Going for the Big 6 on Yorke Peninsula farms
Chris Davey, partner and director of YP AG at Kadina has worked with growers on the Yorke Peninsula of SA for over 20 years, assisting them to devise weed control programs that reduce the impact of herbicide resistance. His group of 20 clients farm between Port Broughton and Arthurton with annual rainfall ranging from 300 to 500 mm and very diverse soil types. Chris initiated the Northern Sustainable Soils farmer group in 2007 to provide growers with the opportunity to research farming system tactics and discuss their ‘fit’ for the highly variable soils found on the Peninsula. YP-AG partner and director, Chris Davey works with his grower clients including Gary Bruce (left), to plan integrated weed management programs that include as many of the WeedSmart Big 6 tactics as possible. “The soils here range from shallow sheetrock and limestone to grey calcareous loams, dune and swale systems to heavy red fertile clay,” he says. “This variability drives many management decisions and has a direct relationship with many of our weed problems.” Chris has used resistance testing services to keep track of herbicide resistance in the main weeds, with growers managing resistance in annual ryegrass, brome grass and wild radish for some time and more recently finding milk thistle, Indian hedge mustard and prickly lettuce increasingly problematic. Annual ryegrass and brome grass on the Peninsula are known to have resistance to herbicides in Groups A (fop and dim), B, D and M and wild radish is resistant to Groups B, F and I. “This area was the home of ryegrass resistance and growers are trying hard to avoid the same blow-out situation with brome grass,” says Chris. “Growers are well aware of the potential consequences if resistant brome grass gets out of hand so most are using some form of patch management and even chemical fallow in blocks where the brome grass has out-competed the crop.” In response to increasing herbicide resistance, 85 per cent of Chris’ clients have adopted some form of harvest weed seed control within their weed management program. “Sixty per cent of my clients are using narrow windrow burning and 25 per cent are using either a chaff cart or chaff lining chute,” he says. “In the 2017 harvest there was also one iHSD and one Seed Terminator operating here.” Chris is a strong supporter of all the tactics in the WeedSmart Big 6 and actively promotes the inclusion of all tactics in his clients’ integrated weed control programs. 1. Crop and pasture rotation The close lentil – wheat rotation that has dominated farming systems on the northern Yorke Peninsula in recent years is acknowledged as a weak link in terms of weed control. This rotation has led to an increase in broadleaf weeds such as milk thistle and prickly lettuce, with bifora, tares and medic also exploding in the lentil phase in some years, leaving a high weed seed bank for the following year as well as increasing the risk of herbicide resistance evolution. Chris says the economic drivers for the rotation can make weed control decisions difficult and there is a need for other profitable rotation options that can assist in reducing weed pressure. The main problem with the short rotation is that weeds are exposed to the same herbicide modes of action every two years. Although imi-tolerant (Clearfield) varieties have been very useful, particularly PBA Hurricane lentils, allowing the use of Group B herbicides in the crop or in previous seasons, the alkaline soils on the Peninsula have expedited the more rapid evolution of Group B resistance in wild radish, mustard, milk thistle and ryegrass. Lentils have provided several economic and weed control benefit to farming systems on the Yorke Peninsula but the short lentil / wheat rotation is a definite weakness when it comes to managing herbicide resistance. 2. Double knock to protect glyphosate Glyphosate resistant ryegrass is widespread on the Yorke Peninsula, primarily along fencelines but as fences are removed to form larger paddocks, there is a significant risk that the resistance gene will be spread by headers. In 2013, the Peninsula had the dubious honour of having the first confirmed case of glyphosate resistant brome grass on a farm near Maitland, and this season, glyphosate resistance in barley grass was observed for the first time on northern Yorke Peninsula. An annual double knock application before seeding is considered very important to help protect the efficacy of glyphosate and is widely practiced on the Peninsula. Sowing earlier to achieve a yield advantage and dry sowing can impact on the use of double knock. Chris advises his clients to avoid early or dry sowing in weedy paddocks and to hold off sowing until the double knock has been implemented, even though there could be a yield penalty. Under dry, dusty conditions most growers will choose two contact herbicides such as paraquat or paraquat / diquat rather than glyphosate / paraquat for the double knock. 3. Mix and rotate herbicide groups There is a heavy reliance on pre-emergent herbicides on the Yorke Peninsula and in weedy paddocks growers need to use additional shots to drive down weed numbers to preserve yield. In cereals, the Boxer Gold and Sakura applications are often spiked with triallate to strengthen the pre-emergent efficacy because there are no in-crop herbicide options in wheat and barley crops. Pre-emergent herbicides are also very important in lentils as the main break crop to reduce ryegrass numbers so there is less pressure on the clethodim / Factor mix in crop. Trifluralin susceptibility in ryegrass has been very low since the late 1990s and so is not a tank mix option, unless targeting broadleaf weeds like wireweed or three corner jack. 4. Stop weed seed set Chris says Yorke Peninsula growers generally use their late fungicide application in August or September to scout for weed escapes in crop. Taking a nil tolerance approach, growers might hand pull small areas, or spot spray. Using paraquat or paraquat / diquat, growers can avoid using glyphosate on potentially resistant individuals when chemically fallowing areas of their crop. The permit for Weedmaster DST use to crop-top in barley provides a useful control tactic for radish and ryegrass at the end of the season, but is often too late for brome grass, which has usually already set seed by this stage of the crop. In blow-out situations Chris often advocates for the ‘short-term pain for long-term gain’ of a chemical fallow using paraquat or Spray.Seed. Chris suggests that the chemical fallow is the best tool to use if brome numbers are building up in a paddock. In his experience, the performance of the following crop usually makes up for the one-year sacrifice due to increased nutrients and moisture availability. He says some growers plan for the inclusion of a small portion of the rotation to be sown as a chemical fallow, while a larger number would use chemical fallow only in a failed crop or for a weedy portion of a paddock as a patch management option. 5. Crop competition Where the soil type allows, Yorke Peninsula growers have readily adopted east west sowing having seen the benefits of this row orientation promoted through AHRI and WeedSmart. Some soil types, such as the sand swales around Port Broughton, dictate sowing direction but it is an option in other areas. Barley is the most competitive crop grown across the Peninsula and growers usually consider choosing the most competitive cultivars available. This is coupled with high sowing rates and narrower row spacing of 22–30 cm (9–12″) spacing, although there is local research that suggests there could be benefits of even narrower row spacing. 6. Harvest Weed Seed Control (HWSC) Chris’ trial work with HWSC shows the importance of getting the weed seed into the header. He says brome grass can be difficult as its flexible stem doesn’t always get cut and can flick back up once the harvester has passed. Wild radish generally stands up well with 70–80% of seed entering the header. Even with a 50 to 60% capture of brome grass, depending on the season and how early harvest occurs, HSWC is still an important part of any weed management program. Capture of ryegrass seed is seasonal with the ryegrass lodging in some years and not picked up by the header, while it will stand up well and achieve 80% capture in other years. Once weed seed is in the header, Chris’ research has shown that it doesn’t matter what HWSC method is used – all are effective. Chaff carts and narrow windrow burning have been widely adopted for many years but Chris expects that chaff lining and chaff decks is likely to increase while NWB will decrease in use. Chaff lining was widely adopted in 2017 harvest as an economical and easy way to manage weed-laden chaff. He also expects some growers with larger areas and some contractors to purchase iHSD and Seed Terminator modules, with one each of these operating in 2017 harvest on the Peninsula. Chris Davey’s trial work with various harvest weed seed control methods has shown that the amount of weed seed entering the header can vary, but once in the header all methods are equally effective at reducing the weed seed bank for the next season.
Winter pulses can compete, even without herbicide
Chickpeas and faba beans now have a permanent place in most northern region farming rotations and, while they offer some diversity in herbicide options, they have been considered comparatively less competitive against weeds than other crops. Back when growers had a number of effective herbicide options available, the lower competitiveness of these pulse crops was less problematic because the herbicides were keeping weed numbers low. In the light of increasing herbicide resistance in many weeds, strong crop competition is required to do more of the ‘heavy lifting’ within an integrated weed management program. Dr Michael Widderick, Queensland Department of Agriculture and Fisheries principal research scientist, is leading the work on crop competition within the multi-facetted GRDC-funded ‘Innovative crop weed solutions for northern region cropping systems’ (US00084) project led by Dr Michael Walsh, University of Sydney. The first round of southern Queensland data was collected for faba bean (PBA Warda) and chickpea (PBA HatTrick) trials harvested in late October 2017, at the Hermitage site near Warwick. Sowthistle is a major winter weed in pulse crops and growers are finding it is increasingly able to escape herbicide control, robbing the crop of valuable resources while setting huge numbers of seeds that increase weed pressure in the following season. There are known populations of sowthistle with resistance to glyphosate and chlorsulfuron in the northern grains region (and 2,4-D resistance confirmed in SA), making non-herbicide control tactics all the more important in driving down numbers of this moisture-sucking weed. Sowthistle is a major winter weed in pulse crops and growers are finding it is increasingly able to escape herbicide control, robbing the crop of valuable resources while setting huge numbers of seeds that increase weed pressure in the following season. “We are looking at optimal row spacing and crop density to combat common sowthistle, and also determining if more competitive crops are also higher yielding,” says Dr Widderick. “The trials are being replicated at sites near Warwick, Narrabri and Wagga Wagga and will run for five years.” The faba bean and chickpea crops were trialled at narrow and wider row spacing, and low, medium and high crop densities in both weedy (sown sowthistle) and weed-free plots. The sowthistle seed sown in the trials all came from the same, non-resistant population and no herbicide was applied to any of the plots. Dr Widderick says sowthistle is definitely susceptible to crop competition, with even the least competitive faba bean and chickpea crops cutting weed biomass and seed production by at least 50 per cent compared to plots where the weed was allowed to grow free of any crop competition. Sowthistle seed production was greatest for both crops at wide row spacing (50 cm) and low (20 plants/m2) crop density. Seed production was progressively reduced as crop competition increased. “In chickpea we found that reducing row spacing from 50 cm to 25 cm further reduced weed biomass and seed production by about 50 per cent at a crop density of 40 plants/m2,” he says. “In this trial, row spacing had no effect on crop yield but increasing plant density did generate a significant and progressive increase in yield for both chickpea and faba bean in weedy plots.” When sowthistle is present, increasing crop density from 20 plants/m2to 70 plants/m2in faba beans, or to 80 plants/m2in chickpea, generated around 0.5 t/ha yield increase. Averaged across all treatments for both crops, controlling sowthistle with crop competition alone (no herbicide applied) was worth approximately 0.25 t/ha in crop yield. This research has measured the effect of increasing the competitiveness of chickpeas and faba bean without the use of any herbicide. On farms, growers usually have some herbicides at their disposal and other research shows that combining effective herbicides with strong crop competition is the best way to control herbicide resistant weeds. In chickpea, reducing row spacing from 50 cm to 25 cm cuts sowthistle biomass and seed production by about 50 per cent at a crop density of 40 plants/m2.
Weed control is a package deal in SA Mid North
Agronomist Craig Davis has been assisting growers in the Mid North and Yorke Peninsula of South Australia to navigate their way around resistance to key herbicides such as trifluralin, Group A and Group B herbicides for 10 years or more. “Some of this chemistry was cheap and dealing with the loss of these modes of action has been difficult,” says Craig. “The key to farming without these herbicides has centred around using crop rotations to control the weed seed bank.” Mid North SA agronomist Craig Davis says harvest weed seed control has been widely accepted as a necessary tool to manage the seed bank in the Mid North and Yorke Peninsula. Narrow windrow burning (NWB) is commonly practiced in the region, and there has been considerable interest in chaff management systems with a few chaff decks operating and some growers now trialling chaff lining. Annual ryegrass control has been and remains a significant cost to growers in these regions. Brome grass and wild oats are becoming increasingly important weeds that were previously suppressed by trifluralin, and stubble retention on many farms has also favoured some weeds, like brome grass. Craig says these weeds are demonstrating increasing resistance to Group A (fop and dim) and Group B (SU and imi) herbicides, and some of the alternative pre-emergence herbicides are relatively ineffective, or variable in their control. For some growers, oaten hay production for export has been a useful enterprise to reign in resistant annual ryegrass numbers. Although a very effective weed control option, it is not for everyone. Brome grass and wild oats are not as well controlled through oaten hay production because a significant amount of seed is shed before the crop is cut. For many hard-to-kill weeds, a breakthrough came with the introduction of new imi-tolerant lentil varieties in the early 2000s, which are now built into the rotation on most farms in the region. “Imi-tolerant lentils have been very useful in managing weeds, and the high grain prices and suitability to the rotation have made them the legume of choice for growers,” says Craig. “In practice though, field peas are the most effective legume option for grass weed control.” Field peas can be sown later without suffering a yield penalty, are a more competitive crop and are a good option for effective crop-topping due to their early maturity. The downside of field peas is the likely build up of snail numbers. Although lentils have been the pulse of choice for several years, field peas are the most effective legume option for grass weed control in the region because they can be sown later without suffering a yield penalty, are a more competitive than lentils and are a good option for effective crop-topping due to their early maturity. Break crops currently make up around 50 per cent of the cropped area, due mainly to the recent high price for lentils. Craig expects this area of break crop to drop in response to the lower lentil price, however, growers generally recognise the benefits of maintaining diversity in their cropping program. “Canola is more competitive than lentils and enables the use of triazine as an alternative chemistry for annual ryegrass control,” he says. “Hybrid canola is particularly competitive against weeds and can suppress seed set even when the herbicide package is not strong.” A large portion of the canola crop is windrowed and there is a long history of spraying under the cutter bar to reduce seed set in lodged and late germinating ryegrass. Many growers have added narrow windrow burning (NWB) to their weed management program to kill any viable weed seed left at the end of the canola crop. A cheaper option is to spray over the top to desiccate the crop, then direct harvest with a narrow windrow burning chute and burn the narrow windrows the following autumn, however Craig has witnessed significant wind damage to standing crops and recommends growers continue to swath and spray under the cutterbar, unless they can guarantee timely harvest. The higher harvest height of direct headed canola also means a significant amount of weed seeds are not captured in the header front. Canola grown on cereal stubble has reached a yield plateau, and along with the increasing incidence of clethodim resistance, Craig expects growers to increase their use of double-breaks in their rotations. The traditional double break in the area was pasture followed by canola, which provides annual grass weed control, a cereal disease break and uses the residual soil nutrients. “There is now an increase in the use of a double break of oaten hay or grain legume followed by canola,” he says. “This allows the canola to thrive in paddocks with lower weed burdens, lowers stubble residue levels and increases soil nutrient levels, particularly nitrogen.” “Adding feed barley to the rotation offers growers the opportunity to implement a triple-break to control brome grass, wild oats and ryegrass, making use of the permit that allows spray-topping of feed barley to reduce weed seed set prior to harvest,” he says. Craig works with his clients to optimise crop competition in tandem with a good pre-emergent herbicide package. He says that effective and relatively cheap pre-emergent herbicides have previously masked the true value of crop competition. “Stubble retention makes the adoption of narrow rows more difficult but many growers have moved from 30 cm to 22 cm row spacing using tined planters,” says Craig. “More commonly, growers are using higher planting rates to achieve stronger crop competition. The other critical aspect is to seed all crops at the optimal time of sowing and to not plant everything early. Early sowing should only be considered for paddocks with low weed numbers.” Mixing trifluralin with another pre-emergent herbicide is an effective tool provided both herbicides in the mix have some efficacy, say over 80 per cent efficacy as a stand-alone herbicide. With high levels of trifluralin resistance now widespread, the use of other effective MOAs in combination is increasing. With heavy stubble loads on the soil surface making it difficult to achieve high levels of control using pre-emergent herbicides, Craig says it is essential that growers diversify and implement other weed control tactics to remove any survivors and stop seed set. Harvest weed seed control has been widely accepted as a necessary tool to manage the seed bank. Narrow windrow burning (NWB) is commonly practiced in the region, mostly in canola and lentil crops because the windrows tend to stay in place and support a hot fire that achieves a high level of weed seed kill. “There has been considerable interest in chaff management systems in the district and several clients have used chaff carts in the past,” he says. “Now there are a few chaff decks operating and some growers are trialling chaff lining. There has been success with chaff lining pulses one year and placing the narrow windrows of the following canola crop on top of the pulse chaff line.” “Growers using chaff decks are seeing improvements in summer spraying efficacy as a result of less dust coming off the tramlines,” says Craig. “The downsides are the increased difficulty in establishing crops in the tramlines and, although the weed seed mortality is high, there are still high numbers of weeds germinating on the wheeltracks.” Getting started with chaff lining Farming 4000 ha of light sandy to heavy clay soil in the medium rainfall district of Halbury and Salter Springs SA, Kevin Simon trialled chaff lining for the first time in the 2017 harvest. Kevin planted early maturing PBA Wharton field peas to help bring annual ryegrass numbers back under control. The field peas yielded around 3–4 t/ha and, being early maturing, offered an opportunity to harvest early and catch the ryegrass before it lodged or set seed. Farming in the medium rainfall district of Halbury and Salter Springs SA, Kevin Simon trialled chaff lining for the first time in the 2017 harvest. He planted early maturing PBA Wharton field peas to help bring annual ryegrass numbers back under control. Kevin plans to plant TT canola into this paddock in 2018 using a disc seeder to minimise disturbance of the chaff line. “Harvesting low and early are important to stop ryegrass seed set but it also comes with difficulties because the ryegrass is still green and can bind up the rotors in the header,” he says. Kevin plans to plant TT canola into this paddock in 2018 using a disc seeder to minimise disturbance of the chaff line. With limited in-crop herbicide options available, Kevin relies on late season cultural control. “We spray over the top of the canola with a self-propelled sprayer then direct harvest to control ryegrass using the chaff lining chute,” he says. “Chaff lining is also a good way to collect volunteer crop seed from the previous season. The plan is to place the canola narrow windrows on top of the previous year’s pea chaff line, and burn the narrow windrows to control weed seeds collected during the harvest process.” Last summer was very dry and so there was very limited germination of volunteers and weed seeds from the field pea chaff lines. In wetter years, Kevin expects that volunteers would be the most dominant plant type within the chaff line, with ryegrass being the next most prevalent species present. If necessary, Kevin is prepared to apply a range of chemical and cultural control measures to target the weeds growing in the chaff lines. Lime applied on other paddocks has also helped reduce the ryegrass population. Related posts Pulses to attack weeds on many fronts Setting up harvesters to capture weed seeds in the chaff stream Mic Fels case study – Stacked rotation and Chaff lining Warwick and Di Holding case study – From narrow windrow burning to chaff decks How chaff lining works
Value in sponsoring herbicide stewardship program
FMC Agricultural Solutions, now the world’s fifth largest crop protection chemical company, has recently signed up as a silver sponsor of the WeedSmart herbicide stewardship program. Dugald North, FMC development manager (crops) said the company’s acquisition of part of the DuPont Crop Protection division late last year has brought to the company a world-class discovery and development team and facilities, a pipeline of 15 synthetic active ingredients currently in development, including insecticides, herbicides and fungicides, and an extensive library of 1.8 million synthetic compounds. Dugald North, FMC Agricultural Solutions development manager (crops) said the company has signed up as a silver sponsor of the WeedSmart herbicide stewardship program to support the ‘WeedSmart Big 6’ strategy for sustainable herbicide use. “FMC is keenly aware of the impact herbicide resistance has on farming businesses and is fully supportive of the ‘WeedSmart Big 6’ strategy for sustainable herbicide use,” said Mr North. “We see WeedSmart as an important component of promoting herbicide use that prolongs the efficacy of our new herbicide molecules when they are released on the market.” “The WeedSmart Big 6 combines best practice herbicide use with cultural strategies to keep weed numbers low, maintaining an environment where herbicides can perform most effectively,” he said. “Herbicide resistance is a central concern for our business and FMC is committed to prolonging the effective life of new chemistries, even if this means foregoing sales in the short term.” Prior to the release of their new herbicide molecules, FMC has contracted the Australian Herbicide Resistance Initiative (AHRI) to conduct multi-generational resistance testing, which Mr North said will provide a scientific basis for the formulation of an effective stewardship program for individual products. In welcoming FMC Agricultural Solutions as a silver sponsor, Lisa Mayer, AHRI centre manager and WeedSmart project leader said the promotion of sustainable herbicide use and cultural practices that drive down weed seed banks is key to securing the weed control productivity gains made by the current generation of Australian farmers. “WeedSmart is an industry-led initiative that brings together knowledge and experience from Australian research partners, commercial entities, Government, advisers and growers to ensure Australian farmers have access to leading-edge weed management technologies and practices,” she said. “With the financial and in-kind support from sponsors secured for a further three years, WeedSmart is geared up to continue providing rural industries with insights into effective integrated weed control programs.” Ms Mayer said gaining the support of FMC Agricultural Solutions was testament to the perceived effectiveness of the WeedSmart program in promoting practical tactics growers could implement to maintain their profitability. “WeedSmart has become an effective conduit of information between growers within and between regions, and between growers, advisors and researchers,” she said. “We have used as many platforms as possible to raise awareness, not only of the extent of herbicide resistance but also to highlight successful management strategies that growers can implement immediately.” “There have been many instances where growers have returned from a WeedSmart Week event or field day, or read about another grower’s success and immediately adopted practices such as harvest weed seed control, patch management, optical spray technologies or greater crop competition.” The ‘Big 6’ WeedSmart tactics known to drive down weed numbers and drastically reduce the impact of herbicide resistance on Australian farms are: 1. Rotate crops and pastures, 2. Mix and rotate herbicide modes of action, 3. Increase crop competition, 4. Use the double-knock, 5. Stop weed seed set and 6. Implement harvest weed seed control. FMC have joined forces with existing platinum sponsor GRDC, gold sponsors CRDC, Nufarm, Sinochem, Syngenta, Monsanto and Bayer, silver sponsors Pioneer Seeds, BASF and Dow AgroSciences and bronze sponsors Queensland Government, ICAN, Delta Agribusiness, The University of Adelaide, CropLife, Rural Directions and AGRIvision to spread the WeedSmart Big 6 message amongst growers and advisors to tackle herbicide resistance in Australia.
Webinar: Pre-ems provide punch to prevent weeds
Join us for our next two-part series April 24 and 26, as AHRI’s Peter Newman chats with experts to deliver the latest on-farm strategies to help you set your crops up for success in 2018. From wherever you are – in the paddock, ute, tractor, office – you can stream this webinar series to your smartphone, tablet or computer. Hear from ICAN’s Mark Congreve and Uni of Adelaide’s Chris Preston who answers the Qs – how to choose and apply the correct pre-em to maximize crop yield. Specific scenarios provided for the north and the south. Listen to both or just tune into the webinar relevant to you. Webinar 1: Use Pre-ems to maximise winter crops in the North Feat: Mark Congreve, ICAN Rural Date: Tuesday 24th April 2018 Time:10:30 – 11.30 am, AWST, 12.30 – 13.30 pm AEST Why do things go wrong with pre-ems? Herbicide choice and farming system are factors to consider, with crop safety being top of mind. Mark takes us through the strategies to maximise pre-em performance particularly in relation to controlling ryegrass, wild oats, fleabane and sowthistle in the north and discusses how pre-ems breakdown and the implications on plantbacks and rotational crops. Scenarios in the northern region that lead to herbicide failure will be discussed as well as strategies to mitigate risk. Webinar 2: Use Pre-ems to maximise winter crops in the South Feat: Chris Preston, University of Adelaide Date: Thursday 26th April, 2018 Time:10:30 – 11.30 am, AWST, 12.30 – 13.30 pm AEST Hitting weeds before the crop phase provides many more shots at the weeds. Chris explains how to give your crop the best start and diminish the weed seedbank with pre-emergent herbicides. Chris delves into the behaviour of pre-emergent herbicides and what pre-emergents to use when sowing your crop dry in the south? What are the characteristics of the products and how should these influence use patterns? How to manage pre-emergent herbicides in different soil types? Why don’t pre-emergent herbicides work as well on brome grass as they do on annual ryegrass? What is the current status of resistance to pre-emergent herbicides and how should this influence the way they are used? Ready to register? Use of Pre-ems in the North with Mark Congreve Registration URL: https://attendee.gotowebinar.com/register/12301726111335937 Webinar ID: 391-027-483 Use of Pre-ems in the South with Chris Preston Registration URL: https://attendee.gotowebinar.com/register/7423634619926422785 Webinar ID: 440-111-339 P.S. For more information about these webinars please contact Lisa Mayer at email@example.com or phone 0414 841 862. For more info on weed management visit our website. WeedSmart is an industry-led initiative aimed at enhancing on-farm practices and promoting the long term sustainability of herbicide use in Australian agriculture. Australian research partners, commercial entities, Government, advisers and growers have joined forces to ensure weed management remain at the forefront of global farming practise. Viable herbicide use will help secure the weed control productivity gains made by the current generation of Australian farmers.
3-year strategy for sustainable brome grass management
Brome grass is showing off its ability to dodge and weave to evade control, making it the most costly weed in the Mallee regions of South Australia and Victoria, and increasingly problematic in other cropping areas of southern Australia. According to University of Adelaide weed ecology researcher Dr Sam Kleemann, the increased incidence of brome grass is associated with management practices that have inadvertently selected biotypes with greater seed dormancy. According to University of Adelaide weed ecology researcher Dr Sam Kleemann, the increased incidence of brome grass is associated with management practices that have inadvertently selected biotypes with greater seed dormancy. “We compared the dormancy behaviour of brome grass seed collected from crop paddocks and fencelines and found that the seed from the cropped paddocks had a greater dormancy, which allowed these biotypes to thrive in no-till, cereal intense farming systems,” said Dr Kleemann. “The adoption of earlier sowing and dry sowing has also favoured this species. Brome grass has the potential to reduce wheat yields by up to 50 per cent if numbers get out of hand.” This process of selection for biotypes that remain dormant longer and avoid pre-seeding controls such as a double-knock or cultivation, is slower but similar in effect to the evolution of herbicide resistance. Herbicide resistance levels in brome grass are currently low, however there are records in Australia of brome grass with resistance to Group A, B, C and M herbicides. “The autumn break has traditionally initiated brome grass germinations, and this is when germination is most likely on fencelines and roadsides,” he said. “The biotypes that have persisted in cropping areas are more likely to germinate in late autumn and through winter, and some even require a period of chilling to 5 °C to break the dormancy period.” Having evaded early control these late-germinating weeds go on to produce a large amount of seed and often lodged or shed their seed by crop harvest time, so they can also largely escape harvest weed seed control measures. The seed can remain viable for up to three years if it remains on the soil surface. Although brome grass has proven to be successful in the no-till farming environment, dedicated research efforts have shown that brome numbers can be driven down quite rapidly using a double-break from cereals, more effective pre-emergent herbicide packages and sowing on-the-row rather than inter-row. Trials on non-wetting sands in the Mallee have shown that sowing on the same row as the previous year improves crop establishment and the ability of the crop to compete with brome seed that is generally more abundant on the row than between the rows. The planting operation can also help break the seed dormancy by burying some of the seed, putting the seedlings in contact with the full rate of pre-emergence herbicide. “At high brome grass densities, trifluralin is generally the least effective pre-emergent option,” said Dr Kleemann. “Better results can be expected from the more expensive Sakura + Avadex package, which resulted in 72 per cent less brome panicles than trifluralin alone in trials. In this 2015 trial the trifluralin treatment resulted in 60 brome grass panicles per metre square compared to just 16 in the Sakura + Avadex treatment.” “Growers will need to weigh up the extra cost in herbicide compared to the likely seedbank benefits and the variability in pre-emergence herbicide performance between seasons. This is why a diverse approach to weed management is essential.” “In years where crop competition is patchy, brome grass can exploit the opportunity and replenish the seed bank, putting increased pressure on pre-emergent herbicides the following season.” 3-year brome grass reduction rotation Growers who are noticing increased brome grass numbers can use a three-year rotational strategy known to effectively drive down the brome grass seed bank. Year 1 – a pulse crop to enable the use of effective pre-emergent herbicides and in-crop grass selective herbicides, followed with crop-topping to reduce brome seed set where there is no yield penalty expected. Year 2 – canola or hay. Canola offers a similar suite of tactics to the Year 1 pulse crop, targeting brome grass germinations throughout the cropping season. Hay is a very effective option, reducing seed set by as much as 90 per cent, particularly if the hay is cut at the commencement of brome grass flowering. Regrowth after cutting hay must be controlled with grazing or knockdown herbicides, particularly in wet seasons. Year 3 – Clearfield wheat allows the use of imidazolinone herbicides, the most effective chemistry available for brome grass control. Using this technology in a low weed situation (due to seed bank reduction in the previous two years) there is less pressure applied to this herbicide, which is known to be prone to rapid evolution of herbicide resistance in high weed density scenarios. Growers who are noticing increased brome grass numbers can use a three-year rotational strategy known to effectively drive down the brome grass seed bank, starting with a pulse crop that is suited to crop-topping without yield penalty. The Brome RIM tool is available for growers and advisors to test the likely effect of different management scenarios on brome grass numbers.
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Is it possible to apply additional competition to inter-row weeds?
with Hanwen Wu, Principal Research Scientist, NSW DPI The inter-row space provides an ideal environment for weeds to grow, particularly if pre-emergent herbicides are not applied or are less effective than expected. NSW Department of Primary Industries principal research scientist, Dr Hanwen Wu says filling the inter-row space with a productive species might be another way to suppress weed growth and reduce seed production of herbicide resistant weeds. Dr Hanwen Wu, NSW DPI is investigating new ways to increase crop competition, particularly in the crop inter-row space. “There is very strong evidence that narrower rows are an excellent way to increase crop competitiveness but there are some practical limitations,” he says. “We have looked at a combination approach, of planting most of the seed in rows and the rest broadcast to ‘fill in the gaps’. We have called this the ‘compound sowing technique’.” In 2016 Hanwen set up two field trials at different locations near Wagga Wagga, NSW to assess the effect of this system on weeds and crop yield in both narrow (22.5 cm) and wider (45 cm) row spacings, with and without IBS trifluralin. Three broadcast species were evaluated – wheat, gland clover and French serradella. The two sites were assessed to have an initial annual ryegrass density of 48 and 25 plants/m2. “We sprayed out the broadcast legumes in early September to prevent them competing with the crop for moisture,” says Hanwen. “Further trials are needed to test a range of parameters such as suitable legume species, optimal seeding rates, proportion of seed broadcast, row spacing for the conventional seeding and different pre-emergent herbicide options.” Although the 2017 season did not allow Hanwen to replicate this trial he is keen to do more trials in 2018. “We think this technique has merit and our initial trial suggested that weed suppression can be achieved without any yield penalty,” he says. “There even seems to be situations where a yield increase can be achieved in response to reduced weed pressure.” Crop competition is rightfully attracting more attention from farmers and researchers in the war on herbicide resistant weeds. It is a numbers game and crop competition can play an important role in vastly reducing weed seed set. Which was the most competitive broadcast species? Short answer: Wheat. Longer answer: At the weediest site the broadcast wheat treatment, without IBS trifluralin reduced annual ryegrass biomass by 71–77 per cent at both the narrow and wider row spacings. In the presence of less weeds the broadcast wheat still reduced weed biomass by 50 per cent in the narrow rows and 27 per cent in the wider row configuration. IBS trifluralin further increased weed suppression at both sites and both row spacings. At the weedier site, annual ryegrass biomass was suppressed by 88–90 per cent. Where there were less weeds present the addition of IBS trifluralin increased biomass suppression from 27 to 70 per cent at the wider row spacing. Compound sowing technique (conventional + broadcast sowing) dramatically increases crop competition in the inter-row compared to conventional sowing. Of the three broadcast species tested, wheat provided the strongest suppression on weed biomass. What was the effect on yield? Short answer: The wheat yield increased by 15–22 per cent at the weediest site when wheat was used as the broadcast species. Longer answer: In the favourable season of 2016, only broadcast wheat generated a yield increase, and only in the presence of higher weed pressure. None of the broadcast treatments caused a yield reduction at either site. Further trials are required to evaluate the impact of site and seasonal climatic conditions on the weed control and crop yield associated with the compound sowing technique. The broadcast legumes may provide additional soil fertility and moisture retention benefits while maintaining crop yields. More work is needed to identify more competitive legume species to have a greater impact on weed biomass and to identify the optimal timing to kill broadcast legumes to maximise weed suppression and minimise yield loss. Using a broadcast legume that is sprayed out in September could have additional soil health and moisture retention benefits and warrants further investigation. Have any farmers tried this idea? Short answer: Yes. Longer answer: Leigh Bryan at Swan Hill has tested this idea on his farm – he calls it zero-row spacing. Also in 2016, a strip-trial in barley resulted in the zero row spacing strip yielding 4.994 t/ha compared to 4.889 t/ha in the conventionally sown crop at 37.5 cm spacing. This was achieved with no pre-emergent or in-crop herbicide applied. Leigh has noticed that the random placement of stubble is easier to sow through the next year and it still provides trellising for pulse crops and shades the soil to conserve moisture and reduce soil surface temperatures.
Resistance testing informs herbicide use plans
Matt and James Toscan have been growing cotton for seven years at Darlington Point in the Murrumbidgee. Speaking to their CottonInfo Regional Extension Officer, Matt Toscan outlined how they are managing the threat of resistant weeds. The primary weeds encountered on their farm are barnyard grass, blackberry nightshade, sowthistle, fleabane, annual ryegrass and thistles. Matt Toscan. Matt and James have tested barnyard grass, sowthistle and ryegrass for resistance over recent years. The barnyard grass and sowthistle were found to be susceptible to glyphosate (Group M), while the ryegrass was found to be resistant to by glyphosate and Group A herbicides. To counter the threat of further incursion and resistance, Matt and James have an integrated weed management strategy (IWM) that is developed over the full course of the year, in close consultation with a crop consultant. The summer crop program is decided in July–August, and the winter crop program in March–April. “We recognise that weed resistance is a threat to the long-term cropping viability of intensive irrigation areas, which is why an integrated weed management approach is so important to us,” said Matt. “There are no new herbicides, so we need to preserve our chemical options by making use of non-chemical control tactics.” “Weed control in cotton will never be as easy as it is right now, while we are a new area and can rely on glyphosate for summer weed control. Being so easy and effective is both a strength and a weakness in the current weed control system. We need to think long term and use multiple tactics.” The Toscan’s take a whole farm approach to management of weeds, with particular attention paid to non-cropped areas, such as the sides of fields, channels, roadways, drains and bankless channels. Their IWM strategy involves a range of control measures, including pre- and at-plant residuals, pre-emergent knock downs, post-emergent herbicide applications and chipping, particularly for ryegrass and milk thistle. The pre-emergents are used sparingly, due to the possible cold conditions at the start of the crop. Not all control measures have worked, so the strategy has evolved over time. “We’ve learnt that spraying in less than ideal conditions can result in spray application failures – like spraying barnyard grass when it is too hot. Timing of applications is critical: there can be advantages re timing with aerial application,” James said. Growers Matt and James Toscan Cropping area Total hectares: 4200 ha. Cotton: 1100 ha irrigated Soil type Majority Grey/brown self-mulching clay with some Transitional Red brown earth Rotations Two-year rotation: cotton (summer); durum wheat (winter); fallow (summer and winter); cotton (summer) Source: CottonInfo Weed Control case studies Further information: CottonInfo weed management page
Using IWM to keep one step ahead of resistance
Ben Thomas has been growing cotton for 15 years across three properties, two irrigated and one broadacre, at Warren in the Macquarie Valley. Speaking to his CottonInfo Regional Extension Officer, Ben Thomas outlined how he is managing the threat of resistant weeds. The most common weeds found on Ben’s properties are fleabane, windmill grass, barnyard grass, sow thistle, turnip weed and ryegrass. Fleabane and windmill grass are the biggest challenges at present, with Ben expecting ryegrass, sow thistle, barnyard grass and feathertop Rhodes grass to emerge as issues in the future. Ben Thomas The threat of resistance is a core reason why Ben has an integrated management plan in place, developed with consultant Andrew Cooper of Landmark. Ben’s approach is to control weeds in his irrigated cotton through a range of tactics including pre-emergent knock downs, post-emergent herbicide applications, layby residuals and cultivations. Chipping is used if required. The pre-emergents and laybys are used sparingly, as high disease levels and cold temperatures can lead to a slow start for the cotton, and he does not want to put any additional stress on the plant. He calculates that the cost for controlling weeds ranges from $50 to $80 per hectare across his fallow, broadacre and irrigation country. Through CottonInfo, Ben has tested for resistance in fleabane, ryegrass and other weeds. Grower Ben Thomas Cropping area Total hectares: 6000 ha. Cotton: 1500 ha irrigated Soil type Cracking clay Rotations Two-year rotation: cotton (summer); winter cereal or legume (winter); long fallow (sum- mer and winter); cotton (summer) Source: CottonInfo Weed Control case studies Further information: CottonInfo weed management page
Adjuvants’ role in combatting herbicide resistance
Andrew Somervaille, Jubilee Consulting has been evaluating the performance of herbicides for more than three decades and says the role of adjuvants is often either over-rated or under-estimated. This may seem a contradiction, but the fact is that sometimes adding an adjuvant is beneficial and sometimes it is detrimental; and there is an art to knowing how to best deploy these additives. When weeds are susceptible to the applied herbicides, the effectiveness of adjuvants generally goes un-noticed. However, correctly applied adjuvants can reduce the impact of low level herbicide resistance by helping to maximise the amount of herbicide taken up by the plant.<! Andrew Somervaille, research agronomist with Jubilee Consulting suggests growers and advisors should not overlook or over-rate the use of adjuvants. “In the best case scenario, the correct use of an adjuvant can optimise performance of a single herbicide, or a herbicide mix,” he says. “This results in the most efficient control of the target weeds, minimises seed set and reduces weed numbers into the future. All research points to low weed numbers as the only sustainable way to manage herbicide resistance.” “In the worst case scenario, the incorrect use of an adjuvant can reduce herbicide performance, may compromise the physical compatibility of mixtures and can alter the function of tank mix components,” says Andrew. “This may result in a sub-lethal dose of herbicide being applied, which is known to amplify herbicide resistance if there are low levels of resistance present in the weed population.” “Once populations are highly resistant then the impact of adjuvants is reduced,” says Andrew. “This highlights the importance of being very deliberate and calculated when making recommendations or decisions about adjuvants.” In one experiment Andrew conducted with two formulations of glyphosate, he measured the negative effect of the adjuvant when in the presence of 2,4-D to control awnless barnyard grass. “We know there is antagonism between 2,4-D and glyphosate in a tank mix in some situations that results in a reduction in the level of control expected from glyphosate alone,” he says. “What we observed in this experiment was that one glyphosate+surfactant formulation mixed with 2,4-D achieved just over 80% control while a second glyphosate+surfactant formulation mixed with 2,4-D achieved 94% control.” Andrew says that although some herbicide products are manufactured with an adjuvant included as part of the formulation, there may still be a benefit gained from adding another type of adjuvant prior to application, depending on the other products in the mix, the water quality or the target weed. In another experiment, Andrew investigated the effect of different adjuvants (LI 700 and Liase) on the efficacy of a RoundUp Power Max (glyphosate) and Amicide (2,4-D) mix. The results clearly showed that while Liase improved the performance of the mix, LI 700 reduced performance to less than 80% control of barnyard grass. Grower experience, research trials and computer modelling all point toward high levels of herbicide performance, coupled with the removal of survivor plants, to reliably and sustainably extend the useful lifespan of herbicides by removing potential carriers of resistance traits. “Even small incremental losses in control at the ‘top end’ can have a large effect on the total seed-bank load,” says Andrew. “While 95% control might still be considered a good result from a herbicide application that could have potentially achieved 98% control, this three per cent loss in efficiency could be the start of a substantial increase in weed numbers and allow herbicide resistance to gain a foothold.” Keeping weed numbers low allows the targeted use of more expensive products (e.g. through an optical sprayer), makes manual control methods economical, and even allows the use of less efficient products to maintain or slightly reduce numbers while adding diversity to the program (provided there is no cross-resistance). What adjuvants do An adjuvant may modify the physical, chemical and biological activity of the herbicide on the target. For example, an adjuvant may be added to improve the physical properties of the spray such as its spray quality, or to allow products to dissolve or mix in water. Adjuvants may also alter the chemical properties of the formulation to counter poor water quality or activate certain components in the herbicide, and from a biological perspective an adjuvant may be used to influence uptake through the plant cuticle and even movement across cell membranes. Very small amounts of surfactants are required to achieve adequate ‘wetting’ of the plant surfaces and adding more surfactant will not necessarily increase the performance of foliar applied herbicides. However, some adjuvants (including surfactants) are added specifically to activate the active ingredients and so are an essential component of the formulation or mixture. Adjuvants can play an incremental role in improved herbicide performance and assist with keeping weed numbers low and reducing the risk of sub-lethal resistance traits. However, their use does not over-ride the need for correct chemical use and application under the right conditions. The same adjuvant may even perform different functions when included in different mixes or added to different formulations. There are also specific responses in certain weeds to certain surfactants, some giving superior results and other inferior. It is not possible to give rule-of-thumb recommendations – each scenario needs to be examined carefully, taking into account the target weed species, the condition of the weeds, the water quality and the specific herbicide formulations. They are not always beneficial and can result in sub-lethal doses being applied if they are not used correctly. Combinations of surfactants can modify the functions of the individual components and it cannot be assumed that the effects are additive to herbicide performance. Also, be aware that the characteristics of the leaf cuticle are not the primary limiting factor associated with the uptake of foliar applied herbicides. Plant stress is usually the main limiting factor and this may only be partly overcome through the use of an adjuvant. Clearly, it is not a simple matter of making recommendations or decisions to include an adjuvant. Growers and their advisors need to have an appreciation of the chemistry behind the adjuvant’s use and the way that it may impact on the uptake of the herbicide into the target weed. Useful resources Adjuvants – Oils, surfactants and other additives for farm chemicals
Weed control program has expanded crop choices
Darren and Leanne Eather have been growing cotton east of Narrabri for some 20 years. Speaking to their CottonInfo Regional Extension Officer, Darren Eather outlined how they are managing the threat of resistant weeds. Darren encounters a range of weeds each season, particularly fleabane, windmill grass, liverseed, barnyard grass, turnip, milk thistle and volunteer cotton. Darren Eather Darren’s approach to weed management varies between his irrigated and dryland cotton, and is tailored field by field and crop by crop. In his dryland crop, he strategically uses rotations to control weeds, along with different chemical modes of action. He applies a pre-plant residual herbicide, followed by an at-plant residual and glyphosate as a pre-emergent knock down. “For grass control, Group D chemicals were our preferred option in order to rotate chemistries. However, we’ve found that windmill grass in particular is not consistently controlled and we get some escapees, which is why we’ve moved towards Group As as an alternative. We’re finding it is providing good control,” Darren said. In his irrigated country, he combines cultivations with two or three applications of post-emergent glyphosate. He aims to meet with his consultant each year following picking to discuss his approach. Darren tends not to apply a layby residual, due to the long-lasting effects and subsequent reduction of options. He believes weed control in non-crop areas of his farm is very important, and actively manages this. “We purchased a farm around a decade ago where we had a very serious issue with black oat and black bindweed,” Darren said. “As a result, we were unable to grow chickpeas on that farm. Now, 10 years later, with a good strategy of weed control and careful crop selection we have controlled the weeds in our system to the stage where we can now grow chickpeas.” Growers Darren and Leanne Eather Cropping area Total hectares: 3,000 ha. Cotton: 400 ha irrigated and 300 ha dryland Soil type Vary from deep black soils to river loams and some hard setting soils Rotations Two-year rotation: Irrigated – cotton (summer); wheat (winter); long fallow (summer and winter); cotton (summer) Dryland – Cotton (summer); chickpeas, canola, wheat (winter); long fallow (summer and winter); cotton (summer) Source: CottonInfo Weed Control case studies Further information: CottonInfo weed management page
Efficient herbicide use pays off
He is faced with a series of weeds each season, including barnyard grass, fleabane, milk thistle, red pig weed, peachvine, feathertop Rhodes grass, bathurst burr, black oats, phalaris and turnip weed. Resistance has been confirmed in barnyard grass (resistant to Group M herbicides – glyphosate) and black oats (resistant to Group A). Tristram Herstlet, Reardon Farms and Michael Brosnan B&W Rural Tristram expects to have additional problems with resistance in the future, particularly with feathertop Rhodes grass and glyphosate. To manage the existing and potential future resistance threats, Tristram has implemented an integrated approach to weed management, in collaboration with consultant Michael Brosnan of B&W Rural at Mungindi. “We regularly discuss our weeds management program with our agronomist. By the time we plant cotton, we have a program in place and know what we want to do,” Tristram said. “Our strategy is threefold: to minimise future resistance, prolong the use life of each herbicide, and avoid the problem of weed shifts. “We do this by having different tactics, such as rotating our chemical groups, cultivation, crop rotation and farm hygiene. We are well aware of the dire consequences of having multiple grass and broadleaf weeds resistant to glyphosate – and we are currently managing two cases of resistance, in barnyard grass and black oats,” Tristram said. Tristram takes a holistic approach to integrated weed management. “We use control methods at a whole farm level, at a management unit level, down to an individual field basis. And we apply as many options as possible to try and control the weeds that are resistant, and prevent further resistance developing,” Tristram said. “We use a Group L treatment instead of glyphosate (Group M) to give the field a break. More recently, we are using a Group K as a post-plant, pre-emergent in cotton. We intend to follow this with cultivation. We haven’t felt that we’ve needed a layby (a residual herbicide used to control weeds in-crop) as the other control methods are currently working. “We also have a range of other tactics. All of our contractors are required to have clean gear when they come on farm. We practice ‘Come Clean Go Clean’ primarily for disease protection, but an added benefit is weed management. “We also use chippers, predominately in non-crop areas, but also in-crop if necessary, such as if fleabane has become an issue. We try to keep everything spotless, as the fewer the weeds, the fewer the seeds for next year.” Tristram believes the future of weed management lies in robotics and microwave technology. “On our dryland areas we use a camera spray system, which we purchased in 2016. The driver behind the purchase was the ability to spray the dryland fallow area when cotton is in, and the ability to put on higher rates of chemical to kill fleabane without using a hormone,” Tristram said. “The system was a serious investment – a total of $640,000, including a tractor, sprayer and boom – but we’re spraying at the moment and it costs only $5 per hectare with this new system, versus $11.60 per hectare with a full boom. “Based on this, we’re saving around $2,000 per day in chemical with the new system. Most importantly, we’re really happy with the results: the cameras work on the chlorophyll in the plants, and the results are fantastic: we’re getting a good weed kill,” he said. Source: CottonInfo Weed Control case studies Further information: CottonInfo weed management page