Double knock to preserve glyphosate

What’s better than an attack on weeds? A second one. Come at them with a different strategy and any survivors left over don’t stand a chance, that’s the beauty of the double knock.

Controlling herbicide-resistant weeds is essentially all about double knocks. This can be one herbicide followed by another, or it could 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.

And then there is the double knockdown. Glyphosate followed by paraquat (or paraquat + diquat). Glyphosate resistance is such a big deal it gets its own, specific weed control strategy. 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.

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Alternative second knock herbicides for broadleaf weeds in fallow

The sequential application of two separate herbicide treatments has become the most common ‘double knock’ approach used in weed management. Unfortunately, these approaches have added cost, complexity and scheduling issues to weed management programs but have been required for two main reasons: 1. To control herbicide-resistant weed populations, that may have been selected by prolonged use of a similar mode of action chemistry; and 2. Control of weed species or stages that are unsuccessfully controlled with single herbicide applications. Paraquat has been the key active ingredient used in the second knock situation and can provide effective management of a wide range of grass and broadleaf weeds. However, it is clear we require other options to use in this management window to: 1. Avoid the more rapid selection of paraquat resistance; and 2. Provide options that may improve weed control in situations where paraquat efficacy is not adequate. Since winter 2016, NGA has been screening a range of herbicides, to identify options that have the potential for this usage pattern. The two key broadleaf weeds being targeted are common sowthistle (Sonchus oleraceus) and flaxleaf fleabane (Conyza bonariensis). DOWNLOAD FACTSHEET
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Case Study

Lance Wise, Bowenville, Qld

Lance and Fallon Wise and Lance’s parents, Murray and Janette crop 1600 ha and run cattle on 45 ha of non-arable rocky ridges. The locality and soft black plains enable the Wises to grow a range of crops including sorghum, mungbean, chickpea, barley and wheat, along with the occasional crop of faba bean, millet and canola. In an effort to reduce their reliance on glyphosate and overcome some of the disadvantages of long-term no-till farming, the Wises have reintroduced light cultivation and are moving toward more targeted application of glyphosate and other herbicide products using an optical sprayer. “Our usual rotation is a legume followed by a cereal, such as mungbean, to sorghum and chickpea to wheat or barley,” says Lance. “We use either a short fallow or double crop to change from a winter to summer crop program and aim for at least one crop every 12 months from each paddock.” Having been no-till farming for 25 years the Wises have seen the weeds transition to those species that proliferate in the absence of cultivation; weeds like fleabane, urochloa, feather top Rhodes grass, cow vine and bladder ketmia. In an effort to reduce their reliance on glyphosate and overcome some of the disadvantages of long-term no-till farming, the Wises have reintroduced light cultivation and are moving toward more targeted application of glyphosate and other herbicide products using an optical sprayer. Nine years ago they had success using the Kelly disc chain to manage urochloa on their less well-structured red earth soils. More recently they have used this implement to target herbicide tolerant feathertop Rhodes grass and fleabane on their main black clay soils. “We are using a chemical / tillage double knock to good effect on feathertop Rhodes grass in the fallow,” says Lance. “We apply glyphosate and then follow up five days later with the Kelly chain, which does a terrific job of pulling out sick, dead and small plants at an operation speed of 11 to 12.5 km/hr.” “The same system works well on fleabane too, pulling up plants with foot-long roots from soft soil, although a higher rate of glyphosate is required. It doesn’t work well for weeds like prairie grass that have deep, fibrous root systems.” The Wises have found the chemical / tillage double knock to work well on feathertop Rhodes grass and fleabane. Used in reverse order, Lance has found the light cultivation is an effective way to stimulate germination after a poor sorghum crop to sprout volunteers and then spray out the crop. Along with the benefits of partial stubble incorporation on soil microbial activity and ease of sowing, Lance says the two short chains in the middle fill in the 3 m wheel track to even out the paddock, avoiding the need to do extra wheeltrack renovation operations. About the Kelly chain “We also use the Kelly chain to incorporate pre-emergent herbicide after sowing to a maximum depth of 2 cm. This does not disturb seed, which is all sown at least 4 cm deep with a presswheel, and the soil is moved sideways without destroying the cracks in the soil or drying out the profile,” he says. “Weed seed is not buried deeply so it doesn’t come back to haunt you years later.” Lance avoids using the Kelly chain more than once in a season on the red soils, which can get very dusty and are prone to hardsetting on the surface. At the end of harvest Lance and Murray assess the stubble load and weed pressure in each paddock. They usually spray glyphosate after a rain event and either double knock with the Kelly chain or spray paraquat through their Weedseeker optical sprayer. After using the Kelly chain, Lance follows 30–45 days later with the Weedseeker rig to clean up any survivors. “The Weedseeker is a new fallow option for us and means that we can treat weeds that we might otherwise ignore, apply higher rates, and use more expensive products to control small areas or patches of weeds,” says Lance. “The 36.6 m boom carries 96 sensors so there are not many weeds that go undetected in the fallow.” At the end of last year, the Wises started sub-soil ripping to a depth of 35 to 40 cm on 75 cm spacing to increase water capture and break up the sub-soil compaction to improve crop growth. Six weeks ahead of planting they apply the final glyphosate spray and then add fertiliser, which they incorporate with the Kelly chain, with the added benefit of removing any weeds present. Liquid fertiliser applied at seeding promotes early seedling vigour and growth, which gives the crops a competitive advantage over weeds. They plant using a Tobin planter that achieves a good even strike in stubble, starting on the red soils as soon after rain as possible, then moving onto the black soils. Pre-emergent herbicide is applied after sowing legume crops and incorporated using the Kelly chain. Herbicide is applied in crop as well as for desiccation purposes in sorghum, mungbeans and chickpea. Being a spray contractor, Lance has also invested in an air boom on his sprayer that enables him to have much greater control of droplet size to match the environmental conditions, while also covering a larger area in a day. He says the elliptical cone delivers spray in both a forward and rear motion to achieve better coverage, even at lower water volumes. The controls in the cab allow the operator to adjust the spray quality from fine to extra course without changing nozzles on the boom and there is no need to have all the different nozzles to suit different conditions and products. The Wises operate a 12 m controlled traffic system and plant all their crops on 375 mm row spacings. Lance has increased the planting rate in sorghum from plants 40 cm apart in the row to 25–30 cm apart to quickly to shade the interspace and suppress weed growth.
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News

Confirmed resistance to the double-knock tactic in tall fleabane  

For weeds that have a natural tolerance to glyphosate, the double-knock has provided growers with an excellent tool to take two swipes at weeds like fleabane, sowthistle and feathertop Rhodes grass and achieve a greater level of control. NSW Department of Primary Industries weeds researcher, Dr Md Asaduzzaman (Asad) has uncovered disturbing evidence of double-knock resistance in tall fleabane (Conyza sumatrensis) samples collected during weed surveys funded by the Cotton Research and Development Corporation (CRDC). NSW Department of Primary Industries weeds researcher, Dr Md Asaduzzaman (Asad) has uncovered disturbing evidence of double-knock resistance in tall fleabane (Conyza sumatrensis) samples collected during weed surveys funded by the Cotton Research and Development Corporation (CRDC). “Our surveys in 2016 and 2017 showed that cotton fields were generally weed-free but herbicide resistance is building in weeds along farm roadsides, drains and channels and around infrastructure,” he said. “We identified two tall fleabane biotypes that have resistance to glyphosate, paraquat and the double-knock tactic of an initial glyphosate application followed with an application of paraquat 7 days later.” The rate response analysis showed that one of these biotypes is 4.9 times more resistant than the susceptible biotype, requiring 2.5 L/ha Paraquat-250 to kill 50 per cent of the plants from the resistant population compared to just 0.5 L/ha to achieve the same result in the susceptible population (see Table 1). While this level of resistance is generally considered ‘moderate’ it is clear that resistance is building and must be taken very seriously given the importance of the double-knock tactic in most cotton and grain production systems in Australia. Table 1 Resistance levels of tall fleabane screened against paraquat, glyphosate and glyphosate + paraquat (R-resistant > 50% survival; DR-developing resistance < 50% and > 20% survival and S-susceptible < 20% survival)   Tall fleabane biotype   % Plant survived under Paraquat-250 @ 2 L/ha Glyphosate-540 @ 1.2 L/ha Glyphosate followed by Paraquat (Double-knock) TFB01 >75 100 75 TFB02 75 75 75 TFb-Suscept 0 0 0 These two populations, collected near Nandi, Queensland and Coleambally, NSW, are the first paraquat-resistant tall fleabane to be identified in Australia. Resistance to paraquat in this species has previously been recorded in Japan, Sri Lanka and Taiwan. Location of confirmed cases of double knock resistance in tall fleabane. “Although the tall fleabane plants from these two populations showed signs of herbicide damage, such as narrowing of leaves and slow growth, when the double-knock was applied, they were able to survive and produce seed,” said Dr Asad. “This species produces a large quantity of seed, germinates quickly and the seed can travel over 10 km in the wind so dispersal of paraquat / glyphosate resistance traits will be impossible to contain.” Tall fleabane seedlings 28 days after the double knock (glyphosate + paraquat) tactic was applied. This discovery makes tall fleabane the second species in Australia to have confirmed resistance to both glyphosate (Group M) and paraquat (Group L), the first being a population of annual ryegrass identified in Western Australia in 2013. Having demonstrated resistance to the dual application of these herbicides in the otherwise effective double-knock tactic is cause for great concern. Weed populations take longer to evolve resistance to paraquat and glyphosate compared to some other modes of action, but it will happen after years of regular applications without survivor control. Like other fleabane species, tall fleabane is susceptible to crop competition but flourishes in poorly competitive, wide-row crops such as dryland cotton. Combatting herbicide resistance and keeping weed numbers low will require the implementation of a wider range of weed control tactics rather than relying heavily on the double knock tactic. “Growing more competitive crops and using a wider range of pre- and post-emergence herbicides and strategic tillage will help manage this weed,” said Dr Asad. “Above all is the need to monitor and remove any survivor weeds in line with the cotton industry’s weed control strategy of ‘2 + 2 and 0’ that recommends two non-glyphosate tactics in-crop plus two non-glyphosate tactics in the fallow and zero survivors.” In other research Dr Asad is testing the opportunities for cotton growers to use cover crops to create additional opportunities for herbicide rotations, run down the seed bank and delay the adaption of weed populations by reducing the frequency of single modes of action herbicide use. Paraquat resistance has previously been confirmed in 10 species in Australia, including flaxleaf fleabane (Conyza bonariensis). Other resources Resistance risk to knock-down herbicides on irrigated cotton farms Protecting knock-down herbicide options What are the herbicide options for the summer fallow
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Case Study

John Stevenson, Lockhart NSW

Orange Park is an 8200 ha corporate dryland cropping operation with eight main blocks, all within a 30 km radius of Lockhart, NSW where John introduced the use of the double break from cereals 10 years ago.   To get the best result possible from OP canola, ‘Orange Park’ manager John Stevenson (left) has their seed professionally graded and only plants seed sized over 2 mm diameter. Karl Grocke (right) has joined the team at Orange Park on their graduate program, making the most of the opportunity to learn from great operators like John. “Our rotation is driven by herbicide resistant weed management,” he says. “A double break, such as hay/canola, pulse/canola, fallow/canola, is implemented once in a 7-year rotation. The rotation is flexible but we do what we can to avoid growing three cereal crops in a row because the result is inevitably a weed blow-out.” The main weeds on Orange Park are annual ryegrass in-crop and fleabane in summer, which has been increasing since 2005, particularly in wet years. Wild oats is a lesser but persistent weed. “We have low level glyphosate resistance and varying levels of Group A resistance to contend with,” says John. “We don’t use much Group B chemistry either, except occasionally in imi-tolerant crops, partly because of decontamination issues with canola, but mainly because of poor efficacy.” The wettest September on record in 2016 saw about 10% of the crop across the Orange Park operation inundated – compromising their weed control and nitrogen management. “Essentially we lost a year of weed control with ryegrass blow outs due to poor crop competition and not being able to do timely herbicide applications,” says John. “We also saw a shift in the weed spectrum with more carryover of weeds that thrive in wet conditions, such as toad rush and lesser loosestrife.” Crop rotation and double break cropping The rotation that is working well on Orange Park since 2008 consists of two cereals followed by canola, then another two cereals and finally a double break before returning to cereals. John incorporates as much diversity within the system as possible to maximise returns and keep pressure on weed numbers. Canola, wheat, barley, pulses (including faba bean, lentils and vetch hay), oaten hay for export, and strategic fallowing to conserve moisture, all feature in the list of options. The diversity in crops enables the rotation of herbicide groups, including pre-emergent herbicides ahead of each crop. Imi-tolerant crops such as Hurricane lentils, IT-canola, possibly barley in the future add to the mix although John often grows hybrid IT-canola conventionally simply for its inherent yield advantage. “The price of lentils is attractive however logistics are difficult, as grain needs to get to Horsham, over 6 hours away,” he says. “Realistically, canola and feed grain for poultry and feedlots are our mainstay crops.” To maximise the competitiveness of canola crops John grows some hybrid crops and also grades OP canola to 2 mm diameter as a cost-effective way to improve crop establishment and early vigour that also suppresses early weed growth. John uses TT canola when weeds become a problem issue and Clearfield canola in low weed population paddocks where he can also apply atrazine on volunteer faba beans. This year John planted 650 ha trial of lentils in a block that would normally have been fallowed. “There was good residual soil moisture from last year’s wet winter and we tried a late planting system to reduce the density of the lentil crop to keep air flowing through canopy, hopefully reducing the incidence of disease,” he says. “Weed control in the Hurricanes XT lentils has been exceptional although the crop has demonstrated the need for better pH amelioration at depth.” “Including lentils will spread the workload and we can target a different weed germination cohort,” he says. “Having a different group of herbicides available will also help add diversity to our control program.” Row spacing, CTF and stubble management John manages Orange Park as eight 1000 ha management units, where a unit may consist of several blocks in close proximity. He is looking at opportunities to implement east–west sowing in suitable blocks to maximise yield and reduce weed pressure. While on a Nuffield Scholarship trip to New Zealand, John saw crops grown on 125 mm (5 inch) row spacing where farmers were able to include ryegrass as a crop in their rotation, without concern over future weed problems. “Historically, our seeding has been on a 300 mm row spacing but we are in the process of investing in a full disc seeding system, which will allow us to narrow the row spacing to 175 mm (7 inches),” says John. The disc seeder will enable John to retain stubble from their 1.7 t/ha pulses, 3.4 t/ha wheat and 4 t/ha barley crops within their 18 m system with 3 m CTF tramlines. Harvest weed seed control John and his team have been narrow windrow burning for three years. Having tried this harvest weed seed control tactic in canola, wheat and barley crops they have found the safest and best results are achieved in canola. “Realistically, narrow windrow burning is not very compatible with the council’s fire regulations so we are looking at alternatives,” says John. “Cereal stubble burns for 4 or 5 hours, and whirlwinds can easily shift burning chaff 300 m into a neighbour’s stubble.” A downside to narrow windrow burning is that more moisture is stored under the narrow windrows, which can cause uneven crop germination the following season. John has been successfully using narrow windrow burning in canola for several years. Twelve days after sowing, this Lancer wheat crop shows the variability in germination where the rows under the narrow windrow have access to more moisture. John is looking into other options for harvest weed seed control and will probably phase out narrow windrow burning over the next few years. Chaff deck systems suit CTF and although John thinks they have merit, there are limitations on the options available when using contract harvesters. Chaff lining seems easier to implement and is likely to feature in the near future. “Narrow rows help push weed seed heads to the top of the canopy,” says John. “Two plants per m2 is too many, especially if the weed is able to adopt a prostrate habit and evade collection at harvest. The big challenge is getting inexperienced header drivers to harvest low, even though we pay the contractor a premium to have this happen.” John uses spray topping in canola, and sometimes wheat and barley, along with hay production to take out late germinating weeds. Fallow management Over summer, John uses a contractor with an optical (camera) sprayer to treat survivors with paraquat following a broadacre spray of glyphosate. He says the optical sprayer is also a valuable tool to help manage cud weed, which is becoming more prevalent. There is no routine cultivation in the system however John does incorporate lime with a speed tiller before planting and a full tillage using a flexicoil is done when there is levelling work required. “When we change over to the disc seeder we will probably need to cultivate to remove the ridges left by the tined system,” he says. “The disc seeders can’t handle too much chaff on the ground either, so burning is still an option for weed control, or when slugs and mice are a problem.” Soil fertility and weeds Across the Orange Park operation John has acidic (pH 4.5) red soil ridges and some sodic vertosols to contend with. He is using variable rate technology (VRT) to apply lime to the red ridges using rates ranging from 1 to 3 t/ha to lift the pH to 5.5. “We saw an immediate response of lower ryegrass population in low pH blocks after lime application due to stronger crop competition,” he says. “Variable rate application and soil testing has been very cost effective for us and has helped reduce weed numbers and improves herbicide efficacy. Fixing soil pH gives the best return on investment through improved nutrient availability, which supports higher yield and better weed control.” John is also using soil sensing and VRT to address constraints in nitrogen and phosphorus. The red soil ridges on ‘Orange Park’ are acidic (pH 4.5) so John is using variable rate lime applications to lift the average pH in these soils to 5.5. In doing so he has observed an immediate reduction in ryegrass numbers due to the improved crop competitiveness.  

Case Studies

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Article
Case Study

Lance Wise, Bowenville, Qld

Lance and Fallon Wise and Lance’s parents, Murray and Janette crop 1600 ha and run cattle on 45 ha of non-arable rocky ridges. The locality and soft black plains enable the Wises to grow a range of crops including sorghum, mungbean, chickpea, barley and wheat, along with the occasional crop of faba bean, millet and canola. In an effort to reduce their reliance on glyphosate and overcome some of the disadvantages of long-term no-till farming, the Wises have reintroduced light cultivation and are moving toward more targeted application of glyphosate and other herbicide products using an optical sprayer. “Our usual rotation is a legume followed by a cereal, such as mungbean, to sorghum and chickpea to wheat or barley,” says Lance. “We use either a short fallow or double crop to change from a winter to summer crop program and aim for at least one crop every 12 months from each paddock.” Having been no-till farming for 25 years the Wises have seen the weeds transition to those species that proliferate in the absence of cultivation; weeds like fleabane, urochloa, feather top Rhodes grass, cow vine and bladder ketmia. In an effort to reduce their reliance on glyphosate and overcome some of the disadvantages of long-term no-till farming, the Wises have reintroduced light cultivation and are moving toward more targeted application of glyphosate and other herbicide products using an optical sprayer. Nine years ago they had success using the Kelly disc chain to manage urochloa on their less well-structured red earth soils. More recently they have used this implement to target herbicide tolerant feathertop Rhodes grass and fleabane on their main black clay soils. “We are using a chemical / tillage double knock to good effect on feathertop Rhodes grass in the fallow,” says Lance. “We apply glyphosate and then follow up five days later with the Kelly chain, which does a terrific job of pulling out sick, dead and small plants at an operation speed of 11 to 12.5 km/hr.” “The same system works well on fleabane too, pulling up plants with foot-long roots from soft soil, although a higher rate of glyphosate is required. It doesn’t work well for weeds like prairie grass that have deep, fibrous root systems.” The Wises have found the chemical / tillage double knock to work well on feathertop Rhodes grass and fleabane. Used in reverse order, Lance has found the light cultivation is an effective way to stimulate germination after a poor sorghum crop to sprout volunteers and then spray out the crop. Along with the benefits of partial stubble incorporation on soil microbial activity and ease of sowing, Lance says the two short chains in the middle fill in the 3 m wheel track to even out the paddock, avoiding the need to do extra wheeltrack renovation operations. About the Kelly chain “We also use the Kelly chain to incorporate pre-emergent herbicide after sowing to a maximum depth of 2 cm. This does not disturb seed, which is all sown at least 4 cm deep with a presswheel, and the soil is moved sideways without destroying the cracks in the soil or drying out the profile,” he says. “Weed seed is not buried deeply so it doesn’t come back to haunt you years later.” Lance avoids using the Kelly chain more than once in a season on the red soils, which can get very dusty and are prone to hardsetting on the surface. At the end of harvest Lance and Murray assess the stubble load and weed pressure in each paddock. They usually spray glyphosate after a rain event and either double knock with the Kelly chain or spray paraquat through their Weedseeker optical sprayer. After using the Kelly chain, Lance follows 30–45 days later with the Weedseeker rig to clean up any survivors. “The Weedseeker is a new fallow option for us and means that we can treat weeds that we might otherwise ignore, apply higher rates, and use more expensive products to control small areas or patches of weeds,” says Lance. “The 36.6 m boom carries 96 sensors so there are not many weeds that go undetected in the fallow.” At the end of last year, the Wises started sub-soil ripping to a depth of 35 to 40 cm on 75 cm spacing to increase water capture and break up the sub-soil compaction to improve crop growth. Six weeks ahead of planting they apply the final glyphosate spray and then add fertiliser, which they incorporate with the Kelly chain, with the added benefit of removing any weeds present. Liquid fertiliser applied at seeding promotes early seedling vigour and growth, which gives the crops a competitive advantage over weeds. They plant using a Tobin planter that achieves a good even strike in stubble, starting on the red soils as soon after rain as possible, then moving onto the black soils. Pre-emergent herbicide is applied after sowing legume crops and incorporated using the Kelly chain. Herbicide is applied in crop as well as for desiccation purposes in sorghum, mungbeans and chickpea. Being a spray contractor, Lance has also invested in an air boom on his sprayer that enables him to have much greater control of droplet size to match the environmental conditions, while also covering a larger area in a day. He says the elliptical cone delivers spray in both a forward and rear motion to achieve better coverage, even at lower water volumes. The controls in the cab allow the operator to adjust the spray quality from fine to extra course without changing nozzles on the boom and there is no need to have all the different nozzles to suit different conditions and products. The Wises operate a 12 m controlled traffic system and plant all their crops on 375 mm row spacings. Lance has increased the planting rate in sorghum from plants 40 cm apart in the row to 25–30 cm apart to quickly to shade the interspace and suppress weed growth.
Article
Case Study

John Stevenson, Lockhart NSW

Orange Park is an 8200 ha corporate dryland cropping operation with eight main blocks, all within a 30 km radius of Lockhart, NSW where John introduced the use of the double break from cereals 10 years ago.   To get the best result possible from OP canola, ‘Orange Park’ manager John Stevenson (left) has their seed professionally graded and only plants seed sized over 2 mm diameter. Karl Grocke (right) has joined the team at Orange Park on their graduate program, making the most of the opportunity to learn from great operators like John. “Our rotation is driven by herbicide resistant weed management,” he says. “A double break, such as hay/canola, pulse/canola, fallow/canola, is implemented once in a 7-year rotation. The rotation is flexible but we do what we can to avoid growing three cereal crops in a row because the result is inevitably a weed blow-out.” The main weeds on Orange Park are annual ryegrass in-crop and fleabane in summer, which has been increasing since 2005, particularly in wet years. Wild oats is a lesser but persistent weed. “We have low level glyphosate resistance and varying levels of Group A resistance to contend with,” says John. “We don’t use much Group B chemistry either, except occasionally in imi-tolerant crops, partly because of decontamination issues with canola, but mainly because of poor efficacy.” The wettest September on record in 2016 saw about 10% of the crop across the Orange Park operation inundated – compromising their weed control and nitrogen management. “Essentially we lost a year of weed control with ryegrass blow outs due to poor crop competition and not being able to do timely herbicide applications,” says John. “We also saw a shift in the weed spectrum with more carryover of weeds that thrive in wet conditions, such as toad rush and lesser loosestrife.” Crop rotation and double break cropping The rotation that is working well on Orange Park since 2008 consists of two cereals followed by canola, then another two cereals and finally a double break before returning to cereals. John incorporates as much diversity within the system as possible to maximise returns and keep pressure on weed numbers. Canola, wheat, barley, pulses (including faba bean, lentils and vetch hay), oaten hay for export, and strategic fallowing to conserve moisture, all feature in the list of options. The diversity in crops enables the rotation of herbicide groups, including pre-emergent herbicides ahead of each crop. Imi-tolerant crops such as Hurricane lentils, IT-canola, possibly barley in the future add to the mix although John often grows hybrid IT-canola conventionally simply for its inherent yield advantage. “The price of lentils is attractive however logistics are difficult, as grain needs to get to Horsham, over 6 hours away,” he says. “Realistically, canola and feed grain for poultry and feedlots are our mainstay crops.” To maximise the competitiveness of canola crops John grows some hybrid crops and also grades OP canola to 2 mm diameter as a cost-effective way to improve crop establishment and early vigour that also suppresses early weed growth. John uses TT canola when weeds become a problem issue and Clearfield canola in low weed population paddocks where he can also apply atrazine on volunteer faba beans. This year John planted 650 ha trial of lentils in a block that would normally have been fallowed. “There was good residual soil moisture from last year’s wet winter and we tried a late planting system to reduce the density of the lentil crop to keep air flowing through canopy, hopefully reducing the incidence of disease,” he says. “Weed control in the Hurricanes XT lentils has been exceptional although the crop has demonstrated the need for better pH amelioration at depth.” “Including lentils will spread the workload and we can target a different weed germination cohort,” he says. “Having a different group of herbicides available will also help add diversity to our control program.” Row spacing, CTF and stubble management John manages Orange Park as eight 1000 ha management units, where a unit may consist of several blocks in close proximity. He is looking at opportunities to implement east–west sowing in suitable blocks to maximise yield and reduce weed pressure. While on a Nuffield Scholarship trip to New Zealand, John saw crops grown on 125 mm (5 inch) row spacing where farmers were able to include ryegrass as a crop in their rotation, without concern over future weed problems. “Historically, our seeding has been on a 300 mm row spacing but we are in the process of investing in a full disc seeding system, which will allow us to narrow the row spacing to 175 mm (7 inches),” says John. The disc seeder will enable John to retain stubble from their 1.7 t/ha pulses, 3.4 t/ha wheat and 4 t/ha barley crops within their 18 m system with 3 m CTF tramlines. Harvest weed seed control John and his team have been narrow windrow burning for three years. Having tried this harvest weed seed control tactic in canola, wheat and barley crops they have found the safest and best results are achieved in canola. “Realistically, narrow windrow burning is not very compatible with the council’s fire regulations so we are looking at alternatives,” says John. “Cereal stubble burns for 4 or 5 hours, and whirlwinds can easily shift burning chaff 300 m into a neighbour’s stubble.” A downside to narrow windrow burning is that more moisture is stored under the narrow windrows, which can cause uneven crop germination the following season. John has been successfully using narrow windrow burning in canola for several years. Twelve days after sowing, this Lancer wheat crop shows the variability in germination where the rows under the narrow windrow have access to more moisture. John is looking into other options for harvest weed seed control and will probably phase out narrow windrow burning over the next few years. Chaff deck systems suit CTF and although John thinks they have merit, there are limitations on the options available when using contract harvesters. Chaff lining seems easier to implement and is likely to feature in the near future. “Narrow rows help push weed seed heads to the top of the canopy,” says John. “Two plants per m2 is too many, especially if the weed is able to adopt a prostrate habit and evade collection at harvest. The big challenge is getting inexperienced header drivers to harvest low, even though we pay the contractor a premium to have this happen.” John uses spray topping in canola, and sometimes wheat and barley, along with hay production to take out late germinating weeds. Fallow management Over summer, John uses a contractor with an optical (camera) sprayer to treat survivors with paraquat following a broadacre spray of glyphosate. He says the optical sprayer is also a valuable tool to help manage cud weed, which is becoming more prevalent. There is no routine cultivation in the system however John does incorporate lime with a speed tiller before planting and a full tillage using a flexicoil is done when there is levelling work required. “When we change over to the disc seeder we will probably need to cultivate to remove the ridges left by the tined system,” he says. “The disc seeders can’t handle too much chaff on the ground either, so burning is still an option for weed control, or when slugs and mice are a problem.” Soil fertility and weeds Across the Orange Park operation John has acidic (pH 4.5) red soil ridges and some sodic vertosols to contend with. He is using variable rate technology (VRT) to apply lime to the red ridges using rates ranging from 1 to 3 t/ha to lift the pH to 5.5. “We saw an immediate response of lower ryegrass population in low pH blocks after lime application due to stronger crop competition,” he says. “Variable rate application and soil testing has been very cost effective for us and has helped reduce weed numbers and improves herbicide efficacy. Fixing soil pH gives the best return on investment through improved nutrient availability, which supports higher yield and better weed control.” John is also using soil sensing and VRT to address constraints in nitrogen and phosphorus. The red soil ridges on ‘Orange Park’ are acidic (pH 4.5) so John is using variable rate lime applications to lift the average pH in these soils to 5.5. In doing so he has observed an immediate reduction in ryegrass numbers due to the improved crop competitiveness.  
Article
Case Study

Aaron McDonald, Horsham Vic

Farming with his parents, Greg and Leanne, Aaron runs 5500 ewes for wool and prime lamb production, utilising pastures, hay paddocks and crop stubble on their 4050 ha property. The McDonalds are finding a rotation of canola, wheat, canola, wheat, then a double break of canola followed by faba beans or clover hay, is profitable and enables them to keep weed numbers down. In barley crops the straw is also often baled after cutting the crop low, allowing sowing without stubble burning. Aaron does most of their oaten hay production on the poorer soils but also uses oaten hay as an effective means to clean-up paddocks that have a higher infestation of ryegrass. Their clover hay is sold locally, predominantly as cattle feed, while their oaten hay is exported most years. “Annual ryegrass and wild radish are our main problem weeds,” says Aaron. “We test for herbicide resistance every couple of years and so far the results have come back as ‘susceptible’ for most of the major groups. The main challenge we have with wild radish is the fact that it germinates all year round. With ryegrass it’s all about keeping plant numbers low.” Although the testing is not showing herbicide resistance, Aaron is seeing evidence of Select not working as well as it did in the past. To add more mode-of-action diversity to their system the McDonalds are using pre-emergent herbicides Sakura and Boxer Gold in cereals with good success and grow both hybrid (RR and 650TT) and open-pollinated (TT) canola cultivars. “The RR canola enables extra knocks with glyphosate in-crop to clean up paddocks where we are concerned over the efficacy of Select,” says Aaron. “All our other in-crop herbicides are still working well but we are trying to rotate as much as possible with Select and Edge, and using paraquat ahead of canola and glyphosate or paraquat ahead of cereals.” The McDonalds have always sown their crops on fairly narrow rows, 250 mm spacing, and use high sowing rates (wheat and oats sown at 100 kg/ha and canola at 3.6 kg/ha) to provide strong crop competition to help with weed control. The sheep grazing stubbles provides quite good control of summer weeds but some herbicide is always required. Aaron’s main summer weed concerns are melons and self-sown crop. In autumn or pre-sowing he occasionally double-knocks but often there are no survivors so the second knock is not needed. Hay making and harvest weed seed control Aaron has implemented narrow windrow burning for the last 4 or 5 years in their canola crops as a harvest weed seed control tactic to capture late germinating weeds. This is supported with strategic crop topping of the canola to desiccate and then windrowing 80 per cent of the canola area each year. In their cereals, crops are cut low and stubble is burnt on about 75 per cent of the cropped area to allow easier sowing operation, and has the added benefit of destroying some weed seed. In barley crops the straw is often baled after cutting the crop low, allowing sowing without stubble burning. Grazing stubble and burning also helps reduce mice and slug numbers. “Oaten hay production enables us to apply a desiccant over the top prior to cutting for hay,” says Aaron. “This gives us the opportunity to implement a herbicide plus non-herbicide double knock on in-crop herbicide escapes.” Aaron McDonald is using oaten hay and clover hay production as weed management tools within their mixed farming operation south of Horsham. “We graze the cereal stubble and canola narrow windrows after harvest but don’t leave the sheep on the paddocks for long,” he says. “We find that the cereals provide better feed value than the canola windrows but we also put lambs on the canola regrowth for a little extra green pick.” Each year about 5000 lambs move through the on-farm feedlot, where the McDonalds feed out gradings from the barley grain and the straw. “Feeding the grain gradings out in the feed lot also brings weed seeds into the confinement area where we can control them quite easily,” says Aaron. The feedlot adds value to the straw and grain gradings, turning off about 5000 lambs per year. Weed seeds that are brought back to the feedlot are easily managed if they survive being eaten.
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Case Study

Daniel Fox, Marrar NSW

For a few years Daniel has been adding components to his system to conserve moisture and keep herbicide resistant weeds at bay. “A series of drought years got us started down this track of better soil moisture conservation,” he says. “We have been able to store more water than we expected really and this has been converted into better yields.” Daniel (left) and David Fox are pleased with the chaff lining chute they have introduced as a harvest weed seed control method on their Marrar farm near Wagga Wagga. The long-term average rainfall at Marrar, north of Wagga Wagga, NSW is 500 mm and although last year was extraordinarily wet, the 15 years prior to this were relatively dry. This long dry stretch made growers like Daniel and his father David think more about conserving soil moisture over summer and using stubble to protect the soil moisture from evaporation. As they add more strategies to their management system they are seeing yields rise from an average 2.5 t/ha for wheat to 4 t/ha in years that would have seen the crop suffer due to a lack of spring rainfall. To tackle increased pressure from annual ryegrass Daniel and David started narrow windrow burning but found that a combination of cutting the crop low at harvest and burning much of the crop residue was impacting on yields. To investigate, they participated in a trial run by Grassroots Agronomy to see if cutting the crop higher, at 30 cm rather than the recommended 15 cm for narrow windrow burning, would still be an effective harvest weed seed control measure. “The results showed a half-tonne difference between cutting barley low and cutting higher,” he says. “It seems that the taller stubble provides better protection for the soil surface and the trial with the taller stubble had better conserved moisture, which was needed to finish the crop that year, where we had no rain from early September to mid October.” Highly competitive crops, like this barley, tend to hold annual ryegrass seed heads up high in the canopy where they can be easily collected by the stripper front on the Fox’s harvester. To maintain the effectiveness of harvest weed seed control Daniel has recently purchased a Shelbourne stripper for the header to collect the grain, and weed seeds, while leaving most of the stubble standing. “Using the stripper we are putting less material through the harvester but still collect grain and weed seed in the crop canopy,” he says. “This means we are picking up yield and reducing the weed seed bank without compromising harvesting efficiency.” Having used narrow windrow burning for a few years and seeing the benefit of capturing seed from late germinated weeds at harvest, the Foxes have now built a chaff lining chute for the header and are delivering the chaff component, including weed seeds, into a 250 mm chaff line in the middle of the 12 m CTF lap. This maintains most of the crop residue evenly across the paddock and avoids the need for burning. “Having the weed seed concentrated in a narrow band reduces the amount of seed that germinates and also reduces the chance of weed seed being buried and ‘stored’ underground at planting now that we are using a disc seeder,” says Daniel. Daniel has had no problem sowing through the chaff and is also able to apply more herbicide to the tramlines if the weed numbers appear to be increasing. He is also keeping an eye on the developments of microwave weed control technology as a potential non-herbicide method to treat the tramlines in the future. “We realise that there might be an impact on soil microbes and earthworms but if the microwave is only treating the chaff lines then it could still be a good option,” he says. Croptopping in non-malting barley, canola and pulses provides an additional opportunity to stop seed set with the chaff lining providing an effective, non-herbicide second knock to support the herbicide. The cereal stubble persists across the four-year rotation of two cereal crops followed by two break crops, providing more shade and wind protection, and keeping the soil surface cooler. Daniel Fox has implemented a double break crop system where the cereal stubble is maintained on the soil surface across the 4-year rotation, conserving soil moisture and improving crop yields. The double break cropping rotation enables Daniel to have a two-year shot at both grass and broadleaf weeds using a combination of herbicide and non-herbicide tactics. “With herbicides we are using robust pre-emergent and in-crop applications and double knocking our knockdown herbicides,” he says. “The non-herbicide tools are collecting weed seed at harvest with the chaff lining chute, strong crop competition from narrow row spacing and haymaking if required. In just three years we have seen a huge reduction in the ryegrass population on the farm.” During the 2000s David stayed with the canola / wheat rotation they had in place even though it meant that they had a few failed crops, which they converted into silage. “By resisting the temptation to go with a long cereal rotation we avoided the weed blow-out that occurred on some farms,” he says. The Foxes grow wheat and barley in the cereal phase with an option for oats on their frost-prone paddocks. “Wheat is our mainstay on the higher paddocks where we sow early and the crop flowers in cooler weather, which can make a 2 t/ha difference in yield compared to sowing later,” says Daniel. “We are wanting to raise our average wheat yield from 2.5 t/ha to 3 t/ha, even in lower rainfall and lower radiation years. Likewise, for barley we are confident that significant yield gains are possible in the system we have developed.” In the broadleaf phase they grow canola and a pulse, usually lupins, and are considering faba bean and lentils as alternative pulse options. They are also investigating whether winter cover crops followed by a summer crop might have a fit in their system to give them the opportunity to use different chemistry at different times of the year to combat weeds. “No-till and glyphosate generated a big jump in productivity on this farm and now we are seeing another big improvement with new gear such as the chaff lining chute, stripper front and high clearance sprayer,” says Daniel. “We could not have got through last season without the sprayer. It has allowed us to get onto weeds when they are small and cover a big area in the best conditions.” Doing their own spraying and planting gives Daniel and David the opportunity to monitor their paddocks during the season to keep an eye on weed numbers, which also helps when they go around the farm with their agronomist to plan the weed control program. A new disc seeder has also made stubble management easier and allowed Daniel to move to 6.5 inch (165 mm) row spacing for all crops. The single disc seeder has 72 units over the 12 m span which, like the sprayer, fits within the controlled traffic system. Daniel is conscious of brome grass and black oats entering the farm from the roadside so he is spraying through the external fences with a mix of glyphosate and residual herbicide to help minimise the risk of weeds moving into the cropping areas. “We sow right up to the fence to maintain competition and if we need to, we bale the outside lap of the crop,” he says. “After harvest we plough along the fencelines as a firebreak, which is a council requirement.” The Foxes look for crop traits that provide a competitive edge such as hybrid canola over open-pollinated types and taller wheats such as Spitfire, while still maximising yield and profit from the available moisture. “The 29 year row spacing trial in WA demonstrated that narrow rows produce more crop and less weeds, and we have seen a 400 to 500 kg/ha benefit through less tiller deaths and more heads here too,” says Daniel. “To achieve this it is essential that the soil fertility is able to support the increased production. Our granite soils tend to leach nitrogen in wet years and that has a big impact on yield.” Related information Getting weed seeds into the header’s chaff stream Michael and Marnie Fels grower case study – chaff lining

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Double knock applications: extent of herbicide resistance in the north

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