between mode of action groups. He does not routinely conduct herbicide resistance testing but he is careful to observe any changes in herbicide efficacy. For example, he witnessed one wild oats plant escape Topik (Group A herbicide) and how rapidly this escalated to a patch of herbicide resistant weeds. He looks for ways to use a range of herbicide options across the cropping phase to control wild radish. Likewise, there are several pre-emergent herbicides used such as simazine in beans, triazine in canola and Sakura in cereals, keeping in mind that the triazine and Sakura need to be applied in seasons where there the likelihood of them being washed off the stubble and into the soil is high. 3. Crop competition Mark chooses competitive wheats, such as Saintly, and follow them with Scope barley, which is a vigourous variety that provides good early competition. Although he prioritises competitive attributes over extra yield he says that all the varieties are quite good for yield. The Bransons have been direct drilling since 2002 and currently use a tyned precision seeder that places the seed one inch apart in a parallelogram configuration. The tynes have individual depth control and presswheels. Mark currently sows crops in 10 inch rows but he would prefer 6 to 9 inch row spacing, which is not practical with his current tyne seeder. He will probably move to a disc seeder to reduce soil disturbance when he is ready to upgrade. The seeder allows inter-row sowing, which Mark says is the key to stubble management. Currently the rows are 10 inches apart but Mark would prefer 6 to 9 inch row spacing, which is not practical with his current seeder. He will probably move to a disc seeder to reduce soil disturbance when he is ready to upgrade. Mark uses VRT seeding and nitrogen application for canopy management to ensure enough moisture is available at the end of the season for the crops to finish strongly. 4. Stop seed set Mark uses both mechanical and herbicide tactics to stop escape weeds setting seed. In the pasture phase, Mark slashes and grazes to prevent seed set and pasture tops with paraquat. He uses crop topping in pulses and in triazine tolerant canola he sprays glyphosate under the cutter bar, then harvests the windrows and drops crop residue into a narrow windrow for burning. This tactic in canola is an excellent way to really drive down ryegrass numbers in a single year. Mark implements this in the first year out of pasture and also within the cropping phase to extend the length of the cropping phase out to 10 to 12 years. Prior to getting weed numbers down, the cropping phase was only 6 years. He finds that hay is a good way to deal with weedy patches. So far, he has successfully used hay making to deal with two patches of herbicide resistant weeds identified using the drone. He says wild oats soon becomes a long-term project if it gets out of hand so he’d much rather accept a short-term sacrifice. 5. Double knock If there is an early break to the season Mark usually implements the double knock pre-seeding. After harvest, the sheep can also provide the first knock on weeds, which are then sprayed out by 5-leaf stage. He doesn’t usually do a second spray for summer weeds but finds that the sheep do a good job of cleaning up any weeds that survive any herbicide treatment. 6. Harvest Weed Seed Control Mark has seen the benefits of narrow windrow burning in canola and plans to have an impact mill within the next five years. He hopes that having an impact mill on the harvester for all crops will take the pressure off some of the other practices currently used.
Article
Case Study

Esperance growers using chaff decks and chaff lining

Ten growers from the Esperance region of Western Australia who have adopted either chaff lining or chaff tramlining to help manage weeds have provided insights into their experience with these harvest weed seed control tactics. Each grower spoke to Planfarm Agronomist, Nick McKenna, who documented their experience as part of a GRDC investment into the practical adoption of HWSC in the area in 2018. Adrian Perks – Esperence grower using an EMAR chaff deck system for harvest weed seed control. Nick says the growers all felt that they needed to use HWSC tactics to stay ahead of the weed pressure on their farms. One grower indicated that he would need to return to a mixed farming operation if he did not take action to reduce the weed numbers in his farming system. “Several growers in and around Esperance had used narrow windrow burning and chaff carts in the past but had found it was often difficult to get a clean and safe burn on the residue, either because summer rain had made them too damp, or because the risk of fire escaping meant it required too much attention to burn safely,” he says. “Changing to chaff lining or chaff tramlining was an easy decision for these growers because there is no further effort required after harvest to get a kill on the weeds.” Experience with chaff decks The chaff lining system involves dropping a narrow line of chaff, including weed seed, behind the harvester. A chaff deck directs the weed seed-laden chaff into the permanent wheeltracks in a controlled traffic system. In both systems the chaff is left undisturbed. Two of the ten growers interviewed were using the chaff lining system and eight had installed chaff decks on their harvesters. Each grower was satisfied with the results they were getting with the system chosen and there were few differences between the two systems. “The two growers with chaff lining chutes had both built their chaff chutes themselves at minimal cost,” says Nick. “One person had moulded plastic chutes with a hot air gun and some tek screws and the other was made of metal sheeting. Both were attached to the harvester with pins and R-clips, making them easy to drop off to access the rear of the harvester. The total cost for materials and labour was about $1000.” Chaff decks are a more expensive option – usually around $15,000 to $20,000 when fitted to new harvests. The commercially available chaff decks have two conveyor belts running at an angle to the harvester to deposit the chaff onto the wheeltracks. Installation on the harvester involves moving the chopper a fair way back to make room for the chaff deck. None of the growers Nick spoke to had experienced any operational problems with their chaff deck systems. “One grower had made his own chaff decks specifically for John Deere S670, S680, S690 harvesters,” says Nick. “His system had two conveyors running across the back of the harvester, and did not involve as much modification work at the back of the harvester. It looked to be a simpler system, and cost about $13,000.” Chaff decks deliver the weed-laden chaff onto the harvester wheeltracks. The growers Nick spoke to all considered annual ryegrass to be their main weed. When using chaff decks the growers had observed greater germination of weed seeds on the high traffic wheeltracks, compared to the low traffic wheeltracks. “Growers using chaff chutes said that very little grass germinates in the chaff lines,” says Nick. “I think this was partly because there is very little seed soil contact in the fluffy chaff left in chaff lines, and the chaff lines seem to do a good job of shedding water.” “Clearly it is not essential to have a full controlled traffic system in place, but it is best if the harvester runs on the same tracks each year,” he says. “Some might consider that having no disturbance and very little germination is better than having weeds germinating on a portion of the wheeltracks; but either way they are concentrated and not spread across the whole paddock.” When it came to seeding, none of the growers had run into difficulties when seeding through chaff lines. Some growers were running disc units either side of the chaff to minimise disturbance of the chaff and maximise the crop competition, so that the crop would suppress any weeds that did germinate. “One advantage of the chaff deck is that the quantity of chaff is split between the two wheeltracks rather than all going into the one chaff line,” says Nick. “The growers all said that using a chaff deck or chaff lining allowed them to sow early with confidence, knowing they wouldn’t have an excessive number of weeds germinating in-crop.” Those using a chaff deck observed that the ‘carpet of chaff’ on the wheeltracks significantly reduced the amount of dust generated during spray operations, giving them better coverage behind the boom, especially in hot conditions. In the day or two after rain the chaff can cause wheel slip during seeding on some soil types. The experiences of these ten growers are documented in ‘Investigating the harvest weed seed control tools chaff lining and chaff tramlining (chaff deck) in the Esperance area – Grower case studies from the Esperance Port Zone’. The project was an initiative of the Esperance Port Zone Regional Cropping Solutions Network and the report was prepared by Nick McKenna and Peter Newman, Planfarm. Nick McKenna, Planfarm agronomist visited 10 growers around Esperance, WA who have adopted chaff decks or chaff lining for HWSC. The growers featured in this report are: Mick Shutz – EMAR chaff deck Adrian Perks – EMAR chaff deck Col de Gussa – chaff tramlining using chutes Carl Rasich and Henry Barlow – EMAR chaff deck Steve Marshall – EMAR chaff deck Elliot Marshman – EMAR chaff deck Con Murphy – EMAR chaff deck Mark and Hayley Wandel – chaff deck (continuous conveyor at 90 degrees to the direction of travel) Patty Barber – chaff line (metal chute) Mic Fels – chaff line (plastic chute)

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