Creating stiff competition against summer weeds
With soil moisture at a premium, there is nothing spare to waste on summer growing weeds. With four of the most difficult to control summer weeds, feathertop Rhodes grass (FTR), awnless barnyard grass, common sowthistle and flaxleaf fleabane, now with confirmed cases of glyphosate resistance, the pressure is on to find effective non-herbicide control tactics. These weeds can produce 40,000, 42,000, 25,000 and 110,000 seeds per plant respectively. Other studies have found these numbers could be even higher, so every effort to reduce seed production is worthwhile. Dr Michael Widderick, is the lead DAF researcher in the mungbean and sorghum crop trials to better understand the agronomic factors that increase the crop’s competitive advantage over feathertop Rhodes grass and awnless barnyard grass. Various trials in mungbean, soybean and sorghum crops have consistently found that planting these summer crops in competitive configurations can reduce weed biomass and seed production while maintaining or increasing crop yield. The change in row configuration may involve set up costs to modify planting equipment but does not require an increase in seeding rate as the effect has been demonstrated using the same established populations for mungbean and soybean. For sorghum, the competitive edge comes through increased plant population rather than narrower rows. Along with narrowing the row spacing in mungbean and soybean, there are also benefits in early weed control. Keeping crops weed-free for the first three to six weeks seems to be a valuable rule of thumb to give crops the head start required to drive down weed numbers. Weeds that germinate in-crop after the 3–6 week mark are fewer in number and individual plants also produce less seed. As a non-herbicide control tactic, crop competition is very important in any integrated weed management program. With investment from the GRDC, researchers from NSW Department of Primary Industries, University of Sydney and Queensland Department of Agriculture and Fisheries are conducting trials to identify ways to increase the competitiveness of sorghum and summer pulses. In the 2017–18 summer sorghum was sown in trials using three row spacings (50, 75, 100 cm) and two crop densities (5 and 10 plants per m2). In a separate trial, mungbean plots were established using three row spacings (25, 50 and 75 cm) and two crop densities (20 and 35 plants per m2). Seed of feathertop Rhodes grass and awnless barnyard grass was spread at planting and the plots were irrigated to ensure optimal crop and weed emergence. With only one year of data from this trial so far it is difficult to make recommendations. Average seed head production in non-crop treatments was 1745 heads/m2 for feathertop Rhodes and 1525 heads/m2 for awnless barnyard grass. Growing either crop more than halved the number of weed seed heads produced, even in the least competitive configuration for the two crops. Row spacing in mungbean had a clear impact on weed seedhead production for both weed species. This effect has been demonstrated numerous times in a range of agronomic trials with mungbean. Narrowing row spacing to 25 cm reduced feathertop Rhodes grass seed heads to 32 plants/m2. For awnless barnyard grass, narrowing row spacing to 50 cm or less reduced seed heads to less than 10 per m2. Note: this represents one year of data only. In these plots, mungbean sown on row spacing 25 cm at low crop density (20 plants/m2) competed strongly with awnless barnyard grass (left) and feathertop Rhodes grass (right). In these plots, mungbean was sown on row spacing 75 cm at low crop density (20 plants/m2). The plot on the left was kept weed free while the centre plot shows limited suppression of feathertop Rhodes grass. Being a low growing weed, the level of infestation of awnless barnyard grass (right) is difficult to see in this photo. For sorghum it seems increased plant population had the best effect, significantly reducing weed seed head numbers for both weed species. Unlike mungbeans and soybeans, sorghum yields were reduced in plots with narrower row spacing configurations. At each row spacing, the higher plant density (10 plants/m2) treatment yielded more than the lower density plant population. In a separate trial, University of Queensland researchers confirmed that row spacing, not plant population, is the key driver to reducing weed growth in soybean crops. In soybeans, weed biomass was reduced by 89 per cent under narrow rows (25 cm) and 75 per cent under wider rows (75 cm) when the crop was kept weed-free for the first three weeks after planting. If weeds were controlled for the first six weeks, then weed biomass was reduced by 98 per cent under narrow rows and 88 per cent under wider rows. In weed-free plots there was a 20 per cent yield benefit in changing from 75 cm row spacing to 25 cm. This yield difference was 65 per cent in plots where weeds were introduced 6 weeks after planting and a huge 121 per cent higher when the weed infestation occurred three weeks after planting. Similarly, if a mungbean crop is kept weed-free for the first 3 weeks after planting, then the narrower row spacings of 25 and 50 cm saw a reduction in weed biomass. In both the 2015 and 2016 summers, the combination of keeping the crop weed-free for at least the first 3 weeks and planting on the narrower rows (25 or 50 cm rather than 75 cm) generated a yield increase of 159–197 per cent in 2015 and 198–223 per cent in 2016. Summer crops are an integral part of many farming systems and play an important role in an integrated weed management program. Many summer weeds only remain viable on the soil surface for a period of around 12 months so if a competitive summer crop is followed with a competitive winter crop and harvest weed seed control, there are more opportunities to drive down weed numbers in the soil seed bank. More resources: Giving summer pulses the competitive edge How can summer crops help drive down weed numbers?
Reducing the glyphosate resistant weed seeds in cotton fields
The Australian cotton industry has benefited enormously through widespread adoption of Roundup Ready technology, with close to 100 per cent adoption since 2010/11. A downside of the uptake of this technology has been the shift in the weed spectrum found in cotton fields. Department of Agriculture and Fisheries (DAF) researcher Dr Jeff Werth says growers have achieved better control of Cyperus sp. (nutgrass and other sedges), but surface germinating and glyphosate tolerant species, along with reduced control of vines and legumes have found the new cropping system favourable. Jeff Werth (DAF) collecting data at the patch eradication trial at Hermitage Research Facility, Warwick. The dense patches of awnless barnyard grass seen in this image are the glyphosate-only treatments. “This shift has taken years to occur and now we are seeing weedy patches establishing in cotton crops,” he said. “We have used crop modelling to show that managing these patches is effective in awnless barnyard grass and now we have field experimental results demonstrating that the industry’s best management practice weed control strategy works.” Dr Werth and the DAF weed research team designed an experiment to field-test the 2+2&0 (2 non-glyphosate tactics in crop plus 2 non-glyphosate tactics in fallow and no survivors) strategy in a dryland cotton system. They chose a dryland cotton field with a dense population of glyphosate-susceptible awnless barnyard grass (ABG) and used a low rate of glyphosate (250 g/ha Roundup Ready®) to simulate glyphosate-resistance with approximately 70% control of the barnyard grass each time glyphosate was used. The treatments applied were designed to compare ‘glyphosate only’ with the ‘2+2&0 strategy’ to see the effect on ABG emergence and seed bank. They also tested a few ‘eradication’ tactics, which were applied at three different times in the cropping season – 1. Early (Oct to mid-Dec), 2. Mid (mid-Dec to mid-Feb) and 3. Late (mid-Feb to March). The experiment ran for a four-year cotton-fallow-fallow-cotton rotation. Table 1. Example of control tactics used on Awnless barnyard grass comparing glyphosate only, to BMP and additional eradication treatments. Phase Treatment 1. Early season 2. Mid-season 3. Late season Glyphosate only Glyphosate (PRE) Glyphosate (OTT) Nil Glyphosate (OTT) Glyphosate (OTT) Best Management Practices (BMP or 2+2) Paraquat + Pendimethalin (PPPE) Diuron (Layby) Nil (Treatments 2-9) (Treatments 2-9) Additional Eradication tactics (Erad) Metolachlor (PRE) Metolachlor (PRE) Hand-hoeing (Treatments 3, 6, 7 and 9) (Treatments 3, 6, 7 and 9) (Treatments 5, 7, 8 and 9) “When glyphosate was used without applying any other weed control tactics, weed emergences were almost always higher than where multiple tactics were used,” said Jeff. “The most consistent tactic for reducing barnyard grass emergences was metolachlor applied six weeks prior to planting in the ‘Eradication phase 1’ treatments.” Pendimethalin applied at planting seemed to have little effect on the major flush of weed germination that usually occurs in spring, but did have some effect on later germinations. “Including residual herbicides in the weed control program can really reduce the number of weeds that emerge, and as a result, there is less pressure on post-emergence herbicides applied later in the crop,” he said. This simulation experiment also demonstrated that the 2+2&0 strategy was effective in driving down the weed seed bank, which is the ultimate goal of any integrated weed management program. Jeff said that it took three years to really see the differences between the two main treatments, so persistence is required if you don’t see immediate changes in weed numbers. Eradication treatments applied early in the crop season were also the most effective in driving down the weed seed bank. Table 2. Total Awnless barnyard grass emergence in each year of the experiment. Means with the same letters are not significantly different. Treatment Year 1 Year 2 Year 3 Year 4 Cotton* Fallow* Fallow Cotton* (plants m-2) 1. Glyphosate only 1118 d 316 b 87 b 118 d 2. BMP 176 bc 45 a 39 a 88 cd 3. BMP + Erad (phase 1) 116 ab 56 a 18 a 23 ab 4. BMP + Erad (phase 2) 257 c 27 a 34 a 26 ab 5. BMP + Erad (phase 3) 324 c 44 a 40 a 60 bcd 6. BMP + Erad (phase 1 and 2) 81 a 42 a 9 a 29 ab 7. BMP + Erad (phase 1 and 3) 129 ab 54 a 6 a 32 abc 8. BMP + Erad (phase 2 and 3) 191 bc 26 a 17 a 16 a 9. BMP + Erad (phase 1,2 and 3) 108 ab 43 a 8 a 11 a P-value <0.001 0.014 0.005 0.004 *Means back-transformed from Log(x+1) The time taken to see a decline in weed populations is related to the longevity of the seed of different weed species. In a cotton farming system small seeded species such as feathertop Rhodes grass, windmill grass, fleabane and sowthistle generally last in the soil for 2–3 years; larger seeded species such as awnless barnyard grass and liverseed grass last about 4–6 years and harder seeded species like bladder ketmia and peachvine last 6–10 years. Awnless barnyard grass produces a large quantity of seed if it escapes weed control tactics, resulting in patches of potentially resistant weeds in cotton fields. “It is reasonable to expect that the longer the 2+2&0 strategy is applied, along with early season eradication tactics, the greater the difference there would be compared to a glyphosate-only approach,” he said. “In years with multiple rainfall events across the summer, there would be increased benefit from employing early eradication tactics to avoid a potential build-up of the weed population. It is critical to ensure that survivors are controlled to prevent potentially resistant seed re-entering the soil.” The 2+2&0 strategy forms the basis of the Cotton Herbicide Resistance Management Strategy and is best applied in all cases to minimise the risks of resistance development. If a problem is detected early, the 2+2&0 can form the baseline response, and extra tactics can be incorporated to limit potential spread of the patch in the field, and drive down the seed bank.
Ask an Expert
How do you manage summer weeds without spraying at night?
Concerns are being raised about the practical implications of this for summer weed control programs. Mary O’Brien, a private consultant with extensive experience in managing spray drift, is keen to see growers fully adopt spray application practices that maximise herbicide efficacy and minimise off-target drift. Mary O’Brien says the ‘community drift’ that can occur when a number of applicators are each putting a small amount of product in the air at the same time can have very damaging effects on off-target sites. “The bottom line is that allowing spray to drift is like burning money,” she says. “Any product that doesn’t hit the target is wasted and the efficacy of the spray job is reduced, mildly resistant biotypes may survive as a result of low dose application and there is potential damage to sensitive crops and the environment.” “The difficulty is that many growers want to spray at night to cover more ground when conditions are cooler and potentially weeds are less stressed. Having a restriction on night spraying does restrict the time available to cover the areas required.” Having heard these concerns from growers across the country Mary keeps coming back to the fact that if there was a limitation to capacity at planting or at harvest, growers would scale up to get the job done in a timely manner. “Buying another spray rig or employing a contractor is an additional cost, especially after a couple of tough seasons, but I really think this is insignificant against the cost of losing key products and the resultant escalation in herbicide resistance to the remaining herbicides,” says Mary. “This problem is not confined to 2,4-D or even to herbicides. I recently spoke to a stone fruit grower who was forced to dump his whole crop after a positive MRL return for a fungicide he had never even heard of, let alone used.” What about just slowing down and lowering the boom during night spraying? Short answer: This, coupled with a good nozzle, will reduce drift but it will never eliminate it. Longer answer: The correct ground speed and boom height will have a large effect on the amount of product that remains in the air. The problem is that it only takes 1 per cent of the product remaining in the air to cause off-target damage. Once there are a few operators putting just 1 per cent of their product in the air at the same time, the amount of product quickly accumulates and can potentially be very damaging. Mary calls this ‘community drift’. Isn’t it better to spray weeds at night when it’s cooler? Short answer: Not really. Longer answer: Research by Bill Gordon showed that even if you keep everything else the same, night spraying can put at least three times more product in the air than daytime application, even if weather conditions are similar and there is no temperature inversion in place. The main difference between day and night is how the wind is moving across the landscape, rather than the wind speed. Under inversion conditions, the air moves parallel to the ground surface and this means that the product can move significant distances away from the target before coming to the ground. To achieve the best results through daytime spraying, applicators should focus on treating small, actively growing weeds. When there is good soil moisture, weeds are unlikely to be stressed even when the temperature is quite high. Temperature inversion conditions are more common at night and in the early morning. These conditions generate a laminar flow of air across the landscape allowing small droplets to travel many kilometres away from the target site before coming to ground. Can I use other products at night and just avoid using 2,4-D? Short answer: The current changes to 2,4-D labels has drawn a lot of attention but the problem is the same for all crop protection sprays – herbicides, fungicides and insecticides. Longer answer: Different products have different properties and some may work better at night but the problem is the sensitivity of some crops to certain products, such as 2,4-D. All products are tested for their efficacy and the label provides detailed information about the required spray quality and spray application conditions. Many products have explicit label instructions regarding wind speed, temperature inversions (or laminar flow) and night spraying. Given the high risk of drift at night, applicators need to be very confident that there is no inversion present, and weather conditions should be measured at least every 15 minutes to ensure wind speed remains above 11 kilometres per hour. An on-board weather station is the best way to monitor conditions. A visual demonstration using smoke to simulate the the lateral movement of small spray droplets when a temperature inversion is in place. What can I do to improve spray efficacy and avoid spray drift? Short answer: If you do just one thing – change your nozzle. Longer answer: All the factors that increase drift also reduce efficacy. To improve efficacy and reduce drift, use a better nozzle (larger spray quality) and appropriate water rates (matched to spray quality and stubble load), slow down and keep the boom low. Wind is required to push product downward and onto the target, and remember that the 3–15 km/h wind speed is for day time conditions only, this does not apply at night.
Using your harvester to destroy weed seeds
Collecting and destroying weed seeds as part of the harvest operation is recognised as the most efficient and effective way to implement harvest weed seed control (HWSC) within an integrated weed management system. Acknowledged as the ‘holy grail’ of the WeedSmart Big 6 tactics to manage herbicide resistance, HWSC was implemented on over 40 per cent of Australian grain farms in 2014 and adoption is expected to increase to 80 per cent by 2020. Chaff impact mill machines render the weed seed unviable, causing the destruction of over 95 per cent of the weed seed that enters the mills. There are currently six HWSC methods being used in Australia, all of which have been invented, adapted and adopted by Australian farmers. When choosing between these methods growers must consider the set-up cost, nutrient removal costs and labour requirements. Most agree that the ultimate HWSC tool would complete the weed seed control in one pass at harvest, retain all stubble and nutrients and not require any follow-up work such as marketing hay or burning chaff. There are currently two machines that meet these requirements – the iHSD (Integrated Harrington Seed Destructor) and the Seed Terminator. These two chaff impact mill machines render the weed seed unviable, causing the destruction of over 95 per cent of the weed seed that enters the mills. In 2017 harvest, both the iHSD and Seed Terminator machines were in commercial operation on farms around Australia and both experienced the teething problems that can be expected for new technology moving into the real-world. They have since been in field trials overseas – the Seed Terminator in Canada and the iHSD in France – where both machines completed around 200 hrs work without a hitch. Kondinin Group Manager of Research and Development, Ben White interviewed 20 growers using either the iHSD or Seed Terminator during the 2017 harvest and reported that their observations suggested both brands were achieving over 95 per cent reduction in seed viability. “Both types of impact mills ran into the same real-world problems of handling high flow rates of chaff, choking on green crop or weed matter and significant damage to the mills from any sand or soil that is picked up by the harvester,” he said. “Both machines also caused a reduction in harvester capacity of between 12 and 20 per cent in wheat, even though the harvesters had been remapped. This is a significant cost that growers must allow for through machine depreciation and base hourly operating costs, as more hours are needed to harvest the same area of crop.” Over 70 per cent of the growers that the Kondinin Group engineers visited had remapped their harvesters to improve the harvest capacity. Operators should note that chaff impact mill technology pulverises the entire chaff fraction, which generates significant levels of dust during the harvest operation. This means that more frequent machine clean-down may be required to minimise fire risk, as well as increased frequency of filter cleaning or replacement. “Although the problems outlined here are important, they are all likely to be resolved as this technology matures in the commercial world,” said Ben. “There is enormous interest in this method of harvest weed seed control and this will ensure that the problems are solved.” Seed Terminator, WA. Australian Herbicide Resistance Initiative’s cost comparison of HWSC methods suggests that the chaff impact mills cost $16-17/ha compared to $22/ha for narrow windrow burning and $6-7/ha for chaff tramlining and chaff lining, depending on crop yield and area. In addition to the weed control benefits achieved through the use of any HWSC method, the chaff impact mill option also reduces crop volunteers. Research into the efficacy of impact mills is an ongoing process, particularly while the two types of machines are undergoing rapid developmental changes. Recent research by Michael Walsh (AHRI and Sydney University) with help from John Broster at Charles Sturt University (CSU), shows that despite the problems that have been experienced with the new machines, iHSD mills are passing the research tests with flying colours. Their research concluded that: The iHSD achieved 96–99% destruction of the seeds of 11 weed species when processed in wheat chaff. Weed seed destruction varied by about 10% depending on crop chaff type – ryegrass seed kill was greatest in lupin (98%) > wheat (92%) > canola (90%) > barley (88%). Weed seed kill dropped by about 4% when chaff moisture increased above 12%. Weed seed kill increases with mill speed and 3000 rpm is the accepted optimal speed for the iHSD. SAGIT funded research conducted by Trengove Consulting in 2017 found similar results for the Seed Terminator: Ryegrass weed seed kill was 93% at 2250 rpm and increased to 98% or greater at normal operating speeds (2500–3000 rpm). Greater than 99% control of several other species including wild radish, brome grass, wild oat, bifora, bedstraw and tares. Increasing chaff flow rate (harvest rate) did not reduce control of these species. Samples analysed in 2018 by the Weed Science Research Group, at The University of Adelaide showed that the Seed Terminator could consistently kill 96% of weed seeds when operated at 2750 rpm. These kill rates refer only to the weed seed that enters the impact mills. To achieve high level of weed control it is essential that all efforts are made to ensure the weed seed enters the front of the header and is then separated and directed into the mills. iHSD, WA. Timing, cutting height, operating speed, weed and crop type and harvester set-up all play a part in achieving maximum harvest weed seed control. As is recommended for all HWSC methods that treat the chaff fraction, separation of the chaff and straw through the harvester often requires the addition and fine-tuning of a baffle plate to achieve greater efficiency. Setting up and operating harvesters to achieve the best weed control outcomes often involves some modification and compromise. By taking the time to get things right, growers usually find that they end up with more grain in the bin and a better sample, making the extra effort worthwhile. WeedSmart has secured the rights to distribute an electronic version of Kondinin Group’s Research Report: Residue Management at Harvest, which is available in the Resources section of www.weedsmart.org.au. WeedSmart encourages growers and advisors to support Kondinin Group’s independent research through subscription to Farming Ahead.
Trevor Syme, Bolgart WA
A few years ago they began an extensive liming and clay delving and spading program across 50 per cent of the 3500 ha cropping area to improve the water holding capacity of the natural non-wetting sands. With 75 per cent of the affected area now treated Trevor is looking forward to having this expensive but very beneficial operation behind him. Treating the non-wetting soils has assisted with weed control through 40 per cent higher yielding crops, more even crop germination and better efficacy with the pre-emergent herbicides. “Treating the non-wetting soils has assisted with weed control through 40 per cent higher yielding crops, more even crop germination and better efficacy with the pre-emergent herbicides,” says Trevor. “It has also enabled us to grow canola in paddocks that were previously not an option and crops seem to finish better and are less prone to frosting.” They have also achieved good results building soil organic matter with brown manured cereal rye crops. Trevor has trialled summer crop brown manuring too but the results over three seasons were unreliable and he has decided to look for other options to reduce evaporation over summer and reduce the need for summer weed control. The Symes’ farming system is 100 per cent controlled traffic and stubble retention with a long winter crop rotation of lupins, wheat, canola, wheat, barley, with brown manured cereal rye grown on the soils not suited to canola. Information on the summer fallow spray program The summer fallow spray program involves 2,4-D ester, triclopyr and glyphosate to control melons, caltrop, fleabane, sowthistle and volunteer cereals. For the last 5–6 years Trevor has applied a double knock of glyphosate followed with paraquat in preparation for sowing. “We try hard to get the timing right and target the right size weeds with the double knock,” he says. “We also avoid mixing a pre-emergent in with the paraquat because the aim is to get the paraquat on weed leaves using a high water rate and fine droplet size, whereas the aim with the pre-emergent is to achieve even coverage of the soil. Doing the pre-emergent spray separately costs us more but I believe it is worth using the right boom set up for the two jobs.” “Rotating crops and herbicide modes of action, and using the double knock tactic, are critical to our weed management program,” he says. “RR canola, Clearfield barley and lupins all have a fit in the crop rotation and allow us to rotate herbicides effectively. The imi-tolerant barley has enabled quite effective control of brome grass and we croptop the canola with glyphosate.In the lupins we are using a pre-emergent propyzamide application followed with clethodim in-crop and finish with a croptopping spray of paraquat.” Trevor is finding that weed control in the lupin phase is more critical than it used to be, but the value of lupins in boosting yields in the following wheat crop motivates him to look after the lupin crops, plant into clean paddocks and do everything he can to keep weed numbers low. The Symes have had good success with high biomass canola on sandy soils where multiple germinations of wild radish are the norm. They usually plan their crop and herbicide program with their agronomist at the end of September and then revise it in February or March. Trevor is going away from the current move toward narrow row spacing and disc seeders. “We are changing back from a disc seeder at 305 mm spacing to tines on 381 mm with a split boot to sow cereals in paired rows and canola and lupin in single rows,” he says. “We are working on the idea that less rows equals less disturbance equals less weeds in a controlled traffic system. The slightly wider row spacing also makes it easier to handle the stubble load accumulated over several years and allows us to inter-row sow.” He has found that high tillering wheat varieties, such as Magenta, offer an alternative way to increase crop competition through additional shading of the inter-row. In the 2015 harvest the Symes added a chaff deck to their weed control progam, directing all the chaff, and weed seeds, into the harvester wheel tracks. Trevor harvests weedy paddocks first to maximise the value of harvest weed seed control and has found the chaff deck easy to use and results in relatively few weeds surviving in the tramlines. The biggest benefit of the chaff deck is that weed seeds are collected across the whole farm every year, and concentrated in the inhospitable tramlines. “The biggest benefit is that we can collect weed seed across the whole farm every year where previously we have only really been able to do narrow windrow burning in the canola phase. Now at harvest the whole job is done, with no need to return to burn.” “It is great to know where the weeds are and they are dumped on a hard, inhospitable surface,” he says. “Any escapes are easily collected at the next harvest. We also have a back-up plan to use a shielded sprayer to weeds in the tramlines, but we really want to avoid using this option.” “In fields with high weed numbers in the tramlines we have tried simply driving a tractor, without any implement, along every tramline to achieve a crimp-rolling effect. This seems to have been a cost-effective way to stop seed set in weedy tramlines.” In fields with high weed numbers in the tramlines Trevor has tried simply driving a tractor, without any implement, along every tramline to achieve a crimp-rolling effect (right). Annual ryegrass, wild radish and brome grass are the main weed challenges on the Symes’ property. Trevor has done some herbicide resistance testing but generally takes the approach that all weeds present are likely to have some level of resistance. “The key is to keep weed numbers low so we take care to spray when weeds are small and avoid frost windows and high temperatures when the sprays are less effective,” he says. “We also use quite high water rates – 80 L/ha for most post-emergent herbicides and 120 L/ha for pre-emergent herbicides and paraquat – and have two sprayers so we can cover as much ground as possible when the conditions are right.” “Fencelines and fire breaks are a weak point in our farming system as a source of glyphosate resistant weeds,” he says. “We have removed as many fences as possible, now that we don’t run any livestock, and are actively looking for an alternative herbicide that is not used in crop to manage weeds on the firebreaks.” Trevor takes considerable care when choosing seed production paddocks, ensuring weed numbers are low to start with and then treating the paddock as a nursery. He harvests the seed crops early and cleans the seed prior to planting.
Lance Wise, Bowenville, Qld
Lance and Fallon Wise and Lance’s parents, Murray and Janette crop 1600 ha and run cattle on 45 ha of non-arable rocky ridges. The locality and soft black plains enable the Wises to grow a range of crops including sorghum, mungbean, chickpea, barley and wheat, along with the occasional crop of faba bean, millet and canola. In an effort to reduce their reliance on glyphosate and overcome some of the disadvantages of long-term no-till farming, the Wises have reintroduced light cultivation and are moving toward more targeted application of glyphosate and other herbicide products using an optical sprayer. “Our usual rotation is a legume followed by a cereal, such as mungbean, to sorghum and chickpea to wheat or barley,” says Lance. “We use either a short fallow or double crop to change from a winter to summer crop program and aim for at least one crop every 12 months from each paddock.” Having been no-till farming for 25 years the Wises have seen the weeds transition to those species that proliferate in the absence of cultivation; weeds like fleabane, urochloa, feather top Rhodes grass, cow vine and bladder ketmia. In an effort to reduce their reliance on glyphosate and overcome some of the disadvantages of long-term no-till farming, the Wises have reintroduced light cultivation and are moving toward more targeted application of glyphosate and other herbicide products using an optical sprayer. Nine years ago they had success using the Kelly disc chain to manage urochloa on their less well-structured red earth soils. More recently they have used this implement to target herbicide tolerant feathertop Rhodes grass and fleabane on their main black clay soils. “We are using a chemical / tillage double knock to good effect on feathertop Rhodes grass in the fallow,” says Lance. “We apply glyphosate and then follow up five days later with the Kelly chain, which does a terrific job of pulling out sick, dead and small plants at an operation speed of 11 to 12.5 km/hr.” “The same system works well on fleabane too, pulling up plants with foot-long roots from soft soil, although a higher rate of glyphosate is required. It doesn’t work well for weeds like prairie grass that have deep, fibrous root systems.” The Wises have found the chemical / tillage double knock to work well on feathertop Rhodes grass and fleabane. Used in reverse order, Lance has found the light cultivation is an effective way to stimulate germination after a poor sorghum crop to sprout volunteers and then spray out the crop. Along with the benefits of partial stubble incorporation on soil microbial activity and ease of sowing, Lance says the two short chains in the middle fill in the 3 m wheel track to even out the paddock, avoiding the need to do extra wheeltrack renovation operations. About the Kelly chain “We also use the Kelly chain to incorporate pre-emergent herbicide after sowing to a maximum depth of 2 cm. This does not disturb seed, which is all sown at least 4 cm deep with a presswheel, and the soil is moved sideways without destroying the cracks in the soil or drying out the profile,” he says. “Weed seed is not buried deeply so it doesn’t come back to haunt you years later.” Lance avoids using the Kelly chain more than once in a season on the red soils, which can get very dusty and are prone to hardsetting on the surface. At the end of harvest Lance and Murray assess the stubble load and weed pressure in each paddock. They usually spray glyphosate after a rain event and either double knock with the Kelly chain or spray paraquat through their Weedseeker optical sprayer. After using the Kelly chain, Lance follows 30–45 days later with the Weedseeker rig to clean up any survivors. “The Weedseeker is a new fallow option for us and means that we can treat weeds that we might otherwise ignore, apply higher rates, and use more expensive products to control small areas or patches of weeds,” says Lance. “The 36.6 m boom carries 96 sensors so there are not many weeds that go undetected in the fallow.” At the end of last year, the Wises started sub-soil ripping to a depth of 35 to 40 cm on 75 cm spacing to increase water capture and break up the sub-soil compaction to improve crop growth. Six weeks ahead of planting they apply the final glyphosate spray and then add fertiliser, which they incorporate with the Kelly chain, with the added benefit of removing any weeds present. Liquid fertiliser applied at seeding promotes early seedling vigour and growth, which gives the crops a competitive advantage over weeds. They plant using a Tobin planter that achieves a good even strike in stubble, starting on the red soils as soon after rain as possible, then moving onto the black soils. Pre-emergent herbicide is applied after sowing legume crops and incorporated using the Kelly chain. Herbicide is applied in crop as well as for desiccation purposes in sorghum, mungbeans and chickpea. Being a spray contractor, Lance has also invested in an air boom on his sprayer that enables him to have much greater control of droplet size to match the environmental conditions, while also covering a larger area in a day. He says the elliptical cone delivers spray in both a forward and rear motion to achieve better coverage, even at lower water volumes. The controls in the cab allow the operator to adjust the spray quality from fine to extra course without changing nozzles on the boom and there is no need to have all the different nozzles to suit different conditions and products. The Wises operate a 12 m controlled traffic system and plant all their crops on 375 mm row spacings. Lance has increased the planting rate in sorghum from plants 40 cm apart in the row to 25–30 cm apart to quickly to shade the interspace and suppress weed growth.
Krui Pastoral Co, Condamine, Qld
East-west sowing between shade lines Half an hour west of Condamine on the western Darling Downs, Jake and Felicity Hamilton work with Jake’s father to farm 4500 ha of brigalow scrub, which was originally cleared for cattle grazing in the decades since 1975. Although the cattle are all gone now, the Hamiltons have maintained the shade lines of native vegetation left when the property was cleared and which occupy about 10 per cent of the farm’s area. Jake says the thick stand of buffel grass in the shade lines prevents other weeds from establishing and the buffel doesn’t move into crop areas. Most of the fencelines are also timbered, with the low soil moisture keeping a lid on weeds. Jake and Scott Hamilton, are well aware of the impact of herbicide resistance on their farm near Condamine, Qld. “When the farm was cleared, the shadelines were left running east west to maximise the shading effect for the livestock and now we are cropping east west in fairly large, square paddocks,”says Jake. “We are now taking advantage of the shading effect on the inter-row to suppress weed germination and growth.” Crop rows run east-west, parallel with tree lines left when the property was cleared, to provide shade for stock. Growing wheat / chickpea / wheat, with few opportunities for summer cropping in recent years, Jake has been working hard to keep on top of herbicide resistance in summer growing species including barnyard grass, liverseed grass, button grass and feathertop Rhodes grass. Not being able to grow summer crops on a regular basis, Jake has implemented a robust fallow management program to keep these weeds under control. “We try to double knock the glyphosate applications with paraquat, especially if the weed burden is high, there are large weeds present or weeds are not dying like they should,” he says. “And we always use full label rates to avoid herbicide resistance.” Jake regularly employs casual labourers to go around the farm on the ‘Gator with the spot spray rig to deal with any individual weed survivors, or if there are weedy patches they use the 6 m boom on the ‘gator’. Spot and patch spraying is time-consuming but very worthwhile. “Spot spraying summer grasses is quite time consuming but incredibly effective and cost efficient,”he says. “We also employ an agronomist to visit the farm once a fortnight to assist with monitoring and planning the weed control program.” “We know we are losing Group M [glyphosate] and can see resistance to Group A [grass selective] chemistry on button grass, which will leave us with very few herbicide options. We rotate crops as best we can so we can use different methods of weed control to try and break the resistance.” Button grass is proving to be quite a challenge to control with herbicide. Following two reasonable winter seasons, the 2016–17 summer was too hot for summer cropping, with no rain falling between September and February. Jake took this opportunity to do more laser levelling to remove the melon holes that are characteristic of brigalow scrub soils. Levelling brings about an immediate increase in yield and more even crops. “We purchased a second hand Caterpillar D11R and fitted it with TopCon GPS,”says Jake. “With the dozer we are able to cut 10 cm below grade on our first pass, which creates a good blend of topsoil with any exposed subsoil to avoid ‘scalping’the paddock.” Every four years the Hamiltons also incorporate 10 t/ha of manure to a depth of 15 cm and plan to utilise variable rate technology to apply manure to ameliorate some areas of soil fertility decline. “After using a chisel plough for several years to incorporate the manure, we are moving toward a program of deep ripping and deep application of phosphorus fertiliser to a depth of 40 to 50 cm, on 50 cm spacings,”says Jake. Since 2001 the farming system has been controlled traffic with 12 m bays, to suit 36 m sprayer, 24 m planter and 12 m header. Their new planter is configured for 375 mm (15″) spacings for wheat and barley, 750 mm (30″) for chickpeas, faba beans and mungbeans and 1500 mm (60″) sorghum and cotton. Jake also uses high seeding rates to maximise crop competition, along with their efforts to improve overall soil fertility and boost crop competitiveness. Although there are some risks associated with the short crop rotation Jake says residuals are doing a good job controlling weeds in-crop, with no late germinations evident. “We use residuals plus picloram and aminopyralid for fleabane control in wheat,” he says. “In chickpea we apply simazine and Balance and follow with an in-crop application of a Group A herbicide.” “If there are weeds present in-crop they usually don’t seed before harvest,” he says. “Black oats is a potential problem though if there is a spray miss.” They also apply pre-emergence herbicides Balance + Flame + diuron in some paddocks to keep them clean over summer while leaving their summer cropping options open in other paddocks.” The Hamiltons store planting seed on farm and grade all their seed through a mobile grader on the Easter long weekend, aiming to achieve a good clean sample –99 per cent purity. Jake spreads their frost risk by planting 50 per cent of the wheat area to Gregory in early May then sowing the chickpea area the following week. The remaining wheat area is sown later to Suntop or Crusader. After suffering severe frost damage in late August 2017 the Hamiltons changed their planting schedule to reduce their frost risk. Jake says late frosts can be a problem in the Condamine area and can badly affect chickpea crops if the temperature drops to zero or below during flowering or podding. “We aim to have all our wheat planted between 7 and 21 May and then plant chickpeas after that,”he says. “Our new planting equipment has superior breakout force, compared to our old machine, which allows us to plant chickpeas to a depth of 200 mm (8″). Planting at this depth delays seedling emergence until after the first week of June, pushing the flowering window back a fortnight, closer to the warmer weather of spring.” “Chickpea makes a huge difference to our farming system with better wheat yields, less fertiliser and softer soil.”
Confirmed resistance to the double-knock tactic in tall fleabane
For weeds that have a natural tolerance to glyphosate, the double-knock has provided growers with an excellent tool to take two swipes at weeds like fleabane, sowthistle and feathertop Rhodes grass and achieve a greater level of control. NSW Department of Primary Industries weeds researcher, Dr Md Asaduzzaman (Asad) has uncovered disturbing evidence of double-knock resistance in tall fleabane (Conyza sumatrensis) samples collected during weed surveys funded by the Cotton Research and Development Corporation (CRDC). NSW Department of Primary Industries weeds researcher, Dr Md Asaduzzaman (Asad) has uncovered disturbing evidence of double-knock resistance in tall fleabane (Conyza sumatrensis) samples collected during weed surveys funded by the Cotton Research and Development Corporation (CRDC). “Our surveys in 2016 and 2017 showed that cotton fields were generally weed-free but herbicide resistance is building in weeds along farm roadsides, drains and channels and around infrastructure,” he said. “We identified two tall fleabane biotypes that have resistance to glyphosate, paraquat and the double-knock tactic of an initial glyphosate application followed with an application of paraquat 7 days later.” The rate response analysis showed that one of these biotypes is 4.9 times more resistant than the susceptible biotype, requiring 2.5 L/ha Paraquat-250 to kill 50 per cent of the plants from the resistant population compared to just 0.5 L/ha to achieve the same result in the susceptible population (see Table 1). While this level of resistance is generally considered ‘moderate’ it is clear that resistance is building and must be taken very seriously given the importance of the double-knock tactic in most cotton and grain production systems in Australia. Table 1 Resistance levels of tall fleabane screened against paraquat, glyphosate and glyphosate + paraquat (R-resistant > 50% survival; DR-developing resistance < 50% and > 20% survival and S-susceptible < 20% survival) Tall fleabane biotype % Plant survived under Paraquat-250 @ 2 L/ha Glyphosate-540 @ 1.2 L/ha Glyphosate followed by Paraquat (Double-knock) TFB01 >75 100 75 TFB02 75 75 75 TFb-Suscept 0 0 0 These two populations, collected near Nandi, Queensland and Coleambally, NSW, are the first paraquat-resistant tall fleabane to be identified in Australia. Resistance to paraquat in this species has previously been recorded in Japan, Sri Lanka and Taiwan. Location of confirmed cases of double knock resistance in tall fleabane. “Although the tall fleabane plants from these two populations showed signs of herbicide damage, such as narrowing of leaves and slow growth, when the double-knock was applied, they were able to survive and produce seed,” said Dr Asad. “This species produces a large quantity of seed, germinates quickly and the seed can travel over 10 km in the wind so dispersal of paraquat / glyphosate resistance traits will be impossible to contain.” Tall fleabane seedlings 28 days after the double knock (glyphosate + paraquat) tactic was applied. This discovery makes tall fleabane the second species in Australia to have confirmed resistance to both glyphosate (Group M) and paraquat (Group L), the first being a population of annual ryegrass identified in Western Australia in 2013. Having demonstrated resistance to the dual application of these herbicides in the otherwise effective double-knock tactic is cause for great concern. Weed populations take longer to evolve resistance to paraquat and glyphosate compared to some other modes of action, but it will happen after years of regular applications without survivor control. Like other fleabane species, tall fleabane is susceptible to crop competition but flourishes in poorly competitive, wide-row crops such as dryland cotton. Combatting herbicide resistance and keeping weed numbers low will require the implementation of a wider range of weed control tactics rather than relying heavily on the double knock tactic. “Growing more competitive crops and using a wider range of pre- and post-emergence herbicides and strategic tillage will help manage this weed,” said Dr Asad. “Above all is the need to monitor and remove any survivor weeds in line with the cotton industry’s weed control strategy of ‘2 + 2 and 0’ that recommends two non-glyphosate tactics in-crop plus two non-glyphosate tactics in the fallow and zero survivors.” In other research Dr Asad is testing the opportunities for cotton growers to use cover crops to create additional opportunities for herbicide rotations, run down the seed bank and delay the adaption of weed populations by reducing the frequency of single modes of action herbicide use. Paraquat resistance has previously been confirmed in 10 species in Australia, including flaxleaf fleabane (Conyza bonariensis). Other resources Resistance risk to knock-down herbicides on irrigated cotton farms Protecting knock-down herbicide options What are the herbicide options for the summer fallow
Is weed seed control an option for managing northern region weeds?
with Dr Michael Walsh, The University of Sydney Harvest weed seed control (HWSC), is a key component in the WeedSmart Big 6 tactics for managing herbicide resistance on grain farms. In the northern region there has been some scepticism surrounding how effective HWSC will be in capturing seed from common weeds in the region. Dr Michael Walsh, Director of Weed Research at The University of Sydney is a pioneer of harvest weed seed control research and is convinced that the tactic can be effectively deployed against northern region weeds. “The concern people usually have is that several key species in the north start shedding seed before the winter harvest,” he says. “Pre-harvest shedding does reduce the impact that HWSC can have on the seed bank of some species, but there is also solid evidence that the harvest operation can collect a significant amount of seed even if the seed shedding process has begun.” “Even in weeds such as sowthistle where the seed is light and wind borne, not all the seed in each seed head matures at the same time. This means that while some might be lost, the immature seeds can be collected and destroyed using any of the harvest weed seed control tools.” Dr Walsh says chickpea crops are a great place to start with HWSC because the crop requires a low harvest height, which increases the amount of weed seed that is collected, and many crops are desiccated prior to harvest, which may assist with seed retention in some weed species. “The concept of harvest weed seed control was invented in Australia in response to herbicide resistance, and has been adopted by about 50 per cent of grain producers nation-wide,” says Dr Walsh. “The idea is now being adopted internationally and is proving beneficial in driving down the seed bank of many weed species.” What northern weed species are the best candidates for HWSC? Short answer: African turnip weed, turnip weed, wild oats, annual ryegrass, feathertop Rhodes grass, sowthistle and bladder ketmia. Longer answer: These species are rated as very high to intermediate for seed retention at harvest. This means that at least 20 per cent, and up to 100 per cent, of the seed is present on the plant at harvest and able to be collected through the front of the header. Once in the header, destruction of the seed is almost guaranteed through impact, burning or breakdown, depending on the HWSC method used. What about flaxleaf fleabane and awnless barnyard grass? Short answer: Seed retention of these two species at harvest is highly variable. Longer answer: Both flaxleaf fleabane and awnless barnyard grass have a wide range of seed retention at harvest. Ranging from less than 20 per cent to over 90 per cent, the impact of HWSC on the seed bank is not a sure thing, but in some years could be very effective. Which HWSC method is best? Short answer: All are equally effective at reducing the weed seed bank. Longer answer: The HWSC methods currently available to growers are narrow windrow burning, impact mills, chaff lining, chaff tram-lining, chaff carts and bale direct. All except the impact mills have some level of nutrient removal or concentration. Narrow windrow burning and chaff carts usually involve a burning operation the following autumn and the bale direct system relies on a market or on-farm use for the hay. The impact mills, bale direct and chaff cart systems require sizeable investment and harvester modification while the other systems are very cheap and relatively easy to set up. All HWSC methods are equally effective at reducing the weed seed bank. The chaff tramlining system shown here delivers the chaff component of the crop residue onto the tramlines where it is left to decompose over time, killing much of the weed seed present. How often does HWSC need to be done to be effective? Short answer: The more the better but it doesn’t have to be every year in every paddock. Longer answer: Long term focus paddocks in WA have shown that HWSC every second year, in addition to in-crop herbicide applications, will consistently drive down the weed seed bank to very low levels. Within a crop rotation many growers choose to implement HWSC in certain crops. For many, the break crops are the preferred crops due to lower levels of stubble, and for pulses, lower harvest heights.
Bruce family, Alford SA
Keeping pressure on brome grass with HWSC Brothers Gary, Paul and Bronte Bruce farm at Alford on the Yorke Peninsula, SA have used harvest weed seed capture as an important tool in their weed management program to bring down grass weed numbers in their continuous cropping business. For the last 15 to 20 years the Bruce family has followed a 3-year rotation of wheat – barley – legume, having exchanged field peas for lentils in the legume phase in recent years. They found that producing export hay on grassy paddocks was a very effective way to manage grass weed seedbank, to the point where they had only one paddock of hay in 2016 and no hay in 2017. Gary Bruce, together with the family’s agronomist Chris Davey, YP-AG sets out a plan for the season, including our weed management program, with different strategies used depending on whether there is a wet or a dry start. “Hay production is hard work and now that we don’t have much of a grass weed problem we are taking hay out of the rotation for a while,” says Gary. “The hard work was certainly worth it in terms of regaining control over herbicide resistant weeds on the farm. Now we’d like to keep more crop residue on the paddocks to improve the hardsetting nature of the soil here.” Having used a chaff cart for many years, the Bruce’s were well aware of the benefits of capturing weed seed in the chaff stream but Gary was very interested to hear HWSC advocate and WA grower, Ray Harrington, speak at a field day about chaff lining. In 2017 harvest they used chaff line chutes on two headers for the first time. As usual they learnt a lot in their first harvest and have plans to make even better use of the system this season. Gary is very aware of the fact that there is very limited research on the long-term impact of chaff lining on weed management. “Our farm is partially set up for controlled traffic with 12 m and 36 m gear so the chaff line ends up on a spray track every third run,” he says. “We found starting the harvester on a spray track at the edge makes the best use of the wheeltracks. If we go to a full CTF system we will probably change to using a chaff deck system but the chaff lining chute is certainly a cheap and effective way to confine weeds to a small area of the paddock while also retaining the stubble.” Gary’s farm is partially set up for controlled traffic with 12 m and 36 m gear so the chaff line ends up on a spray track every third run. So far they have found using the chaff lining chute is a cheap and effective way to confine weeds to a small area of the paddock while also retaining the stubble. HWSC and late germination Brome grass is the most problematic weed on the Bruce’s farm with limited options for control in the cereal phase. There are limited chemical control options to kill early germinating brome grass before seeding and so Gary relies on HWSC to take care of late germinating cohorts. They recognise that hay making has played an important part in keeping this weed in check and acknowledge this could be more difficult if they get out of hay production altogether. All crops are sown to achieve greatest crop competition possible using 25 cm row spacing and cultivars that are well suited to the different soil types. Two-thirds of the farm is inter-row sown while paddocks with hardsetting topsoil generally follow the same furrow as the previous year. As the soil improves through increased residue retention Gary hopes most of the farm will eventually be sown in the inter-row. Generally they find, Scepter wheat yields better than Mace, Compass barley produces the most straw, PBA Bolt lentils give salt and boron tolerance where it’s needed and PBA Hurricane lentils offer Group B herbicide tolerance. “Early in April we usually speak with our agronomist, Chris Davey, about a plan for the season, including our weed management program,” says Gary. “For example, wet and dry starts need different strategies such as ensuring there is sufficient moisture to activate metribuzin and propyzamide before sowing lentils. We have also experienced more summer rainfall recently and often need to do two sprays for summer weed control.” Other resources: Implementing the WeedSmart Big 6 on the Yorke Peninsula
Edwards family, Port Broughton SA
Stacking weed control tactics for maximum effect Farming on the sand hill swales near Port Broughton on the Yorke Peninsula, Pete Edwards is doing everything in his power to stop herbicide resistance in brome grass and wild radish. “We take a zero tolerance approach to escapes, particularly with brome grass, and have used a chemical fallow in areas with high brome numbers,” he says. “It’s a case of ‘short term pain for long term gain’ and even after a chemical fallow we will chase any survivors by hand rouging or spot sprayer. Keeping on top of brome survivors has certainly paid off and we have seen numbers decline.” L-R: Tim Edwards, Chris Davey (YP-AG) and Peter Edwards. Chaff carts have served a purpose but their time on the Edwards’ farm is limited and this harvest they will most likely introduce a chaff deck system to replace the chaff cart. In wheat Pete has had good results with non-imi chemicals such as Avadex + Sakura and Avadex + Boxer Gold, in conjunction with narrow windrow burning, which helps manage the stubble and maximises the efficacy of these more expensive herbicides. “There are very few options for wheat so it is essential that we keep pressure on brome numbers in our other crops and also give the group B herbicides a rest to help preserve the imi-tolerant crop options,” he says. “We are only a few applications away from serious resistance issues with fop and dim chemistry. When patches of weeds are not killed by our normal herbicide applications we go back and apply high rates of clethodim to achieve 95 per cent kill, and then go back again to hand rogue any survivors.” Pete is also mixing fops and dims such as Select, Verdict and Factor and the Intervix brew to extend the life of these modes of action. He has seen the value of including adjuvants such as Supercharge for Factor and ammonium sulfate to maximise the impact on hard-to-kill brome grass. The Edwards have installed a digital weather station on their farm that also provides local data to ten other growers who subscribe to access the data. Having access to local, real-time weather information, including automated Delta T calculations, means that Pete and his neighbours can avoid frosty and dewy conditions and minimise spray drift, making every application as effective as possible. When collecting seed for herbicide testing Pete looks specifically for plants that are stunted or deformed as they are likely to be indicator individuals of what might be happening in the paddock and the results help him to plan ahead with chemical choices. The Edwards family have used chaff carts for 12 years and through extensive testing have proven that operating at a slower speed really does capture more weed seed. Rather than dropping small chaff piles across the paddocks the Edwards build large chaff dumps about 200 m apart. In addition to the chaff cart, Pete has designed a narrow windrow chaff management system of his own that drops the straw on the ground and places the chaff on top. “We did conventional narrow windrow burning 10 to 15 years ago and had several years where the windrows got wet and didn’t burn the weed seeds effectively,” he says. “Putting the chaff on the top of the narrow windrow means that even if they get wet the straw underneath will still give a good hot burn to destroy the weed seed.” Pete has designed a narrow windrow chaff management system of his own that drops the straw on the ground and places the chaff on top to give a good hot burn to destroy the weed seed, even if the windrows get wet. Narrow windrow burning is done mostly in the wheat paddocks with a known brome grass history. In recent years Pete has achieved very good results using his modified narrow windrow burning system in paddocks with very high brome and ryegrass numbers. The main disadvantage of narrow windrow burning is that it removes all the crop residue. Chaff carts remove between 10 and 25 per cent of the crop residue but the rest is spread on the paddock and has a dual benefit of suppressing weeds and conserving moisture. Pete says the extra soil moisture can save a crop germination in a year with a dry start. Even so, nothing can replace narrow windrow burning completely in very high weed pressure situations so Pete will continue to use his modified narrow windrowing chute when necessary. Chaff carts have served a purpose but their time on the farm is limited and this harvest they will most likely introduce a chaff deck system to replace the chaff cart. Pete sees some advantages of the chaff deck system over chaff lining, such as less dust off the wheel tracks during spray applications and not having any piles of chaff impeding sowing. Pete reckons the iHSD will revolutionise harvest and weed seed control and thinks there could be opportunities for contractors to invest in iHSD machines to assist growers by harvesting their weediest paddocks. “Even under best operating conditions the chaff cart puts 50 per cent of the brome grass seed in the cart, 25 per cent on the ground and 25 per cent goes over the rotor and into the bin. The suction system of the iHSD reduces weed seed losses over the rotor making it a more efficient option,” he says. Pete follows a 5-year rotation of wheat, barley, lentil, wheat, lentil in large, 100–200 ha paddocks. He sows all crops on 25 cm (10″) row spacing at high seeding rate for increased crop competition and, where practical he sows paddocks east-west to gain better weed control.To improve soil fertility, chicken manure is applied at a rate of 3 t/ha every three years on paddocks that need it; often ahead of wheat. Deep ripping on the sand hills has been an effective measure to alleviate compaction and improve crop performance. Pete hopes to eventually implement a controlled traffic farming system that will help preserve the value of operations like deep ripping and also make the chaff deck system more effective. The Edwards are also lifting productivity and reducing weed pressure on their poorer sand hill soils by double sowing barley, wheat and lentil crops. In just a few years Pete has noticed a real difference in the soil structure and moisture holding capacity. Other resources: Implementing the WeedSmart Big 6 on the Yorke Peninsula
Getting the edge on brome grass on non-wetting soils
On water-repellent soils, such as the Mallee sands of South Australia and Victoria, stronger crop competition has been shown to have an immense impact on brome seed production. In a difficult environment, where crop establishment is often patchy, researchers have demonstrated that water and nutrient harvesting within the crop furrow can result in better establishment when crops are sown on or near last year’s row. Results from four years of trials on non-wetting sands at the Mallee Farming Systems (MSF) trial site at Karoonda, SA consistently show that the increased surface soil moisture, crop establishment, crop biomass and crop / brome competition effects achieved through edge-row sowing can reduce brome grass seed set. Blue dye shows the higher moisture that can be found beneath last year’s row (left) and crop sown using edge row placement into last year’s crop stubble. Photos: Bill Davoren CSIRO Dr Rick Llewellyn, research group leader (agricultural systems) with CSIRO says that brome grass is the most costly weed for Mallee farmers to manage, even though herbicide resistance in brome grass is currently low in the region. “A series of trials have investigated the effect of different herbicide use, particularly pre-emergence herbicides, and row placement on crop yield and brome grass seed production,” he says. “To successfully manage brome grass it is necessary to keep weed seed numbers low and avoid blow-out situations. Our aim was to find the best options for reducing seed set.” When this year’s crop can make use of the resources in last year’s furrow there is more reliable crop germination and it can allow earlier sowing in years with marginal rainfall. On non-wetting sands, the practice of edge-row sowing has led to reductions in brome seed set of at least 55 per cent, and as high as 75 per cent, over the past four seasons. “Using edge-row seeding to achieve stronger establishment and crop competition on these difficult but widespread sands has resulted in a large and relatively reliable impact on brome grass seed production,” says Dr Llewellyn. “Growers will need to weigh this benefit against any potential disease risk and any stubble management issues in parts of a paddock that are not non-wetting sands, before changing their seeding set-up for edge-row sowing.” One important observation was the extent of brome grass germination in the crop row at the time of applying the pre-seeding knockdown. With seven times more brome grass seedlings emerging on the row, a successful knockdown is very important and a great opportunity to give the pre-emergence herbicide the best chance of success. Pre-emergent herbicides have the potential to achieve up to 75 per cent control of brome grass under optimal conditions but these products are notoriously variable from season to season. Trifluralin (1.5 L/ha) was commonly the least effective pre-emergent herbicide option while Sakura mixed with Avadex consistently achieved the greatest reduction in brome grass seed set. “In the 2015 trials at Karoonda, Sakura alone resulted in 55 per cent less brome panicles than trifluralin alone, and Sakura + Avadex resulted in 72 per cent less brome panicles than trifluralin alone,” says Dr Llewellyn. “Reducing seed production is the most important component of effective weed management. In some seasons, while the trifluralin and metribuzin treatments halved early brome grass density, they did not result in significant seed set reduction.” “Unfortunately, the more reliable Sakura plus Avadex treatment, with its extended period of activity is too costly for common use in low input regions. This leaves growers to get the most from lower cost but less reliable pre-emergence herbicide options and increases the need to include non-herbicide tools, such as improved crop competition through tactics like edge-row sowing.” Brome grass is a weed that demands an integrated approach to keeping the seedbank low, especially where growers are wanting to reduce their reliance on Group B tolerant crops. More resources Crop row placement (MSFP) Crop Row Placement – 10 things to consider Take a look at edge-row sowing submitted by one of our MSF members. Travelling at 9km/hr and sowing with a John Deere Conserva Pak, and StarFire guidance system giving 2cm accuracy. The dry start meant there was very little moisture mid row but moisture was found in the previous year's crop row. Sowing as close to the moisture band helps to get a better germination in dry conditions. However, the practicalities of edge-row sowing are still being worked through. It can be hard to manage stubble and keep it standing when sowing so close to last year's row. In this situation it has worked with accurate guidance systems that allow you to sow on the same row year after year and always in the same direction. Thanks to the GRDC Stubble project you can learn more about crop row placement in stubble retained systems specific to the Mallee at the link belowhttp://www.msfp.org.au/farmtalk-crop-row-placement Posted by Mallee Sustainable Farming on Friday, 22 June 2018