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Using tank mixes to extend herbicide ‘life’

Before herbicide selection has taken place it is very rare for an individual weed to be resistant to two herbicides. Mixing herbicides at full label rates in a single application takes advantage of this fact.
Armed with this knowledge growers can get in early and hit weed populations hard with multiple modes of action to stave off herbicide resistance. Even weeds that may possess the mutation to allow them to survive either or both modes of action on their own are very unlikely to survive an application of both at the same time.
Look for product combinations of two or more herbicides to safely apply to the crop at full label rates for the target weed. The products must be physically compatible with no antagonism between them and no existing resistance to any of the herbicides in the mix.

This is similar to the idea of using a double knock and it is not necessary that all the ‘knocks’ are from a drum. Teaming an effective tank mix with crop competition and clean seed, for example, would reduce weed seed set in that season and lessen the pressure in following years, potentially allowing a less competitive crop to be grown.
This concept was proven through research in the United States following an observation that some fields were unaffected by waterhemp while a neighbouring field had this weed overshadowing the crop. Waterhemp is a big, competitive weed that sets a lot of seed and readily evolves resistance to herbicides. It is common for individual plants to be resistant to multiple herbicide modes of action.
It is now well known that over-reliance on a single herbicide group will inevitably result in resistance and US growers have created the world’s biggest herbicide resistance problem by abandoning all other forms of weed control in favour of glyphosate alone.
Researchers Pat Tranel, Jeff Evans, Aaron Hager, Adam Davis, Brian Schutte, Chenxi Wu and Laura Chatham from the University of Illinois, the USDA-ARS Global Change and Photosynthesis Research Unit, and the State University, New Mexico used spray records from a local spray contractor to compare 50 fields with glyphosate resistant waterhemp and 50 fields without. They looked at a total of 61 management and environmental variables and found that mixing herbicides was the single management strategy that made the most difference to whether or not glyphosate resistant waterhemp became a problem in any field.
In a review of herbicide application records from 2004 to 2006 and glyphosate resistance tests in 2010 the researchers found that adding more products to the tank at full rates for a single application causes the probability of resistance in these fields to decline sharply. (See graph below)
In a review of herbicide application records from 2004 to 2006 and glyphosate resistance tests in 2010 the researchers found that adding more products to the tank at full rates for a single application causes the probability of resistance in these fields to decline sharply. (MOA = mode of action = herbicide group).
In Australia, herbicide mixes are often used but in many cases the products included in the mix are not added at full label rates. While there are constraints such as crop safety or label restrictions for some product mixes, there are many product combinations that are safe and effective when combined at full label rates.
Look for product combinations of two or more herbicides to safely apply to the crop at full label rates for the target weed. The products must be physically compatible with no antagonism between them and no existing resistance to any of the herbicides in the mix.
This strategy needs to be used wherever possible and in addition to herbicide rotation, not instead of it. Mixing is most useful when managing weeds that use very specific resistance mechanisms to survive a herbicide spray. Where the target weed uses resistance mechanisms that can give cross-resistance to a number of herbicides, mixing may not be useful as the weed may be resistant to several modes of action and will survive the spray, going on to set seed and proliferate. In these situations, it is even more important that non-herbicide tactics are included in the weed management plan.
Mixing herbicides does not halt the evolution of herbicide resistance in a weed population, it can only delay the process.
You can read the scientific paper about this research here and check out the AHRI insight on this research.
 

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Herbicide resistant wild radish in central NSW

Wild radish has proven to be a champion when it comes to herbicide resistance. In central NSW where the first population of Group I (e.g. 2,4-D) resistant wild radish was confirmed in late 2013, trials have shown that there are other herbicide options that still work.
Wild radish in the Nyngan trial was shown to be susceptible to several herbicide modes of action but simply rotating herbicides is risky and certainly not a long term option. Image: T. Cook.
Tony Cook, NSW DPI extension officer and weeds technical specialist, says although this brings some reassurance to growers, the real message is that reliance on herbicides to manage wild radish is very risky.
“In Western Australia growers have had to first contend with Group B resistance in wild radish and in NSW it appears that Group I was the first herbicide to fail,” he says. “This weed has the proven capacity to evade several modes of action so simply rotating herbicide groups is not the long term answer, in fact reliance on rotation of herbicide chemistry alone leads to resistance to multiple modes of action.”
“All herbicides are more reliable in low weed population situations,” he says. “It is essential that the highest priority be to maintain low weed numbers and this may involve a concerted effort to use non-herbicide tools such as manuring, cultivation and weed seed collection at harvest to protect current herbicides.”
The NSW DPI weeds research team set up a trial near Nyngan to test wild radish susceptibility to herbicides from groups B, C, F, G, H, I and M.
“In this trial the wild radish did not display resistance to 2,4-D and early applications of this herbicide still achieved excellent control,” says Mr Cook. “However, 2,4-D applied at flowering was largely ineffective, achieving only 20 per cent control.”
In WA, pyrasulfotole + bromoxynil (Velocity®) is currently giving excellent control of Group I resistant wild radish although over-reliance is likely to lead to pyrasulfotole resistance. This product was also highly effective in this trial, as was MCPA + bromoxynil + diflufenican (Triathalon®), pyrasulfotole + MCPA (Precept®), diflufenican and early MCPA with or without diuron.
“The glyphosate treatments resulted in poor control of radish,” says Mr Cook. “The data indicate that only controlling emerged plants provided limited benefit as many wild radish seedlings emerged soon after treatment and went on to maturity.”
The trial also highlighted the importance of application timing and rate. Some herbicides such as bromoxynil were applied outside the optimum application timing and at too low a rate for adequate control. Some pre-emergent herbicides, such as atrazine and isoxaflutole, demonstrated post-emergent activity and achieved 80 per cent control of 4 to 8 leaf radish.
All of the WA research has shown that it is best to spray small (2–4 leaf) wild radish with multiple herbicide groups and, if necessary, spray a second time with an alternative herbicide brew—avoiding seed set at all costs.
[WS-wildradish-24D] 2,4-D applied at the 4–8 leaf stage achieved good control in non-resistant wild radish. Image: T. Cook
[WS-wildradish-precept.jpg] Wild radish in the Nyngan trial was shown to be susceptible to several herbicide modes of action but simply rotating herbicides is risky and certainly not a long term option. Image: T.Cook.

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Getting weed seed into the header’s chaff stream

All harvest weed seed control methods rely on getting the weed seed in the front of the header and then onto the sieve, along with the harvested grain and chaff. Sounds easy enough, however experience has shown that doing some modification to the header set up can capture more weed seed and prevent it going out the rotor along with the straw.
The bonus that comes from making adjustments that capture more weed seed is that you will also capture more grain—another win win.
In the back end of the harvester, a separator baffle can be installed to split the air flow from the rotor and the air flow from the sieve. The 25–30 cm high baffle stops the weed seed from being blown over the top of the chaff stream and into the straw spreader.
Ray Harrington, a West Australian grain grower and long-time innovator, believes that all modern harvesters need some adjustment so they are better setup to target weed seed during harvest. It is critical that all the weed seeds exit in the chaff for harvest weed seed control (HWSC) systems such as chaff carts, Harrington Seed Destructor and chaff tramlining.
Assuming that the harvester is operated low to the ground, with the front cutting no higher than beer can height, most weed seeds that are present at harvest will go into the harvester.
Once inside the machine the key for successful weed seed capture is to make sure that the weed seed and the grain all comes out of the rotor and onto the sieves. To achieve this Ray recommends modifying the second concave, such as removing every second wire in the concave frame in the Case 8230. Other harvesters have different construction but the principle remains the same.
Since the straw component is still very long at this point of the process Ray says there is no need to have narrow slots in the second concave. Keep experimenting until you find the perfect set up for your machine.
Likewise, there can be a benefit derived from making larger holes in the harvester grates of some models. In the Case 8230 Ray has found that the grates don’t need modification as the holes are already quite large.
With harvested material only being in the rotor for a few seconds, it is important to make sure that the inside wall of the concave is not lined with straw, making it difficult for the weed seed and grain to go through the gaps and onto the sieve. Ray has installed an extra bar inside the rotor to help keep all the harvested material moving as it flows through, maximising the opportunities for weed seed and grain to separate from the straw and fall through the concave.
For each model, and even for different crops, there needs to be a different set up. Ray recommends experimenting and adjusting until maximum weed seed and grain are being collected on the sieve.
He knows from his own farm that a surprising amount of grain, let alone weed seed, can travel in the front and straight back out on the paddock if the settings are not right. In canola particularly Ray has seen more than 0.5 t/ha of grain going back out through the spinners.
In the back end of the harvester Ray is using a separator baffle to split the air flow from the rotor and the air flow from the sieve. The 25–30 cm high baffle stops the weed seed from being blown over the top of the chaff stream and into the straw spreader.
Ray says that because the weed seed has a kernel it will not rise higher than the baffle height and so joins the chaff stream and is directed into the Harrington Seed Destructor, onto the chaff cart belt or down the narrow windrow chute.
Keeping a 25–30 cm gap around the baffle allows the high volume, low pressure air flow to efficiently separate the grain from the chaff and weed seed, and the baffle keeps the weed seed from being caught up in the straw as it flows over the top through the choppers and out through the spinners.
In the diagram below, drawn by engineer Nick Berry, shows how a separator baffle can be used to divert more weed seeds into the Harrington Seed Destructor (HSD) mills. These baffles come in all shapes and sizes, and are often custom made by grain growers to fit their harvesters. The aim is to divert the weed seed containing chaff fraction below the baffle to collect at least 95 to 98% of the weed seeds with one of the many HWSC tools.
This diagram, drawn by engineer Nick Berry, shows how a separator baffle can be used to divert more weed seeds into the Harrington Seed Destructor (HSD) mills. The same concept applies for chaff carts and chaff lining.
Once everything is correctly set up, Ray says his experience, and trials conducted by Dr Michael Walsh from AHRI, indicate that it is realistic to expect that only 2 per cent of the weed seed that enters the header will end up evading harvest weed seed capture.
Dr Michael Walsh from AHRI conducted 25 trials across Australia comparing weed seed capture of the chaff cart, narrow windrow burning and the Harrington Seed Destructor. He and Charlie Aves did ryegrass counts in the following autumn and found that the three HWSC tools performed equally, reducing the ryegrass germination by 56% on average. If there were significant rotor losses, and weed seeds were spread with the straw, the narrow windrow burning treatment would be expected to perform better than the other treatments because windrow burning removes all of the straw and chaff while the chaff cart and HSD remove the chaff only.
Listen to Ray talk with AHRI’s Peter Newman about setting up your harvester:

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Is barnyard grass the next threat to cotton?

In a recent northern region WeedSmart trial, more than twenty per cent of barnyard grass samples tested were found to be resistant to glyphosate, with another twenty per cent identified as developing resistance.
Dr Chris Preston, University of Adelaide will be speaking about residual herbicides and how to correctly use them to minimise resistance in problem weeds such as barnyard grass.
Conducted last summer, the trial tested 30 samples of suspected glyphosate resistant barnyard grass submitted by agronomists from northern NSW and southern Queensland. The results provide a snapshot of the growing problem of resistance in these areas.
Most growers and agronomists in the northern cropping areas are aware of the rising risks associated with glyphosate resistance and are keen to know what their options are for regaining the advantage. A robust residual herbicide package, combined with a knockdown or double knock, is essential to drive down weed numbers early in the crop. Growers and agronomists should work together to develop a plan to rotate and mix pre-emergent herbicides and take advantage of the new herbicides that have been registered for weed control in recent years. Plan to use them carefully to get best results and make them last.
Planning for weed control across the whole rotation is a complex business that requires growers and their advisors to be well-informed and up-to-date with the latest advances in crop and weed science.
To assist, University of Adelaide’s Dr Chris Preston delivered the latest information on best use of residual technology to combat weeds and minimise herbicide resistance when he spoke at the WeedSmart-Monsanto event ‘More cotton, fewer weeds’ on Thursday 3 December, 2015.
“Some of the earlier practices regarding residual herbicides need to be reconsidered in light of greater experience under different field conditions and changes in sowing technology,” Chris says.
“Residual herbicides on the market vary in their water solubility, ability to bind to soil components, behaviour under different soil moisture conditions and rate of degradation over time,” he says. “Unfortunately, the seasonal conditions that unfold can have a significant effect on the efficacy of any product applied.”
 

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Herbicide tolerant summer cropping choices

Summer weeds are a challenge in the northern cropping region. In sorghum and corn crops, weeds like barnyard grass, liverseed grass, fleabane and bindweed are notoriously hard to kill and often survive herbicide treatments. They also have the potential to reduce yields by up to 30 per cent if left untreated.
Rob Crothers, Australian grain corn and sorghum product manager with DuPont Pioneer, says that effective weed control prior to and at planting is essential to preserve yield in both sorghum and corn crops.

Following a broadleaf winter crop, sorghum and maize allow effective in-crop control of broadleaf weeds and crop volunteers. With limited in-crop herbicide options available to control grasses however, added emphasis must be placed on preparing a clean seedbed and making agronomic choices that favour vigorous early crop growth to suppress weed germination and development, especially in sorghum.
Rob Crothers, Australian grain corn and sorghum product manager with DuPont Pioneer, says that early effective weed control is essential to preserve yield in both sorghum and corn crops.
“Grass weeds cost yield in sorghum and corn, particularly early in the season if weeds have not been well controlled in the fallow,” he says. “With in-crop grass weed control options limited to the pre-emergent herbicide, metolachlor (Herbicide Group K3) in sorghum, there is a place for herbicide tolerant summer crop hybrids.”
“DuPont Pioneer is developing sorghum hybrids with Group B tolerance to expand the herbicide options in-crop,” says Mr Crothers. “If we are successful in bringing this new technology to the market place it will enable growers to spray grass weeds with a post-emergent herbicide in crop for the first time. This will add to our suite of imidazolinone tolerant hybrids in canola and corn, all of which tolerate over-the-top spraying with certain ‘imi’ herbicides.”
Imi-tolerant sorghum hybrids currently in the development phase are showing promise for improved control of grass weeds in-crop. (Photo: Rob Crothers, DuPont Pioneer)
These new hybrids are not expected to be fully commercial for a couple of years although field trials are planned for late 2016 for growers to inspect. For now, planning to use a variety of herbicides and non-herbicide tactics across the whole crop sequence is the only way to preserve herbicide effectiveness.
In preparation for the coming summer cropping season, now is the time to get on top of grass weeds after harvesting a winter crop or as a final task in the fallow.
Atrazine and glyphosate can provide adequate weed control in no-till and minimum-till fallows, which also conserve more soil moisture and improve the chances of planting crops at the optimum time. Grass weed resistance to glyphosate is becoming a major problem in no-till cropping programs and as a consequence many farmers are using strategic tillage to manage resistant weed populations.
The decision to use atrazine rules out many crops other than sorghum and maize for 18 months due to crop sensitivity to the residual herbicide, and so must be considered when planning the whole cropping sequence.
Coming out of a winter crop, desiccation provides an aid to harvest in pulses, canola and cereals and is an opportunity to control weeds present at harvest. Taking stock of the weed spectrum and density in spring can assist with summer cropping decisions. If grass weeds are present in significant numbers there may be a case for avoiding sorghum and choosing another summer crop that offers more weed control options.
“If sorghum is chosen as the best option, growers have had varying success with inter-row cultivation or shielded spraying between the rows,” says Mr Crothers. “The other important tactic available in current sorghum crops is to desiccate with glyphosate pre-harvest to assist with the harvest operation, reduce subsoil moisture losses through the sorghum plants post-harvest and prevent seed set in some weeds.”
There are currently more herbicide options (both pre and post emergent) and a wider variety of hybrids, including ‘imi’ tolerant genetics, for corn. Depending on the weed spectrum and pressure, corn may be a useful crop to assist in summer weed management.

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Dual trait herbicide tolerance extends IWM options

Plant breeders have incorporated single trait herbicide tolerance into many canola, cereal and pulse varieties and Australian growers have readily adopted the technology that provides alternative weed control options in-crop. The latest development in the field has been the release of a canola variety with dual trait herbicide tolerance, a first for Australian crops.

Justin Kudnig, Pacific Seeds canola technical manager says the new dual-tolerance canola hybrids released this year, Hyola® 525RT® and Hyola® 725RT®, will add to the number of options growers have to tackle weeds throughout the crop rotation.
The widespread, and often intense, adoption of these herbicide tolerant varieties has raised some concerns that they may increase the risk of herbicide resistance in weeds. When used as part of a planned and strategic rotation however these crops and their tolerance traits can be used to drive down weed numbers across the rotation.
Traits ‘built-in’ to varieties through conventional breeding include tolerance of imidazole (‘imi’) and triazine herbicides. In canola (and cotton) there are also genetically-modified (GM) varieties that endow tolerance to glyphosate.
Justin Kudnig, Pacific Seeds canola technical manager says the new dual-tolerance canola hybrids released this year, Hyola® 525RT® and Hyola® 725RT®, will add to the number of options growers have to tackle weeds throughout the crop rotation.
“The traits these varieties bring to the table are particularly valuable in situations where growers are facing serious resistance to clethodim,” he said.
“Hyola® RT® canola will tolerate ‘over the top’ applications of both the knock-down Roundup Ready Herbicide with PLANTSHIELD and residual triazine herbicides. While both herbicides may be applied to the same crop, tank mixing of the two herbicides is currently not registered.”
The herbicides should be applied at full label rates and according to the label conditions and Monsanto’s Roundup Ready® canola Crop Management Plan (CMP).
Mr Kudnig said growers in both the cotton and canola industries who have adopted Roundup Ready technology have embraced the stewardship programs designed to protect the technology and the world’s most valuable herbicide, glyphosate.
Professor Stephen Powles, director of the Australian Herbicide Resistance Initiative said the high level of compliance in the cotton industry, where 90% of the Australian cotton crop is currently Roundup Ready, has been successful to date.
“The adoption of herbicide tolerant varieties must always be seen as another tool in a diverse suite of weed control tactics, applied strategically on a paddock by paddock basis,” said Professor Powles.
“Decisions must be made with consideration to the weed burden present in the paddock. If the weeds are resistant to ‘imi’ herbicides then growing Clearfield varieties will not help control weeds, similarly if weeds are triazine or glyphosate resistant then the single trait TT or RR varieties will not assist in weed control.”
Professor Powles reiterates the need to support technologies such as the single and dual trait canola varieties with other techniques such as harvest weed seed control to remove any survivors.
Trials that Dr Chris Preston, University of Adelaide conducted on the effectiveness of resistant canola varieties on annual ryegrass show that triazine products applied to triazine-tolerant varieties achieve approximately 60% weed control compared to 92% control using glyphosate in Roundup Ready canola. In the dual-tolerant RT® variety growers can expect 97% control of weeds such as annual ryegrass, wild radish, silver grass and brome.
“The triazine-tolerant trait does carry a 10% yield penalty so hybrids with this trait incorporated are less likely to show advantage in low weed density paddocks when compared to RR hybrids,” said Mr Kudnig. “In paddocks where there is a moderate to high level of clethodim (Group A) or Group B herbicide resistance in the weed population some growers may consider using the RT® technology in three successive canola seasons within a 10-year period to drive down weed numbers as a short-term strategy.”

In less serious situations the recommendation is always to rotate crops and herbicide tolerance technologies. The single-trait TT technology is currently adopted on 65–70% of the canola area, Clearfield varieties represent 10–20% of the area and the remaining 10–15% is Roundup Ready (RR).
In the 2015 season, Hyola® RT® has been sown on approximately 5% of the canola area, predominantly in Western Australia.
“Twice as much Hyola® RT® seed will be available next year and by 2020 we expect this dual-trait technology to represent about one-quarter of the Australian crop,” he said.
Being able to apply triazine chemistry late in the cropping season helps control late flushes of weeds such as wild radish. The advantages of better in-crop weed control are long-lasting through reduced herbicide requirements in future crops as well as potentially higher yields in the current crop.
There are pros and cons surrounding the genetically-modified (GM) status of this variety that growers should take into account when deciding whether to include Hyola® RT® in their cropping plan. As a GM canola with an additional conventionally-bred trait for triazine tolerance, grain harvested must only be delivered to designated GM delivery points.
Extensive research and investigations are underway to achieve registration for tank mix applications of glyphosate and triazine for use in RT® canola, potentially for the 2016 season. This will increase the cost effectiveness of weed control in RT® canola and is also supported by the principle that mixing herbicides at full rates can delay the onset of resistance in weeds.
Research conducted in the United States shows that when growers use tank mixes with an average 2.5 modes of action (MOA) in the mix the risk of glyphosate resistance in weeds is 83 times less likely than when an average 1.5 MOAs are included in a tank mix.
The lead researcher, Pat Tranel concluded that ‘rotating herbicides buys you time, mixing buys you shots’. In all instances herbicides must be applied according to the label rates and conditions and all components in the mix must be compatible.
Visit the Pacific Seeds website for specific details related to the use of Hyola RT technology. For more information about managing herbicide resistance, check out our 10 Point Plan.

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Crop competition — give your crops the edge

The uncomfortable truth is that in many paddocks the weeds are winning the battles for space and resources.
Growing crops that out-compete weeds gives a double whammy benefit of more crop and less weeds — generating more profit!

Try some or all of these ideas to give your cropping system the competitive advantage:

Get the soil pH right and do what you can to improve overall crop nutrition
Set up your planter to sow crops on the narrowest row configuration possible within the other constraints of crop production
Sow within the optimal planting window for the crop and your location
Choose the most competitive crop type (e.g. barley over wheat) and the most competitive variety or hybrid of your chosen crop
Select crops with early vigorous growth
Set the crop up for success with optimal weed control prior to planting, using double knock tactics and effective pre-emergent herbicides
Sow east-west rather than north-south if you can
Use sowing rates at the upper end of the recommended range for the crop

And here’s more advice from the WeedSmart crop competition experts:

Can planting a tight crop improve weed control?
Use your crop as a weapon
Using your crop to fight weeds
Webinar with Prof Deirdre Lemerle: Using your crop to fight weeds 
Up the competition
Employ crop competitiveness to combat weeds
Higher seeding rates lower weeds 
Narrow row spacing: is it worth going back?
AHRI insight: Sow west young man
AHRI insight: Left jab, right hook
AHRI insight: Heal thy soil, heal thy crops, kill thy weeds

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Control ‘summer weeds’ like fleabane in winter and spring

There is mounting evidence for the value of managing summer weeds like fleabane and feathertop Rhodes grass during the winter crop phase.
Richard Daniel, Northern Grower Alliance (NGA) CEO says results improve dramatically when growers stop targeting large plants in the summer fallow as the primary management timing for these weeds.
Northern Grower Alliance CEO Richard Daniel says that managing fleabane and feathertop Rhodes grass (FRT) in-crop or immediately after harvest is more effective than later in the summer when the plants are large and moisture-stressed (Photo courtesy of GRDC).
“Fleabane plants growing in the summer fallow are generally more difficult to kill as they are often large, moisture-stressed and frequently resistant to glyphosate,” he says. “Targetting fleabane populations pre-plant, in-crop or immediately post-harvest in the winter cropping phase is usually far more effective.”
Crop competition, and particularly avoiding wide row cropping, considerably suppresses fleabane growth. If wide row cropping is required then an emphasis must be placed on effective residual herbicides.
Although many populations of fleabane are resistant to glyphosate, fleabane is sensitive to quite a wide range of residual chemistry. Applying residuals pre-plant combined with crop competition will minimise establishment in-crop and reduce the initial summer fallow weed pressure.
“It is important to realise that fleabane can still survive at very small growth stages under a competitive crop and is easily overlooked,” says Mr Daniel. “Once the crop is removed, these plants develop very quickly and the opportunity for effective control can be missed if the in-crop escapes go un-noticed.”
“The effectiveness of a double-knock treatment at any stage in the summer fallow is improved by using 2,4-D or picloram + 2,4-D with glyphosate in the first spray rather than glyphosate alone, followed by paraquat 7 to 10 days later,” says Mr Daniel.
Several crops are sensitive to the residual effects of picloram so the planned rotation must be taken into account when making product choices.
Cultivation may be the most economic and effective strategy to kill large, stressed plants growing in fallow, however growers must also prepare and implement strategies to manage the next flush of fleabane emergence.
Mr Daniel says there are several knock-down and residual herbicides that growers can use to target small and actively growing fleabane before, during and immediately after the winter cropping program or in a winter fallow.
Fleabane thrives where there is no crop competition and small plants can easily go unnoticed late in the winter crop. (Photo: Anthony Mitchell, NGA)
Another weed that has been very difficult to manage in a summer fallow is feathertop Rhodes grass (FTR). In paddocks with a feathertop Rhodes grass problem, sorghum is generally not the best crop choice because there are no effective post emergent control options and available residual chemistry will not provide season-long suppression. Crops that allow selective in-crop grass control, such as mungbeans or even sunflowers, can provide more management flexibility.
“Like the fleabane situation, there are also opportunities to commence feathertop Rhodes grass management late in winter or during spring,” he says. “Intensive patch management of feathertop Rhodes grass is also an effective strategy as feathertop Rhodes grass is generally found in well-defined patches in the first few years of colonisation.”
For small patches or new incursions, chipping, pulling, spot spraying or cultivation can be used. Burning, followed by cultivation and or the use of residual herbicides, appears to be a salvage strategy for removing mature plants. Although not an option for common sowthistle, time spent trying to eliminate small patches of feathertop Rhodes grass will be cost-effective in the long run.
The in-crop options for feathertop Rhodes grass in winter crops are not extensive and, like fleabane, feathertop Rhodes grass is generally one of the key weeds that survives in fallows where glyphosate is the dominant herbicide.
Mr Daniel recommends using residual chemistry wherever possible and controlling ‘escapes’ with camera spray technology. “A double-knock of Verdict® followed by paraquat can be used in Queensland, but only under permit prior to planting mungbeans where large spring flushes of feathertop Rhodes grass occur,” he says.
 

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Can we grow broadleaf crops without clethodim?

Broadleaf crops such as canola and pulses offer grain growers an opportunity to use different herbicides to control grasses such as the super-adaptive annual ryegrass. Clethodim herbicides such as Select® have provided good control until recently where there have been increasing occurrences of resistance across southern and Western Australia.

Most growers in Western Australia are aware of the rising risks and are keen to know what their options are for regaining the advantage, given there are no highly effective alternatives to clethodim for post-emergent control of annual ryegrass in canola and pulses.
To grow canola and pulses without clethodim growers will need to implement a robust pre-emergent herbicide program, consider tank mixes, and stop seed set through crop topping and harvest weed seed control tactics.
A robust pre-emergent herbicide package combined with a knockdown or double knock is essential to drive down weed numbers early in the crop. Growers can work with their agronomists to develop a plan to rotate and mix pre-emergent herbicides and take advantage of the new herbicides that have been registered for ryegrass control in recent years. Plan to use them carefully to get best results and make them last.
Applying clethodim post-emergent is still a good idea where some level of control is expected. Clethodim is a good low cost option in susceptible populations and is worth protecting through the control of plants that survive treatment. Where resistance to clethodim is present, a mix of clethodim plus butroxydim may give better results than clethodim alone.
Crop topping helps stop seed set. Weedmaster® DST is the only product registered for crop topping in canola. As glyphosate is widely used in crop rotations, using paraquat for crop topping pulse crops is a good resistance management strategy.
Finally, harvest weed seed control should be employed as often as practical to stop ryegrass entering the seed bank and to reduce total weed numbers so that future control methods have a better chance of being effective.

Dr Chris Preston, University of Adelaide spoke about integrated weed management, with a special focus on clethodim resistant ryegrass, at spring field days across Western Australia in September.
Hybrid cultivars of canola can provide additional competition against weeds like ryegrass, compared with open-pollinated cultivars. This becomes particularly important when post-emergent herbicides like clethodim fail. Combining crop competition with effective pre-emergent herbicides is an effective way of reducing ryegrass seed production. Adding seed set control techniques to this reduces weed seed banks even further.
Planning for weed control across the whole rotation is a complex business that requires growers and their advisors to be well-informed and up-to-date with the latest advances in crop and weed science.

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Pre-em herbicides for grass weed control in break crops

In the central western grains region of NSW, annual ryegrass is becoming increasingly difficult to control. WeedSmart champion farmer and Grain Orana Alliance (GOA) CEO, Maurie Street has been leading on-farm trial work to identify improved control measures in break crops that can add diversity to farmers’ weed control systems.
Grain Orana Alliance CEO, Maurie Street led trialwork across central western NSW to investigate the pre-emergent herbicide options for controlling weeds in broadleaf crops.
“In the last few years we have seen a large increase in the number of annual ryegrass and wild oats plants surviving the traditional herbicide treatments used in cereal crops,” he says. “Recent herbicide resistance surveys have made it clear that key herbicides used in cereal crops are losing their effectiveness. Over 90% of samples collected were resistant to Group B herbicides such as Logran and over 70% of samples were resistant to Group A herbicides such as Axial and Hoegrass.”
He says the situation has led to high levels of seed set in the cereal phase, which is putting considerable pressure on the few remaining in-crop grass selectives, that is Select or clethodim, in the following broadleaf break crops.
The 2014 weed survey revealed that resistance to clethodim is increasing rapidly with 60% of submitted samples showing resistance. Continuing to spray high density populations with clethodim will soon see the loss of this herbicide option in the region. Maurie says the industry risks losing the use of Select altogether if something is not done quickly to bring the weed population back under control.
This prompted GOA to establish GRDC-funded trials across central western NSW to investigate the effectiveness of a range of pre-emergent herbicides in chickpea, lupin and canola crops last winter.
The trial identified pre-emergent product combinations that provided significantly better control (right) than the district standard practice (left) for herbicide resistant annual ryegrass.
Although the use of pre-emergent herbicides is not new to growers, the trials have demonstrated that there are several options available that can achieve better results than the current district standard practice.
In chickpeas, the standard approach in the region is to use simazine and Balance as a pre-emergent weed control tactic. Generally this combination provided poor control, with control in some trials being as low as 50%, which was no better than in the untreated control strip. This left populations of 200 plants per m2 that growers would have to target in-crop with clethodim.
“While we only have one year of results, it is clear that there are a number of other options that are far more effective than the district standard practice,” says Maurie. “Generally, the newer pre-emergent herbicides such as Sakura and Boxer Gold showed improved weed control over the standard.”
The most striking results over all the trial sites was the improvements gained through multiple product combinations, or tank mixes, of pre-emergent chemistries compared to single product treatments.
The simple addition of trifluralin to herbicides already used in the district resulted in much higher levels of control. For canola growers the recent registration of the propyzamide product, Rustler, has shown great potential for improved ryegrass control, particularly when combined with other products such as atrazine or trifluralin. In some trials untreated populations of 320 plants per m2 were reduced down to an impressive 10 plants per m2.
The new registrations of Sakura and Boxer Gold in pulses, and Rustler in canola, have broadened the options available to growers. Observations from the trials suggest that it would be unwise for growers to simply change from one pre-emergent herbicide to another because generally product combinations were more effective than any single product.
“It is also important that we introduce as many different tactics as possible into the cropping rotation, all aimed at keeping weed density low,” he says. “Any reliance on a small range of products or tactics will inevitably bring us back to the same situation that we are finding ourselves in now.”
When considering a multi-product treatment, care is required to ensure the products are compatible and that the use is registered for the crop. It is essential to apply each product at its full label rate.
“The use of these strategies must be considered a short-term option to bring the weed population down while taking steps to reduce the reliance on herbicides that has landed many growers in this situation in the first place,” says Maurie. “Other tactics that will support and protect both pre-emergent and knock-down herbicides include fallow management, harvest weed seed control and hay making.”
These general principles also apply to other grass weeds such as wild oats and barley grass that have also been increasing in number and often display multiple-MOA resistance.
When planning an integrated weed management strategy, Maurie suggests growers consider what other weeds are present and the effectiveness of the alternatives treatments on these species, the comparative costs, crop tolerances, plant-back or herbicide residue constraints and the resistance status of the weeds present.
For more information about the GOA trials visit their website.

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Which harvest weed seed control tool is right for you?

“To win the war you must win the battles. Harvest weed seed control is an important battle” – Ray Harrington, WA grower & inventor of the Harrington Seed Destructor
Our harvest weed seed control special edition e-news was included in a recent GRDC Weed Alerts email. We felt that it’s a handy resource that was worth including on our Bulletin Board. Read on for more info and our “which HWSC tool is right for you” checklist!

 
WeedSmart enews #8
Welcome to our harvest weed seed control (HWSC) special edition (we like to get in nice and early).
We’ve included links to further info on the five main HWSC tools, plus a quick little checklist to work out which tool is right for you.
Remember, if you have any questions, feel free to contact us on Twitter, Facebook or via the contact form on this website.
Which HWSC tool is right for you?
Follow the links below for more info on the HWSC tools relevant to your farming operation:

Do you have sheep? Chaff cart / grazing dumps
Are you a CTF grower? Chaff deck
Are you a low cost, low rainfall grower? Windrow burning or chaff cart
Are you hell bent on residue retention (are you a stubble hugger?)? HSD
Are you CTF with a disc seeder? Chaff line / windrow rotting (early stages – stay tuned!)
Do you have a market for straw near your farm? Bale Direct

Narrow windrow burning
By mounting a chute to your grain harvester, all of the exiting chaff and straw residues are concentrated into a narrow windrow about 500-600mm wide which is later burnt. There’s a 6 step intro vid, chute CAD drawings, plus tonnes of other handy resources over at the website.
Chaff cart
Chaff carts are towed behind harvesters to collect the chaff fraction as it exits. The dumps are later burnt or grazed. Super quick video, handy financial factsheets and more are available for you here.
Harrington Seed Destructor (HSD)
A unique system developed by the awesome Ray Harrington that processes the chaff fraction to destroy any weeds before returning the material to the paddock. There is no need for any post-harvest operations and all harvest residues are retained (win/win!). More info? Here you go.
Bale Direct
The Shields family in WA developed the Bale Direct System. The large square baler is attached directly to the harvester and constructs bales from the chaff and straw residues. For more info plus resources click here.
Funnel seed onto tramlines
In controlled traffic farming systems, weeds are funnelled onto an inhospitable environment – compacted by soil and run over by machinery (weeds deserve it). Find out more
Miss or want to review our harvest-themed webinars?
Recordings are available here.

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Silverleaf nightshade can be beaten

 
The focus of a weed control program is to run down the seed bank—doing everything possible to prevent seed set. But, what about weeds that spread vegetatively?
Treating silverleaf nightshade before it flowers and again when it reshoots has proven to be an effective strategy to control this difficult crop and pasture weed. Photo: Rex Stanton
What could possibly control a perennial weed with a huge network of roots that is able to produce multiple stems metres apart, propagate new plants from tiny root fragments and produce seeds that remain viable in the harshest soil conditions and in the gut of grazing animals?
These are the questions that researchers are keen to find solutions to as silverleaf nightshade infiltrates crops and pastures across southern Australia. Silverleaf nightshade infestations typically reduce crop yield by 20–40 % and render pasture unusable if it is not contained. A collaborative project between NSW Primary Industries and Murrumbidgee Landcare, with funding from Meat and Livestock Australia (MLA) and Australian Wool Innovation (AWI) is targeting silverleaf nightshade control across four states.
Project officer Phil Bowden, Murrumbidgee Landcare at Cootamundra, NSW said that silverleaf nightshade (SLN) is of increasing concern in NSW, Victoria, South Australia and Western Australia, yet many landholders are unaware of the effect of the weed or how easily it is spread.
“Silverleaf nightshade has an extensive root system, linking plants across the paddock and up to several metres in depth, making control very difficult,” he said. “It competes with pasture and crops for soil moisture and nutrients, and does not respond to the usual chemical control measures.”
The good news is that field trial results confirm that a ‘dual action’ spray program, implemented over successive years can reduce the impact of this difficult weed.
“The dual action program involves spraying silverleaf nightshade at the early flowering stage, both in spring or autumn, to prevent seed set. A follow-up spray in autumn controls re-shoots and helps run down the root reserves,” said Mr Bowden.
Several herbicides, such as picloram, glyphosate and 2,4-D amine products, are registered for the control of silverleaf nightshade. Consult with your local agronomist for advice on product choice, application rates and adjuvants, keeping in mind that application timing is more important than product choice.
Crop and pasture competition can suppress silverleaf nightshade over winter and delay emergence in spring, however silverleaf nightshade stems will emerge during summer if there is no competition for summer rainfall.
Competition in spring reduces the number of new shoots that emerge and helps synchronise flowering, making herbicide application at flowering more efficient.
Although SLN does produce a large quantity of seed, the predominant source of new stems is its rootbank. Cultivation is more likely to spread the weed than control it because fragments just 1 cm in length are capable of forming a new plant.
Silverleaf nightshade is easily spread on machinery and can establish new plants from very small root fragments. Photo: Rex Stanton
Trials have shown that managing smaller (<0.25 ha) or less dense infestations (less than 1 stem/m2 and less than 1 ha) will lead to a decline in the rootbank and the seedbank to the point where eradication is realistic. However, to eradicate it requires intensive monitoring and control for up to 5 years to ensure no re-infestation occurs.
Optical weed detection technology such as the Weedseeker® is worth considering when applying expensive herbicides in low density situations.
A series of workshops are planned for many of the SLN ‘hot spots’ around Australia in early spring.
For more information on SLN workshops and control strategies, contact Phil Bowden on 0427 201 946 and visit the website.

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Options for crop topping canola

One downside of the widespread production of canola is the increase in clethodim resistant annual ryegrass populations on many farms across southern Australia.
What’s the best option for crop topping canola?

Nufarm’s weedmaster® DST® is the only glyphosate product registered for pre-harvest weed control in canola, providing another tool to reduce weed seed set.
Dr Chris Preston, University of Adelaide (UA) Associate Professor—Weed Management says growers are noticing that in some areas clethodim may be only suppressing rather than controlling ryegrass. “All tactics in the weed management program need to minimise seed set,” he says. “End of season control measures have been limited to narrow windrow burning in canola and this is not always a practical option for growers.”
Through a GRDC funded trial Dr Preston investigated the pre-harvest use of a number of herbicides, looking at efficacy, crop safety and residue levels. “Our trials concluded that only glyphosate was effective and safe to use for pre-harvest weed control in canola,” he says.
This research supported the registration of Nufarm’s weedmaster® DST® as the only glyphosate product registered for pre-harvest application in canola.
Dr Preston, who is also Chair of the Australian Glyphosate Sustainability Working Group says that, once again, glyphosate has proved to be a valuable chemical but a word of caution is required. “Pre-harvest weed control with glyphosate must not be over-used in the rotation. It is essential that many other non-glyphosate measures are also being used in a weed management strategy.”
“Keep track of how often you are applying glyphosate across the rotation and include as much diversity as possible,” he says. “For example, if you use glyphosate for pre-harvest control in canola it would be wise to use a different harvest weed seed control tactic in your cereal crop and consider paraquat as a better choice to crop top pulses.”
“Both over the top and under the windrow applications are equally effective as weed seed set control measures,” he says. “Efficacy is reduced in hot, dry weather conditions so an over the top crop topping application offers some extra flexibility provided growers have access to a self-propelled boom with sufficient clearance. In some situations this will make direct harvesting a more practical option too.”

For optimal ryegrass control and no impact on yield, wait until at least 20 per cent of the canola seed has changed to dark brown or black before a pre-harvest application of glyphosate in a standing crop.
A harvest weed seed operation, such as narrow windrow burning, will also assist to remove any survivors and help prolong the efficacy of glyphosate across the rotation.
Nufarm field development manager (broadacre) at Horsham, Mark Slatter says the expanded registration of weedmaster DST for harvest aid and weed control applies to triazine tolerant (TT), CLEARFIELD®, Roundup Ready® and conventional canola varieties. “Label rates for applications of weedmaster DST to standing canola or under the cutterbar at windrowing @ are 1.4 – 4.1L/ha, however Nufarm trials showed best results were achieved at rates of 2.8 – 4.1L/ha with an adjuvant (LI 700®) to increase penetration into the crop canopy and for drift management,” says Mr Slatter. “The recommended water rate for ground application is at least 80 L/ha applied to standing canola.”
The product is also registered for aerial application at a maximum rate 3.1L/ha.
Mr Slatter says the timing of the application is critical and must not occur before there has been a minimum of 20% grain colour change across the paddock as going in too early will cause yield reductions. “No withholding period applies when the product is applied under the windrow but direct harvest must not occur until five days after application to a standing crop,” he says.
While annual ryegrass is a key target weed for this use pattern, other key target weeds controlled include wild radish, sow thistle and many other annual grass and broadleaf weeds.
Mr Slatter says that Nufarm has developed this new pre-harvest registration as an additional tool for reducing weed seed set of annual weeds because a ‘zero tolerance’ approach to weed seed set is one way of reducing the risk of herbicide resistance developing. “It is very important to use a pre-harvest application of weedmaster DST as part of a broader integrated weed management (IWM) strategy to minimise the risk of glyphosate resistance,” he says.
“Crop safety trials proved that this use pattern has no negative effects on yield or oil content in canola, however it must not be used on crops intended for seed because germination and vigour is affected,” he says. “Nufarm’s extensive MRL trials also showed residues are well below maximum levels for all canola systems so there will be no impact on product export suitability.”

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Narrow row spacing: is it worth going back?

Narrow row spacing can deliver an average 6% yield increase along with a 98% decrease in annual ryegrass seed heads—more crop, less weeds.
Forward thinking DAFWA researcher Glen Riethmuller has recorded significant yield benefits in wheat sown at narrow row spacing, along with a remarkable suppression of weed numbers in a 28-year long trial at Merredin Research Station.
Nearly thirty years ago, forward thinking researchers in Western Australia laid out a row width trial at Merredin Research Station to investigate the effect of stubble retention versus stubble burning. Ten years into the trial they found herbicide resistant annual ryegrass was becoming a problem in the wide row plots.
The research team decided to introduce rotation crops to the trial site in an effort to rotate chemical groups and bring the weeds under control. While the thinking was sound it was not very successful in the wide row plots.
This scenario has played out on minimum tillage farms around Australia, eking away the potential gains through better moisture conservation.
Glen Riethmuller is the Department of Agriculture and Food acting Technical Services Manager responsible for the design and management of this long-term trial in WA that Steve Porritt initiated in 1987.
“The average yield from the 15 wheat crops has been 5.7% higher in the retained stubble plots compared to plots where the stubble is burnt,” he said. “When it comes to row width we find yield decreasing by an average 0.4% for every centimetre, or 1% loss per inch, as the row spacing increases over 180 mm (7 inches).”
Left: narrow rows. Right: wide rows.
For wheat crops sown at 360 mm (14 inches) this equates to an average 6.8% yield loss due to increased row width when sown into burnt stubble and a huge 7.9% loss in stubble retained situations. In the six pulse crops (2 field pea, 1 faba bean, 1 lentil and 2 chickpea) the retention of stubble and row spacing had little effect on yield. The two canola crops showed little response to stubble management but a sizeable response to row spacing with yield declining 1% for every centimetre row spacing increase over 180 mm.
Left: narrow rows. Right: wide rows.
Further narrowing the rows to 90 mm increased yields in most stubble situations, indicating that very narrow rows can improve yields even in the low rainfall zones.
When these yield results are considered together with the effect of narrow rows on weed seed heads, the case for narrower rows becomes very compelling. All plots were treated with full rates of herbicide yet annual ryegrass remained a problem in the wider row plots while there was a 98% reduction in ryegrass seed heads in 2013 in the narrow rows plots.
In the narrow row stubble retained plots, ryegrass head counts in 2013 were very low at 0.17 heads per m2 compared to 7.67 seed heads per m2 at 360 mm row spacing. This is a great example of how well herbicides work in the presence of competition.
“Our experience with managing weeds in the trial sites has been that none of the available herbicide options are able to overcome the extra weed pressure in wider rows,” he said. “We typically used trifluralin pre-sowing at 1 L/ha for ryegrass control in the trial. In two years we tried 2 L/ha and it made no difference to ryegrass control in the wide row plots.”
In recent years the researchers have switched to using full label rates of the new herbicides Sakura® and Boxer Gold® pre-sowing.
“Finding ways to practically sow through stubble at the narrowest row spacing possible is the way to grow more grain, reduce herbicide costs and combat herbicide resistance in weeds.”
These results were confirmed across the country when researchers examined data from 89 wheat experiments measuring the effect of row width. “The consistent message from the data was that widening row spacing is an enabling method of dealing with high stubble load but there is always a yield penalty in doing so,” said Mr Riethmuller. “The penalty is greatest in high production areas where the yield potential is highest. There is no question that growers are best off sowing at the narrowest practical row spacing possible.”
“At narrow rows and lower seeding rate along the row we see the highest germination rate and overall plant density,” he said. “High seeding rates along wider rows has lower establishment rates as the crop plants compete for resources or are affected by high fertiliser rates close to the row. In canola, planting on narrow rows could cut seed costs in half while increasing yield.”
Crops sown on narrow rows achieve full canopy cover quickly, reducing evaporation from the soil. With precision planting equipment now available Mr Riethmuller believes planting between rows can achieve great benefits in disease and soil nutrient management.

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Gearing up to use pre-emergent herbicides

Pre-emergent herbicides are not without their challenges. Working out the best pre-emergent herbicide choice for a particular situation requires a thorough knowledge of how the herbicide works.
Dr Chris Preston, University of Adelaide (UA) Associate Professor—Weed Management says some of the earlier practices regarding pre-emergent herbicides need to be reconsidered in the light of greater experience under different field conditions and changes in sowing technology.
Competitive (right) v non-competitive canola — growers can take advantage of the canola varieties with greater competitive ability.
The latest recommendations from research in the high rainfall zones of southern Australia can be summed up as: sow a competitive crop early, on the first opening rain, with pre-emergent herbicide; sow the cleanest paddocks last and implement harvest weed seed control.The latest recommendations from research in the high rainfall zones of southern Australia can be summed up as: sow a competitive crop early, on the first opening rain, with pre-emergent herbicide; sow the cleanest paddocks last and implement harvest weed seed control.
“Pre-emergent herbicides on the market vary in their water solubility, ability to bind to soil components, behaviour under different soil moisture conditions and rate of degradation over time,” he says. “Unfortunately, the seasonal conditions that unfold can have a significant effect on the efficacy of any product applied. For example, some products are not well suited to higher rainfall zones because multiple weed germinations are more likely and by later in the season the herbicide has dissipated or moved too far down the soil profile to have any effect on later germinations.”
One solution to this problem is the pre-emergent application of trifluralin followed with the recently registered use of Boxer Gold applied post-emergent. This relies on rainfall to incorporate the Boxer Gold and has provided excellent control, even of trifluralin-resistant weeds.
The method that provided the highest level of control in the high rainfall zone was pre-emergent Sakura + Boxer Gold post-emergent.
A third option for the high rainfall areas is Sakura + Avadex. This is also expensive but provided a high level of control, and avoids using Boxer Gold in wheat, leaving it to be used in other crops in the rotation.
“Keep in mind that Sakura can only be used in wheat crops so it is good to avoid using Boxer Gold in both wheat and barley crops. Sakura + Avadex may be a better choice in the wheat crop rather than Sakura + Boxer Gold,” he says. “There is a very high risk of losing Boxer Gold as an effective herbicide if it is used frequently in a rotation, so it is essential to plan herbicide use across the crop rotation and use different chemicals in break crops.”
Early (left) v late sown cereals — ryegrass head count was lower in early sown crop.
These combinations of herbicides aim to reduce seed head production through season-long control but rely on harvest weed seed control to manage any survivors.
“Herbicide resistance has been shown to occur rapidly if these new chemistries are used unwisely,” says Dr Preston. “They can be part of a weed management plan but must not be relied on without the implementation of supporting non-chemical tactics, including harvest weed seed control and competitive cropping.”
For pre-emergent herbicides to be effective the chemical needs to be in the right place at the right time—beginning with the right stubble management, sowing equipment and sowing depth. “The guiding principle is that the pre-emergent herbicide must be in contact with the soil to have any effect. Some products wash off stubble better than others and so stubble load and whether it is standing or laying flat will influence the efficacy of the pre-emergent,” says Dr Preston. “Large droplets and high water rates are generally required when stubble is present to ensure the herbicide reaches the soil.”
Dr Preston’s trial work clearly demonstrated that planting equipment, such as single disc seeders, which do not remove soil from on top of the crop row, causes an increased incidence of crop damage from pre-emergent herbicides. He says there is a need to make some compromise in a zero till system to ensure soil containing the herbicide was thrown to one side as the crop seed is sown. “It is also important that the planter closes the seeding slot, particularly if a product such as Boxer Gold is to be applied post-emergent,” he says.
Sowing date is also important. Initial research suggests that sowing early, while the temperatures are still warm, with a fast growing crop and pre-emergent herbicide will suppress early weed germinations and any later germinations will occur under the crop canopy and be less likely to out-compete the crop.
“What we saw with later sown crops was that ryegrass was able to grow above the crop canopy and competition from the crop did not affect ryegrass seed head production,” he says. “This suggests that sowing weedy paddocks as early as possible with a pre-emergent herbicide could be a very useful tactic in helping to drive down weed seed production, particularly when harvest weed seed control is added to the system.”
To hear more from Dr Preston on his trial work with pre-emergent herbicides in the high rainfall zones of southern Australia, watch the ‘Setting crops up for success’ webinar recording available here.