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.
Implementing ‘mix and rotate’ strategy to combat herbicide resistance
with Tony Lockrey, consulting agronomist, AMPS Moree Mixing and rotating herbicide modes of action is a key strategy in the WeedSmart Big 6 – but it’s a herbicide response to a herbicide problem. So, while it’s critical, it must be implemented within a diverse weed management program. Tony Lockrey, senior agronomist with AMPS Agribusiness at Moree has seen herbicide resistance get out of control on some farms in northern NSW while other growers have responded early and managed to maintain a broader spectrum of effective herbicides in their program. AMPS Moree consulting agronomist Tony Lockrey has seen good results when herbicides are rotated and mixed in each phase – the fallow, pre-sowing, in-crop and for desiccation. “It has to start with herbicide resistance testing – specifically for susceptibility,” he says. “Knowing what does work is very important as you’ve probably already got a fair idea about what doesn’t.” Once all the effective actives are ‘on the table’ it’s time to look at what crops can be grown to allow the use of the widest range of herbicide groups in the rotation, and where you might be able to find synergistic mixes that can further delay resistance and potentially allow the use of actives that are no longer effective on their own. “When we sit down to plan out an integrated weed control program we want to make sure there is rotation and mixing going on in each phase – in the fallow, pre-sowing, in-crop and for desiccation, where required,” says Tony. “When this is done in conjunction with a determination to stop seed set and remove survivors then it is possible to keep weed numbers low.” With an increasing number of proprietary herbicide mixes coming onto the market and the broad spectrum of synergistic and antagonistic interactions between potential mixing partners it pays to be well-informed and to seek advice. If I already rotate modes of action why do I have to mix too? Short answer: Rotation buys you time; mixing buys you shots. Mixing and rotating buys you time and shots. Longer answer: Rotation of effective modes of action can significantly delay the onset of herbicide resistance and needs to be built into your crop rotation plan. Herbicides in Group A and Group B are particularly susceptible to multiple exposure resistance with as few as six exposures being enough to select for the resistant mutation. By mixing MOA groups, either in the same tank mix or applied separately to the same population (like a double knock), those plants that survive one MOA are often killed by the second. How does testing for susceptibility help when there’s a weed blow-out? Short answer: Knowing what will work against a resistant population helps drive down the seed bank and helps you regain control. Longer answer: One real-world example is a paddock near Moree where Group A resistant wild oats were discovered in 1998 following a history of repeated use of Topik® (Group A – fop), Verdict® (Group A – fop) and, later, Axial® (Group A – den). Testing of this population showed the wild oats was very susceptible to Group B sulfonylurea, so Atlantis was used to drive down the weed numbers. A new plan was then put in place with Groups B, A, C and M used across the winter cropping program, but there was still too much reliance on Group B. The current plan for the farm now includes pre-emergent herbicides from Groups K, J and D used individually and in mixes. How do I integrate more mixes into my herbicide program? Short answer: Look for opportunities for synergistic mixes throughout the fallow and cropping seasons. In many instances the most important mixing partner is more water. Longer answer: Many growers are looking for tank mixes to improve control of glyphosate-resistant seedlings. Knowing which mixtures are beneficial and which are antagonistic is important. In the fallow, there are often opportunities to use the mix and rotate strategy to great effect in a double-knock application, such as: Group M (glyphosate) + Group I (2,4-D or fluroxypyr or picloram) followed by Group L (paraquat) Group M (glyphosate) followed by Group L (paraquat) + Group G (Sharpen® or flumioxazin) Group M (glyphosate) followed by Group L (paraquat) + Group K (Dual® Gold) Group A (Shogun®) followed by Group L (paraquat) + Group K (Dual® Gold) The fleabane on the right was unresponsive to glyphosate on its own but mixing picloram with triclopyr or 2,4 D to the glyphosate application was effective (left). Pre-plant examples include paraquat plus a triazine herbicide (Group C) or paraquat plus an imidazalinone (Group B), which are commonly used to provide broad spectrum knockdown and residual control. Dual® Gold (Group K) is another common fallow residual option which is very compatible with glyphosate, triazines and paraquat. An example of an in-crop mix is the addition of clethodim to haloxyfop (both Group A) to improve control of fop-resistant grasses in broadleaf crops where both are registered. At the end of the season there is also some opportunity to mix desiccants for some crops. None of these mixes are provided as recommendations – seek advice for your own situation and always read and follow the label. What about application set up for mixtures? Short answer: Some herbicides require better coverage. In many instances the most important mixing partner is more water. Longer answer: Suitable product and water rates, droplet size and the right adjuvant, are critical for optimising herbicide efficacy. For example, while a fallow mix such as glyphosate plus a Group A, or a Group G (depending on the target weed), is physically compatible, the components have different requirements for optimal performance. Seek advice about the best water rate to use, the potential impact of an oil-based adjuvant (required for most Group A and Group G herbicides) on glyphosate efficacy for some summer grass weeds, and other possible risks. Factsheet – Mixing knockdown partners with Group G How do I avoid generating multiple and cross-resistance? Short answer: Implement as many different weed control strategies as possible. The WeedSmart Big 6 is a practical foundation for an integrated program of herbicide and non-herbicide tactics. Longer answer: Rotating and mixing herbicide groups can give you room to move in holding off resistance or getting more out of some marginally effective products. The only way to stave off herbicide resistance completely is to have low weed numbers and to be vigilant about preventing survivors from setting seed. Have a diverse cropping program, use herbicides to provide early weed control, set your crops up to compete strongly and monitor and remove survivor weeds.
Big 6 winter – 4. Crop competition
A competitive crop will suffer less yield loss at the hands of the weeds, and will also reduce seed set of the weeds compared to an un-competitive crop. In other words more crop, fewer weeds. Principle #1Stay ahead of the pack Crop competition with weeds is a ‘winner-takes-all’ battle. When the crop wins their is higher grain yield plus lower weed biomass and lower seed set. For the crop to win this battle it is very important to give it a head start with effective early weed control. Keeping the crop weed free for the first three to six weeks seems to be a practical target. To maximise the effectiveness of using the crop as a weed control tactic, start planning the year ahead and do everything possible to reduce the weed seed bank using effective herbicides, weed seed burial, competitive cultivars and harvest weed seed control tactics or hay-making. Back this up with registered pre-emergents and as many non-herbicide tactics in-crop as possible. Principle #2 Adopt at least one competitive strategy (but two is better) There are six main avenues to increase crop competition: 1. Increased seed rate 2. Narrower row spacing – without changing seeding rate) 3. Row orientation – sowing east-west where practical 4. Crop choices – more competitive species and / or variety 5. Soil health – less compaction, fix pH and nutrient limitations 6. Time of sowing – early sowing is usually best It’s hard to include all six in every crop or every paddock – the more you can do the better the odds for your crops to suppress weed growth and seed set. https://www.weedsmart.org.au/whats-the-best-way-to-out-compete-resistant-annual-ryegrass-in-cereals/ https://www.weedsmart.org.au/whats-the-best-way-to-manage-annual-ryegrass-in-chickpea-crops/ https://www.weedsmart.org.au/sow-east-west/ https://www.weedsmart.org.au/paired-rows-give-entry-level-crop-competition/ https://www.weedsmart.org.au/taking-the-competition-to-the-weeds/ https://www.weedsmart.org.au/crop-competition-give-your-crops-the-edge/ https://www.weedsmart.org.au/up-the-competition-with-professor-of-agricultural-innovation-deirdre-lemerle/ The Big 6 1. Rotate crops and pastures 2. Double knock – to preserve glyphosate 3. Mix and rotate herbicides 4. Stop weed seed set 5. Crop competition 6. Harvest weed seed control – the holy grail WeedSmart Wisdom
Big 6 winter – 3. Double-knock to protect glyphosate
The idea of a double-knock for weed control is to use one tactic, usually a herbicide, to kill the majority of weeds and follow-up with another tactic, usually a herbicide from a different mode of action group, to kill any survivors. This can also be a herbicide followed by a non-herbicide tool (eg. the ‘Canola Combo’ – crop top followed by HWSC). All that really matters is any resistant survivors to the first herbicide are hit with another control measure so that the weeds don’t set seed. Principle #1 Follow glyphosate with a high rate of paraquat to control survivors in a fallow or pre-sowing situation Glyphosate is the world’s most important herbicide and nothing else comes close as a low cost, reliable knockdown, so we really need to look after it. In the fallow and / or pre-sowing apply glyphosate as the first knock, followed by a second knock with paraquat or paraquat + diquat to take out any resistant plants that have survived the glyphosate. If the main weed problem is annual ryegrass then using paraquat on its own as the second knock is an appropriate choice. If there are also broadleaf weeds present then the paraquat + diquat combination (e.g. Spray.Seed®) will be more effective overall. A herbicide double knock is all about timing and relies on using the second knock while weeds are still small – usually one to seven days after the first knock. With a non-herbicide second knock the timing is less critical, provided surviving weeds are not permitted to set seed. Building the double knock treatment into a whole-of-season weed management plan provides opportunities to get more ‘bang for your buck’. For example, follow a pre-sowing double knock with pre-emergent herbicides, and increase the level of crop competition with narrow row spacing, optimal sowing time and varieties with vigorous early growth. The first knock is to kill all plants still susceptible to glyphosate—applying a lower rate risks higher survival rates, increasing the pressure on the second knock products. The second knock of Spray.Seed® or paraquat is to kill plants that survived the glyphosate. Reducing the rate of the second knock risks survival of potentially glyphosate resistant individuals and damages the integrity of the double knock tactic. Remember that paraquat and Spray.Seed® are contact herbicides and require robust water rates to ensure adequate coverage and allow for losses on stubble. If there is a mix of weeds present it can be useful to include a compatible herbicide ‘spike’ such as 2-4D low volatile ester, carfentrazone or oxyflouren to enhance control of broadleaf weeds. Be very mindful of plant-back requirements of some herbicide ‘spikes’ before planting sensitive crops such as pulses and canola. Optical sprayers such as Weedseeker and WEEDit are an efficient way to apply the second knock to kill any survivor weeds. Even the highly effective double-knock tactic is at risk if growers don’t remain vigilant and ensure removal of any surviving plants. https://www.weedsmart.org.au/protecting-knock-down-herbicide-options/ https://www.weedsmart.org.au/confirmed-resistance-to-the-double-knock-tactic-in-tall-fleabane/ https://www.weedsmart.org.au/whats-the-latest-in-optical-sprayer-technology/ The Big 6 1. Rotate crops and pastures 2. Double knock – to preserve glyphosate 3. Mix and rotate herbicides 4. Stop weed seed set 5. Crop competition 6. Harvest weed seed control – the holy grail WeedSmart Wisdom
Big 6 winter – 2. Mix and rotate herbicide MOA
Before herbicide selection has taken place it is very rare for an individual weed to be resistant to two herbicides. Mixing herbicides at full label rates in a single application takes advantage of this fact. Within an integrated weed control program, try to make sure there is rotation and mixing going on in each phase – in the fallow, pre-seeding, in-crop and for desiccation. When done in conjunction with a determination to stop seed set and remove survivors, it is possible to keep weed numbers low. Principle #1 Rotating buys you time, mixing buys you shots Herbicide products are classified and grouped according to their mode of action (MOA). That is, products that target the same lethal pathway are grouped together. Rotating between herbicide modes of action has the beneficial effect of ‘buying time’ because if a MOA is used once every two years the lifespan of the herbicide effectively doubles. Rotation of effective modes of action can significantly delay the onset of herbicide resistance and needs to be built into your crop rotation plan. Herbicides in Group A and Group B are particularly susceptible to multiple exposure resistance with as few as six exposures being enough to select for the resistant mutation. By mixing MOA groups, either in the same tank mix or applied separately to the same population (like a double knock), those plants that survive one MOA are often killed by the second – this ‘buys you shots’. Principle #2 Rotate between herbicide groups Start with a herbicide susceptibility test to find out what herbicides and herbicide mixes are still effective. Rotating between products within the same MOA group is the same as using one product all the time and is a very high risk weed control tactic. Crop rotation can drive rotation of herbicide MOA. For example, if you use trifluralin in canola, consider another registered MOA option for wheat. Based on research from the Australian Herbicide Resistance Initiative, the best advice to growers and agronomists is to rotate between these three groups of pre-emergent herbicides – 1. trifluralin, 2. Sakura, Boxer Gold and triallate and 3. propyzamide. Full label rates must be applied. Principle #3 Use different groups within the same herbicide mix Mixtures are more effective than just rotating MOA in delaying resistance as mixes generally achieve a greater kill rate. While some mixes are physically compatible, the components might have different requirements for optimal application – such as droplet size and and water rates. With an increasing number of proprietary herbicide mixes coming onto the market and the broad spectrum of synergistic and antagonistic interactions between potential mixing partners it pays to be well-informed and to seek advice. Rotating herbicide groups is an effective way of slowing resistance build up and managing resistance while ever there are actives to go to. Mixing herbicides from the same or separate active groups can also give you room to move in holding off resistance or getting more out of some marginally effective products. In fallows, where there is no additional crop competition, a second (double knock) application to the same weed germination can be very effective. Some common double knock approaches that use the mix and rotate strategy are: Group M (glyphosate) + Group I (2,4-D or fluroxypyr or picloram) followed by Group L (paraquat) Group M (glyphosate) followed by Group L (paraquat) + Group G (Sharpen® or flumioxazin) Group M (glyphosate) followed by Group L (paraquat) + Group K (Dual® Gold) Group A (Shogun®) followed by Group L (paraquat) + Group K (Dual® Gold) The only way to stave off herbicide resistance completely is to have low weed numbers and to be vigilant about preventing survivors from setting seed. Have a diverse cropping program, use herbicides to provide early weed control, set your crops up to compete strongly and monitor and remove survivor weeds. Principle #4 Always use full label rates Reducing the application rate of herbicides increases a weed’s ability to evolve resistance. Any saving in chemical costs is significantly outweighed by the risk of the low dose causing faster herbicide resistance evolution. Having dual action does not negate the need to change herbicide products and rotate modes of action. Repeated use of any single strategy will reduce the effectiveness of that strategy over time. Some herbicides require better coverage. In many instances the most important mixing partner is more water. https://www.weedsmart.org.au/using-tank-mixes-to-extend-herbicide-life/ https://www.weedsmart.org.au/how-does-mixing-moas-buy-more-shots/ https://www.weedsmart.org.au/dont-start-mixing-water-quality-right/ https://www.weedsmart.org.au/factsheets/mixing-requirements-for-spraying-operations/ The Winter Big 6 1. Rotate crops and pastures 2. Double knock – to preserve glyphosate 3. Mix and rotate herbicides 4. Stop weed seed set 5. Crop competition 6. Harvest weed seed control – the holy grail WeedSmart Wisdom
Big 6 winter – 1. Rotate crops and pastures
Short rotations cause herbicide resistance! This is because of the inherent lack of diversity. Weed populations quickly respond to routine management practices – those that survive will set seed and their progeny have an advantage when the same control tactic is used again soon after. Principle #1 Diverse herbicide choices, diverse cultural practices Following a longer crop rotation, and including a pasture phase if possible, means having more tools in the toolbox—better herbicide rotation, a range of seed set control options, varied planting times, competitive crop species or varieties and the ability to implement a variety of harvest weed seed control options. If you can’t see your way clear to lengthen your crop rotation, look for ways to increase diversity within the crops you grow. Changing varieties may allow a different sowing time and in herbicide tolerant crops such as canola, you can rotate between the RR and TT hybrids. In a tight rotation harvest weed seed control and maximum crop competition are even more important. Principle #2 Use double breaks, fallow and pasture phases to drive the weed seedbank down over consecutive years Rotating to a double (or triple) break crop is a great way of smashing the weed seed bank, setting the paddock up for a long crop phase. Examples of double break combinations are hay/canola, pulse/canola and fallow/canola and single breaks are still often used in the rotation. Some growers also include two crops of the same type (e.g. two cereals) in succession and rotate chemistry or change planting date. If you can include a pasture, it is important that you always go into the crop phase with low weed numbers and also go into the pasture phase with low numbers. Sowing a pasture should not be seen as a re-set option after a weed blow out. Take a planned approach right across the pasture phase and use a number of tactics known to be highly effective at preventing seed set. Several of the tactics available for use in a pasture phase can provide over 90 per cent control of the target weeds. The plan needs to outline how the pasture phase will fit into the crop rotation and what tactics will be used seasonally and rotationally to maximise the effect on weed numbers. Including a pasture phase does not always mean gearing up to run livestock. The pasture could be grown for hay or silage or even as a fallow cover crop. https://www.weedsmart.org.au/does-diversity-help-with-weed-control-and-herbicide-resistance/ https://www.weedsmart.org.au/why-is-diversity-so-important-in-the-battle-with-herbicide-resistance/# https://www.weedsmart.org.au/is-crop-rotation-an-economic-option-for-managing-weeds/ https://www.weedsmart.org.au/will-longer-rotations-really-help-manage-weeds/ https://www.weedsmart.org.au/can-use-pasture-phases-beat-herbicide-resistant-weeds/ The Big 6 1. Rotate crops and pastures 2. Double knock – to preserve glyphosate 3. Mix and rotate herbicides 4. Stop weed seed set 5. Crop competition 6. Harvest weed seed control – the holy grail WeedSmart Wisdom
Trends in HWSC – the days of doing nothing are over
A simple online survey of 147 farmers from around Australia has added weight to the observations that growers are rapidly adopting harvest weed seed control methods that best suit their farms. WeedSmart has previously conducted a similar survey in 2017 (269 respondents) and 2018 (95 respondents), and in 2014 a GRDC funded grower practices survey led by Rick Llewellyn from CSIRO, 600 growers answered questions related to the adoption of harvest weed seed control methods. Peter Newman, WeedSmart and AHRI extension agronomist in Western Australia is thrilled to see more evidence of growers adopting harvest weed seed control tactics to their farming systems. Peter Newman, WeedSmart and AHRI extension agronomist in Western Australia has been following the adoption trends closely. “We know that these surveys are biased and are not statistically rigorous, but together they are showing trends that we are also seeing in the field,” he says. “As growers invent, modify and trial different harvest weed seed control tools there is a rapid move toward actively managing survivor weeds at harvest and the adoption of tools that don’t involve burning.” The most important and encouraging finding is that the percentage of growers ‘doing nothing’ to capture and destroy weed seeds present at harvest has declined dramatically since 2014 harvest, from almost 60 per cent, down to around 5 per cent predicted for 2022 harvest. “This is a significant change in attitude and suggests that growers are taking the opportunity to tackle herbicide resistance head-on. When it comes to choosing the best tool for the job, growers can be assured that each of the tools available are equally effective at capturing and destroying weed seeds,” says Peter. “Some tools have a particular fit for certain situations, such as a chaff cart might be chosen for a mixed farming operation, or chaff tramlining chosen to help manage dust and erosion risk in a controlled traffic system.” Adoption trends for harvest weed seed control tactics on Australian grain farms. Around 10 per cent of growers are using and expect to continue using chaff carts and there is steady adoption of chaff tramlining, with almost 20 per cent of respondents planning to use a chaff deck this harvest. “It is clear that narrow windrow burning has been superseded and few growers will be disappointed about having better options that conserve nutrients and involve less risk,” he says. “Less than five per cent of growers expect to still be doing narrow windrow burning in the 2022 harvest.” While chaff lining has been rapidly adopted as a simple and cheap alternative to narrow windrow burning, many growers indicated that they would not be using this method in 2022. The trends indicate that many of these growers will be looking carefully at recent developments with weed seed impact mills. “With three weed seed impact mill manufacturers now offering machines in Australia, growers are the beneficiaries of increased competition and many see this as the ultimate solution to weed seed, stubble and nutrient management at harvest,” says Peter. Harvest weed seed control is one of the WeedSmart Big 6 suite of tactics to contain the threat of herbicide resistance in weeds. Other resources: AHRI Insight paper: Spoiled rotten – the sequel AHRI Insight paper: HWSC is now mainstream
What do vineyards and fencelines have in common?
Keeping weed numbers down in crops is a high priority on most farms, yet herbicide resistance can quietly increase along fencelines and around infrastructure. Having a ‘set and forget’ weed control option for these areas could save money and arrest the evolution of herbicide resistance in weeds. In vineyards the under-vine area is often kept bare using a limited number of suitable herbicides, opening the door to herbicide resistance. Populations of glyphosate-resistant annual ryegrass and fleabane have been confirmed in Australian vineyards and along fencelines and roadways. Chris Penfold, research agronomist at the University of Adelaide, Roseworthy Campus says effective living mulches can provide a long-term management solution to stop fencelines being a source of herbicide resistant weeds. Having worked previously in broadacre cropping, and more recently in the wine industry, research agronomist Chris Penfold, University of Adelaide is interested in identifying alternative ways to manage under-vine and mid-row areas in vineyards, which also has implications for fencelines on grain and mixed farming properties. “In many cases it might be better to replace weeds on the fencelines with a competitive but palatable option,” he says. “In vineyards, the continual use of herbicides and cultivation for weed control under the vines has a long-term detrimental effect on soil health and grape quality. Consequently, our research aimed to identify cover crop species that would build soil health and conserve soil moisture for the vines. Since this is not a priority on grain farms, a range of other options might be chosen but the principle can remain – establish permanent cover and stop fenceline spraying,” says Chris. Of the treatments Chris included in his trial, Kasbah cocksfoot and wallaby grass stood out as competitive species that did not spread into neighbouring areas and could be suitable for controlling weeds on fencelines. “Kasbah provided good suppression of fleabane and thistles in vineyards, especially in irrigation areas. It is a summer dormant perennial that doesn’t recruit, even in vineyards. It did suppress vine growth so it isn’t a great option for vineyards but could work for fencelines,” says Chris. “The other competitive border species we tried was wallaby grass, a native perennial, which provided good cover, but seed is expensive and it can be hard to establish. By not applying herbicide to fencelines growers will save money, which can be partly re-directed to the establishment of effective living mulches to provide a long-term management solution to stop fencelines being a source of herbicide resistant weeds.” Perennial species and self-regenerating annuals are the preferred options to minimise on-going management costs. The best species to establish will vary markedly between regions with prostrate saltbush having potential in drier areas, and lucerne and wallaby grass providing good control, even against caltrop, in other situations. In the vineyard situation a medic plus annual ryegrass cover provided good winter weed control and soil health benefits. By not spraying the annual ryegrass herbicide resistance does not evolve. Native perennials such as wallaby grass, can provide good cover along the borders without spreading into the crop. Another option Chris has investigated is in-crop grazing with sheep. With living mulches growing around the borders, sheep can be allowed to graze in established crops such as chickpea, faba bean, fenugreek and lupins, at light stocking density. The sheep will preferentially graze the in-crop weeds and may also assist with weed control along controlled traffic wheeltracks, especially if weed seed is directed onto the wheeltracks using a chaff-deck for harvest weed seed control. “Sheep are selective grazers and lambs are more selective than older sheep,” says Chris. “Different sheep breeds also graze differently so these things need to be considered for each farming system. The principle to apply is to incorporate non-chemical management practices where possible into the farming system, which should then extend the useful life of herbicides.” Where pastures are part of the crop rotation it can be as simple as establishing the pasture species along the fencelines and leaving them in place when the paddock rotates into the cropping phase. Similarly, the crop can be sown right up to the fenceline and either mown or baled for hay prior to harvest. Nipping herbicide resistance in the bud in non-cropping areas is an important strategy often overlooked. These areas are often sprayed when weeds are large, often using the same herbicide (usually glyphosate) each time, and there is rarely any follow-up treatment of survivors. This is a recipe for rapid evolution of herbicide resistance. Other resources for fenceline management: Managing fencelines
And then there were three – impact mills on the market
Crop residue management is core business for Canadian company Redekop Manufacturing and now they have added harvest weed seed control to their offering to Australian grain growers. Redekop have recently commercialised the Seed Control Unit (SCU), a weed seed impact mill that incorporates their well-known MAV straw chopper. This new impact mill makes three options commercially available on the Australian market – adding to the Australian-built iHSD and Seed Terminator. Redekop Manufacturing’s president, Trevor Thiessen. Redekop’s president, Trevor Thiessen said the company inadvertently became involved in harvest weed seed control when they noticed their chaff carts were being used in Australia to manage weeds rather than as a fodder collection system they were first invented for in the 1980s. “Herbicide resistance in Canada is about five years behind the situation in Australia but it is definitely an increasing problem,” he said. “We have been working toward the development of the SCU since 2013 and tested the first units in 2017 in Australia and Canada.” “Testing continued in 2018 to gather weed kill rates, which are consistently above 98 per cent, but there are some weeds and some conditions that we are yet to test.” Breanne Tidemann, a research scientist in field agronomy and weed science with Agriculture and Agri-Food Canada in Lacombe, is conducting the independent testing of the SCU. Breanne has also been testing a tow-behind HSD unit in Canada since 2016 harvest. The Redekop system combines the SCU chaff stream with the MAV straw stream, mixing the two streams in the same air flow at the back of the harvester to achieve improved residue spread and distribution. Redekop Seed Control Unit (SCU). Peter Newman, AHRI and WeedSmart Western agronomist said the recent expansion of options for growers wanting to use impact mills as their harvest weed seed control method was phenomenal. “The three impact mills currently available are all integrated into harvesters, making harvest weed seed control very time efficient,” he said. “One important aspect that Redekop have really focussed on is achieving even spread of the crop residue out the back of the harvester. This is critical to the integrated mill systems achieving the most cost-effective outcome for growers by re-distributing nutrients across the full cutter-bar width.” In a recent WeedSmart survey of over 100 growers around Australia, close to 50 per cent of growers plan to adopt a weed seed impact mill into their system within the next 3 to 5 years. Redekop will have 20 SCUs operating in Western Australia this harvest with a team of support and research personnel on hand to further assess the units’ performance in Australian conditions and address any mechanical issues. The SCUs are available as either a complete unit incorporating a MAV chopper suitable for all harvester types or as a purpose-built mill that fits onto a John Deere residue manager. Being integrated with the straw chopper, the SCU can be easily switched from chopper to chopper plus weed seed control. Redekop are also involved in introducing the Australian-built EMAR chaff decks to Canadian growers as an entry level investment in harvest weed seed control. Other resources Podcast – Redekop impact mill Vertical iHSD Using your harvester to destroy weeds Webinar – Comparing the iHSD and Seed Terminator https://www.weedsmart.org.au/app/uploads/2019/10/integrated-design-render.mp4
The best way to out-compete resistant annual ryegrass in cereals
with Chris Davey, Agriservices Agronomist, YP AG Often regarded as the ‘poor cousin’ to herbicides, crop competition is making a come-back as a simple way for growers to increase crop yield and reduce weed seed set, without breaking the bank. Chris Davey, partner and director of YP AG at Kadina has worked with growers on the Yorke Peninsula of SA for over 20 years in an on-going battle with weeds such as annual ryegrass, brome grass and bifora, and mounting resistance to herbicide. YP AG agriservices agronomist Chris Davey says several Yorke Peninsula growers have adopted east-west sowing after seeing the benefits of competitive crops combined with pre-emergent mixes in a recent trial. “Working with our grower group we have demonstrated that stacking crop competition tactics at sowing really does make a difference,” he says. “When you add an effective pre-emergent herbicide to the top of the stack to provide early weed suppression, the resulting increase in yield and reduction in weed pressure definitely puts money in the bank.” In the 2018 trial, two cultivars of wheat (Scepter and Emu Rock) and barley (Compass and Spartacus) were sown into lentil stubble. The trial compared the performance of these four cultivars when sown east-west v north-south, and with a range of pre-emergent herbicide packages. “The result was clear – when you plant a competitive crop like barley in fertile soil – such as following lentils, row orientation doesn’t make much difference, but if you plant a poorly-competitive crop like wheat, it really pays to stack as many things in its favour, including east-west sowing and an effective pre-emergent herbicide,” says Chris. “In wheat we measured a consistent 0.5 t/ha yield gain through east-west sowing across the two cultivars and pre-emergent herbicide packages. In barley, stacking a premium pre-emergent herbicide mix onto an already-competitive crop boosted yield by 1.1 t/ha and reduced ryegrass plant numbers ahead of the following seeding by over 80 per cent, compared to the least competitive, nil pre-emergent barley treatment.” With harvest weed seed control already adopted by many growers on the Yorke Peninsula, the results of Chris’ trial has prompted the adoption of even more WeedSmart Big 6 tactics to tackle herbicide resistance head-on. In the trial, the package of competitive crops and cultivars plus east-west sowing plus a premium pre-emergent herbicides mix combined to make an impressive difference in annual ryegrass numbers while also producing more grain. What is the effect of crop competition on weed seed production? Short answer: Crop competition makes a massive difference to weed seed production in-crop. Longer answer: Ahead of this trial in 2018 the weed seed potential of the site was calculated as 87,000 annual ryegrass seeds/m2. The annual ryegrass population was known to be 100 per cent resistant to trifluralin (e.g. Treflan), 50 per cent resistant to triallate (e.g. Avadex) and 30 per cent resistant to prosulfocarb + s-metolachlor (Boxer Gold). Applying crop competition plus pre-emergent herbicide drove this number down to around 4000 seeds/m2leading into the 2019 cropping season. The owner of the trial site chose to cut the surrounding crop for hay to prevent further blow-out of the annual ryegrass population. Although the crop competition plus pre-emergent herbicide package made a vast difference to weed seed production it is not a one-year fix for a ryegrass blow-out. It is important to keep the pressure on. After seeing the results of the trial, several members of Chris’ grower group immediately adopted east-west sowing on paddocks where the change was practical. It is understood that it is often necessary to sow according to land type, such as on dune swale paddocks, or other constraints, such as established CTF systems that run north-south. Where changing row orientation to east-west is not possible there are still many other ways to boost crop competition. Left: No crop competition, just solid annual ryegrass. Middle: Least competitive treatment (N/S sown non-competitive wheat variety – Emu Rock, with standard pre-emergent – trifluralin + triallate). Right: Most competitive treatment (E/W sown competitive barley variety – Compass, with premium/stacked pre-emergent – Boxer Gold + triallate). Where did the reduction in weed seed production come from? Short answer: Stacking competition tactics and pre-emergents in barley reduced ryegrass weed seed set by over 80 per cent. Longer answer: Changing from a less competitive (Spartacus) to more competitive (Compass) cultivar reduced ryegrass plant numbers at seeding in 2019 by 13 per cent on north-south orientation and 24 per cent on east-west orientation, with no pre-emergent applied. Keeping the cultivar the same and changing row direction reduced weed numbers by 26 per cent in Compass and 16 per cent in Spartacus. This suggests that changing to east-west sowing will not achieve much in barley unless a more competitive cultivar is chosen. Changing both the competitiveness of the cultivar and the row orientation achieved a very useful reduction in weed numbers of 34 per cent (without using any pre-emergent). The result may be even greater in a more common rotation where barley is planted after wheat and the initial soil nutrient status is less than after lentils. When you add a standard pre-emergent mix (trifluralin plus triallate) to the east-west sown Compass, weed numbers are driven down by 50 per cent. Using a premium mix of (Boxer Gold plus triallate) achieved an 82 per cent reduction in annual ryegrass plants going into the 2019 season. This is particularly impressive given the field’s known resistance to the applied pre-emergent chemistry and highlights the value of stacking pre-emergents together and growing a competitive crop. What impact did the treatments have on yield? Short answer: East-west sowing increased wheat yield in this trial, probably due to extra competition at a very weedy site. Longer answer: In wheat there was a consistent 0.5 t/ha yield gain through east-west sowing across the two cultivars and pre-emergent herbicide packages. In barley, stacking a premium pre-emergent herbicide mix onto an already-competitive crop boosted yield by 1.1 t/ha compared to the nil pre-emergent, north-south treatment. E/W sown barley (left) v N/S sown wheat (right). Why worry about crop competition if there are new pre-emergent herbicides coming to market? Short answer: The new herbicides will provide another useful tool for growers but are not the answer on their own. Longer answer: The choice of pre-emergent herbicide should be the final decision after you have stacked as many crop competition tactics as possible. Look for the most competitive combination of crop species/cultivar, row spacing, seeding rate, row orientation, sowing time for early vigour and healthy soil, then add a pre-emergent that is known to be effective. If the crop competition is strong then the pre-emergent just needs to provide the early weed suppression that gives the crop a head start. Strong competition plus a current premium pre-emergent package (Boxer Gold plus triallate) performed as well as the ‘experimental’ pre-emergent products in this trial. Other resources: AHRI Insight – Easy to adopt crop competition tools