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Case Study

Aaron McDonald, Horsham Vic

Farming with his parents, Greg and Leanne, Aaron runs 5500 ewes for wool and prime lamb production, utilising pastures, hay paddocks and crop stubble on their 4050 ha property. The McDonalds are finding a rotation of canola, wheat, canola, wheat, then a double break of canola followed by faba beans or clover hay, is profitable and enables them to keep weed numbers down. In barley crops the straw is also often baled after cutting the crop low, allowing sowing without stubble burning. Aaron does most of their oaten hay production on the poorer soils but also uses oaten hay as an effective means to clean-up paddocks that have a higher infestation of ryegrass. Their clover hay is sold locally, predominantly as cattle feed, while their oaten hay is exported most years. “Annual ryegrass and wild radish are our main problem weeds,” says Aaron. “We test for herbicide resistance every couple of years and so far the results have come back as ‘susceptible’ for most of the major groups. The main challenge we have with wild radish is the fact that it germinates all year round. With ryegrass it’s all about keeping plant numbers low.” Although the testing is not showing herbicide resistance, Aaron is seeing evidence of Select not working as well as it did in the past. To add more mode-of-action diversity to their system the McDonalds are using pre-emergent herbicides Sakura and Boxer Gold in cereals with good success and grow both hybrid (RR and 650TT) and open-pollinated (TT) canola cultivars. “The RR canola enables extra knocks with glyphosate in-crop to clean up paddocks where we are concerned over the efficacy of Select,” says Aaron. “All our other in-crop herbicides are still working well but we are trying to rotate as much as possible with Select and Edge, and using paraquat ahead of canola and glyphosate or paraquat ahead of cereals.” The McDonalds have always sown their crops on fairly narrow rows, 250 mm spacing, and use high sowing rates (wheat and oats sown at 100 kg/ha and canola at 3.6 kg/ha) to provide strong crop competition to help with weed control. The sheep grazing stubbles provides quite good control of summer weeds but some herbicide is always required. Aaron’s main summer weed concerns are melons and self-sown crop. In autumn or pre-sowing he occasionally double-knocks but often there are no survivors so the second knock is not needed. Hay making and harvest weed seed control Aaron has implemented narrow windrow burning for the last 4 or 5 years in their canola crops as a harvest weed seed control tactic to capture late germinating weeds. This is supported with strategic crop topping of the canola to desiccate and then windrowing 80 per cent of the canola area each year. In their cereals, crops are cut low and stubble is burnt on about 75 per cent of the cropped area to allow easier sowing operation, and has the added benefit of destroying some weed seed. In barley crops the straw is often baled after cutting the crop low, allowing sowing without stubble burning. Grazing stubble and burning also helps reduce mice and slug numbers. “Oaten hay production enables us to apply a desiccant over the top prior to cutting for hay,” says Aaron. “This gives us the opportunity to implement a herbicide plus non-herbicide double knock on in-crop herbicide escapes.” Aaron McDonald is using oaten hay and clover hay production as weed management tools within their mixed farming operation south of Horsham. “We graze the cereal stubble and canola narrow windrows after harvest but don’t leave the sheep on the paddocks for long,” he says. “We find that the cereals provide better feed value than the canola windrows but we also put lambs on the canola regrowth for a little extra green pick.” Each year about 5000 lambs move through the on-farm feedlot, where the McDonalds feed out gradings from the barley grain and the straw. “Feeding the grain gradings out in the feed lot also brings weed seeds into the confinement area where we can control them quite easily,” says Aaron. The feedlot adds value to the straw and grain gradings, turning off about 5000 lambs per year. Weed seeds that are brought back to the feedlot are easily managed if they survive being eaten.
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Taking the pressure off glyphosate across crop rotation

Now is the time to take pre-emptive action to reduce the incidence of glyphosate resistance in weeds. Eric Koetz, NSW DPI weeds research agronomist, says the majority of agronomists and a growing number of farmers recognise the need to implement management practices that help protect the efficacy of glyphosate in farming systems. “We know that it takes between 14 and 19 years of routine use of glyphosate to evolve resistance,” he says. “We have now had Roundup Ready cotton for 15 years and there are many instances of glyphosate resistant populations of weeds such as fleabane, windmill grass and barnyard grass.” “The 2 + 2 + 0 strategy developed in the cotton industry to protect glyphosate and Roundup Ready technology is also applicable to other farming systems,” says Mr Koetz. “When planning an integrated weed management program, the Cotton RDC recommends including two non-glyphosate tactics in-crop, two non-glyphosate tactics in the fallow and ensuring zero survivors.” This is where the use of residual herbicides can play a part, along with non-herbicide tactics, such as strategic tillage in both summer and winter crops and in fallow situations. Including residual herbicides in both the fallow and crop phases increases the diversity of herbicide modes of action and places downward pressure on the weed seed bank. Eric Koetz, NSW DPI weeds research agronomist says residual herbicides need to play a part in the control of glyphosate resistant weeds in crop and in the fallow. “Roundup Ready technology has been of great benefit to the cotton industry, and has a fit in other farming systems too, but it can not stand alone. It must be supported and protected through an integrated weed management strategy,” says Mr Koetz. “To preserve glyphosate it is necessary to reduce the total number of applications across the crop rotation.” What are the non-glyphosate options for in-crop weed control? Short answer: Residual herbicides applied at sowing, inter-row cultivation, crop rotation, maintaining ground cover and increasing crop competition. Longer answer: Residual herbicides that require incorporation are best applied at sowing. There are some older herbicides that have not been used for several years that are still quite effective and could make a come-back to farming systems that have come to over-rely on glyphosate. There are also new use patterns being registered for a number of different products that can be used to add diversity to control weeds at different growth stages or to control later in-crop germinations. Increasing crop competition and promoting rapid canopy closure has a significant impact on in-crop germination. Diversifying the crops grown automatically makes more herbicide options available to use against weed populations that may be evolving glyphosate resistance. Residual herbicides applied at seeding or soon after harvest help reduce the number of glyphosate applications across the cropping cycle. What are the non-glyphosate options for controlling weeds in the fallow? Short answer: Residual herbicides applied soon after harvest, strategic tillage, double knock, optical sprayer, cover cropping. Longer answer: Choose residual herbicides carefully. Some products have long plant back periods and will reduce the grower’s options for the following season. Tillage is widely practiced in irrigated cotton and is an effective way to eliminate weeds. In dryland systems tillage operations may be best suited to low crop residue situations such as following a chickpea crop. The cultivation operation may be done across the whole paddock or in small patches and can be coupled with paddock renovation, the incorporation of soil ameliorants or deep banding of nutrients. Several research projects are currently investigating the usefulness of cover cropping and brown manuring on weed numbers. What can be done to ensure there are no survivors? Short answer: Scouting and chipping, optical sprayer, patch tillage. Longer answer: Actively looking for survivors must become a key management practice. A few large plants that have survived all control tactics can generate a huge number of seeds that are very likely to carry some level of herbicide resistance. If these plants are physically removed before they set seed they will not contribute to the seed bank for future germinations.
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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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Can I retain stubble and keep weeds under control?

Tony Swan, Senior Experimental Scientist with CSIRO Agriculture and Food says growers can manage stubble without compromising weed, disease and pest management or the timeliness of the seeding operation. Tony Swan, Senior Experimental Scientist with CSIRO Agriculture and Food says crop sequence, including a double-break, is an effective way to manage weeds, improve profit and manage stubble residues in southern grain farming systems, with or without livestock. “Decisions at harvest, post-harvest/pre-sowing and at sowing influence the success of a seeding operation into stubble,” he says. “With a flexible approach, growers can manage stubble loads to suit their seeding operations, weed control tactics, herbicide choice and profit.” “As a rule of thumb, the stubble load after harvest is 1.5 to 2 times the grain yield for wheat and 2 to 3 times the grain yield for canola,” says Mr Swan. “A high stubble load can create issues for all types of seeding systems by restricting herbicide choice, effectiveness, contact on the soil or weed target and even reduce crop emergence.” In 2014 an experiment was established at Temora, NSW in a paddock with high levels of Group B resistance in annual ryegrass. The trial compared the yield, profit and annual ryegrass (ARG) population status in three management strategies in a no-till (tine opener) or zero tilled (disc opener) farming system. Introducing more crop and herbicide diversity into the farming system generated a higher average net margin over three years while reducing the seedbank from 1864 plants per m2 to 351 plants per m2 in just 24 months. Following the wet 2016 season, with a soft late finish, three years of the diverse strategy (which included a double break) reduced the ryegrass seed bank by 70% compared to the aggressive (high input) strategy (145 cf 573 seeds/m2), while the conservative (low input) strategy increased the seedbank by 600% to above 4000 seeds/m2. “Crop sequence is an effective way to manage weeds, improve profit and manage stubble residues in southern grain farming systems, with or without livestock,” says Mr Swan. Mr Swan will be presenting his research into double-break cropping at the WeedSmart Forum on 21 August, in Wagga Wagga. Go to the website to register. Does choice of seeder type influence weed control? Short answer: In our experiment, after 3 years ARG seed numbers were generally lower when crops were sown with a tine seeder. Longer answer: Averaged across the three management strategies, ARG seedbank populations were lower in tine seeded plots in 2016 (650 seeds/m2 in tine cf 1080 seeds/m2 in disc) and 2017 (384 seeds/m2 in tine cf 944 seeds/m2 in disc). However, the use of expensive pre-emergent herbicides eliminated any significant difference in ARG seedbank populations in crops sown with a disc or tined seeder. In the conservative strategy where trifluralin can not be used with a disc seeder (not on label), the result was a higher ARG seedbank population (4045 seeds/m2) with a disc seeder compared to 1840 seeds/m2 with a tine seeder. By February 2017, following the 2016 decile 9 season the lowest average ARG seedbank population was found in the diverse cropping strategy sown with a tine seeder (82 seeds/m2). In the conservative strategy weed populations continued to increase when sown with a tine seeder (2322 seeds/m2) and with a disc seeder (7631 seeds/m2). Tony Swan inspecting the stubble management trial plots, looking at the ‘Conservative (lower input)’ second year wheat treatment sown with a tine seeder (left) compared to the ‘Conservative’ second year wheat treatment sown with a disc seeder where trifluralin could not be applied (not on label for disc seeders). What options do I have if stubble is too thick to sow through? Short answer: Reduce stubble load by grazing, baling, mulching, incorporating with nutrients, or use a strategic late burn. Longer answer: Tine seeding systems will struggle to establish crops into large stubble loads >6 t/ha. While disc seeders may penetrate the stubble more easily and plant crop seeds into high stubble loads, patchy crop establishment and ineffective herbicide application can result in any seeding system sown into high stubble loads. Retaining stubble, with all its benefits, should not be allowed to compromise effective weed control. Mulching, incorporation and grazing all potentially retain more nutrients in situ however mulching or incorporation are likely to lead to nutrient tie-up in the soil unless additional nutrients are added. Grazing and late burning both improve in-crop nitrogen availability, and often the yield of the following crop. It is not recommended to grow wheat after wheat unless the stubble from the first wheat crop is burnt or grazed, or supplementary nitrogen is applied to offset N immobilisation. To try and avoid burning at all costs, the best option is to sow a diverse crop sequence and use the legume crop to reduce the cereal stubble.
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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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Ask an Expert

Does ambient temperature affect herbicide performance?

with Chris Preston, Associate Professor, Weed Management
 at 
The University of Adelaide Temperature affects the absorption, translocation and metabolic degradation of herbicides applied to plants. Herbicides applied under the wrong conditions can appear to fail, however the reason may not be herbicide resistance. Dr Chris Preston, Associate Professor, Weed Management
 at The University of Adelaide says most herbicides have a temperature range at which they are most effective in controlling target weeds. “Applying herbicides outside the optimal temperature range is likely to contribute to a spray failure, even in susceptible populations,” he says. “Alternatively, applying herbicides within the correct temperature range can improve the control in populations known to have a level of resistance to that herbicide.” Dr Chris Preston suggests testing whole plants rather than seed for responses to a range of post-emergent herbicides. The Quick-Test is conducted in the same growing season as herbicide will be applied so the testing will occur under similar conditions to field conditions. Dr Preston says the effect of frost on the efficacy of clethodim is a striking example. Spraying clethodim in non-frosty conditions achieves vastly better results than spraying after three days of frost, even on populations that are resistant to this chemical mode of action. “Combining the optimal temperature with optimal weed size will give the best results possible,” he says. “The current common practice of applying clethodim to tillered ryegrass in the coldest months is not making the best use of this herbicide.” As a general rule of thumb, Group A (fops), paraquat (Group L) and glyphosate (Group M) are more effective at lower temperatures while Group A (dims), atrazine (Group C) and glufosinate (Group N) are more effective at higher temperatures. However, weeds that are resistant to paraquat become less resistant in warmer temperatures. “The other implication of this research is the effect of ambient temperature on herbicide test results,” says Dr Preston. “Seed collected in winter and grown out in the glasshouse in summer will be tested for resistance in conditions that are not representative of field conditions when growers are next treating that weed species. The Quick-Test using whole plants overcomes this problem and improves the reliability of herbicide susceptibility testing.” How can I get the best performance out of clethodim? Short answer: Avoid applying clethodim during frosty periods. Longer answer: Twice as much clethodim is required to kill susceptible annual ryegrass if the product is applied after three days of frost. Even higher rates are required if the plants have resistance to clethodim. Planning to apply clethodim for grass control outside the coldest months of June and July, and avoiding night spraying in winter, will see better results in both resistant and susceptible populations, particularly in tillered plants. Clethodim is most active when temperatures are over 20 degrees C. Weed seed that is tested during summer may return false negative results, which could translate into spray failure in the field the next season. Twice as much clethodim is required to kill susceptible annual ryegrass if the product is applied after three days of frost. Even higher rates are required if the plants have resistance to clethodim. When it is it too hot for glyphosate? Short answer: Efficacy is much better at 20 degrees C than at 30 degrees C. Longer answer: Spraying glyphosate resistant barnyard grass at lower temperatures is more effective than under hotter conditions. If barnyard grass is tested for herbicide resistance during the cooler parts of the year it may appear susceptible to the field rate of glyphosate but then when this rate is applied to the population in summer there may be many survivors. When glyphosate is taken up rapidly it tends to limit its own translocation, which can mean that although symptoms may appear more rapidly in warmer temperatures, plant kill is less reliable. Which herbicide resistance test should I use? Short answer: The weed resistance Quick-Test for post-emergent herbicides. Longer answer: The Quick-Test involves testing whole plants rather than seed for responses to a range of herbicides and rates. The Quick-Test is conducted in the same growing season as herbicide will be applied so the testing will occur under similar conditions to field conditions. The results of the Quick-Test are available within the same season, potentially giving growers an opportunity to apply an effective weed control tactic before the end of the season. The Quick-Test is not available for many pre-emergent herbicides. The Quick-Test is available through Plant Science Consulting and results are normally available after four weeks. Relevant links Maximising clethodim performance and the impact of frost fact sheet Keeping clethodim working in broafleaf crops Plant Science Consulting herbicide resistance testing – Quick-Test GRDC Update Paper – New developments and understanding in resistance mechanisms and management
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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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