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Beating multi-resistant weeds in the Northern region

Dryland cotton and grains farmer Paul Slack is battling weeds that have high levels of resistance to several important herbicide modes of action. Managing 4850 ha of cropping land within 30 km radius of his home farm at Gurley, east of Moree, NSW Paul is using summer and winter cropping, strategic tillage and a long fallow spray program to get on top of resistant annual ryegrass and black oats populations. Tony Lockrey (AMPS Agribusiness agronomist), Paul Slack (Moree farmer) and Caleb Torrance (AMPS trainee agronomist) inspecting Paul’s corn crop, which is adding diversity to his cropping and herbicide program. A few years ago Paul was faced with a blow-out situation of 90–100 annual ryegrass plants per square metre in a Clearfield canola crop, along with some black oats and barley grass. The ryegrass present was tested for resistance, revealing an alarming profile of resistance to five herbicide mode of action groups. Groups A, B, M and two others, where the lowest level of resistance was to mesosulfuron-methyl (Atlantis, Group B) at 15 per cent. The annual ryegrass present was tested, revealing resistance to five herbicide mode of action groups. A dedicated program aimed at preventing seed set has seen a huge reduction in weed numbers with annual ryegrass now confined to a few isolated patches near waterways. With stubble cover required for the fallow ahead of a dryland cotton crop, Paul and his agronomist Tony Lockrey, AMPS Moree decided to run down the weed seed bank, starting with a double knock application to treat the first germination in autumn. Residual herbicides were incorporated using a Kelly chain through the canola stubble prior to sowing a short season wheat crop. “Sakura + Avadex Xtra provided upwards of 80 per cent control of ryegrass, but it must be used wisely in the rotation — we would try not to use this combination more than twice every four years,” said Tony. “In our experience, Group K herbicide Sakura is more robust in a variety of conditions, proving more stable than other residuals in dry conditions following planting, which often occurs in this region.” An in-crop application of the selective herbicide (Group B Atlantis) in wheat followed by a long fallow and a dryland cotton crop resulted in a huge reduction in weed numbers. Paul said annual ryegrass is now confined to a few isolated patches near waterways. “Using the Kelly chains in canola stubble represented some challenges but it was much easier than in other crop stubbles,” said Paul. “Now that the chain is worn-in I think it could be used in a chickpea crop to incorporate pre-emergent herbicides without damaging the crop. Mostly though we use it to chop chickpea stubble and to control weeds on the headlands.” Having had success with this regime to control multi-resistant annual ryegrass Paul decided to use a similar program to rein in Group A resistant black oats that had spread over about 100 ha. Black oats has been a problem for the last 15 years or so after gaining Group A resistance from the short wheat / chickpea / wheat rotation commonly used at the time, where there was heavy use of Group A products such as Verdict and Topik. Black oats pressure is clearly seen in this area where the crop was not sown. The addition of dim chemistry (Group A) in the chickpeas has helped extend the life of Group A chemistry, even though there is 50 to 60 per cent resistance to Verdict (a Group A ‘fop’) in the black oats population. Paul has used a long fallow period to regain control of resistant black oats, bringing the problem back to a very small area. “We did a long fallow after wheat then back to cotton followed by chickpea and then a short fallow and back to wheat,” he said. “This meant we could apply glyphosate in the fallow and two fop + dim mixes in the following chickpea crop. The addition of dim chemistry (Group A) in the chickpeas has helped extend the life of Group A chemistry, even though there is 50 to 60 per cent resistance to Verdict (a Group A ‘fop’) in the black oats population.” “We might repeat this clean-up program to really run down the black oats seed bank before returning to our normal program, which now features both summer and winter crops and a broader range of herbicide tactics,” said Paul. Black oats blow-outs are most likely in wheat crops and Paul is considering cutting weedy crops to make round bale silage. However, without a strong nearby market for the fodder and the large nutrient loss involved in baling, this decision will be a hard one to make. Milk thistle is looming as another challenging glyphosate-resistant weed that will require a different non-herbicide solution, possibly a mechanical innovation. “We know that zero-tillage farming led to a 30 per cent yield improvement in this environment,” says Paul. “We can’t afford to be forced back to a full tillage system to control weeds.” “There is potential to cut the crops lower in problem areas to expose the summer weeds to knock-down control and to improve herbicide-soil contact and efficacy with residuals,” he says. “In doing so we then also need to find ways to better spread the increased volume of crop residue out the back of the header, right across the 12 m to maximise fallow moisture efficiency. Using a chaff deck system to gather weed seeds at harvest and place the chaff on the wheel tracks is also something we are considering.” The current rotation of corn and cotton in the summer and wheat and chickpea in winter has helped bring all resistant weeds back to a manageable level. Bringing Group B chemistry into the herbicide program has been an effective tool in reducing the number of multi-resistant grass weeds and adding a Clearfield wheat into the rotation is another option for the future.
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Taking the competition to the weeds

Competitive crops are the ultimate weapon against herbicide resistant weeds as a non-herbicide tactic that suppresses weed germination and boosts crop yield. When stubble retention and harvest weed seed control are also enlisted in the tactical war on weeds then productivity and profitability become the clear winners. Greg Condon (right) is working with the Fox family at Marrar to build an integrated weed management system that also promotes productivity. Greg Condon, Grassroots Agronomy says growers can consider putting together several components that enable narrower row spacing, which is known to generate a one per cent increase in grain yield for every inch reduction in row spacing. “It is important to remember that this benefit can be gained without going to ultra-narrow rows,” he says. “I’d suggest growers go as narrow as they can within the constraints of their existing equipment and farming system to gain as much yield benefit and weed suppression as possible. Then, when it’s time to buy new equipment growers could look at what’s available that would enable more competitive configurations.” Green crops provide the best possible shading effect to suppress weed growth with a competitive crop having shading power equivalent to 10 t/ha retained stubble. This varies considerably with crop architecture where erect cereals provide less shading of weeds than varieties with a prostrate plant structure. Narrowing the row spacing increases the competition while also contributing to crop yield. One system that some of Greg’s clients are using combines stubble management and narrow rows using a disc seeder at planting and a stripper front at harvest. “The real advantages of stubble retention are seen in improved water holding capacity in the soil, which enables earlier sowing,” says Greg. “One year of retained stubble is generally not a problem for any of the modern seeders but we are seeing disc seeders do a better job handling stubble accumulated over a few years and in various stages of decay.” Front loss from a stripper front can be 1–2 per cent but in some cases this can be compensated by reduced harvest cost and header depreciation as stripper fronts harvest faster. Correct harvester and front setup is essential to minimise harvest losses. Including canola and pulses in the crop rotation also plays an important part in managing the quantity and decomposition of crop residue, particularly in a narrow row configuration. Pulses and canola crops assist in stubble management across the rotation. “Using a stripper front at harvest greatly reduces the amount of crop residue that is cut, chopped and spread out the back of the harvester,” says Greg. “The rearwards rotating rotor and stripper fingers strip the grain off the heads and leave the bulk of the crop residue standing in situ. About 85 per cent of the threshing occurs at the front end of the harvester, enabling double the harvest capacity of a draper, using 60–70 per cent less engine power and 60 per cent less fuel.” Grower experience suggests that stripper fronts work well in lodged crops and still allow the operator to have the front down low to collect any weed seeds, such as annual ryegrass and brome grass, present at harvest. This is particularly effective if the crop is sown on narrow rows, forcing the weed seed heads upwards in the crop canopy. Research into the efficacy of this system for harvest weed seed control is planned for the coming harvest. “The tall stubble left after harvest provides very effective soil shading and protection from drying winds over summer to retain more moisture and enable early sowing, rather than growers needing to wait for breaking rains,” says Greg. “The stubble dries and becomes brittle rather than rotting on the soil surface, making it easier for the disc seeder to operate.” The tall stubble left by the stripper front at harvest has widened their planting window all the way from January to May, giving them incredible flexibility in their cropping program decisions. The chaff line is subject to a high level of shading and higher moisture conditions that suppress germination very effectively. Harvest weed seed control is an additional component that growers like Daniel Fox at Marrar, NSW are adding to the ‘strip and disc’ system. Daniel has moved away from narrow windrow burning and now uses a chafflining chute to deposit the small amount of chaff, along with weed seeds, into a thin band behind the harvester. This contains the weed seeds to a very small portion of the paddock where they either rot away or have to face stiff competition from the following crop. “We are putting much more emphasis on cultural weed control methods now and reducing our reliance on herbicides,” says Daniel. “The tall stubble has really widened our planting window all the way from January to May, which gives us incredible flexibility in our cropping decisions. The system is easier to manage if you start with low weed numbers but we really believe that it can be used to drive down weed numbers after a blow-out too.” In a nut-shell, Daniel and his father David have implemented a controlled traffic farming system based on 16.5 cm row spacing, competitive cultivars, disc seeding, stripper front, chafflining, double-break cropping and sowing east-west where it is practical. On the herbicide front they have a strong pre-emergent program and utilise double-knocks and crop topping to manage in-crop survivors. The Fox family of Marrar, NSW have implemented a controlled traffic farming system based on 16.5 cm row spacing, competitive cultivars, disc seeding, stripper front, chafflining, double-break cropping, and sowing east-west where it is practical. On the herbicide front they have a strong pre-emergent program and utilise double-knocks and crop topping to manage in-crop survivors.
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Surveys highlight the cross-resistance to herbicides

John Broster, senior technical officer (herbicide resistance) at Charles Sturt University leads the weed survey project in NSW and has just completed crunching the numbers and finalising the results of the 2016 survey. John Broster, CSU “We gathered samples from the northern NSW and plains regions in 2016, which means we now have survey results from across the major grain growing regions of NSW,” he said. “The target weeds that we collect and test for herbicide resistance are, in order of importance, annual ryegrass, wild oats, sowthistle, barley grass, brome grass, wild radish and Indian hedge mustard.” The weeds that are collected in the surveys are tested for their susceptibility to the major herbicide groups used for their control. “Across NSW the extent of ryegrass resistance to Group A ‘fops’ and Group B ‘SU’ herbicides is by far the highest with about 60 per cent of samples being resistant, and 46 per cent of samples being resistant to Group B ‘Imi’ herbicides. There was less extensive resistance to the Group A ‘dims’ and Group D herbicides at 10 and 11 per cent of samples respectively,” said John. “When we looked at cross-resistance in the ryegrass samples collected in NSW we found that while 24 per cent of samples were susceptible to all five of the major herbicide groups used for ryegrass control, a huge 43 per cent were resistant to three or more of these five herbicide categories.” Speaking at the recent WeedSmart Week forum, John Broster, senior technical officer (herbicide resistance) at Charles Sturt University presented results from the latest weed survey conducted in NSW where 43 per cent of surveyed annual ryegrass plants were resistant to three or more of the five important herbicide categories used to control this weed. These surveys clearly illustrate the level of cross-resistance that exists in cropping paddocks across NSW, and in other states around Australia. At the recent WeedSmart Forum in Wagga Wagga where John presented the latest survey results, 170 growers, agronomists and researchers compared notes and experiences about a whole raft of weed management tools, some largely untested but showing promise in the field. Harvest weed seed control options were of great interest, as were the demonstrated benefits of double-break cropping, utilising livestock in mixed farming enterprises and ways to extend the effective use of herbicides. The ‘Big 6’ WeedSmart tactics known to drive down weed numbers and drastically reduce the impact of herbicide resistance on Australian farms are: Rotate crops and pastures, Mix and rotate herbicides, Increase crop competition, Use the double-knock, Stop weed seed set and Implement harvest weed seed control. Herbicide resistance can’t be beaten with herbicides alone — that’s the take-home message from these surveys. However, even in paddocks where herbicide resistant weeds are almost as common as susceptible ones, this doesn’t mean ‘game over’, as many Western Australian farmers have shown. It does mean that farming systems need more diversity and weed management programs need to include a range of tactics aimed at reducing weed numbers at every opportunity during the year.
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Setting up harvesters to capture weed seed in the chaff

Getting weed seeds into the chaff fraction Separating the chaff (including the weed seeds) from the straw is a great way to retain more crop residue at harvest. There are several harvest weed seed control (HWSC) systems that manage just the chaff, including chaff decks, chaff carts and chaff lining. All these systems rely on the weed seed entering the front of the header and then being captured in the chaff stream. Chaff lining – new, cheap, simple [but not fully tested] Chaff lining is a new harvest weed seed control method that has sparked incredible interest from growers throughout Australia. Similar in concept to the chaff deck system (called chaff tramlining), chaff lining places the chaff fraction directly behind the harvester rather than on the CTF tram tracks. It is a grassroots grower solution to HWSC that is cheap to try and seems to be a very effective tool. Essentially weed seeds are collected at harvest and dropped in a narrow line behind the harvester. There is no burning required and all the straw is spread behind the harvester so there is very little loss of ground cover. Getting started involves the construction of a simple chute that is then fitted to the harvester. The chaff lining chute can be used in all crops and does not affect harvester operation. Like all harvest weed seed control methods, the harvester must be set up and operated, correctly to ensure the maximum number of weed seeds enter the front of the header and are contained within the chaff fraction. Below are a number of videos and farmer case studies showing how to implement chaff lining. This method of HWSC is well suited to controlled traffic farming but it can also work in non-CTF systems provided the harvester runs in the same lines for a few years in a row. Grower case studies Mic and Marnie Fels have developed a farming system where herbicides are used to back-up their cultural practices, rather than the other way around. Mic Fels has used a modified version of chaff tramlining as their harvest weed seed control strategy. The idea is that the chaff component is funneled into a narrow strip in the middle of the CTF runs behind the header. In a controlled traffic system this means that the weed seeds collected through the header are concentrated into the same zone every year and any seeds that germinate through the mulch are subject to the full force of crop competition. Similar to the experience of growers using a chaff deck to channel the chaff into CTF permanent wheeltracks, Mic finds that the chaff and the weed seeds simply rot away and there is no need to burn the chaff to gain the benefits of this weed control measure. Daniel (left) and David Fox are pleased with the chaff lining chute they have introduced as a harvest weed seed control method on their Marrar farm near Wagga Wagga. Marrar farmer Daniel Fox is chasing higher yields across his 2100 ha cropping program while also driving down weed seed numbers. For a few years Daniel has been adding components to his system to conserve moisture and keep herbicide resistant weeds at bay. Having used narrow windrow burning for a few years and seeing the benefit of capturing seed from late germinated weeds at harvest, the Foxes have now built a chaff lining chute for the header and are delivering the chaff component, including weed seeds, into a 250 mm chaff line in the middle of the 12 m CTF lap. This maintains most of the crop residue evenly across the paddock and avoids the need for burning. “Having the weed seed concentrated in a narrow band reduces the amount of seed that germinates and also reduces the chance of weed seed being buried and ‘stored’ underground at planting now that we are using a disc seeder,” says Daniel. Setting up harvesters to capture the weed seed in the chaff https://www.weedsmart.org.au/resources/hwsc/
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Spray out low yield potential crops now or crop top later?

WEEDSMART DRY SEASON SPECIAL As dry conditions continue to impact on crops in many regions of Australia, affected growers will be faced with difficult decisions that will have long lasting effects on the weed seed bank. The lack of crop competition in drought-affected crops leaves the door wide open for more weeds to germinate and set seed, adding to weed control costs in future years. North Tenindewa, WA grower Glenn Thomas is considering the best option for this low yielding canola crop to manage future wild radish weed pressure. Faced with a similar situation in 2001, and again in 2006, North Tenindewa, WA grower Glenn Thomas made the hard decision to sacrifice his low yield potential lupin crops to escape the consequences of an inevitable blowout in annual ryegrass and brome grass. “In 2001 we had a paddock with a very poor lupin crop and about 140 ryegrass plants per square metre,” he said. “In that August we decided to spray the crop out using a glyphosate mix, leaving the best part of the paddock for comparison, and in the hope of late rains that might save the crop. Although we lost the value of a 250 kg/ha lupin crop, we measured a 700 kg/ha yield increase in the 2002 wheat crop as a result of fewer weeds, more nitrogen and more soil moisture. This was particularly pleasing given that 2002 was also a drought year in this district.” The un-sprayed section was still managed with selective herbicides to control weeds in-crop, however this section of the paddock stayed weedy for six or seven years, while the sprayed out area had no weeds, clearly illustrating how much Glenn had saved in chemical and operating costs in the area he had sprayed out. When the same scenario played out in the 2006 season Glenn again decided to spray out the low yielding lupin crop in the same paddock to avoid a build-up of weeds. This time he sprayed out the whole paddock, being more confident in the long-term benefit of this decision. This photo from 2016 shows how clean Glenn’s sprayed out paddock has remained, 10 years after the last drought-affected crop was sprayed out. In both 2001 and 2006 the drought conditions did not improve as the year progressed so Glenn had no reason to regret his decisions to forego the crop and spend the $25–30 per ha to spray out the failed crops and reset the weed seedbank. In the end, Glenn’s decision has created a legacy of very clean paddocks and he has taken a diverse approach to his weed management program including narrow windrow burning, chemical fallow and brown manuring in weedy paddocks. With annual ryegrass now well under control Glenn is more concerned about managing wild radish. Glenn’s experience was also demonstrated in a 4-year trial at Mingenew conducted by AHRI communication lead, Peter Newman while working for DAFWA. “In this trial we sprayed out a weedy lupin crop and compared this to harvesting the lupin crop and returning ryegrass seeds to the seed bank,” he said. “The following year 163 ryegrass/m2 germinated in the area where lupins were sprayed out compared to 1433 ryegrass/m2 germinating in the area where lupins were harvested.” This trial ran for 4 years and the difference in ryegrass seed bank was evident for the duration of the trial. “Although a full spray out now might provide the best outcome for weed control, it is still an expense. While there is no cash flow into the business, there is also no further expense with harvesting a low yielding crop where grain losses can also be high, particularly in short pulse crops,” he said. “Another option is to crop top in October, which will still reduce seed set while preserving some cash flow from this year’s crop. Implementing a harvest weed seed control tactic such as chaff lining or using a chaff cart will further reduce the risk of a future weed blowout from a low rainfall year.” Other advantages of crop topping over an earlier spray out is that paraquat is a lower cost herbicide application and there will be more ground cover left to protect the soil surface from the wind over summer. “Although crop topping these paddocks in October will not necessarily achieve as good a result as spraying the paddock out in August, it is a lot better than simply harvesting the crop and returning weed seeds to the seed bank,” said Peter. As the current season unfolds Glenn is once again looking at weed numbers in low yielding crops. He reckons there will be a percentage of his lupin crop that will be sprayed out along with a small area of canola where wild radish numbers are of concern. “This year we probably won’t actually spray crops out until later in the season when we have grown as much biomass as possible,” he says. “In 2001 and 2006 the season started well but then deteriorated so the weeds grew with the crop and needed to be sprayed in August when it was clear the crops could not compete with the weeds. This year, the dry start has kept weed numbers relatively low and we are only just seeing a response to the couple of double-digit rainfall events from the last week or two.” Glenn is now watching the weeds respond to the rain and will monitor them carefully so he can prevent seed set while still maximising biomass and nitrogen production in the lupins. He is also watching his wheat crops that have already come to head and the weeds are growing but it’s too late for in-crop herbicide applications. “This is a real dilemma for us and others in the district,” he says. “There might be a case for a pre-harvest herbicide application in these wheat crops to target late germinating weeds but there is a lot to consider before making this decision.”
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Zero row spacing could take crop competition to a new level

Grain grower Leigh Bryan doesn’t shy away from an unconventional idea. His crop-guided shielded sprayer is working a treat, he is confident with chaff lining and now he is testing the possible advantages of zero row spacing. His aim is weed-free paddocks with crops growing at their full potential across the 2400 ha of cultivation within 30 km of Swan Hill in Victoria’s Mallee region. “Being crop-guided, the shielded sprayer provides precise control over weeds and crop volunteers,” he says. “It makes it possible to suppress medic and other hard-to-kill weeds in lentil crops and take self-sown wheat plants out of barley paddocks. Keeping crops as clean as possible.” Shielded sprayer used to apply paraquat for control of medic in lentils. Using the shields strategically over the past seven years, Leigh has drastically reduced weed numbers and can concentrate on preventing seed set in just the odd plant here or there. The shields allow Leigh to use more cost-effective pre and post emergence herbicide options to prevent seed set of grass and broadleaf weeds in cereal crops. “The shielded sprayer also makes it possible for me to crop top at the optimum time to have maximum impact on weed seed set without damaging the crop, regardless of the crop maturity stage,” he says. The shielded sprayer has played a significant role in managing herbicide resistant brome grass and annual ryegrass. Leigh’s crop-guided shielded sprayer in action, controlling brome grass in a barley crop. As a harvest weed seed control tactic, narrow windrow burning was a good ‘get out of gaol’ tactic but Leigh has been chaff lining now for three years. He says depositing the chaff-only fraction in a narrow line between the harvester wheeltracks is a very effective way to keep weed numbers low. “Dropping the chaff line between the wheeltracks, rather than into the wheeltracks, minimises disturbance of the seeds, reduces weed seed contact with soil and promotes more rotting down over summer,” says Leigh. “The chaff lining chute is also cheaper to make and install than a chaff deck.” Last year Leigh used the chaff lining chute in all crops except canola and found there was no problem pulling the tines through at planting this year. “We first tested the idea in clean paddocks hoping to keep them clean,” he says. “We are now completely confident in the system and will be using the chaff lining chute in all crops across the farm this season. It has proven particularly valuable in lentil crops.” If weeds become a problem in the chaff line Leigh is prepared to band spray the chaff line with pre-emergent herbicide, but this has not been necessary to date. For the last three years Leigh has also been trialling zero row spacing in a bid to capture optimal yield from his crops. The planter has been fitted with splash plates that spread 35 per cent of the seed at random while the remaining 65 per cent of the seed is sown conventionally, down the tube. Leigh uses splash plates fitted to his planter to spread 35% of the seed randomly across the soil surface to achieve ‘zero row’ spacing. Close-up on the splash plate. “This will only work in relatively clean paddocks,” he says. “With no trifluralin applied the in-crop weed control is reliant on strong crop competition and very, very low weed seed bank. Next year I will be looking at different pre-emergent herbicide options and how they might fit in this system.” The seeding operation is faster than normal and this helps throw sufficient soil to enable successful germination and establishment for the seeds spread on the surface. In Leigh’s on-farm side-by-side trials, the zero row spacing strips are showing that the idea has promise. “There are others playing around with the idea of zero row spacing too and I think it has potential,” he says. “In 2016, a strip-trial in barley resulted in the zero row spacing strip yielding 4.994 t/ha compared to 4.889 t/ha in the conventionally sown crop at 375 mm spacing.” This result gave Leigh the confidence to sow one-third of the farm using zero row spacing this season. To achieve the best results Leigh sows considerably more seed but says this is cheaper than pre-emergent herbicide and results in potentially higher yielding crops. The results of this large scale trial will be very interesting in terms of both weed management and crop yield. Leigh takes a weed-point view in zero row spacing (left) and 375 mm spacing (right). “The random placement of stubble is easier to sow through the next year. It still provides trellising for pulse crops and shades the soil to conserve moisture and reduce soil surface temperatures,” he says. “There can be a 10-day delay in germination between seeds sown on the surface compared to those sown into the soil because the surface seed needs rain to germinate.” When it comes to growing a competitive crop Leigh emphasises the need to get the crop planted on time, keep it healthy and well-fed. Leigh’s continuous, no-till cropping system includes wheat, barley, canola, lentil, field pea and lupin brown manure. When planning the crop rotation for paddocks he ranks them according to weed burden and uses a 4-year break crop system to clean up paddocks with high levels of grass weeds. “In a weedy paddock we start with a pea/lupin brown manure, then plant canola, in year 3 we plant a cereal and use the shielded sprayer in-crop then finish with a lentil crop,” he says. “This gives us a 4-year run at grass weed control and then we can return to ‘normal’ rotation with a low weed seed bank.” Once weed numbers are low, Leigh says it is relatively easy to keep them low through the consistent use of both herbicide and cultural practices. “When weed numbers are low it is possible to look at ways to improve yields and reduce production costs,” he says. “That’s what I hope to achieve with zero row space planting, supported by crop rotation and chaff lining to manage survivors. If there is evidence that weed numbers are increasing, then we have other tools at the ready to stop a weed blow-out.”
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Controlling glyphosate-resistant grass in irrigated cotton

When glyphosate-resistant summer grass starts to cause yield losses in cotton, growers obviously need to add some non-glyphosate options to their system to protect yields and prevent further weed blowouts. The questions then become where to add non-glyphosate tactics to get most benefit, and how many are needed? Developer David Thornby used the Barnyard Grass Understanding and Management tool, BYGUM to investigate three key questions relevant to irrigated cotton systems. Scenario #1 – Ask BYGUM: the value of glyphosate What’s the remaining value of glyphosate in rotations with glyphosate-resistant awnless barnyard grass? BYGUM developer David Thornby has developed a series of scenarios to demonstrate this new decision support tool. Since the first confirmation of glyphosate resistance in awnless barnyard grass, many other resistant populations have been found, and these populations don’t all display the same level of resistance. While glyphosate is no longer effective as a stand-alone control measure against any of them, some populations are less strongly resistant than others. In the case of the first-confirmed population, field rates still had around a 40 percent efficacy on small seedlings. For other more recently confirmed populations, efficacy even on small seedlings is much lower. Given that glyphosate is going to be applied to these populations anyway, it’s important not to overstate the usefulness of glyphosate by hoping to be able to rely on it for some level of control. BYGUM can test the difference for us, between populations with strong resistance and those with moderately strong resistance. David said he used a simple irrigated rotation, with modest use of non-glyphosate options in an otherwise glyphosate dominated system. He varied the effectiveness of glyphosate from around 40 percent (‘moderate’ resistance) to around five percent (‘strong’ resistance). Key outcomes The results show two key things. First, both systems are still making money after five years. High levels of crop competition keep seed production per escaping weed low, and the addition of a few effective tactics reduces the number of surviving plants to moderate/know levels of between six and 14 plants per square metre at the end of the fifth season. Secondly, however, both systems are heading towards failure. Weed and seedbank numbers are increasing, however slowly. And while gross margins are the same at the end of season one, there is a predicted difference of around $500/ha between the gross returns in season five. David says there are three lessons here. First, strong crop competitive effects might mask the seriousness of resistance issues in irrigated cotton, should they be present. Second, there are good reasons to determine just how strongly resistant your resistant awnless barnyard grass population is, if you’re going to be sticking with a system that is predominately about the use of glyphosate. And third, allowing a slow decline with somewhat-inadequate weed management looks likely to have a substantial cost as the years pass by. We’ve made many assumptions in this example – in particular, that irrigated cotton is planted and provided with resources to allow for strong competitiveness against the weed. We’ve also made assumptions about crop and herbicide costs, average yields and prices. “You could run BYGUM with a different set of assumptions that fit your experiences, and see if the results change. Scenario #2 – Testing the value of a cover crop Can summer cover crops be used to get on top of weed populations? In a one-in-one-out rotation of dryland cotton, summer fallows offer a chance to get on top of weed populations through vigorous use of non-crop herbicides. However, with no crop competition present, they can also offer weed escapes an opportunity to set a lot of seed, especially when the key herbicide in both crop and fallow, glyphosate, is no longer effective. “Cover crops allow growers to maintain some competition even in non-crop seasons,” David Thornby says. “A good stand of millet (as simulated in BYGUM), sprayed out before seed set, allows for a combination of late season herbicide use to clean up survivors and mid-season competition with glyphosate- resistant barnyard grass, reducing seed set per plant.” The first scenario is a basic one-in- one-out rotation. This contains the assumption that the barnyard grass population is resistant to glyphosate, and that an early season residual and mid-season inter-row cultivation are used to provide some control in crop: summer fallows use two cultivations and a double knock. In scenario 2 David replaced the second summer fallow with a cover crop. The cover crop includes cultivation, a double knock, spray out (assuming this is with a non-glyphosate product effective on glyphosate, such as paraquat), and a late application of paraquat over the now-dead millet. “The cover crop is more expensive than the summer fallow, and actual plant numbers per square metre are not reduced all that much (1.1 to 0.8 per square metre),” David says. “But there is a substantial difference in seeds returned to the seed bank.” The comparison scenario shows a substantial increase in the yield from the final cotton crop, due to the strong reduction in seed bank numbers at the end of the cover crop season. “The benefits of the cover crop come due, as expected, in the following crop, where the seed bank has been driven down and emerging weed numbers are low,” David said. “Over the course of the whole rotation, incorporating one cover crop every second summer fallow is predicted to be worth almost $200/ha in increased yield. “There is more than one way to protect future yields in a dryland rotation, but using cover crop competition certainly seems to bear looking at. “We’ve made many assumptions in this example – in particular, that planting time and summer rainfall are conducive to good cover crop growth, resulting in high competition, that the barnyard grass population is strongly resistant to glyphosate, and that the cover crop doesn’t reduce moisture availability to the following cotton crop. “We’ve also made assumptions about crop and herbicide costs, average yields and prices. “Once again, users could run BYGUM with a different set of assumptions that fit their experiences, and see if the results change.” Scenario #3 – Residual answers to resistance Can you control a glyphosate-resistant grass by adding a residual in irrigated cotton? In situations where a glyphosate-resistant summer grass starts to cause yield losses in cotton, growers obviously need to add some non-glyphosate options to their system to protect yields and prevent further weed blowouts. The questions then become where to add non-glyphosate tactics, to get most benefit, and how many are needed? David Thornby used BYGUM to investigate this question. First he compared a system with glyphosate-resistant barnyard grass where only glyphosate is used with the same system with an early-season (pre- or at-planting) residual added. Residuals tripled gross margins The yield results of adding a single residual are striking. The glyphosate-only system is still producing some yields (Figure 2 – primarily due to the competitiveness of irrigated cotton), but end-of-season weed numbers are very high and the potential of the system is being seriously under-utilised. “Adding a single residual can reduce early-season weed numbers dramatically, and because this is when most of the competition effects occur, this has a huge benefit for the bottom line,” David said. Figure 1: Irrigated cotton rotation with an early-season residual. While we’ve used ‘a residual’ in the notation here, a rotation of suitable products from different modes of action should be used in the field. The glyphosate-alone system is the same as this one, without the early season residual. Figure 2: A comparison of gross margin and barnyard grass numbers at end-of-season between glyphosate alone (top) and glyphosate plus a single, early-season residual. “Gross margins are almost tripled compared to glyphosate alone when the weed population is strongly glyphosate resistant. “However, end-of-season weed numbers (and seedbank density) are still unacceptably high, so a single residual doesn’t appear to be enough of an addition, despite the dramatic effect. “A single year of poor control from the residual (rather than the average of around 85 percent efficacy) would certainly result in a blowout.” Adding a mid- or late-season tactic provides some insurance against weed blowouts and seed production. Because late weed germinants in vigorous cotton stands don’t produce a lot of seed per plant, the effects on yield aren’t so dramatic. However reducing surviving plants and especially reducing the seed bank size are critically important insurance against future blowouts and selection of resistance for other modes of action. David tried two different tactics in BYGUM, adding either a layby residual to each crop or a mid-season knockdown. Adding a layby reduces the seed bank somewhat, and cuts surviving plants at end-season down to around 25 per square metre. This still appears to be too many survivors for comfort, but it does represent a substantial improvement over an early- season residual alone, and offers insurance against future blowouts. BYGUM predicts that it can be sustained at least for the five-year rotation. This comes at a cost, however: the reductions in late-season weed numbers are offset by the price of the extra residual and BYGUM includes a penalty due to phytotoxicity. In comparison with the layby system, a system with a mid-season knockdown, rotating between options including Group A herbicides, shielded paraquat and inter-row tillage improves the gross margin (due to a combination of taking out some weed competition and having some options with lower phytotoxicity-related yield penalties), but leaves more end-of-season survivors. “So this is not an ideal system either – but is certainly an improvement in all ways over a single-residual system,” David said. “These analyses show that while a single early-season residual can do a lot of heavy lifting in terms of reducing weed competitiveness, it’s not enough on its own for long-term sustainability. Late or mid-season tactics provide some insurance.” “BYGUM predicts that while good returns can be sustained at least for five years with this ‘plus two’ strategy, more non-glyphosate tactics would be needed to drive the seed bank to very low levels. We’ve made many assumptions in this example—in particular, that irrigated cotton is planted and provided with resources to allow for strong competitiveness against the weed, that resistance to glyphosate is quite strong, and that good efficacy is generally the case for residual applications. Pre-simulation weed numbers are assumed to be moderate and we’ve also made assumptions about crop and herbicide costs, average yields and prices.” Case study reproduced courtesy of CRDC, following publication in CRDC’s Spotlight magazine, Winter 2016. To access BYGUM, visit: www.cottoninfo.com.au/barnyard-grass-understanding-and-management-bygum.
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Paired rows take off on Twitter

Recently we started a hashtag on Twitter to share information about paired row sowing. We used the hashtag #Pairedrow. You can still use it now to engage in the discussion and tag WeedSmart. Thank you to everyone who has already contributed to the discussion about paired row sowing on Twitter. Here is a summary of the pros and cons. You’ve got to love the names of some of the brands out there! Below are the names of some of the paired row sowing options that growers had tried. Rootboot, Stiletto boot, Agmaster twin seeker, Bourgault, Ausplow, Conservapac, Morris C2 boot, Seed master, Burando Hill.
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Testing for weed susceptibility to herbicide pays off

Sam and Emily Eagle run 2500 merino ewes on their 3000 ha mixed farm near Horsham, Victoria. They say the livestock and cropping activities complement each other, keeping their pastures and crops performing at their best. Herbicide resistant annual ryegrass is their main weed challenge with one test revealing resistance to glyphosate (65 per cent) and clethodim (80 per cent), and full susceptibility to chlorsulfuron (Group B, Glean). Sam and Emily Eagle run a mixed farming enterprise near Horsham, Victoria where grazing and cropping are mutually beneficial for weed management. “We test annual ryegrass from two or three paddocks each year to monitor any changes in susceptibility to the herbicides we use,” said Sam. “Knowing which herbicides are effective makes it easier to plan our herbicide use without relying solely on the products that still work. Every year we have at least one tactic in place specifically to reduce the weed seed bank.” Knowing that the tested weeds were susceptible to Glean gave Sam an opportunity to regain control of a potential blow-out situation, using a herbicide that is much cheaper than alternatives that he might have chosen if he had to make the decision without the herbicide resistance test results. The Eagle’s agronomist usually collects the seed for testing and the results are considered to be representative of the whole paddock, each one being around 35 to 70 ha. “We can fairly safely assume that all our weeds have some level of resistance so we concentrate on managing survivors, mostly treating with a double-knock whenever possible,” he said. “Annual ryegrass is our main problem weed however we are keeping a close eye on brome grass that is present on one of our lease blocks.” Triazine resistance on one block precludes the use of TT canola so the Eagles grow conventional canola on this block, aiming for the most competitive, highest yielding crop possible. Along fence lines Sam uses a 2-year program where he slashes in spring in one year and then sprays a knockdown + residual herbicide mix the next year. “When we slash, we know that the weeds will still set seed. We keep the slasher low to the ground to ensure any seed heads present at harvest are below header height so they won’t get spread,” said Sam. The pasture paddocks are de-stocked over summer with the sheep grazing on the stubble. If the stubble runs out early the sheep are returned to the containment area where they are fed screenings, hay and grain until the pastures are ready. The ewes return to the pastures to lamb in autumn. Sam and Emily use narrow windrow burning in the canola as their harvest weed seed control tool. They have had trouble using this tactic in cereals, where the fires often don’t burn right to the ground, leaving weed seed concentrated in bands. On the other hand, the canola burns well, destroying the weed seed, and Sam is able to safely burn several paddocks on the one day. Grazing the canola narrow windrows has not caused any problems with burning or with weed seed being spread. Narrow windrow burning in canola has worked very well for Sam, driving down herbicide resistant ryegrass numbers. “Canola actually gives us a few opportunities to control late germinating weeds,” said Sam. “Firstly with an over the top spray to desiccate the crop, secondly windrowing the crop early and third, using the narrow windrow chute at harvest in preparation for narrow windrow burning in autumn. We also spray top wheat and barley, with the sheep providing the second knock for any survivor weeds.” Growing faba beans, canola, wheat and malt barley enables them to use a different pre-emergent herbicide each year of the rotation. At the end of this 4-year program any paddocks that are carrying a weed burden are thoroughly cleaned using a pasture and a 3-year hay program. Moby forage barley sown with clover gives a nutrient boost to the perennial ryegrass pasture phase, which may last up to ten years. “We supply hay for export and generally grow two oat crops and one vetch,” said Sam. “Any failed crops or additional production is stored as silage in underground pits to drought-proof our breeding flock. Silage is a particularly good way to clean up weeds because we spray out when the crop is actively growing and not under any moisture or heat stress, then cut in early September.” At the end of a 4-year cropping program any paddocks that are carrying a weed burden are thoroughly cleaned using a pasture and a 3-year hay program. The Eagles supply hay for export and generally grow two oat crops and one vetch. The 2017 seeding represents the beginning of the Eagles’ fully aligned controlled traffic farming (CTF) system. The transition to 12 m wide CTF has taken several years but Sam and Emily are convinced that the efficiencies gained will be well worth the investment. They sow all crops on 300 mm row spacing and aim to achieve the most competitive crops possible. Although Sam knows 380 mm row spacing would make some management operations easier, they pick up extra yield and suppress weeds with the narrower spacing. In the seven years that Sam and Emily have been managing the farms they have seen the benefits of the rotation in keeping weed numbers low. “All of our worst paddocks have now had the ‘rotation treatment’ and we have avoided weed blow-outs,” said Sam. “Two wet years in a row could potentially challenge our weed management but having the sheep in the system gives us more options while still earning income from each paddock.” Related links 10 Point Plan – Test for resistance to establish a clear picture of paddock-by-paddock farm status Plant Science Consulting herbicide resistance testing CSU Herbicide resistance testing
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Delay spraying stressed weeds after rain

WEEDSMART DRY SEASON SPECIAL Dry season agronomy is difficult. In affected areas there is a reasonable chance that pre-emergent herbicides applied at or before seeding will not work as well as they usually would, even when it does rain. This fact, combined with the significantly reduced crop competition in most paddocks, will mean weeds will have the opportunity to grow in greater numbers. Knowing that spraying moisture stressed weeds in dry conditions is less effective, many growers will be looking for any sign of rainfall as an opportunity to quickly apply post-emergent sprays in an attempt to reduce weed seed set. Australian Herbicide Resistance Initiative communication lead, Peter Newman says waiting for new leaves to grow after a rainfall event is likely to give better results than spraying just a few days after rain. “When plants are stressed, one of their survival mechanisms is to thicken the cuticle of their leaves,” he says. “This reduces moisture loss from the leaf during hot, dry periods and also reduces the uptake of post-emergent herbicides.” “These leaves remain thicker and waxier, even when it rains and the plant freshens up,” he says. “Waiting for new leaves to emerge after rain will result in a much better level of control and help minimise weed seed set. The use of the correct adjuvants and spray quality to counteract the increased waxiness of the leaves will also improve herbicide efficacy.” However, waiting for new growth also has its problems if dry conditions return. “These decisions are not easy, but if rain has fallen and more rain is forecast, perhaps waiting for new growth of the weeds will give the best results,” he says. Department of Agriculture and Food WA research conducted by Dr David Minkey and John Moore in the 1990s demonstrated the impact of moisture stress and low humidity on herbicide efficacy. Their research showed a 20-fold difference in efficacy of glyphosate sprayed on weeds of the same age under favourable and stressful environmental conditions. “Unfortunately, spray events are going to be difficult to time and the results are probably going to be less than optimal. This is out of the grower’s control in most instances,” says Peter. “Given that there is a good chance of more weeds surviving in-crop weed control efforts, implementing some form of harvest weed seed control will be an even higher priority this year.” “High numbers of annual ryegrass is a concern but we know that we can get back on top of a ryegrass seed bank in just a few years,” he says. “Wild radish however produces seed that remains viable in the soil for 5 to 10 years so it takes much longer to drive weed seed numbers down if this weed blows out.” If faced with a crop failure, spraying out early could be a good option and for crops that are harvested consider a low cost harvest weed seed control option, such as chaff lining, to minimise the potential impact of a weed blow-out. Chaff lining involves placing a chute on the rear of the harvester that concentrates the chaff-only fraction into a narrow band between the wheeltracks of the header. The straw is chopped and spread as usual. The chute can generally be built on farm at a very low or even nil cost. Relevant links AHRI Insight – Why thirst weeds are hard to kill Spray application manual – product requirements module WeedSmart search – chaff lining
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How chaff lining works

WEEDSMART DRY SEASON SPECIAL Weeds are a constant factor in farming, regardless of the seasonal conditions. The lack of autumn rains in areas like the Eyre Peninsula in SA and no follow-up rain for dry sown crops in some Western Australian districts means there will be many crops with variable establishment and variable growth rates, making weed control more challenging. Social media shows impact of 2017’s dry conditions Twitter has provided stark visual examples of just how dry it is this season in some parts of the country. @ZimStead is an agronomist in Western Australia and recently shared the below two pictures taken a year apart from the same farm in North Tammin. The more lush picture was taken on June 1, 2016, and the second, showing the effects of dry conditions was taken on June 1, 2017.  North Tammin June 2016 (photo @ZimStead) North Tammin June 2017 (photo @ZimStead) Chaff lining – an effective tool It’s understandable that in a dry year, grain growers staple the chequebook shut and stop spending money on their crops to keep costs down and minimise their loss.  However, this can result in weeds setting seed in crop, which can quickly undo many years of hard work to erode weed seed banks. Perhaps this may be the year for growers to consider adopting the simple, low-cost option chaff lining, to cost-effectively deal with weeds setting seed in these low yielding crops. Chaff lining involves placing a chute on the rear of the harvester that concentrates the chaff only into a single line in the centre of the header.  The straw is chopped and spread as usual.  The idea is to drive the harvester on the same tracks for years to come, repeatedly placing chaff lines in the same place each year. Growers using this practice find that these chaff lines are often a lot less weedy than they would expect and they believe that a lot of the weed seeds rot, however, unfortunately, we don’t have any data to confirm or deny this observation as yet. There’s also the option to place a narrow windrow of all residue in the same place in a future crop which can be burnt to remove the chaff line and destroy surviving weed seeds. Our aim in a dry year should be to set ourselves up for success next year, and chaff lining could be a low cost, easy tool to put growers on the right track. Join the conversation on Twitter by following @WeedSmartAU and using the hashtag #chaffline
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Ranking paddocks for weed expenditure in a dry year

WEEDSMART DRY SEASON SPECIAL Weeds are a constant factor in farming, regardless of the seasonal conditions. The lack of autumn rains in areas like the Eyre Peninsula in SA and no follow-up rain for dry sown crops in some Western Australian districts means there will be many crops with variable establishment and variable growth rates, making weed control more challenging. Making decisions early about a paddock’s weed control program is one way to make sure that money spent on weed control is cost-effective. The The Big 6 is a useful tool for growers and advisors to use when planning an integrated weed management strategy and also for situations like this where adjustments are required due to an unexpected set of environmental circumstances. Australian Herbicide Resistance Initiative (AHRI) southern extension agronomist, Greg Condon says ranking paddocks according to their potential returns and future spending is a good way to channel resources to the most critical areas. “The key is to look at how to minimise losses rather than to try to optimise production. From a weed management perspective this usually means looking at each paddock and considering the likely effect of different weed control options,” he says. “For example, the future financial cost of a paddock with low ryegrass numbers will be far less than a paddock on the verge of a wild radish blowout if no herbicide is applied. If the future cost of ‘doing nothing’ will be high, then higher level expenditure is justified.” AHRI southern extension agronomist, Greg Condon suggests growers talk to their advisors about ways to minimise the future cost of weed control as well as implementing low cost options for the current year in areas experiencing a dry start to the season. The next step is to rank the crops in order of their potential value. For lower value crops, consider spray fallowing, grazing or cutting for hay. Wherever possible, avoid using expensive herbicides and look at low cost cultural weed control measures that will reduce weed seed set. Canola, pulses and feed barley all have crop top registrations that can be used to prevent seed set and lessen the weed burden for future years. This will be a valuable option for crops that do not warrant a full post-emergent spray program if the season stays dry. “Cereals are generally lower risk crops that tend to handle drier conditions better than broadleaf crops. One exception to this is short season Roundup Ready canola, which can be quite resilient, and is supported with low cost post-emergent herbicide options,” says Greg. The other thing to consider when ranking paddocks is the crop’s yield potential. For example, a canola crop on a deep ripped fallow would get priority over a low fertility weedy block. Looking at the establishment of crops is a good way to rank the paddocks ‘in the middle’. Putting available resources into crops that have the best establishment means that there will be some competition for weeds and if the paddock has had a history of harvest weed seed control then the weed burden should also be lower. Ranking paddocks and crops early in the season will help target expenditure and minimise costs for this season and future seasons in terms of weed burden. As the season unfolds, harvest weed seed control will be the next major decision to impact on the weed seed bank.
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Pulses to attack weeds on many fronts

Evidence is mounting that shows pulses can play an important part in weed control, particularly in the war against herbicide resistant annual ryegrass. In the past, pulses have often been named as ‘the weak link’ in crop rotations when it comes to weed control however recent research indicates that pulses can make a valuable contribution to an integrated weed management program. “Field pea is a particularly useful crop for growers to launch a strategic multi-pronged attack on grass weeds,” says former NSW DPI researcher, Dr Eric Armstrong. “The idea is to apply a double knockdown prior to sowing, use pre- and post-emergent herbicides, crop top in spring and harvest early to stop weed seed set.” Dr Eric Armstrong says that when crop topping, timing is critical to prevent seed set of the target weeds. For crop topping to be effective, spray the paddock before the weed seeds are viable. “Hitting weeds before, during and at the end of the pulse crop phase with different herbicide and cultural tools has a big impact on weed numbers and largely eliminates the addition of weed seed to the soil bank. Not many other crops allow this many tactics to be applied to weeds in one season,” he says. Leader of the NSW DPI Pulse team, Mr Mark Richards says the early flowering and maturing field pea varieties PBA Pearl and PBA Oura are the best candidates for crop topping, even though they were not released with this management strategy in mind. These earlier maturing varieties of field pea provide better weed control options than Kaspa field pea, chickpea and lupin, all of which generally mature later, sometimes after the target weeds have set seed. Early flowering and maturing field pea varieties PBA Pearl and PBA Oura are the best candidates for crop topping. “As early maturing varieties of faba bean, lentil and lupin become available, their adoption in crop rotations for weed control alone will be justified, especially given the broad spectrum of herbicides registered for use in pulse crops,” he says. Dr Armstrong recommends growers give greater consideration to the value of pulse crops in the rotation to achieve agronomic stability and improved profitability. “If weeds are a priority, growers can include a pulse crop with the intention of crop topping to prevent weed seed set—accepting a small yield penalty in return for bringing the weeds under control,” he says. “Brown manuring the pulse crop is a last option and would only be chosen in very high weed burden situations.” “When crop topping, timing is critical to prevent seed set of the target weeds,” says Dr Armstrong. “The weed seeds must be at or before the milky dough stage for crop topping to be an effective weed control measure.” If brown manuring is chosen, end the crop when the weeds are flowering and before the weed seeds reach the milky dough stage to be sure of 100 per cent seed set control. If herbicide resistant weeds are the main priority, spray out the paddock before the weed seeds reach milky dough stage. Some of the decisions surrounding the use of manuring and crop topping can occur during the growing season as seasonal conditions dictate. However, Dr Armstrong recommends growers give careful consideration to the use of pulses when they are planning their crop sequence several years in advance. “When choosing a pulse crop, consider the species’ adaptation to the farm and whether it is suited to crop topping and or desiccation as part of an integrated weed control program,” he says. From an economic point of view, it is important to calculate returns over the whole crop sequence rather than for each crop on its own as this will take into account any benefits or savings in soil moisture, soil nitrogen or pest and disease management. “Although there are significant soil health benefits in green or brown manuring a pulse crop it is rarely economical across the crop rotation,” Mr Richards says. “This is because growing two cash crops and a manure crop, or fallow, rarely earns as much income as three consecutive cash crops, even though the crop grown following a manure crop is likely to produce higher yield.” A 5-year study led by Tony Swan, Senior Experimental Scientist, CSIRO Agriculture clearly identified that a two-year break from cereal production and the implementation of all available weed seed control options is the best way to run down the ryegrass seedbank. Where herbicide resistant annual ryegrass is a major problem, an alternate three-year sequence of wheat-hay (sprayed afterwards) in year one, pulse-grain (spray topped) in year two, and Roundup Ready (RR) canola in year three can be profitable and also reduce the seed bank to extremely low levels. Mr Mark Richards leads the New South Wales Department of Primary Industries (NSW DPI) Pulse team at Wagga Wagga that was previously led by senior research agronomist, Dr Eric Armstrong. Both researchers have worked with pulses for many years and are passionate about the options pulse crops can provide the farming system. The on-going research investment by NSW DPI and the Grains Research and Development Corporation (GRDC) continues to examine weed control options and management in pulse crops.
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Strip grazing cattle to manage weeds

As the 2013–2016 drought bit harder in NSW’s Riverina, Ardlethan farmers Lou and Charlie Clemson were thinking about ways to better utilise more of their property, particularly the 200 ha of non-arable country. Using a NSW State Government drought assistance grant to supplement their own funds they have installed a laneway through the middle of their property, Wongajong, to link the hilly paddocks with the stockyards and provide easy access to all the cropping paddocks between. Lou Clemson says the laneway allows easy movement of stock through the cropping area and also provides an excellent confinement area with troughed water and creep feeders. The timbered hill paddock is key to the system’s success, providing native pasture for the breeding herd. Lou says the changes to their business and their weed management have been amazing. “We now have another income stream, and cattle have been very profitable since the drought,” she said. “And we are using less herbicide to manage weeds.” The re-introduction of livestock to Wongajong started in 2010 when the Clemsons bought 300 steers to make use of a frosted wheat crop. “We fed the steers for 5 months and made good money out of what would have otherwise been a failed crop,” said Lou. “After that we fenced off the hill and added the central laneway and watering points. We are really happy with how well this system is working and see benefits across our whole cropping operation.” “Growing early varieties is the key to maximising the feed benefit of fodder crops such as Moby barley and Brenan and Naparoo feed wheats, which we plant in February or March,” she said. “In paddocks where we have some annual ryegrass pressure we have sown feed barley in February–March, weaned calves onto it in May and grazed until September. This 73 ha paddock alone turned off 200 prime yearlings.” With some welcome rain in December, the Clemsons sprayed out the barley and took the opportunity to sow cowpeas over summer. “This year we weaned part of the herd in January and the calves went straight onto the cowpeas where they remained until late April. The cowpeas even podded up and we could have stripped them but decided to just continue grazing. The added nitrogen will also boost the next crop and build soil fertility.” Cowpeas planted opportunistically on some December rain provided perfect feed for newly weaned calves from January until late April. In addition to the feed value the cowpeas have also provided a boost to soil fertility. With two back to back seasons of crop competition and sustained grazing pressure, the ryegrass is well under control and the Clemsons have sown Condo grain wheat this winter. After removing the young stock from the cowpeas the Clemsons introduced them to creep feeders offering hay, feed barley and a magnesium calcium supplement in the central laneway. Lou said their system relies on the 200 ha of hilly country where they run their breeding herd. The cows calve in the hill paddock in July then have access to crop stubbles straight after harvest until January when the cows return to the hill paddocks and the calves are weaned onto feed. “In this system, Wongajong can carry 200 breeding cows and 50 replacement heifers but no more,” she said. “This is working so well that we are keen to build our herd and will replicate the laneway and fodder cropping system on a second property nearby. We have been expanding our area for both cropping and livestock with additional land purchased and leased.” Looking across Wongajong, the top paddock grew cowpeas that were grazed over summer, the next paddock down the hill has feed barley ready for grazing and then the laneway where the young cattle are introduced to hay and grain once their rumens are mature. The Lemken speed tiller will be used to prepare the cowpea paddock for sowing the high yielding, short season Condo wheat. “We identify paddocks that need a spell from cropping and also look at the weed burden,” said Lou. “Grazing barley is our go-to crop for weedy paddocks. It does a good job competing with annual ryegrass and gives us several options such as making hay or grazing and then spraying out.” Canola has been a mainstay crop for the Clemsons along with barley for grazing, hay and feed grain, and wheat for grazing and feed grain. The cattle strip graze the fodder crops at a density of 2 head/ha to maximise the feed value and weed control benefits. Electric fencing is used where necessary to manage the grazing intensity and provide fresh feed. Most of the fodder crops will be grazed out and sprayed in spring to clean-up for the following winter. The Clemsons are now planning to extend their fodder cropping program to hay and silage production. Forage barley has proven to be the most useful crop for livestock production and weed control. Charlie and Lou use a Lemken Helidor speed tiller to lightly cultivate paddocks that have been sprayed out after grazing. Paddocks are then rested for seven months, from late spring through summer, before they are re-sown. The combination of several non-herbicide weed control tactics such as strip grazing, fodder conservation and the speed tiller have resulted in an overall reduction in herbicide use. “Sowing early gives us the greatest number of choices,” said Lou. “Some years we would expect about 10 per cent of our crops to be frost affected, but by sowing early we can achieve higher yields and this can make up for losses to frost.” Lou said there has been a noticeable change in their attitude towards weeds with Charlie being much less stressed. Having the canola and wheat sprayed on time is important while there is more flexibility with spraying times for the grazing crops. “If there are weeds visible in the paddock we can stay relaxed knowing that once the cattle have finished grazing and been sold, the paddock will be sprayed out before the ryegrass sets seed, and any survivors will be killed with the Lemken Helidor,” she said. The Clemsons use a Lemken speed tiller straight after harvest to manage stubble and weeds. Provided there is some soil moisture present the cultivation to a depth of up to 10 cm or so causes about 80 per cent of the weed seeds to germinate, allowing a very effective spray opportunity. Cultivation with the Lemken Helidor machine stimulates weed germination and breaks up the stubble. Operating at 15–16 km/hr, the 12 m wide cultivator also breaks up and spreads the stubble and throws soil over some of the stubble to aid decomposition. The cattle still have access to valuable feed in paddocks where the Lemken has been used. This light cultivation means there is no need to burn stubble and seeding the next crop is easy. “Summer cropping opportunities seem to be more common in recent years and we have had success with both cowpeas and sorghum,” said Lou. “The Supa Sudan sorghum we grew this past summer came back three times and provided excellent feed value but it also used too much soil moisture and might limit our immediate cropping choices for that paddock.” “In winter, forage barley is followed by TT canola then a grazing wheat with the option to graze, make hay or harvest the grain.” In addition to annual ryegrass incursions the Clemsons have also seen black oats, wild radish and brome grass populations cleaned up through this combination of grazing and cropping.  
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Making pre-em herbicides work in high stubble

Whether stubble is standing or laying flat on the ground it represents a challenge for farmers using pre-emergent herbicides to control weeds early in the cropping season. Most growers and advisors are aware that products such as trifluralin are quite tightly bound if they contact stubble during application, however the behaviour of newer products has been largely unknown. For pre-emergent herbicides to be effective the product must be placed in contact with the soil and must provide an even layer of chemical to intercept germinating weeds. Decisions at harvest will have a direct bearing on pre-emergent choices and efficacy for the next season. Yaseen Khalil is a PhD candidate at the UWA School of Agriculture and Environment, studying the availability of pre-emergent herbicides applied to crop residue and then exposed to different rainfall simulations. Decisions at harvest will have a direct bearing on pre-emergent choices and efficacy for the next season. Yaseen Khalil, PhD candidate at the UWA School of Agriculture and Environment, is studying the availability of pre-emergent herbicides applied to crop residue and then exposed to different rainfall simulations. The three pre-emergent herbicides investigated were trifluralin, Sakura (pyroxasulfone) and Arcade (prosulfocarb). As expected, trifluralin was very resistant to leaching from crop residue with minimal amounts of the product washing off stubble in rainfall events simulated just one day after herbicide application. On the other hand, a sufficient quantity of Arcade was leached by rainfall applied after 7 days to provide some control of annual ryegrass. Sakura was the clear ‘stand-out’ when it comes to efficacy of leachate. Product applied to 4 t/ha crop residue plots provided 100 per cent control of annual ryegrass when just 5 mm of simulated rainfall was applied 14 days after the herbicide application. “The implications for growers are that they can rely on significant amounts of Sakura and Arcade being washed off crop residues and into the soil if there is a rainfall event of at least 5 mm within about one week of applying these pre-emergent herbicides,” says Mr Khalil. “If the crop residue is already wet when the pre-emergent herbicides are applied, the products are more tightly held and less product leaches off the residue in subsequent rainfall events, compared with spraying onto dry stubble.” Mr Khalil’s supervisor University of Western Australia senior lecturer, Dr Ken Flower says an important factor to consider is the unevenness of residue spread at harvest. “While the residue level across the paddock may average out to an acceptable 3 t/ha it is common for the residue to be as high as 10 to 15 t/ha directly behind the header,” he says. “This in itself has implications when it comes to growers’ decisions about their weed management tactics.” Australian Herbicide Resistance Initiative communication lead Peter Newman says getting the pre-emergent product through the crop residue and onto the soil at application time is still the priority. “It is good to know that some products remain effective and can be leached off the crop residue with rainfall following the application,” he says. “Yaseen’s research has added to the growing knowledge bank about the most effective use of pre-emergent herbicides in no-till, stubble retention systems.” Whilst quite extensive in itself, this study only compared three pre-emergent herbicides. The chemical properties of the over 50 active ingredients that possess pre-emergent, or residual, activity vary enormously, and they are found in 10 mode of action groups. The efficacy of these products relies on different environmental, soil and crop residue conditions. “Understanding how these products can best fit into an integrated weed management program on a farm requires considerable thought, taking many, many factors into consideration,” says Mr Newman. “There are great opportunities to use these products to add diversity to weed management but it is essential that they are not over-relied on as 100 per cent weed control is uncommon, even when the conditions at application are as good as possible.” “We used to talk a lot about rotating herbicides from one year to the next, now we are more focused on herbicide mixes as the best way to go — mixing two pre-emergent herbicides together where possible, and then perhaps rotate to another mix next year,” he says. “They say that rotating herbicides buys you time, but mixing herbicides buys you shots. Mixing and rotating buys you time and shots, which is the best that we can hope for.” Mr Newman recommends growers take the time to discuss a variety of options with agronomists and take on board research like Yaseen’s, along with their own observations, to build a robust and ever-changing weed management program. “The aim is to keep overall weed numbers low as this is the best way to minimise the risk of herbicide resistance,” he says. Other relevant resources Podcast: Herbicides and stubble – some wash off, some don’t AHRI Insight – Herbicide and stubble GRDC Pre-emergent herbicides manual What’s the safest way to manage pre-emergent herbicides at seeding