News

Article
News

Windrow to collect early shedding weed seed

Looking toward harvest, the pressure is on to get the timing right to maximise yield and grain quality. Delta Ag senior farm consultant, Tim Condon, says it is also a great time to be capturing weed seeds, particularly from wild oats plants that have escaped in-crop herbicides, using a non-herbicide tool to manage herbicide resistance. “Windrowing, or swathing, barley has been traditionally used as a harvest management tool when growers have a number of different crops to harvest in a short time,” he says. “The really good thing about this technique is that it also gives growers another shot at collecting and destroying weed seed.” Successful windrowing begins with cutting the crop low and, where possible at an angle to the seeding direction. When followed with any harvest weed seed management tactic, even early shedding weeds such as wild oats can be effectively controlled. Swathing barley at the earliest opportunity maintains the crop’s yield, and if done correctly, the swaths protect the grain from weathering. Mr Condon recommends checking the crop away from the paddock edges and looking for signs of physiological maturity in the barley plant. “Barley, and wheat, can be swathed when the grain is at 30 to 35 per cent moisture,” he says. “This is indicated by the peduncle [the little stem just below the head] of the grain head turning from green to brown and if you press your thumbnail into the grain there should be no dent created in the grain.” “Once the crop is mature, the key to effective swathing – and also for the best results with weed seed collection – is to cut the crop low,” he says. “Cutting at boot or beer can height provides sturdy support for the swath, keeping the grain and the weed seed off the ground and making harvest more efficient.” In some situations, it can also be beneficial to swath at an angle to the seeding direction to provide extra support under the swath. Good results have been seen in Western Australian crops swathed 15, 45 and 90 degrees to the seeding direction. In controlled traffic systems, using a mixer belt, or setting the belts at different speeds, is an alternative to swathing at an angle to achieve the necessary cross thatching to keep the swathed crop off the ground, maintain grain quality and allow easy pick up. “Crops sown on narrow row spacing will also swath better, and there is good evidence that narrow row spacing also suppresses weed seed production,” says Mr Condon. “In southern NSW the main weed that we can target with swathing is wild oats. Wild oats is renowned for shedding seed before crop harvest so swathing can reduce the amount of seed shed onto the ground. Even with good control of wild oats germinations around sowing, there are often later germinated weeds that grow with the crop but are less mature at harvest than earlier germinations would have been.” Wild oats is notorious for shedding its seed early. Windrowing is an excellent way to collect the seed from wild oats plants that have escaped in-crop herbicide treatment. Swathing, followed with any of the harvest weed seed control tactics, becomes a very useful non-herbicide tactic to use with weed species that shed their seed early. Other potential targets with this strategy are wild radish, brome grass and annual ryegrass. Once the swathing is done, the barley can be left for several weeks until there is an opportunity to harvest. However, there is always a risk of the windrow not drying quickly if wet weather persists, which may cause grain quality to deteriorate. Options for destroying the weed seed captured in the swath include narrow windrow burning, chaff carting, Harrington seed destructor, hay baling or chaff lining (in controlled traffic systems), all of which are detailed on the Weedsmart website. “Narrow windrow burning can be risky in leafy crops like barley, especially in high yielding districts,” says Mr Condon. “A new technique being trialed in these situations is chaff lining, where the chaff component is dropped into a narrow band and left to rot down. Early observations suggest that weed seeds don’t survive, especially when the chaff stream is directed into the wheel tracks in a controlled traffic system.” Avoid confusion: The terms ‘swathing’ and ‘windrowing’ refer to the same practice. In NSW and Vic ‘windrowing’ is the more commonly used term while ‘swathing’ is the more commonly used term in WA and SA. However, ‘narrow windrow burning’ is a completely different practice. Relevant links Webinar – Windrowing and crop topping to stop weed seed set AHRI Insight – Make time stand still
Article
News

Why consider sowing east-west?

In winter, when the sun is travelling at a lower angle the additional shading of the inter-row that occurs when crops are sown in rows running east-west can help suppress weeds growing in-crop. This effect is most noticeable in southern latitudes. In Western Australia, Department of Agriculture and Food researcher Dr Catherine Borger demonstrated in six trials that east-west sowing can halve annual ryegrass weed seed set, even though weed biomass may not be reduced. This is a rare opportunity for free weed control that could be worth implementing in suitable paddocks. Weeds researcher Dr Catherine Borger measured the difference in light penetration through the crop and weed growth when the crop was sown east-west compared to north-south. Photo: DAFWA cent weed biomass reduction when crop rows ran east–west compared to north–south. At Trangie the barley varieties Hindmarsh and Granger had higher yield and were more competitive against weeds when sown east–west. In these trials weed biomass was measured rather than weed seed production, however both are good indicators of the weed response to the treatments. NSW DPI research and development agronomist, Greg Brooke says that in many cases there are other, more practical, ways to suppress weeds but that row orientation is well worth considering and implementing if it can be easily done. “The more non-herbicide tactics a grower can use to support their herbicide program the better,” he says. “Crop yield is not compromised under east–west sowing.” Researchers in NSW also noticed a stark difference in the growth of the weed fumitory, with the weed being prolific in the north–south rows and absent in the east–west rows. Growing crops in rows at right-angles to the sun decreases the amount of solar radiation that the weed plants can intercept and use for photosynthesis. This translates into lower biomass production and potentially decreased seed production. Importance of early weed control A weed seedling can impact crop yield potential well before the weeds are large enough to take moisture, light and nutrients away from the crop. Canadian researchers Dr Clarence Swanton and Dr Jessica Gal observed this effect in both corn and soybean. The weeds emerging alongside or soon after the crop seedlings reduced the crop yield potential, with the effect occurring at the seedling stage, long before the weeds could be competing directly for resources such as moisture, nutrients and light. The differences in light wavelengths bouncing off bare soil compared to growing weeds triggers a reaction in the crop plants to put a disproportionate amount of resources into growing taller, with more leaf area—resulting in a comparatively smaller root system. This response can pre-condition the crop to a lower yield, particularly in years where the crop may encounter moisture stress and have limited ability to seek deeper stored moisture. DAFWA researcher Dr Catherine Borger says that crop plants adopt this ‘shade avoidance growth characteristic’ to allow them to more effectively shade weeds as the plants mature and begin directly competing for light. “Since crop plants in an east-west orientation physically shade weeds at an earlier growth stage, weeds have less opportunity to trigger the shade avoidance growth characteristics,” she says. The interrow area is shaded earlier in the season when the crop is sown east-west, suppressing weed germination and growth early. Choosing competitive crops and varieties “The row orientation is one part of increasing crop competition,” says Mr Brooke. “The other factors to consider are row width, seeding rate and crop and variety selection.” “The difference in competitiveness between crop types is well known with general rules of thumb such as triticale, barley and rye being more competitive than wheat; and cereals are generally more competitive than pulses and canola,” he says. “What is less well understood are the differences between varieties. In one trial Skipper barley achieved a 30–40 per cent greater weed biomass reduction compared to Hindmarsh barley, however the competitive ability of different varieties varies widely between sites and seasons.” Generally, varieties that exhibit rapid early growth and early canopy closure will provide better weed suppression than less vigorous varieties of the same crop type. Seeding rate and row spacing also play a part in increasing the crop’s competitiveness. Choosing a highly competitive cultivar in one year of a three to five year program can have a significant and lasting effect on the weed seed bank. If this is coupled with harvest weed seed control, and possibly east–west sowing, the result could be impressive and achieved at a very low cost. “Introducing more non-herbicide tactics into the farming program gives crops the advantage over weeds and reduces the pressure on the herbicide,” says Mr Brooke. “Farmers have started using tactics like double-sowing known weed areas such as along irrigation channels. With GPS, double pass seeding automatically gives narrow rows, doubles the seeding rate and makes those key management areas much more competitive.”
Article
News

Dry sow clean paddocks first

More and more growers are dry seeding wheat to avoid terminal drought at the end of the season. Research undertaken by CSIRO and WANTFA has shown that this can result in significant yield gains and larger whole farm grain production albeit with a small increase in frost risk. However, WANTFA executive director Dr David Minkey said that there is a greater risk of weeds germinating alongside the crop. “Unless the weed seed bank is very low, the heavy reliance on in-crop selective herbicides can quickly lead to herbicide resistance,” he said. The breakdown patterns of pre-emergent herbicides under a variety of seasonal conditions can affect the efficacy of early and staggered germinations of annual ryegrass. WANTFA executive director Dr David Minkey recommends dry sowing the cleanest paddocks first to minimise the risk of poor weed control results. With this risk in mind WANTFA has been investigating the behaviour of pre-emergent herbicides under early dry sowing conditions to determine the rate of breakdown under various seasonal conditions. “While the first step is to sow the cleanest paddocks, the next important strategy is to lay down pre-emergent herbicides to take care of any early germinating weeds,” he said. “We need to determine the rate of decay of the pre-emergent herbicides so growers will have a good idea whether the pre-emergent herbicide will still be effective when the rain comes, and can take action early if necessary.” “Our research is focusing on overlaying emergence patterns for annual ryegrass and the efficacy of different pre-emergent products in different seasonal scenarios,” said Dr Minkey. “When the pre-emergent herbicides are applied to dry soil there is usually very little decay of the product. The biggest risk of decay is in years where a small rain event occurs that is enough to activate the herbicide but is insufficient to initiate crop germination. Under these conditions the pre-emergent product will have reduced efficacy when good rains arrive.” “Some annual ryegrass seeds can remain dormant through April and May, creating a situation where the early germinating ryegrass is controlled but later, staggered flushes occur after all the pre-emergent herbicide has decayed. In these situations the need for effective harvest weed seed control is important,” he said. With the 2016 season being off to a hot and wet start in Western Australia Dr Minkey expects ryegrass dormancy to be broken down early, suggesting that the main flush of ryegrass germination could be early in the season when the pre-emergent herbicide is active if cool conditions are met. “Where several light rainfall events occur after dry seeding the rate of pre-emergent herbicide breakdown is more rapid. If these conditions are forecast, applying a higher registered dose and mixing compatible products can extend the efficacy of the herbicide,” he says. “If the initial application decays before the weeds germinate it may be possible to apply early post-emergent residual product such as Boxer Gold, keeping in mind that the result may not be fully effective and the operation will be expensive.” Pictured with Craig White, Bayer Crop Science Technical Advisor and Leader of Integrated Weed Management, Dr David Minkey is determining the decay curves for a range of pre-emergent herbicides under different season conditions. The potential for herbicide resistance is high if dry sowing is not managed well, and many supporting strategies must be in place to eliminate survivors. “Pre-emergent herbicides must be supported by other weed control practices,” says Dr Minkey. “Clean paddocks are a must,” he says. “Then consider planting crops with early vigour or crops with in-crop herbicide options, such as RR and TT canola, include harvest weed seed control and invest in summer weed control to preserve moisture and nitrogen to support early crop growth.” The WeedSmart 10 point plan provides information on a diverse range of crop management practices that can be used to eliminate weed survivors throughout the season. What is the safest way to manage pre-emergent herbicides at seeding? Using tank mixes to extend herbicide ‘life’ Soil behaviour of pre-emergent herbicides in Australian farming systems: a reference manual for agronomic advisors
Article
News

Making clean seed your business

In 1980 the Bach family of Toowoomba diversified their farming operation to include a commercial grain storage and handling facility. With a background in grain production the family knows what’s needed to provide an efficient and safe grain handling service for other farmers. Not only do they know the importance of cleaning and grading grain to bring it ‘up to spec’, they also understand the value of removing weed contamination from seed that is being retained for planting, removing extraneous matter that can lead to problems in long-term storage and selecting the largest seed with the highest germination percentage and early vigour. David Bach from Toowoomba Grain and Storage suggests harvesting much more grain than you need for seed, getting it cleaned and keeping the largest grain aside for seed. David Bach manages the family’s grain handling facility near Toowoomba, on Queensland’s Darling Downs. He says that since retained seed must be stored for longer than most grain is held on farm, it must be stored in optimal conditions. “Grading grain at harvest will remove trash such as leaf and stem material that can attract insects and mould while the grain is in storage, either awaiting sale or being retained for seed,” he says. “Once cleaned the seed then needs to be kept cool and dry to maintain seed quality.” “When planning to retain seed on farm, select the best part of the paddock and harvest it first,” says David. “This way you will have collected the seed with the greatest vigour, which will provide the most competition for weeds in the early growth phase.” If there is not an area of the paddock that is clearly better than the rest, David suggests harvesting much more grain than you need for seed, getting it cleaned and keeping the largest grain aside for seed. “Grading it hard means that you have the best chance to remove a large proportion of the weed seeds present and you will also have a more consistent line of seed with the highest germination percentage,” he says. “It is very important that grain is cleaned at harvest, before it is stored. Clean seed that is stored and managed properly can remain viable for over 9 years.” David’s brother, Peter Bach manages the family’s farming operation—1620 ha of barley, wheat, sorghum, corn, mungbean and some faba bean—50 km west of Toowoomba. Retaining seed not only represents a cost saving for them, it also provides a back-up if some or all of a paddock needs to be re-seeded for any reason. Having a good supply of seed on hand means that growers can take advantage of favourable seasonal conditions. “We try to store enough seed here to plant half of the farm’s cropping area as soon as the soil moisture conditions allow,” says David. “This way we can make last-minute decisions and be confident that the seed we plant is clean and good quality.” “Especially when the price is up it can be difficult to source seed, so we clean five times as much seed as we expect to use and store it,” he says. “To get that seed we might clean 120 tonne of grain and just keep the best 10 tonne for seed knowing that it has been thoroughly cleaned and graded.” David cites black oats as the main problem in their area for barley and wheat crops, and sees that the wild turnip is soon going to be a major concern for growers. “It pays to clean mungbean seed very hard,” he says. “Just one tonne of seed is required to sow 40 ha so it makes sense for that tonne of seed to be the very best that you have available, and free of weed seed contamination.” Johnstone grass is the most difficult weed to remove from sorghum and maize crops in summer and David sees the herbicide tolerant hybrids providing some useful options for grass control in these summer crops. However, he has noticed an increasing problem with herbicide resistant crops growing as volunteers in other crops and contaminating that grain. “For example, imi-tolerant sorghum might grow as a volunteer in another, conventional crop, and will not be controlled by the herbicides applied in that crop,” he says. “Further cross contamination can occur if that seed is unintentionally kept for planting. It is easy to become complacent about the herbicide tolerant crop plants growing on roadsides and the potential flow of seed from roadsides into grain paddocks.” Seed cleaning equipment There are several types of grain cleaning equipment available that vary in their efficiency when it comes to weed seed removal. The Bachs use a rotary screen machine that has two main sections—1. an aspirator, where a fan sucks air through the grain, removing fine particles such as dust, and light material such as husks and some weed seeds and 2. the screens, where the grain rolls around inside a drum with different sized screens that allow the grain to be separated according to size. “Usually the grain is sorted into two sizes plus the gradings or screenings, where the vast majority of weed seed is collected,” says David. “Improving the grade of the sample is usually fairly simple, but cleaning for seed is much more time consuming and therefore costs more.” “Sometimes growers think that their grain is cleaner than it really is,” says David. “On farms where the spraying is contracted out the farmer may not be as aware of the weed populations around their property.” David says the value of having a commercial grain handling contractor do the seed cleaning lies in the contractor’s knowledge about how to set the machine up to achieve the best result. “The screens are expensive but it pays to use the right combination of screens to suit the grain and the weed spectrum,” he says. “It is probably not economic for a grower to invest in the large number of screens required to do the best job in all situations.” “Grading table gear does an excellent job to remove weed seeds too,” says David. “These machines are most commonly found at commercial grain packing and processing facilities and could be a viable option for growers to use in some situations.” Research conducted in Western Australia confirms David’s comments about the value of having seed cleaned by a specialist rather than using equipment, such as sieves or in-field rotary screens, that some growers use to clean their seed on farm. Economics of seed cleaning Growing seed for future planting needs to be a planned operation—start with clean seed, sow into a clean paddock, grow a competitive crop that suppresses weeds, keep the crop weed-free by taking action if individual plants survive treatment, harvest the best, cleanest part of the paddock, clean the seed hard and store it under optimal conditions. “Seed is very valuable and is worth investing in,” says David. “If you plant clean seed into clean paddocks the cost savings in time and herbicide will soon pay for the cleaning of the seed.” To determine how many weed seeds are present in a potential seed lot, collect a 1 kg sample and separate the crop seed from all other material. 100 weed seeds per kilo of cereal or pulse seed sampled equals around one weed per square metre when the crop is sown. A survey in Western Australia by the GRDC-funded Australian Herbicide Resistance Initiative 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. The AHRI survey found that the gravity table method of seed cleaning consistently produces the cleanest seed sample, reducing contamination to about 25 weed seeds per 10 kg. Sieves alone can bring the number down to about 150 weed seeds per 10 kg. For more information try these links Clean weed-free seed – don’t plant weeds When is clean clean enough?
Article
News

Fleabane control in the south and west

There are many hard to kill weeds, including flaxleaf fleabane, however one approach delivers consistent success – spray small weeds and use the double knock technique. At the end of grain harvest in the southern and western regions flaxleaf fleabane will be establishing and growing strong root systems ready to take up any soil moisture available over summer. Flaxleaf fleabane plants feature hairy leaf surfaces, thick cuticle and few stomata, a combination that affords the weed a natural tolerance to herbicide. Fleabane seedlings germinate throughout the spring and summer, making the timing of control very difficult. In South Australia fleabane seeds start germinating in late winter to late spring, but initial seedling growth rate is very slow. With suitable spray conditions being few and far between over summer, fleabane is able to establish and take advantage of any small falls of rain to produce up to 120 thousand viable light fluffy seeds per plant that disperse on the wind and in runoff water over summer and autumn. Weeds researcher Ben Fleet from the University of Adelaide says the timing and staggered germination of fleabane, coupled with the need to treat plants when they are small, is a combination that makes the weed very difficult to control with herbicides. “All flaxleaf plants have a natural tolerance to herbicides but they are much more susceptible to herbicide control when the plants are young, less than a month old,” he said. “While rosette stage plants can be easily killed with lower rates of glyphosate, once stem elongation begins a far greater dose is likely to be required to achieve similar results.” “In NSW and Queensland, glyphosate resistance has been identified in flaxleaf fleabane populations, indicating that while glyphosate has proven an effective tool on fleabane, increasing resistance will mean this herbicide will be less effective in the future.” In summer fallow, herbicide control trials at Bute and Pinnaroo in South Australia, robust rates of glyphosate provided the greatest level of control. Use of paraquat in a double knock herbicide strategy helped to achieve high levels of control, but only when the first herbicide application was capable of providing at least 60 per cent control in its own right. “Controlling fleabane in summer conserved 45 mm and 71 mm of soil moisture at the Bute and Pinnaroo sites respectively, as measured in April,” said Mr Fleet. Flaxleaf fleabane, melons, sow thistle, windmill grass and feathertop Rhodes grass have all been associated more with the northern region but in fact they are all weeds that perform well in zero and minimum tillage systems. As these practices are becoming more common in the south and west, so the associated weeds are becoming more of a problem, particularly in years with mild, wet spring and autumn conditions. “The mix of weeds present in a summer fallow varies dramatically between seasons in the southern region as these weeds respond to the prevailing seasonal conditions,” he said. “A few years ago, the combination of wet springs and good summer rainfall led to serious infestations of fleabane on many farms in South Australia. Then the subsequent run of dry spring and summers led to a decline in fleabane populations on farms to the point that researchers had difficulty in finding suitable trial sites.” Mr Fleet emphasised that the efficacy of glyphosate on fleabane varied considerably in different seasons. “For example, glyphosate alone applied at 2 L/ha provided a modest 55% weed kill in 2012 but gave 97% control in 2014. In all seasons a double-knock of paraquat after glyphosate treatment ensured a higher weed kill,” he said. Aside from herbicide controls, don’t underestimate the value of strong crop competition. Fleabane thrives along crop borders and in gaps that may appear within the crop. Mr Fleet said that while herbicide control can be effective, particularly when plants are treated at the seedling stage (rosette), it is also important not to underestimate the value of crop competition in the winter cropping phase. “Fleabane seedlings are highly sensitive to crop competition and any bare patches in a paddock provide an ideal environment for fleabane establishment,” he said. “Under moisture stress conditions in spring there tends to be extremely high seedling mortality.”
Article
News

It’s time for a Glyphosate Intervention

If you knew some folks were outside your house and planning a home invasion would you encourage them or do what you could to intervene? Of course you wouldn’t invite them in or give them the weapons they needed to wreck your home and steal your stuff. The problem is that weeds along roadways and fences are getting ready to invade crops all over the country, having been afforded the opportunity to train with the best herbicide available and now more and more of them have the weapon they need—glyphosate resistance. Weeds along roadways, fences and farm infrastructure are getting ready to invade crops all over the country, having been afforded the opportunity to train with the best herbicide available and now more and more of them have the weapon they need—glyphosate resistance. At a meeting of concerned growers, agronomists and researchers at the Crop Updates in Perth earlier this year, discussion centred on the fact that the weeds growing on non-crop areas in and around farms are without doubt the main source of glyphosate resistant weed seed. There is also no doubt that these weeds are ready and able to move into crop areas, as soon as the opportunity arises. The audience heard from Esperance grower, Chris Reichstein, who has brought glyphosate resistant ryegrass growing on a newly purchased property under control. Chris’ message was encouraging in that glyphosate resistance is manageable but it has placed a burden on his business that would have been avoided if better practices had been employed in the non-crop areas of the farm over the previous 15 or 20 years. Chris has used every tactic possible to reduce weed seed numbers on the farm, including rotation planning to make the most of crop and herbicide combinations, including swathing and croptopping, narrow windrow burning, chaff carts, autumn tickle and a triple knock strategy of two chemical applications followed with a competitive crop. Containing the problem is now a permanent part of his farming system. It is unrealistic to ‘ban’ the use of glyphosate along fences, roadways and around infrastructure, but it is clear that growers need to find other ways to manage these weeds without reaching for glyphosate as the first and only option. There are other options, albeit more difficult, time consuming or expensive but imagine how difficult farming the cropping area would be without glyphosate. Depending on the situation, some fenceline tactics to prevent seed set could be to use different herbicides and change the timing of sprays to target weeds when they are small, planting the crop right to the fenceline and then cutting the first round for hay, using a ‘slash and spray’ approach, cultivation and knife rolling—anything but glyphosate! Just last year a flood of evidence emerged, all pointing toward the imminent and widespread threat of glyphosate resistance: Sally Peltzer, DAFWA, released the results of a GRDC funded survey that sampled ryegrass from 175 paddocks, finding glyphosate resistance in 40% of them. John Moore, DAFWA, reported finding similar levels of glyphosate resistance when sampling trucks at CBH, Albany. Dr Michael Ashworth, AHRI, reported the first case of glyphosate resistance in wild radish. Adam Jalaludin, AHRI student, found a population of crowsfoot grass in Malaysia with resistance to glyphosate, glufosinate and paraquat. In NSW, glyphosate resistant sowthistle was confirmed and Queensland announced glyphosate resistance had been confirmed in sweet summer grass. Concerned agronomists raised the alarm as knockdown failures became evident in the field. Now is the time for action and the implementation of a new system for managing weeds in the non-crop areas of Australian farms.
Article
News

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.  
Article
News

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.
Article
News

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:
Article
News

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.”  
Article
News

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.
Article
News

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.
Article
News

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
Article
News

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.  
Article
News

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.