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.
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Does delayed sowing help manage weed populations?
The answer to this question is a very simple ‘no’. Waiting for weed seeds with longer dormancy to germinate before sowing costs yield and weeds often set more seed in late sown crops. Dr Gurjeet Gill, Associate Professor of Weed and Crop Ecology at The University of Adelaide says sowing a competitive crop ‘on time’ has better outcomes for both crop yield and suppressing weed seed production. Dr Gurjeet Gill, Associate Professor of Weed and Crop Ecology at The University of Adelaide is one of the four experts presenting the new WeedSmart Crop Competition 101 online course. “The lack of effective in-crop herbicides leaves growers with few chemical options when it comes to controlling weeds like annual ryegrass and brome grass that are emerging later in the crop,” says Gurjeet. “Our field trials in South Australia demonstrated that sowing ‘on time’ is the best way to maximise crop yield and suppress weeds that germinate in-crop, both with and without the use of pre-emergent herbicides.” The time of sowing x seeding rate x herbicide field trials were conducted at several sites in South Australia in 2018 and 2019 with GRDC investment. “The other aspect of these trials was investigating the effect of seeding rate on weed density and seedhead production,” says Gurjeet, “Higher seeding rate increased the yield in wheat at Minnipa at both times of sowing, and did not increase screenings.” Early sown crops consistently produce more crop and less weeds. Dr Gill is one of the presenters in WeedSmart’s new Diversity Era ‘Crop Competition 101’ course, which can be completed online in less than 10 hours, giving you a solid grounding in ways to effectively implement tactics that give crops a competitive advantage over weeds. This free online course can be found at www.diversityera.com/courses/crop-competition-101 Why are weeds in cropping systems becoming more dormant? Short answer: Increased cropping intensity and routine use of pre-emergent herbicides selects for the longer dormancy trait in annual ryegrass and brome grass. Longer answer: Weed populations have a mix of individuals with different levels of seed dormancy. In self-regenerating pastures, there is likely to be a penalty for high seed dormancy and germinating later than the neighbouring plants. Therefore, high dormancy late germinating plants remain a minority in the population. However, the situation changes when growers switch to intensive cropping where knockdown herbicides routinely kill the very early germinating plants. In such systems, weeds that emerge with or soon after the crop have a greater survival because they escape the effects of the knockdown herbicides. After several years of cropping, weed populations change from being early germinating to later germinating. These later germinating weed populations are less responsive to delayed sowing and are now common in southern farming systems. See the
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.”
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.
FTR grass demands attention to stop seed set
Feathertop Rhodes (FTR) grass is quickly becoming one of the biggest weed threats in Australian farming systems, demanding swift and decisive action.The vast number of seeds produced per plant and the species’ ability to germinate and establish on very small rainfall events, gives this weed a real competitive advantage, particularly in a fallow situation. Feathertop Rhodes grass is a serious weed challenging no-till farming in Australia. In the northern cropping region researchers have observed FTR grass (Chloris virgata) germinating almost all year round, at temperatures ranging from 15/5° to 35/25°C (day/night temperatures). While many seedlings that establish in winter are killed by frost, some will survive and it only takes a few plants to produce a large number of viable seeds for the next generation. Recent research by Queensland Alliance for Agriculture and Food Innovation (QAAFI) weed researcher, Dr Bhagirath Chauhan has demonstrated that some populations of FTR grass are producing seed that is capable of germinating just two weeks after they mature. “Night temperature does affect seed production of feathertop Rhodes grass so it is important to concentrate efforts on preventing germination or controlling these weed populations in spring and early summer,” says Dr Chauhan. “These early germinated populations are also more able to compete with summer crops and then set seed in-crop.” Being able to tolerate both knockdown and residual (pre-emergent) herbicides, FTR grass can quickly gain a foothold in no-till farming systems. No-till and stubble retention also provide a favourable environment for germination, establishment and survival of FTR grass because of the moist soil conditions around the weed seed. An integrated approach, like the WeedSmart Big 6, is needed to tackle this serious weed before it forces a return to full cultivation for weed control. Diverse crop rotations – FTR grass is a year-round weed. Having diverse and competitive crops in rotation reduces the risk of a blow-out situation. Mix and rotate herbicide MOA – FTR grass is not reliably controlled with a single post-emergent herbicide application. To be effective, the weeds must be sprayed when they are very young and not stressed. At this stage, high rates of glyphosate with the best surfactants available, along with some group A products, can reduce the weed population. Residual herbicides like metolachlor, applied in late winter fallows, are very useful in moist soil conditions. Herbicide is largely ineffective on FTR grass unless it is applied to small, actively growing seedlings. Double knock glyphosate – Plan to follow any glyphosate application with a double knock to reduce the number of FTR grass survivors. Grow competitive crops – FTR grass is sensitive to crop competition. All efforts to increase crop competition through crop and variety choice, narrower rows and stubble management will suppress FTR grass germination. Early weed control in sorghum can effectively suppress weed seed production of FTR grass plants that germinate later in the crop. A competitive cover crop could also be a valuable option. FTR grass is susceptible to crop competition. Front – FTR from fallow, Middle – FTR from 1m row sorghum and Back – FTR from 0.5m row sorghum. Stop weed seed set – This is the single-most effective tool to prevent an FTR grass incursion. FTR grass is a prolific seed producer and can quickly get out of hand. Initial invasions often occur as a weedy patch forms around a few ‘mother’ plants. Removing large FTR grass plants before they seed, using patch cultivation, chipping, hand pulling or fire, is the best option. Seed is easily spread in overland flow and on vehicles, machinery (particularly headers), people and animals. Extreme care is required when managing weedy patches to avoid spreading the problem. Burning individual plants is one option to stop seed set on FTR grass. Harvest weed seed control – FTR grass could be a good candidate for weed seed collection and destruction at harvest. One study has shown that as much as 93 per cent of the weed seed was retained (held) on the plant at the time of mungbean harvest (Chauhan et al., unpublished data). Increased crop competition tends to encourage taller FTR grass plants, making it easier to capture the seedheads at harvest. “We also found that FTR grass seed on the soil surface is not viable after 12 months. Burying the seed lengthens the period that the seed remains viable, so unless the seedbank is completely buried to a depth of 5 cm or more and left undisturbed for more than 18 months, cultivation on its own might not be a good control tactic,” says Dr Chauhan. “If FTR grass seed is left on the surface, and no more seed is allowed to set, the seed bank will deplete in 12 months. In dry years the seed is likely to persist longer and some seed can be buried at planting or simply falling down cracks in the soil.” Feathertop Rhodes grass is already widespread across Australia and it is easily transported to new areas during floods, on machinery and in hay. Roadsides, water channels, head ditches, and on-farm tracks are all sources of weed seed, which can then easily enter cropping areas. If hay is brought in, it is wise to feed out in defined areas so any FTR grass plants can be more readily seen and removed before they set seed. It is also important for agronomists, researchers and contractors to strictly follow biosecurity practices and ‘Come Clean, Go Clean’. Find out more: Weed biology insights to improve management of feathertop Rhodes grass and barnyard grass Spring into action with fallow residuals How do I deal with an emerging feathertop Rhodes grass problem?
Weed management programs for pigeonpea
WeedSmart Audio · WS – Pigeonpea – 5-min – Read – 3 01 Pigeonpea might not be well known in Australia, but there are more than a billion people in Asia and Africa who eat this dried grain legume in a variety of dishes, and global demand is high. This demand is driving renewed interest in the crop, which was introduced to Australia in the 1970s but never developed into commercial production. In fact, it has only been grown as a trap-crop to monitor the incidence of Helicoverpa armigera (pod borer or bollworm) in Bt cotton crops. This trial used paired row sowing (right) to give pigeonpea a competitive advantage over weeds compared to sowing in a wider configuration (50 cm, left). As an emerging crop of importance to the grains and livestock industries, researchers have begun the task of investigating the agronomic requirements of pigeonpea in the Australian environment. Leading the way on the weed management front are researchers Gulshan Mahajan, Rao C. N. Rachaputi and Bhagirath Chauhan from the Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland at Gatton. “Pigeonpea is of interest because it is a drought and heat-tolerant summer legume, and provides both grain for human consumption and high quality fodder for livestock,” says Dr Bhagirath Chauhan. “Its slow growth habit is a significant limitation, making the crop very susceptible to yield loss as a consequence of competition from weeds.” In the summers of 2017 and 2018 the researchers tested the effect of row spacing and herbicide applications on crop yield. Their findings suggested that narrow row spacing (25 cm) and sequential herbicide applications provided effective weed control that preserved yield in pigeonpea. Across the two years there was a marked difference in seasonal conditions and weed flora. In 2017, the only weed present at the site was giant pigweed but following a deep tillage operation there was a more complex community of weeds, particularly grasses, growing at the trial site in 2018. “At the narrow (25 cm) and wide (50 cm) row configuration, a single application of the pre-emergent (pendimethalin) or a sequential application of pre-emergent and post-emergent (imazapic) herbicide reduced weed biomass and increased yield, compared to the no-control treatment,” he says. “When the sequential herbicide program was applied, it was equally effective in the narrow, wide and paired row configurations, giving growers more flexibility.” Narrow row spacing (25 cm) and sequential herbicide applications provides effective weed control that preserves yield in pigeonpea. “In seasons where conditions are too dry for the pre-emergent herbicide to be effective and there is a heavier reliance on the post-emergent herbicide alone, or where there are multiple weeds present, having the crop sown on narrower rows provides better weed control and preserves crop yield.” In the right conditions, the sequential use of herbicides addresses the common problem of multiple flushes of weeds over summer.
2019 Top 5 WeedSmart experts, bulletins and podcasts
This year we have collected the topics that you, our audience, found the most interesting – based on how many people browsed, downloaded or listened to material on the website. Here are the results! Starting with our expert columns where we ask industry leaders for their take on big decisions facing weed managers. 1. WeedSmart Expert https://www.weedsmart.org.au/whats-the-latest-in-optical-sprayer-technology/ 2. WeedSmart Expert https://www.weedsmart.org.au/is-mechanical-site-specific-weed-control-a-practical-fallow-management-option/ 3. WeedSmart Expert https://www.weedsmart.org.au/how-can-i-avoid-getting-stuck-in-an-imi-herbicide-cycle/ 4. WeedSmart Expert https://www.weedsmart.org.au/is-rapid-on-farm-herbicide-resistance-testing-possible/ 5. WeedSmart Expert https://www.weedsmart.org.au/does-diversity-help-with-weed-control-and-herbicide-resistance/ Next we will count down the top 5 articles on the bulletin board. 1. WeedSmart Bulletin https://www.weedsmart.org.au/stacking-the-big-6-in-a-strip-and-disc-system/ 2. WeedSmart Bulletin https://www.weedsmart.org.au/robotics-opens-up-more-non-herbicide-options/ 3. WeedSmart Bulletin https://www.weedsmart.org.au/and-then-there-were-three-impact-mills-on-the-market/ 4. WeedSmart Bulletin https://www.weedsmart.org.au/vertical-ihsd-maintains-the-brands-98-weed-kill-rate/ 5. WeedSmart Bulletin https://www.weedsmart.org.au/is-sunlight-breaking-down-pre-em-herbicides-where-farmers-are-dry-sowing/ Last but far from least, here are the top three podcasts! 1. WeedSmart Podcast https://www.weedsmart.org.au/podcasts/chaff-dump-management-and-strip-and-disc-systems/ 2. WeedSmart Podcast https://www.weedsmart.org.au/podcasts/vertical-ihsd-test-results-and-the-weedit/ 3. WeedSmart Podcast https://www.weedsmart.org.au/podcasts/weather-forecast-accuracy-and-crop-competition-trial-results/ The WeedSmart team looks forward to bringing you more great ideas from growers, agronomists and researchers across Australia to help manage weeds.