Mix and rotate herbicides

Rotating buys you time, mixing buys you shots. Mix and rotate buys you time and shots.

  • Mix two herbicides at full rates where possible
  • Rotate between mixes, not just between individual herbicides

We have made a big fuss in the past over rotating between herbicides from one year to the next. This is still a good message, but an even better message, based on what we now know, is that mixing herbicides is even more effective than rotating between them. And combining the two messages is the best approach that growers and agronomists can take. What we mean by this is to mix two herbicides, both at full rates, and then rotate to another herbicide mix. Weeds find it easy to evolve resistance to simple, predictable weed control. Mix and rotate is neither simple nor predictable for the weeds.

Articles

View all
Article
Article

Post emergent herbicides

Part 1: Spray small radish twice Western Australian research reveals that careful timing, effective application and using different herbicide groups are more important than product choice for controlling wild radish. A range of herbicide combinations can provide effective control of herbicide-resistant wild radish if small plants were sprayed twice and attention is given to achieving good herbicide coverage. Peter Newman (Australian Herbicide Resistance Initiative) and agronomist Grant Thompson (Crop Circle Consulting) discuss the results of their wild radish research. Resources Spray resistant radish early for best efficacy and yield (Grant Thompson, Crop Updates paper 2014) Herbicide resistant wild radish (Peter Newman) Controlling herbicide resistant Wild Radish in wheat in the Northern Agricultural Region of WA with a two spray strategy (Peter Newman) Diverse weed control: Left jab, right hook (AHRI insight) Part 2: When is it worth rotating from clethodim (Select®) to butroxydim (Factor®)? Is there any value in rotating the post-emergent herbicides clethodim (Select®) and butroxydim (Factor®)? The research suggests that Factor® will sometimes kill plants that are moderately-resistant to Select® that could help in driving down the weed seed bank. Dr Peter Boutsalis from the University of Adelaide discusses his latest research and observations using both products with AHRI’s Peter Newman.
Article
Article

Increase pre-em efficacy through a mix and rotate strategy

Have you got the best and most cost efficient strategy to nuke your weeds before seeding? The case is clear: summer weed control is essential! Controlling weeds through summer and prior to seeding is key to securing moisture and nitrogen for the following crop. Part 1: Control summer weeds for yield and profit Every $1 spent on summer weed control can potentially return up to $8/ha through moisture and nitrogen conservation. The impact on grain yield as a result of various summer weed control treatments is what Colin McMaster (NSW DPI R&D) refers to as “buying a spring”. Listen to Colin and Pete Newman (AHRI) as they investigate the $$ benefits of controlling summer weeds. Part 2: Increase pre-em efficacy through a mix and rotate strategy We’ve done a good job of promoting herbicide rotation over the years. And whilst this advice still stands, recent research shows the benefits of mixing herbicides as well. As American weeds researcher, Pat Tranel, puts it, “rotating buys you time, mixing buys you shots (of herbicide)”. Listen to Pat and Pete as they explore the benefits of the mix and rotate strategy.
Article
Case Study

Trevor Syme, Bolgart WA

A few years ago they began an extensive liming and clay delving and spading program across 50 per cent of the 3500 ha cropping area to improve the water holding capacity of the natural non-wetting sands. With 75 per cent of the affected area now treated Trevor is looking forward to having this expensive but very beneficial operation behind him. Treating the non-wetting soils has assisted with weed control through 40 per cent higher yielding crops, more even crop germination and better efficacy with the pre-emergent herbicides. “Treating the non-wetting soils has assisted with weed control through 40 per cent higher yielding crops, more even crop germination and better efficacy with the pre-emergent herbicides,” says Trevor. “It has also enabled us to grow canola in paddocks that were previously not an option and crops seem to finish better and are less prone to frosting.” They have also achieved good results building soil organic matter with brown manured cereal rye crops. Trevor has trialled summer crop brown manuring too but the results over three seasons were unreliable and he has decided to look for other options to reduce evaporation over summer and reduce the need for summer weed control. The Symes’ farming system is 100 per cent controlled traffic and stubble retention with a long winter crop rotation of lupins, wheat, canola, wheat, barley, with brown manured cereal rye grown on the soils not suited to canola. Information on the summer fallow spray program The summer fallow spray program involves 2,4-D ester, triclopyr and glyphosate to control melons, caltrop, fleabane, sowthistle and volunteer cereals. For the last 5–6 years Trevor has applied a double knock of glyphosate followed with paraquat in preparation for sowing. “We try hard to get the timing right and target the right size weeds with the double knock,” he says. “We also avoid mixing a pre-emergent in with the paraquat because the aim is to get the paraquat on weed leaves using a high water rate and fine droplet size, whereas the aim with the pre-emergent is to achieve even coverage of the soil. Doing the pre-emergent spray separately costs us more but I believe it is worth using the right boom set up for the two jobs.” “Rotating crops and herbicide modes of action, and using the double knock tactic, are critical to our weed management program,” he says. “RR canola, Clearfield barley and lupins all have a fit in the crop rotation and allow us to rotate herbicides effectively. The imi-tolerant barley has enabled quite effective control of brome grass and we croptop the canola with glyphosate.In the lupins we are using a pre-emergent propyzamide application followed with clethodim in-crop and finish with a croptopping spray of paraquat.” Trevor is finding that weed control in the lupin phase is more critical than it used to be, but the value of lupins in boosting yields in the following wheat crop motivates him to look after the lupin crops, plant into clean paddocks and do everything he can to keep weed numbers low. The Symes have had good success with high biomass canola on sandy soils where multiple germinations of wild radish are the norm. They usually plan their crop and herbicide program with their agronomist at the end of September and then revise it in February or March. Trevor is going away from the current move toward narrow row spacing and disc seeders. “We are changing back from a disc seeder at 305 mm spacing to tines on 381 mm with a split boot to sow cereals in paired rows and canola and lupin in single rows,” he says. “We are working on the idea that less rows equals less disturbance equals less weeds in a controlled traffic system. The slightly wider row spacing also makes it easier to handle the stubble load accumulated over several years and allows us to inter-row sow.” He has found that high tillering wheat varieties, such as Magenta, offer an alternative way to increase crop competition through additional shading of the inter-row. In the 2015 harvest the Symes added a chaff deck to their weed control progam, directing all the chaff, and weed seeds, into the harvester wheel tracks. Trevor harvests weedy paddocks first to maximise the value of harvest weed seed control and has found the chaff deck easy to use and results in relatively few weeds surviving in the tramlines. The biggest benefit of the chaff deck is that weed seeds are collected across the whole farm every year, and concentrated in the inhospitable tramlines. “The biggest benefit is that we can collect weed seed across the whole farm every year where previously we have only really been able to do narrow windrow burning in the canola phase. Now at harvest the whole job is done, with no need to return to burn.” “It is great to know where the weeds are and they are dumped on a hard, inhospitable surface,” he says. “Any escapes are easily collected at the next harvest. We also have a back-up plan to use a shielded sprayer to weeds in the tramlines, but we really want to avoid using this option.” “In fields with high weed numbers in the tramlines we have tried simply driving a tractor, without any implement, along every tramline to achieve a crimp-rolling effect. This seems to have been a cost-effective way to stop seed set in weedy tramlines.” In fields with high weed numbers in the tramlines Trevor has tried simply driving a tractor, without any implement, along every tramline to achieve a crimp-rolling effect (right). Annual ryegrass, wild radish and brome grass are the main weed challenges on the Symes’ property. Trevor has done some herbicide resistance testing but generally takes the approach that all weeds present are likely to have some level of resistance. “The key is to keep weed numbers low so we take care to spray when weeds are small and avoid frost windows and high temperatures when the sprays are less effective,” he says. “We also use quite high water rates – 80 L/ha for most post-emergent herbicides and 120 L/ha for pre-emergent herbicides and paraquat – and have two sprayers so we can cover as much ground as possible when the conditions are right.” “Fencelines and fire breaks are a weak point in our farming system as a source of glyphosate resistant weeds,” he says. “We have removed as many fences as possible, now that we don’t run any livestock, and are actively looking for an alternative herbicide that is not used in crop to manage weeds on the firebreaks.” Trevor takes considerable care when choosing seed production paddocks, ensuring weed numbers are low to start with and then treating the paddock as a nursery. He harvests the seed crops early and cleans the seed prior to planting.
Article
News

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

Case Studies

View all
Article
Case Study

Trevor Syme, Bolgart WA

A few years ago they began an extensive liming and clay delving and spading program across 50 per cent of the 3500 ha cropping area to improve the water holding capacity of the natural non-wetting sands. With 75 per cent of the affected area now treated Trevor is looking forward to having this expensive but very beneficial operation behind him. Treating the non-wetting soils has assisted with weed control through 40 per cent higher yielding crops, more even crop germination and better efficacy with the pre-emergent herbicides. “Treating the non-wetting soils has assisted with weed control through 40 per cent higher yielding crops, more even crop germination and better efficacy with the pre-emergent herbicides,” says Trevor. “It has also enabled us to grow canola in paddocks that were previously not an option and crops seem to finish better and are less prone to frosting.” They have also achieved good results building soil organic matter with brown manured cereal rye crops. Trevor has trialled summer crop brown manuring too but the results over three seasons were unreliable and he has decided to look for other options to reduce evaporation over summer and reduce the need for summer weed control. The Symes’ farming system is 100 per cent controlled traffic and stubble retention with a long winter crop rotation of lupins, wheat, canola, wheat, barley, with brown manured cereal rye grown on the soils not suited to canola. Information on the summer fallow spray program The summer fallow spray program involves 2,4-D ester, triclopyr and glyphosate to control melons, caltrop, fleabane, sowthistle and volunteer cereals. For the last 5–6 years Trevor has applied a double knock of glyphosate followed with paraquat in preparation for sowing. “We try hard to get the timing right and target the right size weeds with the double knock,” he says. “We also avoid mixing a pre-emergent in with the paraquat because the aim is to get the paraquat on weed leaves using a high water rate and fine droplet size, whereas the aim with the pre-emergent is to achieve even coverage of the soil. Doing the pre-emergent spray separately costs us more but I believe it is worth using the right boom set up for the two jobs.” “Rotating crops and herbicide modes of action, and using the double knock tactic, are critical to our weed management program,” he says. “RR canola, Clearfield barley and lupins all have a fit in the crop rotation and allow us to rotate herbicides effectively. The imi-tolerant barley has enabled quite effective control of brome grass and we croptop the canola with glyphosate.In the lupins we are using a pre-emergent propyzamide application followed with clethodim in-crop and finish with a croptopping spray of paraquat.” Trevor is finding that weed control in the lupin phase is more critical than it used to be, but the value of lupins in boosting yields in the following wheat crop motivates him to look after the lupin crops, plant into clean paddocks and do everything he can to keep weed numbers low. The Symes have had good success with high biomass canola on sandy soils where multiple germinations of wild radish are the norm. They usually plan their crop and herbicide program with their agronomist at the end of September and then revise it in February or March. Trevor is going away from the current move toward narrow row spacing and disc seeders. “We are changing back from a disc seeder at 305 mm spacing to tines on 381 mm with a split boot to sow cereals in paired rows and canola and lupin in single rows,” he says. “We are working on the idea that less rows equals less disturbance equals less weeds in a controlled traffic system. The slightly wider row spacing also makes it easier to handle the stubble load accumulated over several years and allows us to inter-row sow.” He has found that high tillering wheat varieties, such as Magenta, offer an alternative way to increase crop competition through additional shading of the inter-row. In the 2015 harvest the Symes added a chaff deck to their weed control progam, directing all the chaff, and weed seeds, into the harvester wheel tracks. Trevor harvests weedy paddocks first to maximise the value of harvest weed seed control and has found the chaff deck easy to use and results in relatively few weeds surviving in the tramlines. The biggest benefit of the chaff deck is that weed seeds are collected across the whole farm every year, and concentrated in the inhospitable tramlines. “The biggest benefit is that we can collect weed seed across the whole farm every year where previously we have only really been able to do narrow windrow burning in the canola phase. Now at harvest the whole job is done, with no need to return to burn.” “It is great to know where the weeds are and they are dumped on a hard, inhospitable surface,” he says. “Any escapes are easily collected at the next harvest. We also have a back-up plan to use a shielded sprayer to weeds in the tramlines, but we really want to avoid using this option.” “In fields with high weed numbers in the tramlines we have tried simply driving a tractor, without any implement, along every tramline to achieve a crimp-rolling effect. This seems to have been a cost-effective way to stop seed set in weedy tramlines.” In fields with high weed numbers in the tramlines Trevor has tried simply driving a tractor, without any implement, along every tramline to achieve a crimp-rolling effect (right). Annual ryegrass, wild radish and brome grass are the main weed challenges on the Symes’ property. Trevor has done some herbicide resistance testing but generally takes the approach that all weeds present are likely to have some level of resistance. “The key is to keep weed numbers low so we take care to spray when weeds are small and avoid frost windows and high temperatures when the sprays are less effective,” he says. “We also use quite high water rates – 80 L/ha for most post-emergent herbicides and 120 L/ha for pre-emergent herbicides and paraquat – and have two sprayers so we can cover as much ground as possible when the conditions are right.” “Fencelines and fire breaks are a weak point in our farming system as a source of glyphosate resistant weeds,” he says. “We have removed as many fences as possible, now that we don’t run any livestock, and are actively looking for an alternative herbicide that is not used in crop to manage weeds on the firebreaks.” Trevor takes considerable care when choosing seed production paddocks, ensuring weed numbers are low to start with and then treating the paddock as a nursery. He harvests the seed crops early and cleans the seed prior to planting.
Article
Case Study

Grant Wilson, VIC

Their no-till cropping rotation, which includes wheat, lentils, canola, barley, lupins and field pea, is governed by disease and weed management considerations, proving that integrated weed and disease management can go hand in hand. “There was a time when we just ignored summer weeds, but not now,” says Grant. “We are very conscious of weed management all year round and the potential for herbicide resistance to really limit our options if it gets out of hand.” Following a ‘no cereal after cereal’ policy, Grant usually tries for a two year break between cereal crops. “We also rotate between different wheat cultivars to make the most of their disease management traits,” he says. “Following a cereal we would be looking to plant a legume, usually a lentil crop, but if we were faced with a broader weed problem we would choose an ‘imi’ tolerant lentil or possibly decide to grow field pea instead of lentils to take advantage of the wider range of selective herbicides registered in field pea.” Grant usually keeps a two year break between cereal crops to maintain effective control of diseases. Pulse crops sown into standing stubble offer the best combination of tactics to tackle ryegrass in-crop using grass selective herbicides and desiccation. Being in a lower rainfall zone (325 mm or 13 inches), the Wilsons find a conservative rotation is safer in the long run and gives them more options to manage annual ryegrass. Pulse crops offer the best combination of tactics to tackle ryegrass in-crop using grass selective herbicides and desiccation. Recently Grant started using pre-emergent herbicides such as Boxer Gold® and Sakura® to reduce their reliance on trifluralin in wheat. “So far we have had mixed results, especially in dry weather, when there was insufficient moisture to properly activate the herbicide, on top of poor crop competition due to the seasonal conditions,” he says. “It is an expensive option but when it works it provides good control across the paddock.” Grant prefers to use Boxer Gold® before sowing with knife-points and press wheels on the seeder. The heavier soils are in a fallow rotation to conserve soil moisture. Most fallow paddocks will usually be sprayed once or twice, depending on rainfall, over the summer. The Wilsons grow vetch as a green manure crop on their lighter soils to improve soil health and control weeds. When the vetch reaches maximum biomass Grant sprays it out to gain maximum benefit from the high biomass production. All other crops are left as standing stubble and this year they will be moving into inter-row sowing. “We now have RTK guidance fitted to the seeder and expect to see some real improvements in crop establishment,” he says. “With a more even sowing depth we should get more uniform germination and that will increase the crop’s ability to out-compete weeds.” The soil type across the Wilson’s farm ranges from sand to loam and varies in pH. Kate, an independent agronomist, takes production-limiting factors such as soil pH and boron levels into account when planning the rotation, particularly with lupins being more sensitive to higher pH and lentils being sensitive to boron levels. The potential for herbicide residues to still be present after a dry summer is also a consideration, particularly on higher pH soils. The Wilsons crop between 4000 and 5000 ha a year and generally do not have livestock, however they do fatten lambs on stubble as the opportunity arises. Annual ryegrass has some resistance to Group A ‘fops’ but so far ‘dim’ herbicides are still effective. Kate customises their herbicide mixes to preserve the effectiveness of the dim herbicides by avoiding unnecessary usage. They have also resisted a move into glyphosate tolerant varieties because they are concerned about the potential over-use of glyphosate that may lead to glyphosate resistance in weeds. However, they do grow some herbicide tolerant crops that utilise different herbicide modes of action. Annual ryegrass on the Wilson’s property has some resistance to Group A ‘fops’ but so far ‘dim’ herbicides are still effective. Kate customises their herbicide mixes to preserve the effectiveness of the dim herbicides by avoiding unnecessary usage. The Wilsons choose not to grow imi-tolerant cereals because they believe this would lead to an over-use of Group B chemistry, which is known to lead to herbicide resistance in weeds such as brome grass. They use imi-tolerant Clearfield canola to a limited degree as another option to control annual ryegrass using imazapic/imazapyr (Group B) products and rotate herbicides as best they can in an attempt to stave off herbicide resistance in grass weeds. “We use crop desiccation to stop weed seed set to avoid the need for narrow windrow burning to destroy weed seeds after harvest,” says Grant. “Desiccation seems most effective in legumes, particularly lentils. In cereals we have also used herbicides to croptop weeds according to product label instructions.” “Fleabane is a new weed in this area having become noticeable for the first time during the wet summer in 2010,” says Grant. “A double knock treatment has been recommended for fleabane control and we will also introduce cultivation if required in some situations.” The Wilson’s tread a fine line between maximising crop competition and conserving soil moisture. “Plant health is our main interest and we use a range of tactics to reduce weed pressure in-crop,” says Grant. “With legumes in the rotation we avoid applying much starter-N fertiliser and we make an effort over summer to get the paddocks as clean as possible before seeding.” The Wilsons plant their crops as narrow as possible using a standard cereal seeding rate of 60 kg/ha on a 250 mm row spacing. They find this row spacing narrow enough to provide early crop competition and not be too rough, while still being able to inter-row sow. Taking a thoughtful and long-term view of herbicide use within their cropping system has kept a lid on herbicide resistance on the Wilson’s farms so far and preserved a wide range of herbicide chemistry. Herbicide use is supported with non-herbicide tactics and the rotation of modes of action within and between crop types.

Videos

View all
Video
Video

Double breaks – a double shot at annual ryegrass

Perhaps you’re a ‘short black’ wheat-canola type, strong on inputs? Or a ‘long black’ type who likes to dilute their rotations a bit more? Or are you a ‘double shot’, throwing in a few break crops in a row for maximum effect? When it comes to managing annual ryegrass populations, Tony Swan and the research team from CSIRO Plant Industry and FarmLink, have shown that ‘double shots’ are the key. Growing two break crops in sequence (broadleaf crop, hay crop or long fallow) was more effective in reducing resistant ryegrass numbers to manageable levels than a single break crop or continuous wheat over a three-year rotation. And it can still be profitable.
Video
Webinar

Increase pre-em efficacy through a mix and rotate strategy

Part 1: Control summer weeds for yield and profit Every $1 spent on summer weed control can potentially return up to $8/ha through moisture and nitrogen conservation. The impact on grain yield as a result of various summer weed control treatments is what Colin McMaster (NSW DPI R&D) refers to as “buying a spring”.  Listen to Colin and Pete Newman (AHRI) as they investigate the $$ benefits of controlling summer weeds. Resources: Ask an Expert column with Colin McMaster GRDC Summer Fallow Weed Management Manual   Part 2: Increase pre-em efficacy through a mix and rotate strategy We’ve done a good job of promoting herbicide rotation over the years. And whilst this advice still stands, recent research shows the benefits of mixing herbicides as well. As American weeds researcher, Pat Tranel, puts it, “rotating buys you time, mixing buys you shots (of herbicide)”. Listen to Pat and Pete as they explore the benefits of the mix and rotate strategy.
Video
Webinar

Post emergent herbicides

Resources Spray resistant radish early for best efficacy and yield (Grant Thompson, Crop Updates paper 2014) Herbicide resistant wild radish (Peter Newman) Controlling herbicide resistant Wild Radish in wheat in the Northern Agricultural Region of WA with a two spray strategy (Peter Newman) Diverse weed control: Left jab, right hook (AHRI insight)   Part 2:When is it worth rotating from clethodim (Select®) to butroxydim (Factor®)? Is there any value in rotating the post-emergent herbicides clethodim (Select®) and butroxydim (Factor®)? The research suggests that Factor® will sometimes kill plants that are moderately-resistant to Select® that could help in driving down the weed seed bank. Dr Peter Boutsalis from the University of Adelaide discusses his latest research and observations using both products with AHRI’s Peter Newman.

Fact Sheets

View all
Fact Sheet

Stewardship First SprayBest Guide

The application of herbicides late in the season to prevent weeds setting seed or to desiccate crops must be carried out with caution and in line with herbicide label recommendations. It is essential to check if these practices are acceptable to buyers, as in some situations markets have extremely low or even zero tolerance to some pesticide and herbicide residues.

Subscribe to the WeedSmart Newsletter