Greg Martin, VIC
Take no prisoners to combat resistant wild radish!
University of Adelaide
Early detection of herbicide resistant weeds, a focused management strategy and being fastidious about controlling survivors is helping Victorian Mallee farmer Greg Martin get the better of herbicide resistant weeds.
Mr Greg Martin is currently attacking Group I herbicide resistant wild radish (Raphanus raphanistrum) that was found growing in a single paddock on his 5500 hectare farm located at Nandaly in the Victorian Mallee. In 2013, a suspected patch of herbicide resistant wild radish was identified and live plants surviving herbicide treatment were tested for resistance. The results confirmed low level resistance to 2,4-D and MCPA.
Mr Martin believes resistance had evolved due to a lack in rotation of chemical groups and not enough importance given to controlling survivors.
Mr Martin’s dryland property features sand/sandy loam soils and a typical annual rainfall of 300-400 mm on average. Grain production is the main enterprise and he has made a conscious effort over the past few years to diversify the cropping mix. This broadacre cropping approach provides farmers with a greater tool kit to battle weed resistance problems, creating more opportunities to use varied weed management tactics.
Over the past 10 years Mr Martin’s enterprise has changed, moving to a no till system that involves a lot more cropping. Whilst this typically requires a greater reliance on chemical management of weeds, for wild radish it keeps the seeds closer to the surface – reducing their longevity and allowing faster management and eradication of a resistance problem.
Mr Martin and his agronomist Matt Elliott (Dodgshun Medlin) developed a 5 year targeted and integrated weed management plan to combat the herbicide resistant wild radish. Mr Martin believes consulting with his agronomist will be key for him to successfully eradicate resistance: “They have a proven record of dealing with this problem on other farms so we consulted with them and formulated a plan to get on top of the problem.” He expects it will take a minimum of five years to get the resistance problem under control. Control may occur sooner but he is mindful to not relent too soon.
Since the discovery of herbicide resistant wild radish on Mr Martin’s farm there is now an emphasis on herbicide chemical group rotation, managing survivors and integrated weed management. Making use of alternative cultivation practices where possible, such as narrow windrow burning and spray toping in the legume phase, has also been included in the management plan. These tactics have been selected as the farmer feels it is important to use as many different control options as possible.
“Mindset is important; test and identify the scale of your problem, get a plan and get stuck in! Maybe with hindsight we danced around the problem for too long” said Mr Martin.
Incorporating Triazine Tolerant (TT) canola into the crop rotation is the primary strategy in place to defeat the resistant wild radish. “There was a heavy reliance on Clearfield cereals in the rotation and another chemical group was needed to control radish in the break crop phase of the rotation” said Mr Martin. “Radish has also shown group B resistance so the use of Atrazine (group C) has given us a greater level of weed control within the crop.” Finding paddocks without a history of group B herbicide use in which to grow TT canola can be a stumbling block for this approach and here accurate farm management records are advantageous.
In the season after resistance was confirmed, TT canola was grown in the problem paddock. This proved to be a good first step for Mr Martin’s management program with the group C herbicide providing effective control of all wild radish growing in the paddock that year.
“We are entering the second year of a five year management plan and the new strategies appear to be successful in getting the resistance problem under control”
Mr Martin also carefully considered his approach to harvesting his canola, creating narrow windrows of straw and chaff to burn. It is not surprising he chose this narrow windrow burning strategy considering how well it has worked in WA to reduce wild radish seed banks and overcome resistance problems.
Tactics to combat spread of the resistance by preventing seed set are also in place.
“To kill any late germinating radish plants that may emerge after the first spray we are using a Double Knock strategy; killing every plant that germinates that year equals a reduction in numbers and reducing their spread” said Mr Martin. In 2015 the paddock will be returned to wheat and the control of wild radish monitored vigilantly.
Wild radish invading a cereal crop (Photo: Peter Boutsalis).
“We are also taking a no prisoner approach to any seed that hits the ground by controlling weeds in non-cropped areas, including fence lines. This reduces their numbers using chemistry that is not used in the crops” Mr Martin highlighted. The main complication with this tactic is timing of herbicide applications as radish can germinate at all times of the year.
As the resistance problem was localised to one paddock the management plan was specific to that area. However, dealing with this problem has increased Mr Martin’s awareness and positively altered his attitude towards weed management for his entire enterprise. The lesson was to make weed management a high priority; vary the control tactics, monitor treatment performance and be prepared to make management changes early.
Mr Martin also points out that all of his resistance control measures have come at a greater financial cost. “Economic circumstances are an issue that should not be underestimated. Realising you are developing a problem yet having the means to act accordingly could be an obstruction.” However, he deems the additional expenses incurred from a comprehensive weed management strategy are justified. Mr Martin declares “We can see that controlling our problem is going to come at a cost to the business but also realize that for us to do nothing, and let the problem intensify, is going to eventually lead to a problem that is so massive it could ultimately make us unviable. Short term pain for long term gain!”
Grant Wilson, VIC
Their no-till cropping rotation, which includes wheat, lentils, canola, barley, lupins and field pea, is governed by disease and weed management considerations, proving that integrated weed and disease management can go hand in hand.
“There was a time when we just ignored summer weeds, but not now,” says Grant. “We are very conscious of weed management all year round and the potential for herbicide resistance to really limit our options if it gets out of hand.”
Following a ‘no cereal after cereal’ policy, Grant usually tries for a two year break between cereal crops. “We also rotate between different wheat cultivars to make the most of their disease management traits,” he says.
“Following a cereal we would be looking to plant a legume, usually a lentil crop, but if we were faced with a broader weed problem we would choose an ‘imi’ tolerant lentil or possibly decide to grow field pea instead of lentils to take advantage of the wider range of selective herbicides registered in field pea.”
Grant usually keeps a two year break between cereal crops to maintain effective control of diseases. Pulse crops sown into standing stubble offer the best combination of tactics to tackle ryegrass in-crop using grass selective herbicides and desiccation.
Being in a lower rainfall zone (325 mm or 13 inches), the Wilsons find a conservative rotation is safer in the long run and gives them more options to manage annual ryegrass.
Pulse crops offer the best combination of tactics to tackle ryegrass in-crop using grass selective herbicides and desiccation. Recently Grant started using pre-emergent herbicides such as Boxer Gold® and Sakura® to reduce their reliance on trifluralin in wheat. “So far we have had mixed results, especially in dry weather, when there was insufficient moisture to properly activate the herbicide, on top of poor crop competition due to the seasonal conditions,” he says. “It is an expensive option but when it works it provides good control across the paddock.”
Grant prefers to use Boxer Gold® before sowing with knife-points and press wheels on the seeder.
The heavier soils are in a fallow rotation to conserve soil moisture. Most fallow paddocks will usually be sprayed once or twice, depending on rainfall, over the summer.
The Wilsons grow vetch as a green manure crop on their lighter soils to improve soil health and control weeds. When the vetch reaches maximum biomass Grant sprays it out to gain maximum benefit from the high biomass production. All other crops are left as standing stubble and this year they will be moving into inter-row sowing.
“We now have RTK guidance fitted to the seeder and expect to see some real improvements in crop establishment,” he says. “With a more even sowing depth we should get more uniform germination and that will increase the crop’s ability to out-compete weeds.”
The soil type across the Wilson’s farm ranges from sand to loam and varies in pH. Kate, an independent agronomist, takes production-limiting factors such as soil pH and boron levels into account when planning the rotation, particularly with lupins being more sensitive to higher pH and lentils being sensitive to boron levels. The potential for herbicide residues to still be present after a dry summer is also a consideration, particularly on higher pH soils.
The Wilsons crop between 4000 and 5000 ha a year and generally do not have livestock, however they do fatten lambs on stubble as the opportunity arises.
Annual ryegrass has some resistance to Group A ‘fops’ but so far ‘dim’ herbicides are still effective. Kate customises their herbicide mixes to preserve the effectiveness of the dim herbicides by avoiding unnecessary usage.
They have also resisted a move into glyphosate tolerant varieties because they are concerned about the potential over-use of glyphosate that may lead to glyphosate resistance in weeds. However, they do grow some herbicide tolerant crops that utilise different herbicide modes of action.
Annual ryegrass on the Wilson’s property has some resistance to Group A ‘fops’ but so far ‘dim’ herbicides are still effective. Kate customises their herbicide mixes to preserve the effectiveness of the dim herbicides by avoiding unnecessary usage.
The Wilsons choose not to grow imi-tolerant cereals because they believe this would lead to an over-use of Group B chemistry, which is known to lead to herbicide resistance in weeds such as brome grass.
They use imi-tolerant Clearfield canola to a limited degree as another option to control annual ryegrass using imazapic/imazapyr (Group B) products and rotate herbicides as best they can in an attempt to stave off herbicide resistance in grass weeds.
“We use crop desiccation to stop weed seed set to avoid the need for narrow windrow burning to destroy weed seeds after harvest,” says Grant. “Desiccation seems most effective in legumes, particularly lentils. In cereals we have also used herbicides to croptop weeds according to product label instructions.”
“Fleabane is a new weed in this area having become noticeable for the first time during the wet summer in 2010,” says Grant. “A double knock treatment has been recommended for fleabane control and we will also introduce cultivation if required in some situations.”
The Wilson’s tread a fine line between maximising crop competition and conserving soil moisture. “Plant health is our main interest and we use a range of tactics to reduce weed pressure in-crop,” says Grant. “With legumes in the rotation we avoid applying much starter-N fertiliser and we make an effort over summer to get the paddocks as clean as possible before seeding.”
The Wilsons plant their crops as narrow as possible using a standard cereal seeding rate of 60 kg/ha on a 250 mm row spacing. They find this row spacing narrow enough to provide early crop competition and not be too rough, while still being able to inter-row sow.
Taking a thoughtful and long-term view of herbicide use within their cropping system has kept a lid on herbicide resistance on the Wilson’s farms so far and preserved a wide range of herbicide chemistry. Herbicide use is supported with non-herbicide tactics and the rotation of modes of action within and between crop types.
Keeping the farm clean using tactics
Case study: Graham Clapham
A diversified cropping system requires great attention to detail and offers many opportunities to implement several tactics in an integrated weed management strategy.
Spray application technology like these multiple-nozzle fittings make it quick and easy for the operator to change the nozzle type if environmental conditions change during the spray operation. The Claphams have placed the nozzles on their spray rig close together (250 mm apart) to maximise coverage and minimise drift.
Graham Clapham started his farming career straight out of school at 15 years of age. Even then he was clear about his desire to own a black soil farm on the Darling Downs. Graham grew up on his parent’s 200 ha mixed cropping farm, growing irrigated and dryland crops including corn, soybean, wheat, sorghum, onions and pumpkin.
With help from his parents, Graham realised his first goal when he was 18, purchasing a farm of his own at Norwin, west of Toowoomba. He now grows mostly irrigated cotton, corn and wheat and dryland cotton, wheat and sorghum on the family’s 1840 ha aggregation in the Brookstead–Norwin district.
On the 700 ha that is usually irrigated each year Graham has two main rotations—irrigated cotton or corn followed with irrigated wheat then a long fallow before returning to cotton or corn. In the corn–wheat rotation there is no cultivation but Graham has different herbicide options available and an opportunity to provide a disease break to combat fusarium wilt.
Rainfall dictates the dryland crop rotation on the rest of the cropping area. Minimum till is practiced to conserve soil moisture with occasional cultivation only to renovate the tramtracks.
Graham is aware of the risk of herbicide resistance, particularly in weeds like flaxleaf fleabane and feathertop Rhodes grass, which have always been hard to kill with glyphosate, and milk thistle is a new concern for the business.
Since the introduction of genetically modified cotton in 1996, the Claphams have practiced pupae-busting cultivations to manage resistance in helicoverpa. This has had the spin-off benefit of keeping hard to control weeds like flaxleaf fleabane and feather-top Rhodes grass under control.
“Pupae busting is a robust cultivation to a depth of 100 mm and is required to remove all large soil clods,” he says. “It must be done before the end of July following the cotton harvest in April–May.”
The deep cultivation after cotton buries weed seeds deep in the profile where they can’t germinate. Unfortunately flaxleaf fleabane seeds remain viable for longer when they are buried than when they are close to the soil surface. This means cultivation in subsequent years can bring viable seed back to the surface where it can germinate so it is not a complete solution but another useful tactic in the farming system.
The cultivation leaves the soil dry and prone to erosion so the Claphams aim to sow a wheat crop after cotton to provide ground cover over winter and stubble for the following summer.
Soil moisture and irrigation water availability govern the sowing rates used although the Claphams have two options when it comes to row width in their dryland crops. When sowing wheat into cultivated soil after cotton they can use an air seeder to plant rows 150 mm apart rather than the single disc planter used in minimum till planting to sow 500 mm rows.
Sowing in narrow rows has several benefits for weed control in the dryland system. To begin with sowing is a full tillage operation that removes any weeds present at the start of the season. The increased shading of the inter-rows suppresses weed germination and after harvest there is more stubble left on the ground, again suppressing weed germination.
Infrastructure such as channels and pump sites are kept clean throughout the year to avoid the risk of weeds spreading throughout the farm in irrigation water.
Graham has not noticed a yield difference between crops sown at the narrow and wider spacing although the air seeder does dry the soil out more than the single disc planter.
“The wheat crop is often not great, especially if winter rain is scarce,” he says. “But it provides good cover and we can use different chemistry to control weeds, especially to achieve a residual effect on flaxleaf fleabane.”
Graham says the chemistry available for use in wheat is very effective, keeping the wheat crops quite clean. Corn can experience some late grass germinations, which they have previously treated with glyphosate at harvest and then burnt the stubble.
When there is additional water available for irrigation early in the year the Claphams often take the opportunity to plant soybeans. Having this as an option they are conscious of the residual action of the herbicides used in the previous wheat crop. “We use herbicides with no residual effect to control broadleaf weeds such as thistles and turnip in the wheat so we don’t need to worry about the plant back period for soybean,” says Graham.
So far the Claphams have not experienced any spray failures that have raised concern about herbicide resistance. Graham is very conscious of the potential risk and is mindful of the experience in the USA with widespread glyphosate resistance in their cotton industry.
“Glyphosate-ready cotton has been a positive innovation for the industry, making it more sustainable and ending the use of environmentally-harmful herbicides,” says Graham. “However, glyphosate does not give 100 per cent control of weeds in cotton. Vines particularly can survive a spray and so we use inter-row cultivation and hand chipping to remove vines as needed.”
Inter-row cultivation in cotton, corn and sorghum also helps maintain the furrow profile and to conserve moisture before the canopy closes. Graham occasionally uses an inter-row shielded sprayer to apply glyphosate in corn and sorghum crops.
The Claphams recently purchased a neighbouring farm with a very heavy weed burden. They have used cultivation and herbicides to drive down the weed seed bank and to treat weeds they have never seen in the area before.
The Claphams do all their own spray operations, mainly so they can control when they spray. “The Darling Downs region is closely settled and there are not many trees across the cropping area. It can be very difficult to find suitable times to spray without the risk of off-field impacts. Having our own gear and labour available means we can spray as soon as suitable conditions prevail.”
Spot spraying larger weeds that have escaped earlier treatment is the last operation before plating clean seed into clean paddocks with clean borders (#8 in the 10 Point Plan).
Graham’s son-in-law, Jonathon Mengel, is responsible for the spraying operations across the farms. They have found that having a person with the designated responsibility to have the chemicals in stock and be looking for spray opportunities has been very beneficial to their operation.
“We have very few weed escapes after a herbicide spray,” says Graham. “On the rare occasion that it does happen we prevent seeding using tillage or a follow-up application of a knockdown like paraquat.”
“In the fallow we look for opportunities to do a double-knock treatment but it can be very difficult to get favourable conditions for two sprays close together,” he says. “Glyphosate, Starane®™ and MCPA®™ are relatively easy to apply using air induction nozzles to splash the product on with minimal risk of spray drift. The second application of paraquat 10 days later is more difficult, especially given the need to apply a fine droplet size.”
The Clapham’s Case Patriot sprayer, with its 36 m boom and 4 m wheel base, fits perfectly into their on-farm control traffic system. They have doubled the number of nozzles on the boom, placing a set of nozzles every 250 mm instead of the traditional 500 mm, allowing greater coverage and helping to extend the tight spraying window.
“This gives us a double overlap so we can consistently use coarse droplet nozzles and still get coverage, and it also enables us to operate lower to the ground,” he says.
When necessary Graham will spot spray or hand rouge weeds prior to planting the next crop to ensure the paddocks are as clean as possible going into the season.
The Claphams are also careful to keep irrigation infrastructure such as head ditches, supply channels and tail drains weed free. They use residual herbicides at high rates to effectively sterilise the soil in these non-cropping areas. “The risk of distributing weeds throughout the farm is of great concern and maintaining weed-free infrastructure is a year-round priority for us,” says Graham. “We also pay attention to planting clean seed each year, buying in cotton, sorghum and corn seed, and grading the wheat seed we keep the next season.”
“Black oats has been a bad problem in the winter cropping program but we seem to have won the battle with a consistent approach to planting clean seed.”
Throughout the crop rotation the Claphams are looking for ways to manage weeds to achieve the best possible productivity and profitability in the long term from their cropping operation.
Watch Graham’s video below!
Tom Murphy, NSW
Aggressive and innovative approach tackles resistant weeds
An aggressive and innovative approach to weed control is helping northern NSW farmer Tom Murphy win the war on herbicide resistant weeds.
Mr Murphy manages the 10,000 hectare North Star Aggregation for the Sustainable Agriculture Fund, which purchased the property four years ago.
Unknowingly, they inherited populations of glyphosate resistant barnyard grass, Group A-resistant black oats (wild oats) and Group B-resistant phalaris, as well as ‘herbicide tolerant’ populations of fleabane and feathertop Rhodes grass.
“A lot of this was discovered purely when we went and did the first spray of a fallow with a reasonably robust rate and found that the barnyard grass would still remain in the paddock – we knew straight away we had a problem,” Mr Murphy said.
“The same year we put a Group B herbicide across a winter crop and the phalaris just did nothing, and that was with little or no Group B history on the farm as well.
“So we sent that seed away for testing and came up with a plan to deal with it.”
As a result of his subsequent success in tackling resistant weeds, Mr Murphy has been chosen as a WeedSmart Champion. WeedSmart is an industry-led initiative managed by the Australian Herbicide Resistance Initiative (AHRI) aimed at enhancing on-farm practices and promoting the long term sustainability of herbicide use in Australian agriculture.
“We got involved in the Weedsmart program purely because we’ve been through the tough lessons,” he said. “We encountered the problem and had to be very quick on our feet to try and get around it.
“If I can share those lessons with other farmers so they can get on top of their problem weeds sooner then that’s a win for industry.
“WeedSmart also allows me to meet people who have tackled these problems differently. If I can find a different way of doing something that’s more cost effective then that’s great for the business that I run.”
The dryland North Star Aggregation property features about 8500 arable hectares under rotation, with 75 per cent each year sown to winter crops of wheat, barley, canola and chickpeas, and the remainder to sorghum and cotton in summer.
The Brigalow-Belah country features highly productive, grey self-mulching soils, which can store 150-180mm of soil moisture, with most of the 620mm average annual rainfall arriving in winter.
Despite the productive potential of the country, the added work and chemical required to control the range of problem weeds was loading $40/ha in costs to the bottom line.
Mr Murphy devised an aggressive integrated weed management plan, featuring crop and chemical rotation, very precise herbicide applications and double-knock treatments, as well as non-chemical methods such as strategic tillage and windrow burning.
“One thing we’ve definitely done is be really aggressive with these weeds,” Mr Murphy said. “It does cost more and while you might not win all of your battles, with that aggressive approach you will win the war.
“The other feature of the plan has been a willingness to think outside the square. If someone told me that windrow burning was the way to go around here I would have laughed at them a couple of years ago.
“But we’re giving it a crack and if it doesn’t work then at least we know. And if it does work and it’s a winner for us then we’re ahead.”
Mr Murphy’s strategy features a strict, managed approach to chemical use.
“We’re managing our use of herbicides through a couple of options. One is the double knock approach, which we’re finding is working very well; the other is mixing up the chemistry – we try not to be too reliant on one active group too much.
“It’s also very important to get your spray rig set up right and to use the correct rates.
“We’ve taken a very aggressive approach to our resistant weeds so we use nothing but the top rates. We found out the hard way that if you try and reduce your rates with any resistant weeds you’ll run into trouble again.”
The ability to grow summer crops as part of the rotation has also delivered benefits to herbicide rotations as well as non-chemical treatments.
“For example, for cotton you have a long fallow leading into it; you’ve got a crop period where you can use different chemistry; and you’ve got a long fallow after it, as well as a mandatory cultivation,” he said.
“Having sorghum in there as well also changes the fallow period and introduces new residual chemicals, so the summer rotation is really key to what we’re doing.”
The non-chemical control method of windrow burning is also being trialled, and although early signs are it may not be suited to the environment, Mr Murphy is maintaining an open mind.
“At this stage I don’t see that it’s a great fit for our circumstances because a lot of our weeds have lost their seed come harvest time or they’re not a problem in crop, but we are looking at it and we are trialling it.
“It’s really important that when you’ve got a herbicide resistance problem that you don’t stick your head in the sand – you need to be proactive about it.”
Murray Scholz, NSW
How to go from total crop failure to overcoming weed resistance
A growing problem with herbicide resistant ryegrass, which culminated in the total failure of a lupin crop 10 years ago, forced Murray and Emma Scholz to tackle the problem head on.
Today, after implementing a range of measures, the couple has reduced the threat to their profitability and sustainability and have their weeds firmly under control.
Mr Scholz said getting on top of herbicide resistance was an ongoing battle and meant taking daily steps to reduce the impact.
“You have got to be constantly planning two or three years out what you are going to do and you need to have strategies. It is not as simple as selecting herbicides, where you can just drive to town and buy a solution,” Mr Scholz said.
The Scholzs grow wheat, canola, lupins and some barley on 1670ha mostly red soils with 600mm annual rainfall at Culcairn, NSW, along with beef cattle on their non-arable country.
As a result of tackling resistant weeds, Mr Scholz has been chosen as a WeedSmart Champion. WeedSmart is an industry-led initiative managed by the Australian Herbicide Resistance Initiative (AHRI) aimed at enhancing on-farm practices and promoting the long term sustainability of herbicide use in Australian agriculture.
The results for Mr Scholz speak for themselves. He has completely eradicated herbicide resistant weeds in the paddock that suffered a total crop failure 10 years ago, simply by not allowing seed set for two years in a row.
“It means taking a paddock out of production for two years, and that’s very expensive,” he said. “But we did that 10 years ago on that paddock and it is still free of ryegrass.”
Across the rest of his farm he has adopted other less drastic measures to keep the problem at bay, including wide scale windrow burning.
By fitting a low-cost chute on the back of his harvester he concentrates all of the straw and chaff into narrow rows, about 18 inches wide and 12 inches high, for slow burning.
“We are aiming to get those high 400C to 500C temperatures that you get when a windrow burns for about 10 seconds making any seeds in that row unviable.
“We are not getting every seed but even if we remove 80 or 90 per cent these are populations of plants that I do not need to hit with herbicide, so it is a very cost-effective method.”
Mr Scholz also cuts silage and said he was happy to go into a paddock and cut the ryegrass patches to get either silage or hay from it.
“That has been a very good technique when you have only got a small area in a paddock. It stops the harvester picking up those ryegrass seeds and spreading them across the paddock.”
In addition, he does “brown manuring”, a process involving planting a crop of lupins without any inputs and then in the spring spraying it out with glyphosate before a double knock with paraquat.
“We let that rot down. It’s a great way of taking weeds out in the spring time and it has the added bonus that although there is no income that year, you get a lot of nitrogen which means a fertiliser bonus in the following year.”
Crop competition through high sowing rates and strategic fertiliser application, where he places urea beneath the plant at sowing to make sure the crop gets the boost and not the weeds, further add to his armoury of weed management tactics.
Mr Scholz also does variable rate pH mapping to ensure the right application of lime is spread across the whole paddock, often finding some areas only need half a tonne of lime while other areas need two or three tonnes.
“By putting that three tonne of lime in the soil it lifts the crop’s ability to compete as ryegrass appears to be a lot more tolerant of acid soils than wheat is,” he said.
Mr Scholz said herbicides were a wonderful resource that had been undervalued through an assumption that there would “always be a new one around the corner”.
“We have to farm as if there will never be another new herbicide.”
While each strategy had its own cost, either in additional time, labour or spending, it was vital to constantly keep chipping away at the problem, he said.
“Where we fell down the first time was that we knew there was a problem, we knew it was building and we just kept hoping it would go away.”
He said the WeedSmart initiative was a wonderful idea because it helped keep farmers motivated and focussed in their fight against weeds.
“This is not a one or two year battle, it is a 20 or 30 year ongoing guerrilla war,” he said.
Maurie Street, NSW
Integrated weed management delivers against herbicide resistance
By using a combination of windrow burning, crop and herbicide rotation, increased crop competition and farm hygiene, Dubbo farmer Maurie Street has halted the previously rapid spread of resistant weeds and significantly reduced their impact on his bottom line.
Mr Street, a former commercial agronomist in Central West NSW and now a researcher with the Grains Research and Development Corporation (GRDC) funded grower solution group Grain Orana Alliance (GOA), has spent much of his time talking to farmers about herbicide resistance, prompting a decision several years ago to practice what he preaches.
“I have spent my entire professional career talking to growers about techniques to manage herbicide resistance but as a small scale cropper I am now trying to put some of that into practice,” Mr Street said.
“I use as many tools as I can to proactively combat herbicide resistant ryegrass on my property.
“To win a war you must win many smaller battles and that is why an integrated approach is our best chance. No one technique is perfect so the key to success is to use as many of them as you can.”
Mr Street only crops 160ha of canola, wheat, barley and lupins on a mixture of sandy loams through to light clay, with an average rainfall of 550mm, but he believes the principles can be applied to farming systems of all sizes.
After trialling a variety of techniques he has found that positive results from integrated weed management appeared almost as quickly as the emergence of the resistance problem.
“This farm has only been cropped for the last six years with at least 14 years of pasture before my wife Kate and I bought it in 2006, which demonstrates just how quickly resistance can develop,” Mr Street said.
“But after a few years of really concentrating on the problem I have gone from having patches of crop suffering about 20-30 per cent yield penalty due to uncontrolled weeds, to almost no impact at all.”
Mr Street is now a WeedSmart Champion, an industry-led initiative managed by the Australian Herbicide Resistance Initiative (AHRI) aimed at enhancing on-farm practices and promoting the long term sustainability of herbicide use in Australian agriculture.
Mr Street said his main problem weed was annual ryegrass.
“But I am also concerned about the development of resistant black oats (wild oats),” he said. “Resistance in summer fallow weeds is the biggest threat, with very few practical alternatives for control.
“I am getting ryegrass tested for resistance this year to confirm my suspicions that the weeds are resistant to at least the FOPs and Group B herbicides, and I strongly suspect they are developing resistance to DIMs, so I may have very few herbicide options left available to me.
“Even if I only have weak resistance of about 20 per cent, and I continue to rely only on herbicides for control it could go to 100 per cent within a few years. I really needed to do something different.”
After hearing of windrow burning at a GRDC integrated weeds management course several years ago, Mr Street trialled the method in one paddock and said the initial success led him to this year expand it across his entire property.
“It has certainly stopped the populations increasing and reduced the population spreading,” he said. “Windrow burning may have slowed my harvest down by about 10pc but only in some crops as much of the time we often harvest quite low anyway.
“It may also have some impact on fallow efficiency and nutrient dynamics but these are costs I am willing to bear.”
Mr Street said the improvements provided by windrow burning had been complemented by other techniques including increasing crop competition.
“Research has shown that crop competition can reduce seed set of weeds by up to 80pc, so this year I increased seeding rates from the traditional 45kg/ha to 75kg/ha.”
It was easy to see how successful it was just by walking around his property and finding areas of thin crop or missed areas.
“In those spots I will find ryegrass with 20 or more tillers, but 20cm either way in thicker crop, the ryegrass plants may have only three tillers, so much less seed is produced and returned to the seedbank.”
Mr Street also believes crop rotations are an important tool.
“Changing crop types allows for easier herbicide rotations but also allows for staggered sowing dates to better accommodate pre-sowing knock downs,” he said.
“To get optimum yields for canola, lupins and long-season cereals the crops are dry sown or sown early, with either no knockdowns applied or knockdowns applied before weeds are fully emerged.
“Shorter season wheat and barley crops allow for effective knockdown of weeds and take the pressure off in-crop herbicides.”
He is also interested in other alternatives such as hay or silage crops where weeds can be cut off before they seed, or summer crops where weeds could be targeted with different herbicides.
“Farm hygiene is important as well – I have enough problems with my own weeds let alone spreading them with seed or machinery,” Mr Street said.
“Grading my own seed to a high standard is the first step because if there are weed seeds in my planting seed there is a very good chance they are resistant, so I am also careful where and who I buy from.”
Mr Street also sprays his firebreaks and fence lines using “double knocks” and residual herbicides, and has minimised the width of his fence line breaks to minimise the potential for fence line resistance.
“I also try to follow the mantra, ‘if I can’t sow it don’t spray it’ particularly for areas such as contour banks and other non-cropped areas.”
Other options he has considered are slashing or cultivating the breaks or planting competitive pasture or plants to try and out-compete the weeds.
“All these techniques do come at a cost, but we have always paid to control weeds so now instead of going to town to buy drums of chemical, we pay for it in a different way,” he said.
Damien Sommerville, SA
Always think about your impact on weeds
Damien Sommerville from Spalding, South Australia, makes sure to consider the impact on weeds in every decision he makes
Damien has a long association with the land. He has been involved with Sommerville Partners for nearly two decades and has seen a lot of different things in his time. His recommendation to growers is:
Think about the impact on weeds with each and every decision you make, all year round.
Damien is determined to help people in his area and further afield to understand the issue of herbicide resistance.
“The issue affects growers everywhere. It’s obviously more high profile in the west but southern growers need to be aware and managing the issue whenever they can,” Sommerville said.
“Growers have to use as many options as they can to prevent weeds setting seed. They can’t afford to lose one year in the battle as things spiral out of control quickly.”
“There really is no one answer. What can work, if your conditions are right, is the use of lupins and or hay in your crop rotations. Using varied rotations each year is a great step towards managing weeds and resistance.”
Rod Messina, WA
Windrow burning beats wild radish
Two key messages have emerged from long-term windrow burning trials in Western Australia’s northern wheatbelt – focus on trash from non-cereal crops and burn in the daytime where possible.
Rod Messina, whose family farming business “Spring Park Farms” has hosted windrow trials for more than a decade, says the practice has underpinned their property expansion.
“We find that when we buy a new property it always has a lot of weeds but after two or three years of integrated weed management (IWM) practices including burning windrows, it’s amazing how quickly weed numbers come down,” Rod said.
“Weeds dictate what we do here, they’re our number one issue. So if a paddock’s dirty, rotation becomes vital and ultimately allows us to continuously crop.
“It is quite expensive to leave paddocks out of production so with the rotation and windrow burning it allows our operation to be more profitable in the long run.”
Rod farms 12,500 hectares with his father Charlie and brother Andrew on the Eradu sandplain east of Geraldton.
They employ a wheat/lupin/wheat/canola rotation and strategically use herbicides to control radish in the cereal phase while windrowing canola and lupin crops to collect and destroy hard-to-kill wild radish seed.
“Wild radish is one our most problematic weeds. We do have ryegrass but radish is our biggest concern because the seed is viable for so long,” Rod said.
“In our lupin and canola phases we try to make sure we control all the seed set either through windrow burning or crop-topping.
“We try to get a germination of wild radish before we sow but in this environment that is not always possible.
“There is no doubt through our long-term IWM strategy, including windrow burning, autumn tickles, crop-topping, a double knock and now the mouldboard plough, that our weed numbers are decreasing.”
The Messinas aim to stop seed set at every stage of the crop production and weed life cycle.
“We deep rip to stimulate a germination of weeds that we can treat with a knockdown herbicide or double knock, then we’ll use one, maybe two post-emergent sprays followed by crop-topping lupins and windrow burning.”
The Messinas have trialled a mouldboard plough and spading but chose to go with the mouldboard plough for its weed and non-wetting soil management benefits.
Rod says the practice of windrowing as demonstrated by the GRDC-supported work by Department of Agriculture and Food WA (DAFWA) weed researcher Peter Newman has been proven over more than a decade.
“The numbers are declining quite rapidly and one of the greatest benefits of windrowing is that it doesn’t slow harvest at all,” he said.
“The hotter the fire the better it is and through the GRDC focus paddocks we’ve learnt that you do need a much hotter fire to control wild radish than for ryegrass.
“We have to try and get the fire as hot as possible. It’s easy in lupins and canola because there is less chance of the fire spreading than in wheat so you can light the windrows up during the day and make sure you get a really hot burn.
GRDC/DAFWA plots across the district are achieving 99% control of weeds using windrow burning.
“In an ideal world you wouldn’t windrow your wheat because there is a chance you’ll lose the paddock but in a lighter year like this year we’ve windrowed all the paddocks in order to use that tool.”
Rod says a cereal crop of more than two and a half tonne per hectare is too dense for windrowing due to the risk of burning the whole paddock and losing valuable soil cover.
“If you’ve got a really dense windrow the fire will run across the top and won’t penetrate the windrow and research shows some of the seed falls to the bottom within about 24 hours.”
He advocates burning late in the day rather than at night as the intensity of the fire drops as the temperature falls.
“Five to seven years ago we windrowed every acre but now that we’ve got our numbers down we can just do the lupins and canola phases,” he said.
“There is more opportunity to control wild radish during the wheat phase using herbicides and other tools and can manage the ryegrass during the non-cereal phases.”
Geoff O’Neill, NSW
Warding off herbicide resistance to rescue no-till
The unpalatable thought of losing his no-till farming system drives grain grower Geoff O’Neill, “Llano”, Bellata, NSW in his fight against the formidable threat of herbicide resistance.
Geoff says moisture retention via no-till farming is the key to crop success in an environment where rainfall is the major limiting production factor.
He says weed control is vital for maximising crop yield.
“We have a 610 millimetre annual rainfall and work on moisture retention the whole time so resistant weeds are going to be a big problem for us if means a return to cultivation for weed management.”
Geoff joined the no-till revolution in 1994 with the purchase of a no-till planter that allowed him to sow into higher levels crop residue on the heavy black clay and sodic grey soils of “Llano”.
“We had a few tough years learning the new system but since then it’s done a great job on these soils,” he said.
“Our production has become more stable under the no-till system.
“We work on a four-crops-in-five-years rotation which includes long fallow durum/chickpeas/short fallow wheat /long fallow to summer crop, either sorghum or cotton.”
Geoff is keen to use an integrated approach to herbicide sustainability management and follows WeedSmart strategies including: rotating chemicals and chemical groups, ensuring spray rates are accurate, rotating crops, diligently controlling weeds (including those in summer fallows) to stop seed set, considering alternatives to glyphosate, researching weed biology, and testing for resistant weeds.
“If herbicide resistance puts our no-till system under threat it would mean a big shift in thinking for us,” he said
“To go back to a conventional tillage system is just not possible. We could not do what we’re doing.”
He says rotation underpins his strategy.
“Rotation is the key word – we rotate crops, we rotate chemicals, we rotate chemical modes of action and we do use strategic tillage when we have to or we can.
“That’s not very often in a no-till system but we use strategic tillage at the end of the cotton cycle which ties in with pupae busting to manage helicoverpa and that’s given us another non-chemical option.”
Geoff welcomes Grains Research and Development Corporation (GRDC) funding into strategic tillage practices currently underway across the northern region by Queensland Department of Science, Information Technology, Innovation and the Arts (DSITIA) researcher, Dr Yash Dang.
“There’s more we can learn about strategic tillage including when and how and do we need to till the whole paddock?” he says.
Rotation is the key word – we rotate crops, we rotate chemical modes of action.
Knowing the herbicide resistance status of his paddocks and farm is important to Geoff and he has tested twice for barnyard grass which is the major weed of concern on “Llano”.
He says while the tests were negative the weed is notoriously difficult to control and he monitors the threat of developing resistance.
“We have trouble killing barnyard grass with glyphosate so timing and stress are obviously factors and we are working on that.”
He says the move to a Case self-propelled spray rig two years ago has provided a “tremendous efficiency boost” in weed control and allowed him to cover more hectares per hour.
The result has been better execution of the double knock technique for difficult-to-control weeds including fleabane.
“We had a trailing spray rig before and we found we couldn’t keep up with the double knock,” Geoff said.
“Using the self-propelled spray rig we can cover the ground more quickly if the conditions are right.
“We also use a disc planter now which allows us to conserve stubble in that we’re not burying stubble when we sow.
“In dry planting times we do miss the tyne planter but we haven’t had too many big issues.”