Taking a single shot at weeds
As farmers get their hands on fast and accurate weed mapping technology, the frequency of blanket herbicide spraying can be greatly reduced. With an accurate digital map that shows where the weeds are right now, most boomspray rigs can become low-cost spot sprayers. For the past two years John Single and his son Tony have been using the air-borne weed sensor, Single Shot, developed by John’s other son Ben, to rapidly detect and map weeds on their dryland cropping property, Narratigah, near Coonamble, NSW. John Single with a drone carrying the Single Shot weed sensor. By separating the weed mapping and weed spraying tasks the Singles can take a planned approach to their weed management throughout the year. Ben saw the benefits of separating the weed detection and weed spraying tasks and set about building the platform and working with Robotic Systems to bring the idea to reality. “The main aim is to stay ahead of herbicide resistance,” says John. “Ten years ago we started work on developing drone-mounted sensors that could take over the task of detecting weeds in a green-on-brown situation. Many sprayers, particularly later models, do not require any modifications and there are many benefits in having the weed mapping done separately rather than on-the-go.” Weed maps enable growers to take a planned approach to their weed management throughout the year and to build a historical record of weeds in a paddock. The Single Shot sensor maps green-on-brown but are not limited to fallow situations. The sensors can be used in newly sown crops to map weeds that emerged on the planting rain or were missed in a previous application. These patches, or individual weeds, can be treated in-crop or a pre-emergent can be applied to the patches at the end of the season. The sensor can also be used in-crop to identify high biomass areas within a paddock where high weed density requires more drastic action, such as cutting for hay, and in wide-row crops where the canopy does not fully close and weeds can be detected between the rows. Screen shot of the Trimble guidance screen in operation with a Single Shot spray map. The Singles have used the Single Shot technology in several different management scenarios already and the possibilities seem endless. John says they have used the sensor to identify survivor marshmallow and milk thistle plants in fallow and then spot spray them with a high rate of Starane to prevent seed set. They have mapped feathertop Rhodes grass in wheat to generate a map for applying pre-emergent herbicide post-harvest and have filtered data to segregate weeds based on size, giving them the option to apply a blanket spray on smaller weeds and a herbicide spike to treat larger weeds, or to use a second boom to apply two different products or rates. Where pre-emergent herbicides are used, a perimeter determined by the user can be added to cover the seed distribution area of the mother plant. Another important role for Single Shot at Narratigah is to scout for survivor weeds after herbicide applications. The Singles crop 4500 ha and can map the farm at a rate of up to 300 ha per hour. This is one of the most important tasks in a herbicide program and yet it is generally not done effectively due to the time required. Having ‘eyes in the sky’ makes routine and accurate scouting practical after every spray treatment. The sensor is capable of covering 300 ha/hr under continuous flight or targeting weeds greater than 5 cm diameter. Under normal operating conditions, and including battery changes, the Singles achieve a work rate of around 200 ha/hour. Critically, data processing can be done in the field, if the internet is available at the site, and is done at a speed 1.7 times faster than flight time. Once a weed map has been created, the drone can be sent out again to take high resolution imagery of plants in specific locations in the paddock for identification purposes, allowing John and Tony to plan a herbicide program with their agronomist, based on exactly what’s in the paddock. When it comes to spraying, having the weeds mapped before the spray operator gets in the cab means that the job can be done when conditions are suitable, including at night. The real power of the Single Shot system is the ability to run simulations and to re-process the data to fine-tune a herbicide program based on weed size or density. The sensor requires just a 1 cm ‘brown’ perimeter around a weed to be able to detect the weed size. The weed maps are built from images that are ten thousand times higher resolution than satellite images, giving a 1 cm sampling size. Every part of the paddock is photographed twice so obstacles such as stubble occlusion can be significantly reduced. The drone flies at a height of 75 m, following a pre-determined path, and can also be flown lower and or slower if necessary to collect specific data. The sensor also accurately identifies stressed weeds. “Information is power and this has really put us back in control of our weed management,” says John. “We know how much chemical to buy to do the job at hand, we know the costs and can alter the chemistry to suit a budget if necessary, we can choose to blanket spray or spot spray, and our ability to apply the double knock tactic is greatly improved.” Ready for unmanned aerial vehicle (UAV) spraying In a bid to be one step ahead of the game, the Single Shot software will also calculate the shortest path for the sprayer, which is most useful when doing spot spraying on an ATV, or in the future, to deliver herbicide via a drone-mounted sprayer (UAV) or autonomous vehicles. “We ran a scenario for treating about two thousand survivor weeds in a 125 ha paddock using a spray drone,” says Ben. “To apply a blanket spray to the paddock, the spray drone would need to travel about 310 km. Using the Single Shot software we determined the shortest path to reach all the weeds, which cut down the time required to do the job to just two and a half hours. The sprayer would only be applying herbicide for 16 km of the 54 km flight, and just 5 per cent of the paddock would have herbicide applied.” Left: Actual weed coverage in a 125 ha paddock (blue line is the boundary, and purple is weed). Right: The path that the UAV would travel using the shortest route computation. Weed mapping using tools and systems like Single Shot are putting growers back in the driving seat to cost-effectively and consistently implement the WeedSmart Big 6 tactics that underpin sustainable herbicide use and maintain productivity gains through no-till farming systems.
Throwing the Big 6 at weeds in South Australia
Low weed seed banks underpin all profitable farming enterprises. Keeping weed numbers low and quickly regaining control of blow-outs is the sole purpose of the WeedSmart program. Each year growers and agronomists are invited to attend WeedSmart Week, somewhere in Australia. This year the 3-day event will begin with a 1-day forum at Clare Golf Club on Tuesday 1 September. The following two days will be spent touring farms in the Clare region 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 – Use the BIG 6 to beat crop weeds’ says it all! YP AG senior agronomist Chris Davey (right) is encouraging growers from South Australia and beyond to attend WeedSmart Week in September as a good opportunity to formulate a plan to manage weeds throughout the year and through the rotation using the WeedSmart Big 6. This flagship event of the WeedSmart program is supported by GRDC as the major sponsor and a wide range of herbicide and machinery companies that have skin in the weed control game. This year’s event will be co-hosted by Pinion Advisory, YP AG and the Hart Field Site Group and will be the sixth WeedSmart Week event. WeedSmart program leader, Lisa Mayer says the event in Clare is the first of its kind for South Australia, giving growers and agronomists access to practical research and implementation of tactics that are known to effectively manage the risk of herbicide resistance in weeds. “Weeds have gained the upper hand on some farms and have too much influence over farming system decisions,” she said. “The herbicide and non-herbicide tactics that form the WeedSmart Big 6 have been researched and demonstrated in the field – we know they work! Growers and agronomists in each region and on each farm can adapt the Big 6 principles to bring more diversity to their farming system and bamboozle weeds.” “WeedSmart is committed to exploring and promoting farming systems and technologies that produce ‘more yield, fewer weeds’ every year.” 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. 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, leading agronomist from YP AG, Chris Davey attended the Horsham event along with Pinion Advisory agronomist, Jana Dixon, and growers Jarred Tilley and Adam Cook. Chris says it was a very valuable experience that gave him the opportunity to interact with growers and industry people involved in weed management in a range of environments. The machinery displays and demonstrations at WeedSmart Week events are a great opportunity to see some of the newest weed management technology and grower innovations. “The interaction between attendees was excellent as growers and agronomists swapped experiences and things they had learned about tackling certain weeds or modifying equipment,” said Chris. “Having WeedSmart week in Clare this year is a fantastic opportunity, particularly for South Australian growers, to get together and discuss new ideas and learn how different tactics are working for other growers.” There will be a focus on both herbicide and non-herbicide tools and plenty of chances to see how mechanical tactics like harvest weed seed control can fit into a variety of farming systems to drive down weed numbers. Jarred Tilley, a mixed farmer at Kapunda, will be one of the host farmers for the WeedSmart Week farm tour. Jarred is tackling glyphosate resistant ryegrass and has recently added a chaff cart to their weed management strategy. He has had good success with baling the chaff and using it to improve the profitability of their livestock enterprise. 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. Day 2 and 3 will be bus tours to farms in the Northern Yorke Peninsula and the Mid to Lower North regions around Clare. Attendees will have several opportunities to see and discuss cutting-edge technologies such as the latest sprayer technology and a range of harvest weed seed control implements, including impact mills and chaff decks, and will find out how other growers in the region are implementing the Big 6 weed management tactics in a variety of farming systems and environments. Register for this important 3-day event for the ‘early bird’ single ticket price of $165 (GST incl), guaranteeing a seat on both the bus tour days as well as the forum, all fully catered here! WeedSmart is committed to the health, safety and well-being of everyone working in, and in support of, the Australian grains industry. WeedSmart Week may be postponed in response to the current coronavirus outbreak, and in accordance with Australian Government advice in relation to social distancing.
Crop competition halves weed seed numbers
Wheat and canola crops offer growers some really practical options to improve crop competition against weeds, particularly grasses, and vastly reduce weed seed set. Researchers at the University of Adelaide, led by Dr Chris Preston and with GRDC investment, conducted an extensive study to identify the agronomic factors that promote strong early crop growth. They found that simple strategies of growing hybrid canola and sowing wheat early, can couple with pre-emergent herbicides to achieve a very effective double-knock. The result is more yield, less weed seed produced and less selection pressure on the herbicides. “In the canola trial we used a range of pre-emergent herbicides and compared open pollinated and hybrid canola,” says Chris. “The bottom line of our trial is that if you grow a hybrid canola with pre-emergent herbicides and do nothing else different, you’re going to reduce your grass weed seed set by 50 per cent.” If you grow a hybrid canola with pre-emergent herbicides (left) and do nothing else different, you’re going to reduce your grass weed seed set by 50 per cent (right, conventional canola and no pre-emergent herbicide). This level of non-herbicide weed control was also measured in an Australian-first study that looked at the competitive ability of 16 canola genotypes against annual ryegrass and volunteer wheat over two contrasting seasons, led by Professor Deirdre Lemerle at Charles Sturt University. In a separate trial conducted by Rohan Brill, former research and development agronomist, NSW DPI based in Wagga Wagga, and colleagues at Trangie and Tamworth, a rule of thumb was established that seed size had a greater effect on early biomass production in canola than did cultivar type (hybrid vs OP). This gave rise to the recommendation that all farmer-retained OP canola seed be cleaned and graded to collect planting seed that is 2 mm in diameter or larger. Their study showed that sowing large canola seed, regardless of the cultivar, is key to strong early crop growth and the crop’s ability to compete with weeds. Having observed that later planted wheat often hosts more weeds, the Adelaide University team looked at the effect of planting wheat as early as possible. “Our previous idea for managing weedy paddocks was to delay sowing, apply another knockdown treatment to control more weeds and then put the crop in,” says Chris. “In this trial we found that even in weedy paddocks you can put the wheat in early with a robust pre-emergent herbicide package, and the result is more wheat yield and less ryegrass seed at the end of the season.” Dr Chris Preston, University of Adelaide, says if you sow the right wheat variety early and apply the right pre-emergent herbicide package, you can halve your grass weed numbers, just from competition in the middle part of the season, and you don’t have to change anything else. “If you sow the right variety early and apply the right pre-emergent herbicide package, again you can halve your grass weed numbers, just from competition in the middle part of the season and you don’t have to change anything else.” There are a few practicalities to consider when looking to sow wheat earlier. Firstly, you need to choose a variety that will still flower in the right flowering window for your location. If you are sowing several weeks earlier than normal you need a longer season variety to manage frost and heat risk at the end of the season. Crop competition trial site at Roseworthy, SA. Secondly, if you are sowing completely dry, then most of the pre-emergent herbicide options are open to you. If there is some soil moisture, but not enough for crop germination, some of the pre-emergent herbicides will not perform well. You need to give careful consideration to your choice of herbicide to suit the environmental conditions of each season. These findings underpin WeedSmart’s aim, to promote farming systems that produce ‘more yield and less weeds’. More resources: Best seed, best establishment and fewer weeds Choose highly competitive canola
Understanding weed competitive traits in barley
WeedSmart Scientific Partner Barley is known as a fairly competitive crop, but not all genotypes are equal when it comes to weed suppression and weed tolerance. To un-pick the complex mechanisms behind competitive ability in barley, QAAFI weed researchers Gulshan Mahajan and Bhagirath Chauhan, and cereal plant breeder Lee Hickey, teamed up to quantify the effect of weed interference on commercial and elite-line barley genotypes. Their two-year field trial compared the competitive ability of eight barley genotypes against a mimic weed (oats) by measuring weed biomass, weed seed production and barley yield. Weeds can cause huge yield losses in barley – between 43 and 78 per cent difference between weedy and weed-free growing conditions for the eight genotypes tested. There is considerable variation in the weed competitive ability of current and elite breeding lines of barley in Australia. The most weed suppressive variety, Westminster, reduced weed seed production by 73%, compared with that of LaTrobe. Similarly, weed biomass of Westminster reduced by 55%, compared with that of LaTrobe. There is scope for the development of high-yielding weed-competitive barley genotypes through additional screening of elite lines in weedy conditions. Higher panicle production in barley appears to be a strong indicator of a genotype’s competitive ability. When it comes to using a crop to compete with weeds there are two discreet mechanisms – weed suppression, where the growth and seed production of weed plants is reduced and weed tolerance, where crop yield is maintained, even in weedy conditions. The most competitive genotypes will use both of these mechanisms and knowing which mechanisms are at play is valuable information when planning an integrated weed control program. Competitive genotypes are a powerful non-herbicide weed control tactic and growers will gain significant benefits if they can plant a strong weed-suppressive crop into a weedy situation, particularly if they do not have to sacrifice yield. While yield and malt quality have driven the barley breeding program to date in Australia, this research suggests that there is great advantage in understanding the response of the variety to weed pressure. Observations on the competitive ability of the four commercial varieties tested: Commander barley is both weed suppressive and weed tolerant. If sown with an effective pre-emergent herbicide, Commander is probably the best choice to maintain low weed numbers. Westminster is the most weed suppressive and might be a better choice if weed numbers are starting to increase, or for use in low input and organic production systems. Westminster is not weed tolerant, so a significant yield penalty should be expected in weedy situations. Although Compass is tall and has a droopy architecture (like Commander and Westminster) it is not weed suppressive or weed tolerant, and should only be chosen for weed-free situations. LaTrobe is the least weed seed suppressive but is weed tolerant, maintaining a reasonable yield in the presence of weeds. The competitive ability of a particular genotype may vary in different locations, seasons and management systems, and in the presence of different weed species. Experimental design features The experiments were conducted in 2017 and 2018 at the University of Queensland research station at Gatton. The crops were sown at a depth of 5 cm in rows 35 cm apart on 17 May 2017 and 23 May 2018. The crops were irrigated to maintain field capacity and were harvested on 4 November 2017 and 28 October 2018. There were eight barley genotypes, weedy and weed-free treatments and three replicates. Four of the barley genotypes are commercial varieties and four are elite breeding lines being assessed prior to commercial release. Like most other plant breeding programs, Australian barley varieties are usually screened in a weed-free environment with a focus on yield and malting qualities. In this experiment, each genotype was sown at the recommended seeding rate (125 kg/ha) in a weedy and weed-free environment. Oats was used as a mimic for wild oats, a serious weed in barley. Wild oats could not be used because it has non-uniform germination and sheds its seed before barley harvest. The plot size was 8 by 1.4 m. The weedy plots were sown with a commercial oat variety at a target density of 40 plants/m2. There was no significant seasonal effects so data from the two seasons could be analysed together. Weed infestation and genotype influenced the number of panicles produced per metre row length of the barley crop and crop yield. Only genotype influenced crop plant height. While genotype had a significant impact on weed biomass, weed seed yield, weed-tolerance ability and weed-suppressive ability, phenotypic traits are not always a reliable indicator of a genotype’s weed suppressive ability or weed tolerance ability. In this experiment, panicle number was a good indicator of both weed suppressive ability and weed tolerance ability, but plant height and architecture were not reliable indicators. Left: Weed seed yield in weedy treatment for each barley genotype.Right: Effect of barley genotype and weed treatment on barley grain yield. Other factors, such as lodging and harvest index, will also need to be considered in a variety selection process but were not measured in this experiment. Some genotypes possess both mechanisms for competing successfully with weeds while others possess one but not the other, and some have poor suppression and tolerance. Table: Plant attributes and mean values for the weed-tolerance ability and weed-suppressive ability of the eight tested barley genotypes. This research suggests that screening barley varieties in a weedy situation may provide valuable information to growers seeking to choose varieties that will provide the greatest weed suppression and or weed tolerance in weedy paddocks. It is not possible to screen for competitive ability in a weed-free environment and there is clearly scope for the development of high-yielding weed-competitive barley varieties in Australia. In the face of increasing herbicide resistance in key weed species, the value of non-herbicide weed control tactics increases considerably. The real value of crop competition (narrow rows, high seeding rate, weed-competitive genotypes) comes to the fore a few weeks after planting and through the main growing season to suppress late emerging weeds. Herbicides will remain the main tool for weed control in preparation for planting and to provide a weed-free environment for the crop to establish and rapidly achieve canopy closure. This research was conducted and funded by the University of Queensland, a WeedSmart scientific partner. Related resources: Read the published paper QAAFI – a WeedSmart research partner WeedSmart Big 6 – Grow a competitive crop
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.
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/
Quick, test your winter weed escapes
This winter, researchers are recommending that growers and agronomists consider collecting live plant samples for herbicide resistance testing as a first step to identify and manage herbicide resistance in crop. The first multi-species herbicide resistance survey conducted in the Northern grain growing regions of NSW and Queensland has shown that testing for herbicide susceptibility is well worthwhile as there are likely to be products that are still effective on weeds that are resistant to other modes of action. Dr John Broster, Charles Sturt University recommends growers conduct regular herbicide resistance testing to better inform their herbicide program decisions. Results from the ‘Quick Test’, offered by Plant Science Consulting, will usually provide a guide for herbicide strategies to use in the current season to stymie the effects of herbicide resistance. If weeds escape herbicide applications early in the season they will add large quantities of seed to the weed seed bank for next year, but if these plants can be killed this season their impact will be greatly reduced. Testing weed seed at the end of the season is also a valuable tool to make more informed decisions for next season’s herbicide program, particularly for pre-emergent herbicides, which cannot be assessed using the Quick Test. There are three weed seed testing services in Australia, including Charles Sturt University. The implementation of a variety of WeedSmart tactics, such as the double knock, mixing and rotating herbicides, stopping seed set and harvest weed seed control will also have a lasting impact on weed numbers. With GRDC investment, Dr John Broster, Charles Sturt University NSW and Dr Michael Widderick, Queensland Department of Agriculture and Fisheries, Queensland led their respective teams through the process of testing samples and analysing the results for weed seed collected throughout the Northern cropping region in 2016 and 2017. Weed seed samples were collected from 440 paddocks across northern NSW (244) and Queensland (196). The seeds were sown in controlled conditions and when the plants reached the three to five leaf stage they were tested for resistance to a range of herbicides. While collecting weed seed samples the researchers also assessed the weed density in each surveyed paddock. The winter-growing weed species collected across the northern region and screened at CSU included annual ryegrass, wild oats, barley grass, brome grass, wild radish, Indian mustard, turnip weed and African turnip weed. For NSW, this survey adds weight to other weed surveys conducted over recent years. Dr Broster says around 1000 paddocks in NSW and Queensland have now been surveyed between 2014 and 2018. Wild oats is widespread across NSW and Queensland, having been found in just over half the paddocks surveyed. Annual ryegrass was also very abundant but so far only found in NSW, where it was present in almost 70 per cent of paddocks surveyed. Barley grass, brome grass, Indian mustard weed and turnip weed were found only in NSW while wild radish and African turnip weed were mainly found in Queensland. “The stand-out finding from our broader testing in NSW is that approximately 60 per cent of collected annual ryegrass populations were resistant to diclofop, sulfometuron and imazamox/imazapyr,” says Dr Broster. “Resistance to other commonly used herbicides for ryegrass control is relatively lower, but must be noted if these herbicides are to remain options for future herbicide programs. We measured resistance to clethodim (6%), trifluralin (7%) and glyphosate (6%) herbicides in the collected ryegrass populations sampled across the NSW regions.” “Glyphosate resistance in ryegrass is more prevalent in the northern NSW regions than other parts of the state. Resistance to selective herbicides is lower in the northern NSW region than other parts of the state.” 2016 northern NSW and Queensland survey results summary for winter weed species All results quoted below are the % of surveyed populations where resistance was detected. Ryegrass only found in NSW – 94 populations tested. Resistance was found to diclofop (Hoegrass, 44%), imazamox/imazapyr (Intervix, 33%), sulfometuron (Oust, 29%), glyphosate (Roundup, 10%) and clethodim (Select, 2%). The sampled populations were susceptible to prosulfocarb + s-metolachlor (Boxer Gold) and pyroxasulfone (Sakura). All but one population was susceptible to trifluralin (Treflan, 1% developing resistance). Glyphosate resistant annual ryegrass, 2016 Northern Region weed survey. Map courtesy of Dr John Broster, Charles Sturt University NSW. Wild oats – 193 populations tested across Queensland (71) and northern NSW (122). Resistance was found to clodinafop (Topik, 38%) and Hussar (idosulfuron, 4%). These populations were fully susceptible to clethodim (Select), glyphosate (Roundup) and triallate (Avadex Xtra). Barley grass – 17 populations, all in NSW. All susceptible to quizalofop-p-ethyl (Targa), clethodim (Select), mesosulfuron-methyl (Atlantis) and paraquat (Gramoxone). Brome grass – 13 populations, all in NSW. Resistance found to mesosulfuron-methyl (Atlantis, 36%) only with all populations susceptible to quizalofop-p-ethyl (Targa), clethodim (Select), imazamox/imazapyr (Intervix) and glyphosate (Roundup). Wild radish – 12 populations from Queensland and northern NSW. Resistance found to chlorsulfuron (Glean, 8%), diflufenican (Brodal, 80%) and 2,4D Amine, 77%. All populations were susceptible to glyphosate (Roundup), imazamox/imazapyr (Intervix) and Atrazine. Indian hedge mustard – 7 populations found only in NSW. Resistance was found to chlorsulfuron (Glean, 17%) and diflufenican (Brodal, 43%). All populations were susceptible to glyphosate (Roundup), imazamox/imazapyr (Intervix), Atrazine and 2,4D Amine. Turnip weed – 32 populations found in Queensland and northern NSW. Resistance was found to chlorsulfuron (Glean, 19%) and imazamox/imazapyr (Intervix, 11%). All populations susceptible to glyphosate (Roundup), Atrazine, diflufenican (Brodal) and 2,4D Amine. African turnip weed – 17 populations found in Queensland and northern NSW. Resistance found to 2,4D Amine while all populations were susceptible to glyphosate (Roundup), chlorsulfuron (Glean), imazamox/imazapyr (Intervix) and Atrazine. Related links: Testing for herbicide resistance and susceptibility Correct preparation of Quick test samples video below
Tackling ryegrass in Tasmania’s high rainfall zone
The wettest April in 60 years is likely to cause growers in Tasmania’s high rainfall zone some unique challenges when it comes to controlling annual ryegrass, the Australian grain industry’s #1 weed. Blow-outs are mostly in wet years and in paddocks with other underlying issues where ryegrass can take advantage of any gaps or areas of lower crop vigour. Many growers are finding that ryegrass is particularly difficult to manage in winter cereal and canola crops where the long cool season allows multiple germinations of ryegrass and the wet conditions reduce the residual benefits of pre-emergent herbicides. WeedSmart southern agronomist Greg Condon says creative farmers and agronomists are addressing the problem head on and finding ways to implement the WeedSmart Big 6 weed management tools to stop seed set and drive down weed numbers. “Farmers need to operate in a low-weed environment so they have more options in their crop and livestock decisions,” says Greg. “The principles of crop diversity, crop competition and mixing and rotating herbicide modes of action are central to keeping farming systems profitable.” Diversity in cropping and livestock operations needs to result in diverse weed control tactics. “The creativity comes in with the problem-solving process needed to apply these principles in challenging environments. The practices that have been developed in other high rainfall zones do not always apply directly to the Tasmanian farming systems.” Growers and agronomists can use the WeedSmart Big 6 to keep ryegrass numbers under control while maintaining maximum flexibility in their cropping program. Greg says all the tactics will work in the Tasmanian high rainfall zone, with the exception of harvest weed seed control. “Growers in the region have a distinct advantage when it comes to diversity in their farming system and this needs to drive the use of different weed control methods to keep the weeds guessing – using both herbicide and non-herbicide tools,” he says. “Unfortunately, harvest weed seed control is far less effective in the Tasmanian cropping zones than it is in other high rainfall zones,” he says. “This is because a large percentage of the ryegrass that germinates in the crop will shed its seed before harvest. Some growers may still find value in this tactic to collect the seed from the later cohorts of the weed but it just isn’t as cost-effective as it is in other areas.” Even without harvest weed seed control as a mainstay option, growers can still implement a three or four year ‘war on weeds’ program to drive down the ryegrass seed bank. “To start with, tactics such as spring cropping, fodder crops and triple break crops can be used to maximise the efficacy of available herbicides and reduce ryegrass germinations,” says Greg. “When it comes to herbicides it is critical that a plan is put in place to mix and rotate herbicides across the whole crop sequence,” he says. “In-crop herbicides are scarce and products like clethodim are registered for use in many crops so it is easy to keep using it, but we know that quickly leads to resistance problems.” Having diversity of crops in the system only helps with weed control if it is used as a way to rotate chemistry. Testing the weeds for their susceptibility to single products and mixes of herbicides allows growers to plan ahead with more confidence. Double knocking each herbicide application preserves the available chemistry, particularly glyphosate. Growers can also take advantage of ryegrass’ poor competitive ability. When placed in a competitive environment, ryegrass sets less seed, reducing the pressure of this weed on farming system decisions. “Crop agronomy has a major impact on competitiveness,” says Greg. “The choice of crop, solid plant establishment, sowing early with a robust pre-emergent herbicide and attending to any soil constraints all swing the advantage toward the crop and away from the weeds.” The final tactic that growers can implement is stopping weed seed set using hay and silage, crop-topping in canola or spraying under the cutter bar when swathing, or using camera-guided shielded sprayer technology to target weeds growing in the inter-row. Cutting weedy areas of the crop for hay is a highly effective tactic that can reduce the impact of a weed blow-out. Ian Herbert, Southern Farming Systems’ Tasmanian Projects and Trials Manager says fodder crops and livestock play a critical role in managing ryegrass on many Tasmanian farms. “Growers can plant fodder crops directly after grain harvest, graze these fodder crops through winter, while allowing multiple germinations of ryegrass to occur, and then remove these plants using broad spectrum herbicides and or cultivation prior to planting a grain crop in spring,” he says. “This tactic reduces the pressure on selective herbicides and changes the timing of when ryegrass is controlled, compared to years where the paddock is in a cereal production phase. Cultivation is often needed to remove the deep pugging from livestock, which often occurs during our wet winters.” Livestock can play an important role in weed management and there are many options available to growers. Michael Chilvers is one grower who is embracing an integrated approach to managing ryegrass on his 1200 ha farm south of Launceston, where he runs a diverse cropping enterprise of around 300 ha of grain production along with intensive lucerne hay, potato and hybrid seed production. Michael says the exceptionally wet autumn across much of the high rainfall zone, and particularly in their region, is going to put heavy pressure on the pre-emergent herbicides applied at planting. “Incorporation of pre-em herbicides is critical and often not easy to achieve,” he says. “Unfortunately, the newly released pre-em products are probably not going to be an option for us in very wet seasons so we need to focus on getting the most out of the existing products.” Michael is also very aware of the heavy reliance on Group A herbicides such as clethodim across his farming system and is doing what he can to rotate away from this key mode of action at every opportunity. “Not only do we use it frequently, we also know that its efficacy can be compromised in our environment through a long cool growing season, which means we are running a real risk of losing it if we don’t adopt a more diverse approach to managing ryegrass,” he says.
Keeping a lid on weeds growing in your crops
In-crop weed control is particularly difficult in some years. Even after you have done all you possibly can to get your crop off to a competitive start the growing season can throw up some major challenges. In this article we explore key principles that impact on the efficacy of in-crop ‘selective’ herbicides. You will most likely have to make some compromises and it is almost impossible to implement every tactic perfectly every time. Herbicide mixes help to preserve the effectiveness of each mode of action by avoiding unnecessary usage. Over the last few years WeedSmart has collected and promoted great advice from seasoned agronomists, wise researchers and crafty farmers on all aspects of weed control. To save you some time we have collected the resources that we think can be of assistance as you make the hard decisions about what to apply, when to apply and how to apply the herbicide and non-herbicide weed control tools at your disposal. Post-emergent herbicides have been widely used in Australian crops because they are generally highly effective and easy to use. Unfortunately, their popularity has led to widespread resistance and most farms will have at least one weed species that is resistant to at least one post-emergent herbicide mode of action. Despite recent increases in resistance, post-emergent herbicides remain an integral component of weed control strategies in many production systems. Key messages: Avoid the routine use of any weed control tactic – mix, rotate and keep changing. Know what modes of action still work – test for susceptibility. Have a plan for dealing with a weed blow-out. Right Product, Right Time, Right Application. Planning your in-crop herbicide use Widespread and increasing herbicide resistance demands a planned approach to herbicide use throughout the crop sequence. If you have been using a particular herbicide or group of herbicides routinely, it is probably because they work well. To ensure these effective products remain an option into the future, it is necessary to use them less often! Testing weeds for their susceptibility to a range of herbicides is cheap compared to applying a herbicide that has limited or no effect. Resistance to one or more herbicide does not mean you have no options. We now know that mixing and rotating herbicides is an effective strategy to prolong the effective life of each mode of action. But even these mixes and rotations need to be change. There are currently very few in-crop herbicides available for grass control. There are more options for broadleaf control. Plan a herbicide use program that spans your crop sequence so you can ‘save’ particular herbicides for use in crops where there might be limited alternatives, while using a range of other modes of action in other crops. All herbicides applied in crop will have some impact on crop safety. Herbicides must be applied according to the correct crop growth stage for each herbicide. Shielded spraying opens up the possibility of using other chemistry in-crop that would otherwise not be an option. Some growers are also looking for ways to include non-herbicide in-crop tactics such as inter-row cultivation or scuffling in wider-row cropping situations.< CLICK IMAGE TO DOWNLOAD FILE For planning herbicide use through the season and the crop sequence the NSW DPI Weed Control in Winter Crops booklet is full of useful tables of selective herbicides for each crop type. Click to download a copy. CLICK IMAGE TO DOWNLOAD FILE If you don’t have a copy of Mark Congreve and John Cameron’s ‘Understanding Post-emergent Herbicide Weed Control in Australian Farming Systems’ GRDC technical manual, you really need to download this resource. CLICK IMAGE TO DOWNLOAD FILE The GRDC Integrated Weed Management in Australian Cropping Systems manual provides a comprehensive guide to IWM, including the use of in-crop herbicides. CLICK IMAGE TO DOWNLOAD FILE This table shows the in-crop herbicides and their application timing for cereals. It is an extract from the NSW DPI Weed Control in Winter Crops booklet. You can download a copy here. WeedSmart resources: What are the ‘mix and rotate’ options for in-crop herbicides? Testing for susceptibility and resistance How can I implement the mix and rotate strategy to combat herbicide resistance? How can I avoid getting stuck in an imi herbicide cycle? Can we grow broadleaf crops without clethodim? What can be done to regain control of herbicide resistant sowthistle? Grower case study: Tim Rethus, Horsham Vic Grower case study: Leigh Bryan, Swan Hill Vic Grower case study: Phil and Brad Jackson, Westmar Qld – Achieving maximum impact Herbicide application decisions are complex and it is almost impossible to have all the important factors in place every time. Start with the product label and follow the instructions on rate, nozzle use, boom height, speed, adjuvants, optimal environmental conditions and so on. When mixing, the order is important to avoid precipitation in the tank but it is also important to ensure that the tank mix partners each retain their efficacy. Some mixes are antagonistic and should be avoided because this will likely result in a significant reduction (up to 50% in some products) in efficacy. Adding an adjuvant can reduce herbicide selectivity and thereby increase crop damage. The GRDC GrowNote Spray Application manual provides detailed information on: Planning your spray operations – things to think about Preparing for spraying – checks, accuracy and efficiency Spraying system – major components and set-up considerations Selecting a spraying system options available and operational considerations Review and planning for future needs CLICK IMAGE TO DOWNLOAD INTRODUCTION MODULE The manual comprises 23 modules and a ‘water flush for residuals’ calculator. Each module includes a series of videos (see playlist below). The video playlist is a great place to start: WeedSmart resources: Getting mixing right to avoid glugs and efficacy issues Don’t start mixing until the water quality is right Spray well: correct nozzles, adjuvants and water rates Are you going spraying or killing weeds? Never cut the rate Right time – Manage multiple germinations Timing is one of the hardest things to get right. Large spray programs and wet weather can make it very difficult to apply herbicides at the optimal time in every paddock for every weed. The guiding principle is to always target small weeds, even if this means multiple applications. In wet years, multiple germinations will occur and waiting for the next germination invariably means the first flush will be much more difficult to kill and more likely to generate lots of seed for next year. All herbicides applied in crop will have some impact on crop safety. Herbicides must be applied according to the correct crop growth stage for each herbicide. Also consider the effect of environmental conditions, particularly frost, on crop safety. Environmental conditions at the time of spraying can make a huge difference to herbicide update in weeds. Look for the directions on the label for optimal conditions as spraying outside these parameters will result in less effective weed control. avoiding chemical residues in grain. WeedSmart resources: Spray small multi-resistant radish twice Does ambient temperature really affect herbicide performance? Be ready for weed blow-outs Wet years are the classic weed blow-out situation. Pre-emergent herbicides breakdown faster, spray applications can’t be applied on time and weeds will take advantage of any gaps that might develop in the crop. Monitoring the weed pressure and having a plan to limit the potential damage might help. The aim is to stop a massive seed set event using tactics such as – crop topping, hay or patching out. And be ready to implement harvest weed seed control – all the methods work well. WeedSmart resources: Grower case study: Trevor Syme, Bolgart WA Grower case study: Mark Branson, Stockport SA Grower case study: Day Family, Lockhart, NSW
Extent of herbicide resistance in summer weeds revealed
The first multi-species herbicide resistance survey conducted in the Northern grain growing regions of NSW and Queensland has shown that while resistance to key herbicides is prevalent, growers are keeping weed numbers low, for now. Rising resistance to glyphosate has been clearly demonstrated but this key herbicide can continue to be a highly effective tool for weed control, provided growers and agronomists implement a variety of tactics, such as the double knock, mixing and rotating herbicides and seed bank management, as a matter of urgency. Dr Adam Jalaludin (DAF) collecting weed seed to be screened for herbicide resistance in the first multi-species weed survey in the northern grains region. With GRDC investment, Dr Adam Jalaludin, Department of Agriculture and Fisheries, Queensland and Dr John Broster, Charles Sturt University NSW led their respective teams through the process of testing samples and analysing the results for weed seed collected throughout the Northern cropping region in 2016 and 2017. This survey was part of a wider GRDC investment in ‘Innovation in Crop Weed Control’ project across the northern region. Weed seed samples were collected from 440 paddocks across northern NSW (244) and Queensland (196). The seeds were sown in controlled conditions and when the plants reached the three to five leaf stage they were tested for resistance to a range of herbicides. While collecting weed seed samples the researchers also assessed the weed density in each surveyed paddock. The summer weed species collected across the northern region and screened in Queensland included sowthistle, fleabane, awnless barnyard grass, feathertop Rhodes grass, windmill grass and liverseed grass. Of these predominantly summer-active species, only sowthistle, awnless barnyard grass and liverseed grass are listed on the label as being controlled by glyphosate alone. There is no label claim that the other three species – fleabane, feathertop Rhodes grass and windmill grass, will be controlled at the registered label rates of glyphosate (729 g active ingredient per ha). “Not surprisingly, all fleabane populations collected failed the glyphosate test,” says Dr Jalaludin. “Interestingly, 32 per cent of the feathertop Rhodes grass populations and 42 per cent of the windmill grass populations were actually susceptible to glyphosate.” “Of concern was that 36 per cent of awnless barnyard grass populations and 14 per cent of the sowthistle populations were resistant to glyphosate.” Dr Adam Jalaludin (DAF) recommends herbicide susceptibility testing as the first step in addressing patches of resistant weeds. “In this survey we detected evolved resistance to haloxyfop in feathertop Rhodes grass and to imazapic in windmill grass, albeit at a low frequency.” Glyphosate resistance is certainly entrenched in the northern region, and for sowthistle is much worse than in other areas of Australia. The good news is that weed density is relatively low and there is susceptibility to other herbicides. “It is essential that an integrated approach is taken to manage these key weeds in summer crops and fallow,” said Dr Jalaludin. “An increasing number of weeds from a range of species are surviving glyphosate treatment, giving a clear indication that over-reliance on this herbicide is unsustainable.” “Herbicide testing is a good place to start to identify which herbicides provide the best control. Herbicide applications should be supported with as many other WeedSmart tactics as possible and any survivors removed.” Summary of results The populations of viable sowthistle seed were screened with glyphosate, 2,4-D amine, Velocity and chlorsulfuron. Glyphosate and cholsulfuron provided poor control while all populations were susceptible to 2,4-D amine and Velocity. Fleabane populations 1 week after spraying with glyphosate. Susceptible control population (right) and a resistant population (left) collected during the northern region herbicide resistance survey. Fleabane populations across the Northern region were screened with glyphosate and 2, 4-D amine. All fleabane populations tested survived treatment with glyphosate while no sample survived the application of 2,4-D amine. Screening of the feathertop Rhodes grass populations revealed 68 per cent were not controlled by glyphosate. One population survived treatment with haloxyfop, while all populations were controlled with clethodim. Thirty-six per cent of the awnless barnyard grass populations collected across the Northern region were resistant to glyphosate. Fortunately, all populations were susceptible to propaquizafop, clethodim and imazapic. Most of the windmill grass populations sampled in the survey were found in NSW. Screening showed that more than half (58%) of the populations were not controlled with glyphosate. Similarly, 40 per cent of the populations survived imazapic treatment. All populations were totally controlled by propaquizafop and clethodim. The screening of the few viable liverseed grass populations collected across the Northern region did not reveal any evolved herbicide resistance. Weeds collected in this survey were screened against several herbicides for which there are no label claims for some species. In field conditions, these weeds are often subject to exposure to a range of herbicides, which may be observed to have some activity. It is illegal to apply herbicides in any way contrary to the label and the results from this research are not a recommendation of use.
Calculating the cost of HWSC for your farm
When it comes to harvest weed seed control methods there is good evidence that all the available options achieve a similar end result in terms of weed seed bank decline. But there is a wide variation in initial outlay, in associated activities and in nutrient removal or concentration. Then there is the on-going problem of using average costs compared to using your own costs when doing the calculations. WeedSmart western extension agronomist, Peter Newman has developed a spreadsheet growers can use to do calculations for their own farm to compare the cost of different HWSC options. To assist, WeedSmart western extension agronomist Peter Newman has developed an interactive spreadsheet tool that growers and advisors can use to compare the costs of the available harvest weed seed control (HWSC) tools, using data and costings from their own farm situation. “We have good data to suggest that harvest weed seed control costs are $7 to $19 per hectare and there are only minor differences in the cost between the available tools when compared using the same farm data,” says Peter. “But because every farm is different and small differences in costs per hectare can make a big difference at the whole farm scale, it is important for growers to have confidence that they can afford and justify the expenses incurred.” 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. There is good data to suggest that harvest weed seed control costs are $7 to $19 per hectare and there are only minor differences in the cost between the available tools when compared using the same farm data. A chaff cart (pictured) is a particularly good fit on mixed farms. “As a general rule, the cost of HWSC is lower per hectare on larger farms with lower yields,” says Peter. “This is because the capital cost is spread over a larger area, less nutrients are removed because the yields are lower and the low biomass crops allow low harvest heights without slowing down the harvester or using extra fuel. The converse is generally true for smaller farms with higher yields.” “By imputing your own figures into the HWSC costing tool you can quickly evaluate the financial impact of the available options,” says Peter. Another important factor to consider is that some of the technology is relatively new to market and there are unknowns such as the expected life of components when operating in commercial field conditions. As time goes by the manufacturers will be able to provide more concrete advice on service and repair costs, and any component failures will be overcome. The easy-to-use spreadsheet takes into account capital cost, nutrient spread/loss, cost of ownership, harvest cost, reduction in harvest capacity, fuel use and replacement of wearing parts. Users also input data about their farm size and crop yields. Peter Newman joined us for a webinar to discuss the HWSC cost estimate tool, you can watch the full recording below.
Interest in cover crops continues to grow
There is a growing interest in planting cover crops in cotton and broadacre systems, providing the potential to preserve soil moisture, improve soil health and manage weeds. As part of the CRDC project ‘Staying ahead of weed evolution in changing cotton systems’, the Queensland DAF Weed Science team investigated the impact of cover crops on weed suppression. Jamie Grant (far right) is pictured with Jeff Werth (DAF weeds researcher). Jamie grows French white millet as a cover crop in rotation with cotton in his dryland cropping system at Jimbour, on the Darling Downs. Research has shown that cover crops can provide a benefit in terms of weed control. However, in order for them to be effective, it is important to start with a clean crop and ensure that the cover provided is adequate and evenly spread. Similar to findings from grower Jamie Grant in the following case study, research showed that when the cover was not adequate, lower amounts of cover provided a haven for weeds to germinate. A clean crop also provides the cover crop with a head start and improves its ability to out-compete the weeds. The project also examined the effectiveness of the 2+2 and 0 strategy (two non-glyphosate tactics in crop, plus two non-glyphosate tactics in fallow and zero survivors or incursions). This strategy was found to be effective, and the use of tools such as WEED-IT can provide an effective way to incorporate other herbicides, and particularly follow-up for effective survivor control. Darling Downs grower Jamie Grant has more than a decade of experience growing cover crops and was a pioneer in including millet in his rotation as a dedicated cover crop. Jamie has modified his machinery and farming style, after much on-farm trial and experimentation. Jamie Grant: experience and experimentation lights the way Jamie is a dryland cotton grower near Jimbour, Darling Downs in South East Queensland. His current crop rotation is cotton every second year and a millet cover crop every other year. He has included French white millet as a cover crop in his rotation for nearly a decade and as a result, he has been able to change from cotton every third year to every second. Jamie said his main reason for including the cover crop is to preserve soil moisture. “The cover crop increases infiltration from rainfall, prevents the majority of run-off in larger events, and also prevents evaporation of moisture from the soil,” he said. “Weed management was not a major focus for the inclusion of the cover crop, however the cover from the millet does give an additional benefit in terms of weed control.” Jamie also highlights the importance of a dedicated cover crop, as compared to a cash crop that is harvested for grain. “The main purpose of the cover crop is to preserve moisture and cover,” he said. “When a crop is allowed to reach harvest maturity, it has taken extra moisture from the soil profile contrary to the objectives of a cover crop.” Crop choice Jamie has settled on French white millet as his cover crop, planted in 15-inch (38cm) rows. As the focus is to preserve soil moisture, millet is a short duration crop and can be grown to near maturity in six weeks from planting in October to December. In this time, the millet provides maximum cellulose to give the maximum length of cover from the stubble. “While growing, the millet only uses approximately one foot or 30 cm of stored soil moisture,” Jamie said. “The gains in soil moisture has improved fallow efficiency from 30 per cent in fallow to 70 per cent with the cover crop.” Before the inclusion of the cover crop, the soil profile required approximately 600mm of rainfall to refill. Now the profile is refilled after 300mm. The millet also creates enough cellulose that the cover remains adequate until cotton is planted the following season. Jamie’s own research has shown that legumes tend to break down too quickly to provide the length of cover required, and French white millet has the right characteristics. Jamie Grant grows cotton every second year rather than every third, using the moisture stored under the cover crop. “I find that if I plant in October, I generally have 40 per cent cover the following November, when I’m ready to plant cotton,” Jamie said. “I don’t use sorghum as a cover crop, as the wider row spacing does not provide the cover needed, and the gaps in the stubble create a suitable microenvironment for weed germination and growth.” “I also noticed that in lighter rainfall events in sorghum and wheat stubble, the rainfall runs down the stalks of the standing stubble and creates a wet patch at the base. This is where the weeds grow and creates weedy patches across the field. A good millet cover crop is more even and allows the rain to penetrate the stubble evenly, and the stubble cover reduces weed emergence and the need to spray.” Cover crops must reach maturity to create the maximum amount of cellulose for longevity. Other crops such as sorghum, wheat and barley take too long to reach maturity and as a result use too much moisture. The main weeds on Jamie’s farm include sowthistle, feathertop Rhodes grass and fleabane. Jamie places a high importance on weed control, however says “if you can grow good weeds, you can grow good crops”. Jamie’s focus on weed management in the cover crop is to ensure adequate cover across the whole field, as gaps in cover create a haven for weeds. “I do this by ensuring good germination, with quality seed, and I put as much effort into growing a good cover crop as I do growing cotton,” he said. “Double knocks are still an important part of the herbicide program and controlling weeds prior to crop emergence (both for millet and cotton) ensure the crop can get a head start to out compete the weeds. An in-crop spray of MCPA and Starane is always done in the millet to control volunteer cotton, however if a heavy cover crop is grown a spray to control volunteer cotton is not always needed.” Jamie also uses a controlled traffic system (CTS), as he considers minimising soil compaction to be very important, has been using WeedSeeker technology on a large boom for a number of years, and is now using a SwarmFarm robot mounted with a WEED-IT sprayer across his fields. The big boom is generally used for broadacre spraying, with the relevant herbicide mixture for the weeds present. The WeedSeeker, and now the SwarmFarm robot with the WEED-IT, will be mainly used to control weeds in fallows between rain events, and broadacre sprays on mass germinations. The spray rig is also rotated across the tramlines in the CTS, so that it does not constantly run up and down the same wheel tracks. This allows subsequent sprays to control weeds that were run over by the rig in the previous spray. Jamie’s key learnings and advice to growers considering growing cover crops is to ‘work it backwards’. “Grow the cover crop that can accumulate the most moisture, and then grow the cash crop that will take the best advantage of the moisture,” he said. “It is important to work out your moisture availability and your crop frequency. The moisture holding capacity of the soil will be better with a cover crop independent of soil type. The lower the capacity of the soil to hold moisture, the greater the effect evaporation has. This increases the importance of having a cover crop.” Growing good cover Jamie has spent a couple of years determining how to germinate and grow a good cover crop. He also stressed the importance of purchasing quality seed. “Patience is the key,” he said. “It is important to do a good job with proper seedbed preparation at planting. An example of this when planting millet, is that it does not like to break through a crust while emerging.” If Jamie gets enough rainfall for planting millet, he checks the forecast to ensure a further heavy rainfall event is not lik Jamie finds that putting the effort into the millet crop means he reaps the benefit in the following cotton crop. “A new tactic I’m considering is intercropping – planting millet between the cotton on a 60-inch row spacing (152 cm), and then spraying the millet out after three to four weeks,” he said. “This will increase ground cover in the cotton crop, with the benefits of increased weed competition, better rainfall infiltration and reduced moisture evaporation in-crop, for the sacrifice of some surface moisture that will evaporate in summer anyway.” Jamie said it is also of key importance to let neighbours know what cover crops you have, to minimise the risk of spray drift, which will reduce their effectiveness by either killing areas or impeding growth and creating areas of less than adequate cover. “Mapping fields with SataCrop is an important tool to do this,” he said. Effect on soil moisture quantified Cover crops serve multiple purposes in a cotton rotation, with research underway to quantify the effect on water infiltration and moisture holding capacity of soils. Research is also underway in the Riverina as part of the ‘Staying ahead of weed evolution in changing cotton systems’ project. Researchers at NSW DPI in collaboration with CRDC, GRDC and Queensland DAF have run a series of experiments at the IREC trial site near Whitton in Southern NSW to better understand the effectiveness of incorporating cover crops into cotton systems. The aim of this research is to evaluate the benefits that cover crops could provide when incorporated into cotton systems, especially improved water infiltration and water holding capacity of soil. An experiment looking at cover crop species and rotation types has been completed and is being analysed by a biometrician to gain insight into the soil water dynamics as influenced by the cover crops. Initial results suggest the type of cover used is less important than the amount of cover or biomass that is grown when it comes to influencing on yield. This season a spray out timing experiment is being conducted to determine how much biomass is required by cover cropping to have an influence on infiltration and water holding capacity. During the winter fallow a cover crop mix was sown and subsequently sprayed out at different growth stages. NSW DPI cotton research agronomist at Yanco, Hayden Petty says the intent was to achieve varying amounts of biomass into which cotton was planted. This will be compared to a fallow that is the control for the experiment. “Cover crops offer many benefits to a cotton farming system, as research is showing with weed suppression and soil health,” Hayden said. “After harvest this year we will have fully analysed the data and will be in a position to offer a quantifiable effect on soil moisture.” For more information, contact Hayden Petty This article appears courtesy of the Cotton Research and Development Corporation (CRDC). It was published in the Autumn 2020 edition of CRDC’s Spotlight magazine: www.crdc.com.au/spotlight. Images courtesy Tom Quigley and Hayden Petty.