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Herbicide resistance in summer weeds becomes reality

For an increasing number of farmers in New South Wales herbicide resistance in summer grasses is no longer a threat but a reality.
Resistance to glyphosate, the world’s most useful herbicide, has been confirmed in three species of summer grasses—barnyard grass, liverseed grass, and most recently sowthistle.
Summer weeds are notoriously difficult to control due to the hot, dry summer weather patterns limiting the efficacy of spray operations and the ability of these weeds to rapidly set seed. Herbicide resistance makes this difficult task even harder.
This week there will be a gathering of minds as a group of agronomists, researchers and consultants meet with experienced farmers from the local area and from Western Australia, where growers have a longer history with finding innovative ways to live with and sometimes beat herbicide resistant weeds.
A series of workshops are being held across the grain growing regions of NSW this week:

10 March, RSL Club, Moree
11 March, 2828 Hall, Gulargambone
12 March, Bowling Club, Dubbo
13 March, Forbes Services Memorial Club, Forbes
14 March, Wine & Food Training Centre, Charles Sturt University Campus, Wagga Wagga

Discussion leaders at the workshops include Peter Newman, Australian Herbicide Resistance Initiative, John Cameron, ICAN Rural and Tony Cook, NSW DPI. Several other researchers and prominent local growers will also be presenting at one or more of the workshops.
The growers, Tom Murphy, Maurie Street and Murray Scholz, have personal experience managing these difficult weeds and have each trialled several strategies as they look for the most effective mix of tactics to meet the challenge that is herbicide resistance.
The purpose of the workshops is for researchers, agronomists and growers to discuss management options that can be implemented to reduce the spread of herbicide resistant weeds and to manage existing resistant populations.
Rural reporters are invited to contact Tony Cook, NSW DPI (details below), to arrange interviews with the presenters during this week-long workshop series.
For more info on the workshops, click here.
For media enquiries contact:
Tony Cook
NSW Department of Primary Industries
(02) 6763 1250
0447 651 607
tony.cook@dpi.nsw.gov.au

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Has Silverleaf Nightshade been a nightmare to control on your farm?

NSW Primary Industries and Murrumbidgee Landcare have a new collaborative project funded by Meat and Livestock Australia (MLA) which will target the perennial summer weed Silverleaf Nightshade across the five states of QLD, NSW, Victoria, SA and WA.
Silverleaf nighshade flower (source: NSW DPI)
Silverleaf Nightshade (Solanum elaeagnifolium) is an introduced perennial weed that can dominate pastures and cropping areas. It can reduce crop yields by as much as 20- 40% by taking moisture and nutrients over summer and autumn that could be used by following crops. In pasture paddocks it can reduce growth of productive species and render areas useless for livestock grazing. It reproduces from both seed and root fragments so can be difficult to control by conventional means. Many common farm activities such as livestock movement and cultivation will spread this weed.
Surveys of grower practices previously have shown that many farmers are not aware of the extent of the problem on their farms and that adoption of effective control methods has been poor.
Silverleaf Nightshade is often not specifically targeted as it occurs in many situations as scattered infestations and if not treated over the long term will re-establish. It has been a frustration for many farmers that efforts to control it have failed and it has spread to other areas of the farm. Recent research has shown that a systematic approach using a dual action control over the growing season from spring to autumn is needed. In many cases more expensive residual herbicides may be required to be used in conjunction with normal summer weed programs to give effective control of Silverleaf Nightshade.
Previous projects have shown the extent of the problem, the species involved and how to give better control. This current project will utilise the existing Landcare networks and farmer groups to build local knowledge and capacity and to foster the adoption of the research by farm communities.
Silverleaf nighshade berries are green striped when immature and turn yellow-orange when ripe (photo courtesy of NSW Department of Primary Industries).
Adoption of research by rural communities requires a combination of extension techniques to give the best results. Several strategies will be used in the project to ensure that communities have the skills to manage this weed problem. The project team will ask each community to come up with strategies that they are comfortable with and develop specific activities, technologies and management practices for their own situation. This may involve large scale demonstrations carried out by local farmers which compare current research with the standard farmer practices and a series of workshops and field days complimented by media articles. Access to information through websites, social media and industry journals will keep individuals and groups up to date. This is all planned to raise awareness of the problem and to get wider adoption of best practices to control this weed by working together.
Project officer Phil Bowden from Cootamundra, NSW will be looking to interact with groups in your area and will present workshops throughout the region to raise awareness of the problem and the best practices to control this weed.
If you would like to assist with this survey, please click here. It will only take a few minutes and give valuable background on this weed.
If your group would like a workshop on Silverleaf Nightshade control contact Phil Bowden, M: 0427 201 946, E: weeds@mli.org.au.

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Double-knock: second knock is essential

Michael Widderick, principal weeds research scientist, Queensland’s Department of Agriculture, Fisheries and Forestry, is a proponent of the double-knock, which he said originally used herbicide as the first tactic followed by cultivation.
“Cultivation was phased out with the advent of zero till farming and replaced with a second herbicide application,” he said.
“Now the first knock is a translocated herbicide, followed with the second knock contact herbicide. While the tactic involves two herbicides it is essential that they have different modes of action.
“Two applications of the same chemical is not a double-knock and is actually likely to increase selection pressure, hastening the development of herbicide resistance.”
The key to implementing the double-knock strategy is to understand that it is a two-phase tactic targeting weeds of the same generation. Therefore the double-knock tactic can be used several times during a fallow period, targeting different generations of weeds.
“Rainfall events are usually the trigger for a double-knock,” said Dr Widderick. “Soon after rain a new generation of weeds will germinate and the first knock application should occur while the weeds are small.
“The optimal time between the first and second knock depends largely on the weed or weeds being targeted,” he said. “The optimal timing can be as short as two days but is generally within one or two weeks of the first knock application.”
Glyphosate remains an effective first knock herbicide however with the increasing number of glyphosate resistant weeds being identified, research is underway to investigate the efficacy of alternative chemistry.

“Group A herbicides are being tested as an alternative first knock treatment for summer grass species, either on their own or mixed with glyphosate,” said Dr Widderick.
“The risk of Group A resistance developing is high so if these chemicals were introduced for fallow weed control it would be vital for any survivors to be controlled.”
For the second knock the options are limited to diquat for broadleaf weeds and paraquat or glufosinate for grasses.
“The double-knock tactic works well and can achieve very high levels of control when implemented correctly,” he said.
“Success hinges on the tactic being applied when the weeds are small. We have found that the first knock needs to achieve at least 70 per cent control so that the second knock does not have to work too hard and this is best achieved when the weeds are small.
“If the first knock is applied to large weeds the rate of control is likely to be low and then it is hard to achieve adequate coverage of the large survivors with the contact herbicide, making the second knock ineffective,” said Dr Widderick.
If some large weeds are present, Dr Widderick suggests looking for a non-chemical option for the second knock. “Chipping or strategic cultivation is likely to be more effective in removing large survivors than applying contact herbicide,” he said.
Dr Widderick said that herbicide resistance is commonly seen following regular use of glyphosate over a period of 15 years or more.
“If a grower has relied heavily on glyphosate in the past I would recommend they consider replacing one or two of their fallow sprays with a double-knock application,” he said.
“For some weed species the first emergence in the fallow is the biggest and so this would be the best generation to target with the double-knock.”
If glyphosate resistance has been identified then using glyphosate on its own is no longer an option in the affected paddock.
Double-knock using a different mode of action for the first knock can be highly effective and some minor use permits are in place for alternative herbicides, provided they are applied as part of a double-knock treatment.
“The use of residual herbicides as a mix partner for either the first or second knock is currently being investigated,” said Dr Widderick.
“If applied at the end of the fallow, a residual does not usually reduce the knockdown efficacy of the tactic and can provide useful residual control during the fallow and even into the following crop. However, careful planning would be required to ensure the residual did not affect future planting options.”

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Research confirms first glyphosate resistant wild radish

The world’s first populations of glyphosate resistant wild radish will be announced at Perth’s Agribusiness Crop Updates, but researchers stress further cases can be minimised if farmers adopt diverse control strategies.
Australian Herbicide Resistance Initiative (AHRI) research has confirmed glyphosate resistance in three populations of wild radish, all from different locations in Western Australia’s far northern grainbelt.
They were identified by Mike Ashworth, a recipient of a Grains Research PhD Scholarship from the Grains Research and Development Corporation (GRDC).
Mr Ashworth is based at AHRI, located at The University of Western Australia.
“Wild radish is arguably the worst weed in WA cropping systems and causes economic losses in 45 crop species in 65 countries,” he said.
“Glyphosate is the world’s most important knockdown herbicide and a vital tool in the control of wild radish, which has evolved resistance to many selective herbicides in WA and other cropping regions.”
Mr Ashworth said two of the glyphosate resistant wild radish populations were identified and tested after survivors were found in fallows treated with glyphosate.
“These populations were confirmed to have moderate levels of resistance, exhibiting high rates of survival (63 and 86 per cent) following label rate glyphosate application on two-leaf plants,” he said.
“The third population was identified following an AHRI survey in 2010 and 2011 of 239 paddocks in WA’s northern and central grainbelt.”

Mr Ashworth said the glyphosate resistant wild radish plants also exhibited resistance to other important herbicides.
“The first two populations identified also had resistance to label rates of the Group B (chlorsulfuron, sulfometuron-methyl, metosulam, imazamox), Group F (diflufenican) and Group I (2,4-D amine) herbicides” he said.
Mr Ashworth said the history of herbicide use where the three populations were discovered was likely to have been a major factor in the evolution of glyphosate resistance.
“The first two populations are believed to have been exposed to at least one and often two glyphosate applications annually over two decades,” he said.
Mr Ashworth said the good news was that finding the populations early meant that growers had the opportunity to adopt pro-active control strategies.
“Herbicides alone should not be used to control wild radish; growers and agronomists should use a range of tactics to control wild radish populations,” he said.
“The aim should be to control weed survivors, eliminate weed seed set and maximise diversity of control strategies.
“GRDC funded research has proven the effectivenes
s of non-herbicide tools including crop competition and harvest weed seed control (HWSC) used as part of an integrated weed management approach.
“HWSC has been shown to be very effective for controlling wild radish, as this weed tends to hold on to its seed at harvest.”

 
Listen to the audio grab.
 
GRDC media releases and other media products can be found here.

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A new glyphosate resistant species confirmed in northern NSW

The world’s first cases of glyphosate resistant sowthistle (Sonchus spp.) have been confirmed in northern New South Wales. Sowthistle is a major summer growing broadleaf weed in many parts of the Australian cropping regions.
The two populations come from mixed cropping farms on the Liverpool Plains, the same area that produced the latest glyphosate resistant liverseed grass that was confirmed this January.
“Sowthistle and other surface germinating weeds are becoming bigger problems with the widespread adoption of reduced tillage agriculture and an over-reliance on glyphosate,” stated Tony Cook, Technical Specialist (Weeds) with NSW Department of Primary Industries and leader of the team that conducted the testing.
“Having glyphosate resistant populations is really going to make weed management more complicated, especially with each plant being able to produce thousands of wind-blown seeds.”
There is also widespread resistance to Group B herbicides such as chlorsulfuron and metsulfuron in the northern cropping zone, so this reduces the number of successful herbicide options. Antagonism between glyphosate and 2,4-D when tank mixed also reduces control of sowthistle.
At stem elongation-early flowering, which is when many growers spray sowthistle, 80 to 90 per cent of the resistant populations survive the application of 1.6 L/ha glyphosate CT.
“Just like the barnyard grass and wild radish stories, the size of plants treated and rate of herbicide applied have a big effect on the level of control. Importantly, the smaller plants are more easily controlled with glyphosate despite having some resistance,” said Tony Cook.
“As yet we are not seeing some of the extremely high levels of resistance seen in other species where herbicide rate has no effect, so this is good for managing sowthistle. The research shows that once a resistant plant grows beyond the rosette stage its ability to survive glyphosate increases rapidly.”
The following points will be critical to successful sowthistle management:

Get sowthistle tested for glyphosate and Group B resistance.
Spray weeds when rosettes are no bigger than the top of a drink can. This may mean spraying more often.
Use full label rates when sowthistle is present and use appropriate water volumes for the herbicide.
Have spray rigs properly calibrated to deliver the maximum amount of the herbicide to the weeds.
‘Double knock’ with another mode-of-action.
Use other modes of action such as Group L, I, L+Q.
Control large survivors by spot spraying which includes using the Weedseeker® or Weed-it® sprayers.
Control sowthistle and other weeds around fences, buildings, roads, irrigation channels.
Use targeted cultivation where appropriate.
Stop all seed set.

“We have already collected nearly 50 populations of suspected sowthistle from around northern NSW which are currently undergoing testing. This is likely to be the start of a much bigger problem with the rapid spread of wind-blown seed.”
If you suspect glyphosate resistant sowthistle on your farm phone Tony Cook at Tamworth on 0447 651 607.
GRDC media releases and other media products can be found here.

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Herbicide resistance management is not a one-year decision

Herbicide resistant weeds can be controlled within a few years using a planned strategy, according to Dr Chris Preston, University of Adelaide (UA) Associate Professor—Weed Management.
Dr Preston advocates using a few different integrated weed management tactics to maintain pressure on weeds. He suggests that the costs associated with herbicide resistant weeds are so great that there are situations where weed control opportunities may need to take priority over other crop outcomes.
Starting with the worst weed and worst paddock, Dr Preston said it is possible to see significant results within two years, particularly with weeds like annual ryegrass that do not stay dormant in the soil for a long time. The next step is to include weed seed set prevention strategies for all weeds in all paddocks.
“A reduction in weed populations can be achieved if in-crop tactics are used in consecutive years to minimise seed set,” he said. “A single operation to reduce weed seed set with no follow-up is rarely as effective as using a number of weed control tools.”
“Weeds that have survived the growing season and set seed at harvest time are the source of a continuing weed burden on cropping land,” said Dr Preston. “Growing crops specifically for the weed control options they offer is one tactic to combat weed seed set.”
Promoting strong crop competition is an important tactic that should be factored into every crop production phase, especially for cereals. “High seed rates, narrow row spacing, early sowing when the soil is still warm and correct use of pre-emergent herbicides all create the best opportunity for the crop to out-compete weeds,” said Dr Preston.
“Growing a brown manure crop or croptopping can be effective options in the long term,” he said. “Using a variety of tactics will remove herbicide resistant weeds whilst conserving herbicide chemistry.”
All pulses can be grown as brown manure crops and will add vital nitrogen and organic matter to the soil. Growing pulses, such as field peas or lupins, specifically for the opportunity to croptop can also be very effective if the operation is done when the weeds are most susceptible. “Croptopping is less effective if it is done as a last minute response to a weed blow-out. If it is planned and the weeds are monitored to determine the best time to apply the croptop herbicide then it will achieve a significant reduction in weed seed set.”
Croptopping is usually used to control grass weeds but it is important to note that it can be difficult to implement in lentils and faba beans and does not usually offer a high level of effective weed control in chickpeas.
In the lead-up to harvest it is worth considering the use of mechanical harvest weed seed control tactics such as producing hay or windrow burning.
“Producing oaten hay is a very valid weed control strategy to use against both broadleaf and grass weeds,” said Dr Preston. “After cutting the hay it is essential to go back with a clean-up operation using a paraquat-based herbicide, which is very effective on new regrowth.”
Mechanical harvest weed seed control tools are a good addition to a weed strategy, with windrow burning being an effective tactic against wild radish.
“The overall key is to be diligent. Monitor the effectiveness of each weed control tactic used and be ready to implement operations at the right time,” he said. “Intensive management of small problem areas or patches can greatly reduce the threat of a weed explosion.”

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Success in tackling weeds

With the harvester back in the shed and seeding around the corner, it’s the time of year when summer spray regimes are front of mind.
Rising chemical costs, greater summer rainfall and the increasing incidence of herbicide resistance mean summer spraying is serious business.
Gnowangerup farmer Knud Nymann is using every trick in the book to attack weeds, and a combined control approach is helping him reduce his summer weed burden.
Maintaining livestock in his operation as well as the recent incorporation of chaff carts and light cultivation methods play an important role in weed control on his 12,000 hectare property which spans the Great Southern region from Gnowangerup to Wellstead.
But for Knud, it was a targeted approach to spray application that not only led to considerable cost savings and reduced environmental impact, but has proven to be the most effective method for successful weed knockdown.
Since introducing Weedit spray technology three years ago, Knud said he had saved up to 90 per cent in herbicide costs.
The technology actively detects live plant matter, only applying chemical when a target plant is detected rather than the blanket fence-to-fence application method used in conventional systems.
Knud started with a 24-metre, hired Weedit unit in 2011, and today uses a 36m unit which is a key tool in his summer spraying toolbox.
“The cost savings are pretty straight forward because if you spray 1000ha and you use a brew that cost $20-$25 and you only spray 10pc – say 100ha out of the 1000ha – then you saved yourself a fair bit of money because it only cost you $2500 in chemicals when it would have cost you $25,000,” Knud said.
“The strike rate will vary from job to job and the year.
“At home this year the weed percentage was only 6pc, so if you work on 10pc chemical use you save 90pc.”
With a cropping program of 11,000ha, Knud said it was easier to justify the expenditure in a bigger operation because although the technology was expensive the potential savings were greater.
“The machine pays itself off relatively quickly but obviously the more weeds you have the slower it pays off,” he said.
Courtesy Farm Weekly
 
 
 
 
 
 
 
Knud said he had noted herbicide resistance issues on-farm, particularly glyphosate resistance in Fleabane and Windmill Grass, and although the cost of older existing chemicals hadn’t increased greatly, he had found he needed to use more to achieve comparable results, which meant the cost per hectare of spraying had increased.
 
“We used to use 150ml of Select to kill ryegrass immediately and now we use half a litre instead,” he said.
“The good thing about the Weedit is you could start using newer, more expensive chemicals, because you are only using so little of them.”
In addition to cost savings, Knud said targeted chemical application had environmental advantages.
“With target application, the environment is obviously not exposed to all these chemicals that are sprayed out on the bare dirt for nothing,” he said.
“You are only striking when there is something to strike for.”
Although pleased with the system, Knud had a few words of caution for those looking to utilise detector spray systems.
“Don’t skip rates when using detector spraying systems, go hard,” he said.
“And conditions are still king, if we do go into warm conditions a spray oil for prep purposes is an absolute must.”
Knud said significant rain on his Wellstead property meant he could only spray a quarter of the program with the Weedit this summer because weed percentages were too high for the process to be viable.
“With strike rate success on Fleabane, depending on size and what brew you use, don’t expect to be getting two thirds or three quarters,” he said.
“Fleabane seems to be extremely hardy.
“We are actually going back to the old double knock in the summer weed context for Fleabane.
“If you have an 80pc strike rate, the last 20pc is still there and it’s a worry.
“We did some spraying with the Weedit, about 1100ha but some of the percentages were too high so we actually sprayed them fence-to-fence.
“We will see if the fence-to-fence was a lethal dose, because it gets pretty expensive with Fleabane.
“And then we’ll go back over it with the Weedit.”
Mr Nymann said he also dabbled in light cultivation, using discs as a way to vary the method of controlling the weed burden.
“You can’t do too much of the same thing,” Mr Nymann said.
“Cultivation is also incorporating the stubble into the dirt.
“It is a misconception that the stubble should stay up in the air – it should be down where all the microbes are.”
Mr Nymann said he had also invested in chaff carts as another tool in combating weed issues and they were largely used on the Wellstead property.
“A chaff cart is a fair bit of outlay so we decided to drop windrows this year just to see how that goes,” he said.
Mr Nymann said chaff carts worked in well with his livestock and weed control program.
“We generally run 350 black breeder cattle in Wellstead, and mate 2800 Dohne ewes,” he said.
“Even when you go in with a detector sprayer, having livestock in the mix is always beneficial.”

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Two sprays tackle stacked resistant radish

 

 
 
 
 
 
 
 
 
Treating wild radish (Raphanus raphanistrum L.) early in the growing season in the northern wheatbelt as part of a two-spray strategy – using robust herbicide rates and excellent application – can boost wheat yields by 0.5-1 tonne/hectare.
That is a key finding from large-scale 2013 trials initiated by the GRDC’s Geraldton port zone Regional Cropping Solutions Network (RCSN) and run by Grant Thompson (pictured), of Crop Circle Consulting.
 
The research was carried out at sites in Northampton, Casuarinas and Chapman Valley and aimed to:

Develop herbicide solutions and sequences that avoid using the same product twice in a single growing season
Get herbicide timing and application rates right
Delay the onset of wild radish resistance to – and prolong the efficacy of – new actives pyrasulfotole (Group H – eg. Velocity® and Precept®) and pyraflufen-ethyl (Group G – eg. Ecopar®)
Develop a best practice management guide for control of wild radish with multiple herbicide group resistance.

Herbicide resistance in wild radish
There is an increasing threat of multiple herbicide group resistant wild radish and ‘stacked’ resistance in the northern wheatbelt.
In this region, there is already widespread wild radish resistance to herbicides such as SU’s, diflufenican, MCPA and 2,4-D amine.
Newer registered chemicals, such as pyrasulfotole and pyraflufen-ethyl are highly effective at controlling radish.
But there is industry concern about repetitive use of these products and a need to prolong their effectiveness.
The value of older herbicides
In the first year of GRDC’s RCSN- funded wild radish control trials in the northern wheatbelt in 2012, Peter Newman – then with the Department of Agriculture and Food WA (DAFWA) and now a consultant with the Australian Herbicide Resistance Initiative (AHRI) and Planfarm – demonstrated older herbicide groups could still be effective against wild radish.
The keys to success were:

Targeting weeds when small – about the size of the top of a beer can
Using a timely two-spray strategy with a quick and timely second spray
Ensuring herbicide rates are robust
Using correct water volumes, nozzles and speed.

For the 2013 trial results and observations, read on here

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Herbicide resistance growing in north

Glyphosate resistance is a growing problem in the northern grain growing region, with concerns several more weed species may be on the cusp of becoming resistant.
Michael Widderick, Queensland Department of Agriculture principal weeds research scientist, said the problem had the potential to drastically alter the industry.
A barnyard grass ‘survivor’ of fallow treatment with glyphosate.
 
 
 
 
 
 
 
 
The northern minimum tillage farming system (with summer and winter cropping) relies on the use of glyphosate to manage a wide range of weeds during the fallow.
“If we were to lose the use of glyphosate it would fundamentally change the way the grain industry operates in the north,” he said.
“The risk of herbicide resistance being present on Queensland and northern NSW farms is increasing and should be factored in to any weed management strategy.”
Herbicide resistance has been found in Queensland populations of wild oats (Group A resistance), African turnip weed, black bindweed, common sowthistle, Indian hedge mustard and turnip weed (Group B resistance), liverseed grass (Group C resistance) and barnyard grass and flaxleaf fleabane (Group M resistance).
“A small survey of barnyard grass in northern NSW and southern Queensland recently revealed that 50 per cent of the samples taken in summer fallows were herbicide resistant and 90pc of glyphosate ‘survivors’ were resistant,” Dr Widderick said.
“The main concentrations were found on the north-west slopes and plains of NSW and the western Darling Downs.”
There are several reasons why a herbicide spray operation may be less effective than expected, Dr Widderick said.
“Weather conditions, size of the weeds, water quality and blocked nozzles can all make a difference but if a spray seems to have been ineffective across some or all of the paddock it is worth investigating the possibility that those weeds may have herbicide resistance.”
Dr Widderick said growers need to take a long-term view to their weed management strategy, beginning with routine testing for herbicide resistance.
“The quick test, which involves sending live plants to the Plant Science Consulting testing service in Adelaide, has the fastest turn-around time and gives growers the opportunity to control areas with known resistance before they set seed,” he said.
“There are suspect populations of both sowthistle and sweet summer grass currently being tested for glyphosate resistance.”
Dr Widderick said that experience in other cropping systems has shown that herbicide resistance can develop largely unnoticed and then appear to ‘explode’ quite suddenly, rapidly taking hold of cropping land and leading to significant yield losses and additional production costs.
“This is why growers need to take notice of the effectiveness of each herbicide application and to act quickly to remove individual plants that have ‘survived’,” he said.
Dr Widderick said over-reliance on any one mode of action is the primary cause of resistance in weeds. This may be repeated use of a single herbicide or of mechanical controls such as slashing or cultivating. A strategic weed management plan will need to include as wide a variety of methods as possible.
“There are several cultural and agronomic practices that are effective and will potentially prevent herbicide resistance on cropping land,” he said.
“Weed management has to become a high priority throughout the farming system because herbicides alone can no longer keep weeds at bay.
“If there are weeds that have not died after a herbicide spray, investigate why they have survived and act quickly to remove them or prevent them from setting seed.
“There is no doubt that herbicide resistance is now a reality in the northern region but the threat can be contained if a range of weed management strategies are implemented on farms across the region.”

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Narrow spacing boosts yield in northern trial

Grain growers in medium and high-rainfall areas have much to gain by narrowing the row spacings used in their seeding programs.
That is the advice from weeds researcher Peter Newman, who coordinated a GRDC-funded trial in the northern wheatbelt in 2013 that showed reduced row spacing (using paired row seeding where a single seeding boot creates paired crop rows – usually 75 to 100mm apart) produced higher wheat yields.
He said narrow row spacing could also potentially help crops to outcompete weeds and this was an increasingly important non-herbicide weed control tactic.
Mr Newman, the communications leader with the Australian Herbicide Resistance Initiative and based at Planfarm in Geraldton, says wide row spacings remain common across WA’s wheatbelt.
He says this is due to the practicalities of continuous cropping, seeders needing to handle increased stubble loads, a need to harvest water in a bigger furrows, chemical safety, cheaper seeding bars, less horsepower required for pulling fewer tynes and perceptions that yields are not penalised.
However, new machinery innovations are making it possible to shift to narrower row systems, for example, harvesters that cut stubble shorter and seeders with well-spaced tyne ranks and no wheels in the frame of the seeder bar.
These machines can handle higher amounts of stubble and ensure good herbicide safety.
“All of the research from around Australia is pointing to significant and incremental yield benefits for every one-centimetre reduction in row spacing when wheat yield potential is higher than 1.5 tonnes/hectare,” Mr Newman says.
Yield benefits
Yield benefits were assessed in a GRDC and Department of Agriculture and Food, WA (DAFWA) 2013 northern crop competition trial that was hosted by Mingenew grower Peter Horwood. It compared:

single row, paired row and ribbon seeding systems;
row spacings of 15cm, 22cm and 30cm; and
seeding rates of 60, 90 and 120kg/ha.

The paired row plots were treated with a deep working knife point and Stiletto winged boot that created paired seeding rows 75mm apart – effectively doubling the length of the crop row.
The ribbon sowing involved planting seed evenly across an entire band (ribbon).
As expected, based on national historical research, the narrow row spacing plots (at 15cm) out-yielded the wider row spacings (at 22cm and 30cm) by an average of 240 kg/ha.
This is the equivalent of 16 kg/cm of row spacing and is consistent with findings from a recent GRDC-funded review of 50 years of national row spacing trial data. These findings were published in Row spacing of winter crops in broad scale agriculture in southern Australia.
Mr Newman says the preliminary data appears to show there is no difference in wheat yield between the single row, paired row and ribbon seeding systems at the Mingenew 2013 trial. “We didn’t really achieve a good paired row with the seeding gear we used in the trial, so unfortunately we didn’t see much yield difference between the seeding systems,” he says.
“There also appears to be little wheat yield variation in plots with different seeding rates – as was expected in this weed-free trial.
“But previous research has demonstrated that narrow row spacing in combination with high seeding rates has a big effect on weed seed set and yield through extra competition.”
Weed competition
Paired row seeding using 30.5cm tyne spacing and a winged boot effectively produced the same length of crop row in a paddock as using 15cm single row spacing.
This provided even seed distribution across the paddock and created a similar potential for crop plant density.
Mr Newman says the trials showed narrow row spacing using high seeding rates increased plant density per square metre, suppressing weed numbers and weed seed-set.
He says this supported previous local research that showed increasing seeding rates by 40kg/ha halved seed-set in annual ryegrass populations.
Narrow row spacing economics
Mr Newman recommends growers aim to use the narrowest row spacings that are practical for their area and this should be a consideration when upgrading machinery.
He says a lot of research has been conducted into row spacing and growers could access results when planning their cropping programs.
Mr Newman will be presenting a full analysis of results from the northern crop competition trial at the GRDC-DAFWA Agribusiness Crop Updates in Perth on 24 and 25 February.

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Rethinking weed control

The increasing incidence of herbicide resistance means the days of relying solely on herbicides for effective knock-down of weeds are largely over, according to Northern Grower Alliance CEO Richard Daniel.
Mr Daniel spoke about the management of four key weeds that have taken hold in the north at the Grains Research and Development Corporation (GRDC) Grower Updates in Queensland and Northern NSW last year.

He said the summer grass weeds feathertop Rhodes grass, barnyard grass, and windmill grass, together with flaxleaf fleabane, were all showing signs of resistance to glyphosate, or had levels of natural tolerance.
“What we have done is pushed our system through the overuse of glyphosate and we are now unfortunately starting to see the results that were forecast back 15 or 20 years ago,” Mr Daniel said.
To rectify the situation it is vital that non-herbicide tactics are incorporated into weed management systems.
“We are at a stage where there are fewer and fewer new chemistry options, so what we have to do is safeguard the products we have got as much as we possibly can,” he said.
“The only way we are going to be able to do this is by introducing other tactics and techniques to assist weed management and focus on reducing the seed bank replenishment for these key weeds.”
Mr Daniel said strategic cultivation was one of the tools that growers were going to be forced to seriously consider.
“Most of the weeds we are having problems with now are shallow germinating weeds, which need light to germinate. For these species a very light cultivation can reduce weed emergence by up to 80 or 90 per cent,” he said.
“Strategies where a cultivation is used and then followed by a residual herbicide can also potentially remove up to two weed generations.
“It is really a case of working out where the least intrusive use of tillage can be implemented to take a bit of pressure off the herbicides.”
Windrow burning is another technique which is gaining momentum where the majority of weed seeds are collected in narrow windrows and then controlled by burning.
This is a technique that can maintain the benefits of stubble management over the majority of the paddock but dramatically reduce the seed bank replenishment.
Mr Daniel said in all cases management required “moving the battle front”. For example, flaxleaf fleabane was an extremely difficult weed to control in the summer fallow, particularly when plants were mature and toughened off.
However, it has proved to be quite easily controlled by a range of residual herbicides in the winter crop or in the winter fallow leading into the summer crop.
“Instead of bashing our heads against a very tough target in the middle of summer, particularly with something like fleabane, you move the battle to a part of the life cycle where the weed is much more exposed or much more susceptible to control.”

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Early intervention: patch management of herbicide resistance

Local knowledge and early intervention can slow the development of herbicide resistance in weeds. This is the view of DAFF Queensland senior research scientist, Dr David Thornby, who has been using computer modelling to investigate the way herbicide resistant populations become established on farms.
“Several management strategies have been developed that are effective in reducing the weed seed bank even after herbicide resistant weeds have become widespread on a farm, though they are most effective if they are implemented before resistance is widespread,” he said. “Our modelling shows that, under the right conditions, local eradication of resistant biotypes is possible, provided action is taken early and the weed species is not very mobile.”
The Spatial Herbicide Resistance Analyser (SHeRA, developed with funding assistance from the Cotton Research and Development Corporation) is used to predict the effect of management tactics on the fates of individual weeds and the movement of seeds and pollen. “Our main interest is in glyphosate resistance but the principles are the same for other herbicides,” he said.
“When patches of resistant weeds are small, up to 100 m2, growers can readily consider intensive management options that would be considered too expensive or risky to be done over the whole paddock or the whole farm.”
Dr Thornby is suggesting that growers become more conscious of the signs of herbicide resistance. “Glyphosate is such a widely used product that a large proportion of growers are likely to have been selecting for glyphosate resistance over many years,” he said. “Other than in very high value and high input systems, glyphosate is relied on as a relatively inexpensive method of controlling a wide range of weeds, particularly in no-till systems.”
“In dryland cropping systems glyphosate-resistant awnless barnyard grass is a significant problem and sow thistle and sweet summer grass are emerging as being at risk of developing resistance.”
Weeds with high rates of reproduction are the most likely to develop resistance. In addition to using strategies to reduce the risk of herbicide resistance, such as rotating chemical modes of action and including non-chemical weed control methods, Dr Thornby is urging growers to assess the efficacy of each herbicide application.
“Herbicide resistance can start with one resistant plant that survives the chemical application,” he said. “If that single plant is noticed and removed before setting seed then a large problem can theoretically be averted. The difficulty is in finding the surviving plants and having strategies in place to remove them immediately.”

SHeRA is used to predict the likely expansion of a herbicide resistant patch through seed dispersal and pollen flow to surrounding susceptible weed populations. The management practices of the grower can restrict or assist the expansion of the patch. For instance, continuing to use glyphosate alone on resistant weed populations promotes rapid expansion while intense intervention within and around the patch, such as double knocking, chipping or cultivating can contain, and potentially eradicate, the resistant population.
“Because of gene flow in pollen it is important to actively manage the patch and the area surrounding it,” said Dr Thornby. “The patch itself can be considered the ‘eradication zone’, the area surrounding it might be the ‘containment zone’ and the rest of the paddock might be managed using best practice spray techniques and agronomy. This way the risk of widespread herbicide resistance is contained while not adding significantly to the production costs.”
“This approach relies on finding patches while they are a manageable size and taking action immediately.”
Herbicide resistant patches frequently occur in non-cropped areas such as along fencelines, irrigation channels and around farm infrastructure so these ‘hot spots’ need close monitoring so they do not become a source of resistant seed that could be carried into cropping areas.
If patches of resistant weeds are evident inside a paddock, chances are that it is the in-crop or fallow weed management practices that are the main cause. Dr Thornby suggested that cultural practices need to be given more consideration as weed control methods to avoid over-reliance on herbicides.
“Minimum tillage has many benefits but there is a place for cultivation to control weeds,” he said. “But cultivation alone is not the answer either because some weeds prosper with soil disturbance. The routine use of harvest weed seed control methods, growing competitive crops and using crop rotations to manage weeds are also very important and require an understanding of weed ecology and the use of local experience.”
“When choosing which crop type and variety to grow in rotation, weed management and herbicide resistance need to be part of the decision,” he said. “Non-competitive crops provide resistant weeds with an opportunity to spread, which then limits your crop choices and increases production costs in the future.”
Strategic management of patches is unlikely to be effective against highly mobile weeds. Some weeds, such as fleabane are mobile because their seeds are widely transported on the wind. Other weeds, such as ryegrass have high rates of gene flow in pollen and are likewise considered highly mobile.

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