News

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.

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.

“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.

  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.

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.”

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.

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.

A cheap herbicide quickly becomes very expensive if it is not effective. Multiple resistance is beginning to show up in wild radish outside WA and testing is recommended if you plan to use certain herbicides again within the next three years. Testing for herbicide resistance has played an important part in understanding how resistance occurs in field situations but now that researchers have a good understanding of the mechanisms involved it is becoming more important for growers to find out which herbicides are still effective in controlling target weeds. John Broster, senior technical officer, Charles Sturt University (CSU) is recommending growers collect weed samples for ‘susceptibility testing’. Dr Broster heads up the herbicide resistance testing service at CSU and the data he has collected over the last 24 years has helped identify resistant populations of a wide variety of weeds across Australia. “If a particular weed, say annual ryegrass, is present in reasonable numbers at harvest time, having survived in-crop treatment, say with a Group A (fop) or Group B herbicide, we can assume with some confidence that herbicide resistance is the reason for survival,” he says. “From a grower’s point of view then, it is not cost effective to test those plants to see if they are in fact resistant to Group A or Group B.” “The big question is ‘what herbicides are those plants still susceptible to?’ and that is what we can help answer through susceptibility testing.” Testing of suspected herbicide resistant ryegrass samples at CSU in 2014 suggest that if you think your ryegrass is resistant to Group A (fop) or Group B herbicides, it probably is and testing is not necessary. If you think it could be resistant to glyphosate, always have it tested. Annual ryegrass is almost always expected to be susceptible to atrazine, so only test if you think your weeds could be resistant. For all other herbicides it is worth testing if you are suspicious of herbicide resistant or cross-resistance. Although annual ryegrass has a reputation for its resistance to important herbicide groups there are herbicides that are still effective options for annual ryegrass control. These include trifluralin, glyphosate, atrazine, propyzamide, Boxer Gold, paraquat, Sakura and Avadex. Having several options still available is good news for growers and it is essential that these herbicide options are protected and incorporated into a diverse weed control plan that includes non-herbicide options. Table 1. Low levels of herbicide resistance in annual ryegrass to a range of herbicides tested in 2014. Herbicide Herbicide group No of samples in 2014 % of samples resistance Trifluralin D 452 3 Glyphosate M 403 4 Atrazine C 375 1 Propyzamide D 278 0 Boxer Gold E, K 75 0 Paraquat L 65 0 Sakura K 17 0 Avadex J 4 0 For wild radish the story is similar. There are high levels of resistance to Group B (e.g. Glean, Logran), especially in Western Australia, so testing for resistance is generally not warranted, although in other states it may still be worthwhile. Resistance to Group C (e.g. atrazine), Group F (e.g. diflufenican) and Group I (e.g. 2,4-D ester 680) is beginning to show up and testing is recommended if you plan to use these herbicides again within the next three years. Similarly with glyphosate, testing is recommended if you suspect resistance. To date there is no resistance to pyrasulfatole (e.g. Velocity, Precept) in Australia, so only test if you are suspicious. For all other herbicides it is worth testing for cross resistance, particularly for herbicides you plan to use over the next few years. Table 2. High levels of herbicide resistance in wild radish to commonly used herbicides tested in 2014. Herbicide Herbicide group No of samples in 2014 % of samples resistance Glean / Logran B 130 88 Atrazine C 158 11 Diflufenican F 128 46 2,4-D ester 680 I 114 17 Glyphosate M 122 1** **This sample is being re-tested to confirm the result. For wild oats, if you suspect Group A (fop) resistance you are probably right and testing is unnecessary. Most samples are susceptible to atrazine (Group C) and glyphosate, so only test if you suspect there is a problem. There is a 50:50 chance of samples being resistant to Axial or Achieve so testing for susceptibility is worthwhile if you plan to use these herbicides over the next few years. For all other herbicides you plan to use over the next few years it is worth checking for cross resistance to determine which products the wild oats is still susceptible to. Table 3. High levels of herbicide resistance in wild oats to commonly used herbicides tested in 2014. Herbicide Herbicide group No of samples in 2014 % of samples resistance Fops (Wildcat, Verdict, Topik) A (fops) 53 78 Atlantis B 49 22 Achieve A (dims) 11 54 Axial A (dens) 30 47 Mataven Z 9 11 CSU researcher Dr John Broster is encouraging growers to collect samples for herbicide susceptibility testing next season. Dr Broster urges growers to not be complacent about herbicide resistance in these weeds. “The situation is becoming increasingly serious for a wide spectrum of weed species,” he said. “These results suggest that growers have time to implement herbicide and non-herbicide strategies to avert a crisis situation, but immediate action is required.” In preparation for next season Dr Broster suggests growers allow for susceptibility testing in the budget and be prepared to collect samples at harvest, even carrying sample bags in the header if possible. To have samples tested simply collect seeds or seed heads from the weeds of concern, often those present at harvest. Place the sample into a paper bag inside an A4 envelope. Double bagging the seeds protects the sample. Don’t use plastic bags because the seeds can easily become mouldy if there is any moisture in the bag. Post the samples to either of the herbicide resistance testing services—Graham Centre for Agricultural Innovation at CSU, or Plant Science Consulting at University of Adelaide. For ryegrass, collect about a coffee cup full of clean seed or an A4 envelope full of seed heads. For wild oats or wild radish, a comfortably full A4 envelope of seed heads or pods is ample. Record information on the sample bag about where the sample was collected and what herbicides you would like the sample tested against. Make sure the sampling occurs across the area of interest, not just at one spot. If you are interested in the entire paddock you need to sample the entire paddock, if you are looking at the area around a blow-out then sample throughout that area. For more information on herbicide testing services visit www.csu.edu.au/research/grahamcentre or www.plantscienceconsulting.com/seedtest.

Barnyard grass continues to cause significant losses in summer crops and deplete stored moisture in fallows across the northern grains region of NSW and Queensland, and in the Ord. Cover crops may provide a useful, non-chemical alternative for weed management in northern region fallows. As a front-runner in the race to glyphosate resistance, awnless barnyard grass (Echinochloa colona) has several advantages, including its ability to germinate throughout the summer and potentially produce up to 42 thousand seeds per plant. There are currently 98 documented glyphosate (Group M) resistant populations of awnless barnyard grass in WA, NSW and Queensland, and resistance to Group C triazines (Atrazine) has also been confirmed in populations growing in WA and NSW. This weed is known to evolve resistance to a variety of herbicides as multi-resistant populations have been found in several other countries, including the USA. As glyphosate resistance in the species becomes more widespread there is a risk that resistance will soon be evident to alternative herbicide groups being used on their own or as part of a double knock in fallow—particularly Group A and Group L herbicides. In an effort to find alternatives to glyphosate, weeds researchers in NSW and Queensland, including Michael Widderick from the Queensland Department of Agriculture and Fisheries, have been investigating the effect of a variety of chemical and non-chemical control tactics. “One alternative we are exploring for awnless barnyard grass are Group A herbicides applied either alone or as part of a double knock, using either paraquat or glufosinate as the second knock,” he said. “We trialed two different timings for treatments to evaluate the impact of weed growth stage on herbicide efficacy. The next important phase is to examine the residual effect of these Group A chemistries on the following winter cereal crops.” Another trial has investigated the impact of a range of residual herbicides for fallow weed control. Dr Widderick said a couple of residual products have shown particular promise and warrant further study. “The third angle in the current trials was to test some cover crop options using various combinations of millet, cowpea and lab lab,” he said. “While we don’t expect to have a definitive recommendation based on the current trial alone, the results will provide a good starting point in helping to fill gaps in the current knowledge about using cover crops in the northern region.” Until alternatives are found Dr Widderick says it is important to implement strategies that deplete the seed bank, control small seedlings in the fallow and stop seed production. “We know the seed of awnless barnyard grass can persist for longer if it is buried in the soil,” he says. “Shallow tillage to a depth of 5 cm or less will keep most seeds within the top five centimetres of soil from which most seedlings will emerge.” Research into residual herbicide controls for awnless barnyard grass is identifying some promising options. Compare the control (untreated) plot on the left with a treatment offering excellent control of annual barnyard grass in the centre plot and a poorer performing treatment on the right, 112 days after treatment. Fallow application of Flame® (Group B) in late spring or early summer may control several flushes of awnless barnyard grass prior to sowing wheat. Similarly, a winter/spring fallow application of atrazine (Group C) may effectively control germinating barnyard grass for a few months prior to planting sorghum, provided rainfall is received within 10 days of spraying to incorporate the herbicide. “Alternatively, atrazine plus metolachlor (Dual Gold®, Group K) incorporated at sowing consistently gave over 95 per cent control of barnyard grass in sorghum. Trials have repeatedly shown that a tank mix treatment of atrazine and metolachlor to be reliably better than atrazine alone, especially in wet seasons.” says Dr Widderick. “A range of residual herbicides is also available for grass control in cotton.” Dr Widderick says double-knock tactics to treat weeds prior to early tillering (up to 3 tillers) remains very effective to target small weeds and reduce the risk of weed escapes. “Large, moisture-stressed plants are very difficult to kill and are most likely to contribute large quantities of seed to the seed bank. Their removal needs to be a high priority task, often requiring manual tactics such as patch cultivation or chipping,” he says. Trials have demonstrated that sorghum planted on narrow rows can compete with awnless barnyard grass and markedly reduce seed production on plants that germinate and grow in-crop. Sowing sorghum in one metre rows at high seeding rates can reduce potential seed bank replenishment by about 50 per cent. Dr Widderick says implementing a robust integrated weed management plan can significantly extend the useful life of herbicides like glyphosate.

Canola has been making positive impacts on farm profitability over recent years but the cost of weed management has also been climbing. The availability of a wide range of herbicide resistant canola varieties, including triazine-tolerant (TT), Roundup Ready (RR), Clearfield® Production System (imidazolinone-tolerant) and dual RR–TT, has not kept a lid on weed management costs. A strongly competitive canola crop can suppress weed biomass at flowering by a huge 50 per cent, significantly reducing the amount of weed seed added to the seed bank. The challenge is to find out which canola varieties are able to out-compete weeds and so reduce the reliance on herbicides, and retard the spread of resistance. Researchers at the Graham Centre for Agricultural Innovation at Charles Sturt University and NSW DPI in Wagga Wagga have focused on this task, comparing the competitive ability of canola varieties against weeds. Lead researcher Professor Deirdre Lemerle said the Australian-first study looked at the competitive ability of 16 canola genotypes against annual ryegrass and volunteer wheat over two contrasting seasons, without using herbicides. “When a crop plays a central role in its own weed management there can be many great benefits,” said Professor Lemerle. “Sowing the most competitive variety can reduce herbicide dependence and costs without any yield penalty. This is an important non-chemical tactic to use against herbicide resistant weeds.” The study showed a wide variation in the ability of current canola varieties to compete in the presence of weeds. Under the same weed pressure some varieties experienced a 50 per cent yield loss while others did not lose any yield. “The most competitive cultivars reduced weed biomass at flowering by a huge 50 per cent, significantly reducing the amount of weed seed added to the seed bank,” she said. “As expected, the suppression of weed growth was strongly tied to crop biomass and early crop vigour. AV-Garnet, hybrid Hyola-50, and the Clearfield hybrids, Hyola-571CL, 45Y77 and 46Y78, were higher yielding and more competitive than the triazine-tolerant cultivars. Although the ranking of the 16 genotypes was influenced by seasonal conditions these genotypes were consistently more competitive than others.” Speedy emergence, early vigour, rapid ground cover and height are all important characteristics of competitive crops, as varieties with these traits can rapidly ‘own’ the space in the field and ultimately squeeze out the weeds. Other competitive traits can include sufficient large, thin leaves to effectively shade weeds, sufficient pod height to over-top neighbouring weeds (without unduly lowering harvest index), combined photosynthetic area (leaves and pods) sufficient to shade weeds at all stages of the growth cycle, high allelopathy and a rapidly established root system to uptake nutrients (N, P, K) and water. Dr David Luckett, Senior research scientist at CSU examines the competitive ability of different canola varieties. “These traits also support high yield, so generally, genotypes that are high yielding—both in grain and oil content—in monoculture are also high yielding in the presence of weeds,” said Professor Lemerle. “When canola plants are losing the battle with weeds they are smaller and have less leaves than when they are growing in a weed-free environment. They are likely more attractive to insect and mouse attack.” Another interesting but more difficult to study trait is the production of allelopathic chemicals that can suppress the growth of other nearby plants, including weeds. Canola is known to produce allelopathic chemicals that can suppress annual ryegrass root systems and the CSU team is leading the way in identifying the chemicals involved and finding the associated genetic markers. “In the longer term we expect to be able to provide canola breeders with the information required to maximise the ability of canola crops to interfere with weed growth in the farming system through strong crop competition and allelopathic interaction,” said Professor Lemerle.

Case study: Graham Clapham A diversified cropping system requires great attention to detail and offers many opportunities to implement several tactics in an integrated weed management strategy. Spray application technology like these multiple-nozzle fittings make it quick and easy for the operator to change the nozzle type if environmental conditions change during the spray operation. The Claphams have placed the nozzles on their spray rig close together (250 mm apart) to maximise coverage and minimise drift. Graham Clapham started his farming career straight out of school at 15 years of age. Even then he was clear about his desire to own a black soil farm on the Darling Downs. Graham grew up on his parent’s 200 ha mixed cropping farm, growing irrigated and dryland crops including corn, soybean, wheat, sorghum, onions and pumpkin. With help from his parents, Graham realised his first goal when he was 18, purchasing a farm of his own at Norwin, west of Toowoomba. He now grows mostly irrigated cotton, corn and wheat and dryland cotton, wheat and sorghum on the family’s 1840 ha aggregation in the Brookstead–Norwin district. On the 700 ha that is usually irrigated each year Graham has two main rotations—irrigated cotton or corn followed with irrigated wheat then a long fallow before returning to cotton or corn. In the corn–wheat rotation there is no cultivation but Graham has different herbicide options available and an opportunity to provide a disease break to combat fusarium wilt. Rainfall dictates the dryland crop rotation on the rest of the cropping area. Minimum till is practiced to conserve soil moisture with occasional cultivation only to renovate the tramtracks. Graham is aware of the risk of herbicide resistance, particularly in weeds like flaxleaf fleabane and feathertop Rhodes grass, which have always been hard to kill with glyphosate, and milk thistle is a new concern for the business. Since the introduction of genetically modified cotton in 1996, the Claphams have practiced pupae-busting cultivations to manage resistance in helicoverpa. This has had the spin-off benefit of keeping hard to control weeds like flaxleaf fleabane and feather-top Rhodes grass under control. “Pupae busting is a robust cultivation to a depth of 100 mm and is required to remove all large soil clods,” he says. “It must be done before the end of July following the cotton harvest in April–May.” The deep cultivation after cotton buries weed seeds deep in the profile where they can’t germinate. Unfortunately flaxleaf fleabane seeds remain viable for longer when they are buried than when they are close to the soil surface. This means cultivation in subsequent years can bring viable seed back to the surface where it can germinate so it is not a complete solution but another useful tactic in the farming system. The cultivation leaves the soil dry and prone to erosion so the Claphams aim to sow a wheat crop after cotton to provide ground cover over winter and stubble for the following summer. Soil moisture and irrigation water availability govern the sowing rates used although the Claphams have two options when it comes to row width in their dryland crops. When sowing wheat into cultivated soil after cotton they can use an air seeder to plant rows 150 mm apart rather than the single disc planter used in minimum till planting to sow 500 mm rows. Sowing in narrow rows has several benefits for weed control in the dryland system. To begin with sowing is a full tillage operation that removes any weeds present at the start of the season. The increased shading of the inter-rows suppresses weed germination and after harvest there is more stubble left on the ground, again suppressing weed germination. Infrastructure such as channels and pump sites are kept clean throughout the year to avoid the risk of weeds spreading throughout the farm in irrigation water. Graham has not noticed a yield difference between crops sown at the narrow and wider spacing although the air seeder does dry the soil out more than the single disc planter. “The wheat crop is often not great, especially if winter rain is scarce,” he says. “But it provides good cover and we can use different chemistry to control weeds, especially to achieve a residual effect on flaxleaf fleabane.” Graham says the chemistry available for use in wheat is very effective, keeping the wheat crops quite clean. Corn can experience some late grass germinations, which they have previously treated with glyphosate at harvest and then burnt the stubble. When there is additional water available for irrigation early in the year the Claphams often take the opportunity to plant soybeans. Having this as an option they are conscious of the residual action of the herbicides used in the previous wheat crop. “We use herbicides with no residual effect to control broadleaf weeds such as thistles and turnip in the wheat so we don’t need to worry about the plant back period for soybean,” says Graham. So far the Claphams have not experienced any spray failures that have raised concern about herbicide resistance. Graham is very conscious of the potential risk and is mindful of the experience in the USA with widespread glyphosate resistance in their cotton industry. “Glyphosate-ready cotton has been a positive innovation for the industry, making it more sustainable and ending the use of environmentally-harmful herbicides,” says Graham. “However, glyphosate does not give 100 per cent control of weeds in cotton. Vines particularly can survive a spray and so we use inter-row cultivation and hand chipping to remove vines as needed.” Inter-row cultivation in cotton, corn and sorghum also helps maintain the furrow profile and to conserve moisture before the canopy closes. Graham occasionally uses an inter-row shielded sprayer to apply glyphosate in corn and sorghum crops. The Claphams recently purchased a neighbouring farm with a very heavy weed burden. They have used cultivation and herbicides to drive down the weed seed bank and to treat weeds they have never seen in the area before. The Claphams do all their own spray operations, mainly so they can control when they spray. “The Darling Downs region is closely settled and there are not many trees across the cropping area. It can be very difficult to find suitable times to spray without the risk of off-field impacts. Having our own gear and labour available means we can spray as soon as suitable conditions prevail.” Spot spraying larger weeds that have escaped earlier treatment is the last operation before plating clean seed into clean paddocks with clean borders (#8 in the 10 Point Plan). Graham’s son-in-law, Jonathon Mengel, is responsible for the spraying operations across the farms. They have found that having a person with the designated responsibility to have the chemicals in stock and be looking for spray opportunities has been very beneficial to their operation. “We have very few weed escapes after a herbicide spray,” says Graham. “On the rare occasion that it does happen we prevent seeding using tillage or a follow-up application of a knockdown like paraquat.” “In the fallow we look for opportunities to do a double-knock treatment but it can be very difficult to get favourable conditions for two sprays close together,” he says. “Glyphosate, Starane®™ and MCPA®™ are relatively easy to apply using air induction nozzles to splash the product on with minimal risk of spray drift. The second application of paraquat 10 days later is more difficult, especially given the need to apply a fine droplet size.” The Clapham’s Case Patriot sprayer, with its 36 m boom and 4 m wheel base, fits perfectly into their on-farm control traffic system. They have doubled the number of nozzles on the boom, placing a set of nozzles every 250 mm instead of the traditional 500 mm, allowing greater coverage and helping to extend the tight spraying window. “This gives us a double overlap so we can consistently use coarse droplet nozzles and still get coverage, and it also enables us to operate lower to the ground,” he says. When necessary Graham will spot spray or hand rouge weeds prior to planting the next crop to ensure the paddocks are as clean as possible going into the season. The Claphams are also careful to keep irrigation infrastructure such as head ditches, supply channels and tail drains weed free. They use residual herbicides at high rates to effectively sterilise the soil in these non-cropping areas. “The risk of distributing weeds throughout the farm is of great concern and maintaining weed-free infrastructure is a year-round priority for us,” says Graham. “We also pay attention to planting clean seed each year, buying in cotton, sorghum and corn seed, and grading the wheat seed we keep the next season.” “Black oats has been a bad problem in the winter cropping program but we seem to have won the battle with a consistent approach to planting clean seed.” Throughout the crop rotation the Claphams are looking for ways to manage weeds to achieve the best possible productivity and profitability in the long term from their cropping operation. Watch Graham’s video below!

It is possible to remove weed seed contamination from farmer-retained planting seed but it requires a high level of care and planning and many farmer-cleaned samples still have a high level of contamination. Un-cleaned seed samples can contain over 1500 weed seeds per 10 kg planting seed, many of which will be seed from herbicide resistant plants. From a crop hygiene point of view it is obvious that planting clean seed is the best way to prevent weed seed being sown with the crop. If in doubt the cost of buying certified clean seed for planting pales into insignificance against the cost of controlling weeds in crop or the difficulties associated with a weedy paddock at harvest. There is more to the story though, as clean seed promotes strong crop establishment and early growth—another key tool to reduce the weed seed bank and to combat the spread of herbicide resistance. Professional seed cleaning machinery not only removes weed seeds, it also removes small and broken seeds and non-seed contaminants. The removal of these other contaminants increases the chance of the retained seed having a high germination rate and strong seedling vigour. Both these factors will increase the competitiveness of the crop and reduce the likelihood of weeds growing and producing seed. Large seed size is generally equated to higher germination and vigour so the removal of small crop seeds also helps with weed control. Similarly, the removal of non-seed contamination reduces the risk of insect damage and fungal diseases that can spoil the seed quality during storage. Following the guidelines for safe on-farm storage is also important to protect the viability of the retained seed. A survey in Western Australia by the GRDC-funded Australian Herbicide Resistance Initiative found that the gravity table method of seed cleaning consistently produces the cleanest seed sample. The AHRI survey found that un-cleaned seed samples can contain over 1500 weed seeds per 10 kg planting seed, which would add extraordinary pressure on the next crop. Sieves alone can bring that number down to about 150 weed seeds per 10 kg and a gravity table reduces contamination to about 25 weed seeds per 10 kg. A fully automated, continuous flow cleaning and grading plant will remove at least 98 per cent of addage. The complete cleaning and grading process will sort the material by weight, length and width as the grain moves over an air screen then a gravity table to remove impurities and finally through indented cylinders to sort the grain according to size. Any cleaning of grower-retained seed is beneficial for reducing weed pressure in the next crop. An in-field rotary screen cleaner can be expected to leave an average 80 weed seeds per 10 kg of grain while a gravity table will produce the cleanest sample, leaving an average 20 weed seeds per 10 kg of grain. Investing in such equipment is not economic to treat planting seed only, however when it is used to treat all grain produced it can be economically viable through saving cleaning costs on delivery and potentially upgrading the overall quality of grain sold to meet premium market requirements. If a grading table is not an economic option in your business, choosing to have planting seed cleaned by a contractor is definitely worth considering over retaining un-cleaned seed or using sieves alone. If the seed being cleaned has come from an identifiable area of the farm, then this is a good opportunity to collect weed seed and send it off for testing to find out what herbicides the weeds present at harvest are susceptible to. This will help you prepare in-crop weed management strategies for next season. Plan ahead for the next seed crop and ensure you harvest seed from the cleanest paddock or the cleanest section of a paddock.

Optical spray, or weed detector, technology has been refined over recent years to be a reliable and flexible option for use in several weed management situations. Weed detector (or optical spray) technology is coming to the fore as a valuable option in the war on herbicide resistant weeds. The technology is mature, reliable and supported with new herbicide product registrations. The most common application of the technology is to treat light, patchy infestations of weeds. This often occurs following a broadacre herbicide application of pre- or post-emergent herbicide and usually requires a different mode of action or higher rate application to kill any surviving weeds and prevent seed set in the fallow. The two systems currently available in Australia, WeedSeeker® and WeedIT®, both use infra-red reflectance units to sense the presence of green plants and can accurately deliver a set herbicide dose to those plants. Once a plant is detected, a solenoid is activated, turning on an individual nozzle and the weed is sprayed. NSW DPI weeds technical specialist, Tony Cook says this makes the optical spray technology a highly effective way to economically treat low density weed populations. Although the general recommendation is to apply herbicide to small weeds, the optical sensors do not recognise plants smaller than about a 50c coin diameter and in wheat stubble weeds are not reliably detected until they are about the size of the top of a beer can (5 cm across). This is why the technology is not recommended for use in high density weed situations. “Some farmers using the optical sprayers have a dual boom spray set up with the normal boom applying a broadacre dose of glyphosate while the optical sprayers treat any larger weeds with a higher dose of glyphosate or a different mode of action herbicide,” he says. Nufarm have recently achieved product registrations for applying several of their herbicides using the optical spot spraying technique. Nuquat® is registered to treat barnyard grass, fleabane, sowthistle, bladder ketmia, caltrop, turnip weed and Australian bindweed. Trooper® 75-D, Comet® 400, Amicide® Advance 700 and Amitrole T are registered for fleabane, sowthistle and caltrop control. “In addition to these registrations, APVMA Permit 11163 is in place to allow users to apply a range of other herbicides using optical sprayers,” says Mr Cook. “Check the permit for application rates and use situations. However, this permit is due to expire on 28 February 2015.” Herbicides covered by the permit include glyphosate, paraquat, paraquat + diquat, amitrole + paraquat, glufosinate, amitrole T, 2,4-D, triclopyr, fluroxypyr, quizalofop, haloxyfop, sethoxydim, clethodim, butroxydim, and fluazifop. Mr Cook says the optical spray technology and the recent Nufarm product registrations may help extend the effectiveness of knockdown herbicides such as glyphosate, paraquat and Group A herbicides. “Using this technology to apply an alternative herbicide group to kill weeds that have survived an application of glyphosate will help drive down the glyphosate resistant seedbank. Along with the use of other strategies that do not rely on knockdown herbicides growers have more tools in their weed management toolbox,” he says. Resistance to paraquat and Group A herbicides may start to emerge in the near future. To prolong the life of these herbicides for use with optical spray technology may require implementation of other weed management options such as an occasional ‘patch’ cultivation to control plants that survive herbicide treatments. Weeds that survive a pre- or post-emergent herbicide application are frequently herbicide resistant and moderate in size, making them ideal candidates for treatment with optical spray technology using a different mode of action. For an investment in the optical spray technology to provide value, the equipment needs to be regularly used. There are some limitations that must be taken into account such as the need to travel slower (16 km/hr) than normal boom spray operating speed. The sprayers must also be correctly set up and operated according to the manufacturer’s operating guidelines. There is also added flexibility with the optical sensors working equally well at night as in the day. This makes it possible to use paraquat-type (Group L) herbicides as the second spray in a double knock program as these products are generally more effective when applied late afternoon, in the evening or under cloudy conditions. Although these products require the use of large nozzles with low drift potential, there is a higher risk of inversion drift conditions when spraying at night. The nozzles on an optical sprayer are set closer together and this, together with the slower operating speed and coarse droplet size, greatly reduces the risk of spray drift. However, it is not recommended to use this technology in high wind situations. “Optical spray units can achieve chemical bill savings of 60–90 per cent compared to broadacre herbicide application,” says Mr Cook. “Herbicide volumes are generally cut by similar percentages, depending on weed density and the sprayer’s sensitivity settings.” Optical spray technology is the only herbicide application method proven to be effective against larger, established weeds. Monitoring after an optical spray application is essential to identify and physically remove any individual survivors. It is a useful follow up to a pre-emergent herbicide application in fallow where weeds are likely to be low density but of moderate size. The technology also has application for treating crop verges, irrigation channels, fencelines and in wide row crops (using shielded nozzles). Watch the video below for more info!

Wild radish is an incredibly adaptive weed, quickly responding to selection pressure and finding ways to evade control measures. AHRI researcher Michael Ashworth systematically collected seed heads from early flowering individuals and planted these seeds to grow the next generation of the selected population. Collecting weed seed at harvest and crushing, composting or burning them has proved to be a very effective method of reducing the number of seeds that enter the seed bank each year. In Western Australia growers have achieved excellent results with chaff carts, baling, narrow windrow burning and the Harrington Seed Destructor, however research shows the efficacy of harvest weed seed control also applies selection pressure favouring early flowering. GRDC funded AHRI PhD scholar Michael Ashworth reported his findings at the Australasian Weeds Conference in Hobart in early September, showing that wild radish populations have sufficient genetic diversity to rapidly adapt their flowering time in response to selection pressure. Starting with wild radish plants that had not been subjected to harvest weed seed control, Mr Ashworth systematically collected seed heads from early flowering individuals and planted these seeds to grow the next generation of the selected population. “Within five generations the population had shifted the time to flowering from 60 days to 29 days,” he says. “As a result these plants will be carrying well-matured pods at harvest, many of which will have dropped their seed, effectively evading seed capture at harvest. This is even more likely in years where there are periods of water deficit, high temperature or high wind.” Within five generations the population had shifted the time to flowering from 60 days to 29 days, effectively evading seed capture at crop harvest time. The rapid reduction in time required for the wild radish plants to flower is alarming but does not mean that the reduction can continue indefinitely. There are biological limits and these early flowering biotypes will be susceptible to other forms of control. The good news is that the early flowering wild radish produced less biomass prior to flowering than the later flowering individuals, making them more susceptible to crop competition. The early flowering plants also had poor structural integrity and set fewer pods below the harvest cutting height. “There is a level of creativity required and a constant need for researchers and growers to think ‘outside the square’ to identify and test new weed control options,” says Mr Ashworth. AHRI communications leader Peter Newman says these findings underline the need for growers to use a spectrum of control tactics when combatting weeds in their crops. “Weeds have an amazing ability to adapt to selection pressures, including the actions of farmers endeavouring to remove them. Herbicides, crop competition, strategic cultivation and harvest weed seed control can all be used to suppress weed numbers,” he says. “Growers using a combination of these techniques have very low wild radish numbers and are winning the war.” Mr Newman recommends the 10 Point Plan as a good place for growers to start planning an integrated weed management course of action.

Growth Farms Australia manager, Chris Bunny, knew that the company was buying a property with herbicide resistant weeds when they purchased ‘Glaisnock’ near Young in 2008. “The ryegrass on the property was known to be resistant to both Group A and Group B herbicides,” he said. Chris and Elise Bunny, ‘Glaisnock’, Young believe narrow windrow burning is an effective non-chemical tactic to add to their weed control strategy. “Twenty-five years of continuous wheat-canola cropping had taken its toll and changes to the farming system were obviously required.” Over the last few years Mr Bunny has implemented drastic changes—reintroducing livestock into the system, changing herbicide application tactics, modifying the rotation and adopting narrow windrow burning—all to address the problem of herbicide resistance in weeds. The 970 ha red earth property, ‘Glaisnock’, located between Young and Temora is well suited to cropping but continuous cropping practice has generated an unsustainable level of weed pressure. Mr Bunny is in the process of fencing paddocks and installing stock waters as they move around the property planting lucerne for stock grazing. “About 20 percent of the property is under lucerne in any one year,” he said. “Lucerne gives us the opportunity to earn income off these paddocks while also winter cleaning with heavy grazing and paraquat in at least 3 of the 5 years of pasture.” They run trade stock, either steers or prime lambs, so they are able to be flexible with the timing and stock density. The lucerne is also breaking up the hard pan that had developed over so many years of continuous cropping. Triazine tolerant canola and wheat are currently sown 50:50 across the remaining farming area. Mr Bunny said the triazine-tolerant canola had proven to be a useful way to introduce different modes of action to the assault on resistant weeds. He hopes eventually to reduce the area sown to canola but for now it is playing an important part in their integrated weed management program. During the summer fallow Mr Bunny employs double knock herbicide applications at every ryegrass germination. “Generally there are two double knock applications in the fallow,” he said. “The timing of the operations is determined by the weed size and the extent of the germination.” “The staggered germination pattern of ryegrass can make it difficult to know when to spray,” he said. “It is also tempting to not do the second knock when the first spray appears to have worked well, but we have seen the benefits when a strip has been left un-sprayed and it is clear that the second application is essential.” To round off their integrated weed management strategy Mr Bunny has also implemented narrow windrow burning of canola chaff as a non-chemical harvest weed seed control measure. This year is the third year of narrow windrow burning on the property and Mr Bunny is convinced of its effectiveness in reducing the weed seed bank. “The only real problem with narrow windrow burning is the chance of the windrows getting wet before you are allowed to burn,” he said. “We try to start burning as soon as permits are available. So far we have had successful burns in 2 out of the 3 years.” A hot fire is the key to effective narrow windrow burning to kill weed seeds. Mr Bunny had previously used stubble burning as a weed control measure but had found that burning the whole paddock was ineffective and there was the associated loss of stubble. “Burning the narrow windrows is a much safer operation and for negligible cost it is possible to modify the header and introduce another weapon against resistant weeds.” The canola chaff easily generates the required 400 degrees Celsius required to kill ryegrass seed. The next challenge for Mr Bunny is to implement the strategy in harvested wheat paddocks. The main difficulty with taking this step is the need to cut the wheat lower than usual and the timing of harvest compared to when the ryegrass seed begins to fall. “We will be working on lowering the header, aiming for ‘beer can height’, and adjusting the chute to make the windrows as narrow as possible without causing blockages,” he said. Being able to effectively burn chaff in every paddock, every year is the aim and Mr Bunny is determined to solve any problems that stand in the way. Mr Bunny said two people can easily burn 400 ha of narrow windrows in one afternoon. Each windrow is lit every 400 metres or so, starting soon after midday. The windrows burn quite quickly and most are burnt out by late afternoon. Mr Bunny checks the paddocks again late in the afternoon and extinguishes any that are still alight. “With the wheat we anticipate the need to burn off smaller areas at a time and that there will be more risk of the fires spreading across the paddock,” he said. Summer rains can cause problems with the wet windrows tending to only burn along the top where the chaff has dried off. Mr Bunny has found that even in years where the effectiveness of the burn is reduced there is still a benefit in concentrating the weed seed into narrow bands in the paddock where germinations can be more easily and cost-effectively targeted. Growth Farms Australia recently hosted researcher Michael Walsh from the Australian Herbicide Resistance Initiative and a group of growers from Western Australia with extensive experience with herbicide resistant weeds, including annual ryegrass. Growers from the Young district were invited to meet the visiting experts and to see narrow windrow burning demonstrated. Delta Agribusiness consultant David Crowley and GRDC funded, Charles Sturt University researcher John Broster arranged field days at Young, Griffith and Lockhart to give local growers an opportunity to meet the West Australian expert panel to discuss their experience with harvest weed seed control methods, including the Harrington Weed Destructor, chaff carts and narrow windrow burning.