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Higher crop yield and less weeds naturally flow from increased crop competition, but the costs involved in changing machinery and farming systems can be a barrier to achieving these benefits.
Narrowing row spacing, while maintaining the same seeding rate, is generally accepted as the simplest way to increase crop competition, but growers who are not ready to change over their machinery can gain much of the weed suppression benefit using paired-row sowing systems. If this is coupled with east-west sowing the benefits are even greater.
Peter Aikman, Annuello, Victoria has used a paired-row system to maintain crop competition to suppress weeds while gaining seeding efficiencies through slightly wider row spacing. This crop of Compass barley was dry sown in April 2018 and germinated on 12 mm rainfall on 4 May.
Peter Newman, WeedSmart western extension agronomist says paired-row systems such as the Stiletto Boot, which is popular in West Australian sandy soils, are a cheap way to increase crop density and achieve earlier canopy closure.
“Generally, there is not a yield response over single row seeding but yield is maintained in weedy situations, taking some pressure off in-crop herbicides without adding significantly to the weed seed bank,” he said. “Paired-row systems reduce the ‘auto allelopathy’ effect that suppresses plant growth when the seeds of crops like wheat are planted very close along the row. Spreading the seed out, essentially in a slightly wider band, gives each crop seed more room to germinate and grow without impacting on the growth of neighbouring crop plants.”

In southern Australian farming systems there has been steady adoption of paired-row systems, such as Rootboot and Groundhog, to improve seedbed utilisation (SBU), which is a measure of the seed and fertiliser spread relative to the row spacing.
Southern WeedSmart extension agronomist Greg Condon says the paired-row systems help avoid the problems with fertiliser toxicity that can occur in single wide row systems.
“Older paired-row setups moved too much soil and left the seedbed very rough,” he says. “They also had poor stubble handling capacity, used more fuel, achieved poor seed-soil contact and growers had problems with pre-emergent herbicide safety in some situations.”
“Most of these constraints have been fixed with the newer configurations now available on the market. Growers who might have had bad experiences before will probably find that paired-row boots now move less soil, have narrower openers and fit better with a wider press-wheel setup.”
Greg says that although paired-row systems are a good interim option, the best long-term solution is to change to narrow single-row spacing, no wider than 250 mm for tynes or 190 mm for disc planters.
Good establishment in paired-row sown canola.
Paired-row system technology options
Dr Jack Desbiolles, senior agricultural research engineer at University of SA has undertaken extensive trials investigating the benefits of increasing the space between seeds in the seedbed. Paired-row sowing is one way to effectively achieve this and can deliver both increased yield and useful suppression of weeds.
“When it comes to paired-row seeding systems, the technology can be categorised into either split or integrated designs,” said Dr Desbiolles. “The split designs use a Y-splitter tail located further behind the opener, which delivers seeds into a furrow backfill. While seed spread can be more limited, seed placement can be accurate, but seed is often exposed to diluted furrow moisture and contamination from residue and pre-emergence herbicide, all of which can reduce the rate of crop establishment.”
Dr Jack Desbiolles says when it comes to paired-row seeding systems, the technology can be categorised into either split or integrated designs.
While these Y-splitter design solutions represent easy and low-cost upgrades for compatible single row seeding systems, the newer, integrated paired-row designs are becoming more mainstream.
“The integrated designs are compact and streamlined, sitting closely behind the opener and are designed to deliver seeds onto an undisturbed ledge on each side of the trench that the opener creates,” he said. “The accuracy of seed placement depends mostly on the primary furrow shape not affecting the integrity of side ledges. These paired-row configurations are more expensive but often achieve good seed-soil contact without diluting soil moisture or allowing residue or herbicide contamination.”
One grower’s experience
Farming at Annuello in the north-west of Victoria, Peter Aikman (pictured at the top) started using a Rootboot paired-row system in 2014 as part of their strategy to increase sowing efficiency after buying additional land and doubling their cropped area.
Peter’s Horwood Bagshaw seeder had been set up on 30 cm, single row spacing for cropping wheat, barley and legumes in rotation. To cover more area per day at seeding Peter changed to 35 cm row spacing but did not want to lose the crop competition benefits that he had seen at 30 cm spacing.
“Widening the tine spacing allowed us to increase sowing speed and add two more tynes to increase the seeder width. Together these changes increased our seeding efficiency from 12 ha/h to 16 ha/h, which means we save seven days at seeding time and can finish planting the whole area on time,” he said. “To keep the crop competition benefits we turned the row direction to east-west where practical, and use the Rootboot opener to seed 10 cm paired-rows on 35 cm tyne spacing.”
Peter has found that this paired-row system moves some soil around, but in some instances this can be a good thing as it helps to fix any small areas left bare after a legume crop or slightly eroded after using the self-propelled sprayer on sand hills.
“Brome grass is one of our major weeds and we are trying to reduce its germination and seed set by using the combination of the paired-row system and east-west sowing, together with other strategies such as robust crop and herbicide rotation, monitoring for weeds, acting early to prevent weed blow-outs and using harvest weed seed control.”
More resources

Quantifying the effect of paired-row systems on crop competition and yield
Podcast with Annuello grower Peter Aikman
Colin McAlpine grower case study 
Hughes/Raszky grower case study 
Ben Webb grower case study
Trevor Syme grower case study 

In 2005 Dr Jack Desbiolles, senior agricultural research engineer at University of SA led research into the effects of seedbed utilisation and seed rate on weed competition and wheat yields on a shallow grey Mallee loam near Minlaton in South Australia.
The SAGIT funded research, in collaboration with the Southern Yorke Peninsula Alkaline Soils Group, centred on investigating the impact of seedbed utilisation (SBU), which quantifies the extent of the row spacing occupied by the crop. Low SBU seeding typically makes a uniform seeding job easier to achieve but there is an increased risk for fertiliser toxicity to reduce seedling emergence, and inter-plant competition can significantly limit the yield potential in higher potential seasons.
Dr Jack Desbiolles’ research favours the adoption of paired-row seeding systems as a practical way to benefit from higher seedbed utilisation. Photo: Birchip Cropping Group (BCG)
Two wheat crop seeding rates were tested – ‘Standard’ seeding rate of 88 kg/ha to establish 180 to 190 plants/m2and ‘High’ seeding rate of 125 kg/ha to establish 250 to 260 plants/m2. Three levels of seedbed utilisation (SBU) were trialled and Marloo oats was broadcast at 40 kg/ha (105 seeds/m2) and incorporated using a prickle chain on the ‘weedy’ plots to simulate weed competition.
A knife blade plus double-shoot rubber seed boot on 25 cm row spacing gave low (15 per cent) SBU. The intermediate treatment was 45 per cent SBU using a double shoot narrow ribbon Anderson opener, also on 25 cm row spacing. Full (100 per cent) SBU was applied using a 20 cm wide share with a 20 cm reach plus Morris spreader boot set on 20 cm row spacing, effectively sowing seed across the full bed area and leaving no inter-row space.
While crop seeding rate had little effect initially, the 100 per cent SBU had a significant effect on early weed vigour. This treatment reduced weed biomass by 16 to 20 per cent, and reduced weed tillering by 25 to 30 per cent in the early stages of growth.
Increasing seedbed utilisation from a common 15 per cent (left) to 100 per cent (right), especially when combined with higher seed rate, effectively suppressed weed biomass and seed production while significantly increasing crop yield.
SBU also had an impact on later weed growth where greater SBU proportionally reduced weed biomass by 11 to 14 per cent (in the 45% SBU system) and 29 to 32 per cent (in the 100% SBU system). A 43 per cent reduction in weed growth was achieved using a high seeding rate combined with 100% SBU.
Weed seed production followed similar trends, with the best results being a 38 per cent reduction in seed weight per weed plant using full SBU and the higher seeding rate. Following a 289 mm rainfall growing season, the full SBU seeding combined with high seed rate increased wheat grain yield by 0.43 t/ha (in a weed-free environment) and 0.83 t/ha (in a weedy environment), relative to the low SBU, low seed rate control.
This research confirmed the principles of crop competition and showed that paired-row systems were a practical option to help achieve greater weed competition and higher yield potential through greater seedbed utilisation.
More recently, Dr Desbiolles conducted research on different soil types in the Murrayville district (Vic) in collaboration with Mallee Sustainable Farming Inc, and with DAFF funding, comparing paired-row systems to a commonly-used single row knife point system. In this trial, the paired-row systems gave the highest and most consistent crop establishment across a swale-dune Mallee sandy soil system, with good moisture conditions at seeding and sufficient in-crop rainfall.
The plant establishment benefits ranged from +15 per cent on the mid-slope and sand hill, to +20 per cent on the sandy stony flats, relative to a district system control, and after a dry season finish, achieved up to 0.15 t/ha gain in wheat grain yield.
“These results correlate well with the earlier work done in Minlaton which measured crop yield and weed suppression benefits through increased seedbed utilisation,” he said. “Improving crop establishment and gaining the crop competitive advantages relies on correct seeder set-up.”
In a review of seeder set-up for the GRDC Stubble Management project, Dr Desbiolles highlighted the following considerations when it comes to using paired-row systems in different situations:

Recommended for use in marginal soil moisture conditions when seeds can be placed onto undisturbed soil moisture.
Recommended for effective incorporation of pre-emergent herbicides (IBS) application. Crop safety is best secured using paired-row attachments closely integrated behind the opener.
Possible use in stony soils if compatible with shallow operating depth.
Possible use in non-wetting poor fertility soils, where seeding is at furrow tilling depth.
Possible use under rhizoctonia pressure if coupled with best practice disease management.
Possible use in high residue situations when coupled with good residue management strategies.

Other resources:

Paired-rows give entry-level crop competition
Peter Newman (AHRI/WeedSmart) and Peter Horwood (Mingenew, WA grower) discuss paired-rows  
Selecting a seeding system for your soil 

About one-quarter of glyphosate-resistant populations within broadacre cropping situations across Australia come from fencelines and other non-cropping areas of the farm.
Along paddock borders, where there is no crop competition, weeds can flourish and, if not controlled, set lots of seed. The traditional approach has been to treat these weeds with glyphosate to keep borders clean but after 20-odd years this option is now failing and paddock borders are becoming a significant source of glyphosate-resistant weed seed.
Weed researcher Eric Koetz said the limited options for managing weeds along irrigation infrastructure and other non-crop areas is a problem and is putting additional pressure on knock-down herbicides in irrigated systems.

In some situations, cultivation can be used to kill the weeds and provide a firebreak, but on light soils this may pose an erosion risk and mowing or slashing may be safer options. Another possible tactic is to continue using herbicides but to ensure that a clean-up operation is carried out before any survivors can set seed.
Some growers are choosing to increase the heat on weeds along the borders by planting the crop right to the fence and then baling the outside lap and spraying with a knockdown herbicide to kill any weeds and provide a firebreak.
Another good option in some situations is to maintain a healthy border of vegetation using non-invasive grasses. In Queensland, buffel grass is a good example of a grass that can outcompete other weeds while not invading crop lands.
If only herbicides are used on fencelines, resistance is inevitable. Surviving weeds on fencelines have no competition and access to plenty of soil moisture, so they set a lot of seed and resistance can easily flow into neighbouring paddocks.

Other resources

It’s time for a glyphosate intervention
Farm hygiene cottons on – Cleave Rogan, St George
What’s new in management of herbicide resistant weeds on fencelines?
Keeping the farm clean – Graham Clapham, Norwin
Don’t jeopardise glyphosate for clean fencelines
Keeping fencelines clean
Resistance risk to knock-down herbicides on irrigated cotton farms

This can potentially reduce crop yield and almost certainly means that the weeds will set abundant seed and most likely shed that seed before the crop is harvested, increasing the weed pressure in future years.

The best way to ensure clean crop seed is to buy certified weed-free seed each year. But many growers prefer to retain some grain on-farm for planting the next year. For best results growers usually harvest seed from their cleanest paddocks and conduct some form of seed cleaning either on or off-farm.
However, research shows that there is a tendency to underestimate weed seed contamination in seed retained for planting.
An AHRI study on 74 farms across the Western Australian grainbelt showed 73% of cleaned crop seed samples had some level of weed seed contamination. The up-side is that 25% of cleaned samples were weed-free, so it can be done!

This means that many unknowingly introduce significant levels of weed and volunteer crop seeds into the farming system at seeding time, even when crop seed has been cleaned. More alarmingly, many of these weed seed populations are resistant to a range of commonly used post-emergent herbicides.
Uncleaned crop seed samples can have almost 25 times more contamination than cleaned crop seed. It is important to remember that resistance will evolve faster from introducing resistant weed seeds into a paddock, compared to resistance evolving independently in that paddock.
The cleaning method used strongly influences contamination levels – a ‘gravity table’ is the most effective, followed by other methods such as rotary screens and sieves.

Contamination levels of each cleaning method for all contaminants.
Crop type also has a significant effect on the amount of contamination, with wheat containing much higher annual ryegrass seed numbers than barley, possibly because barley was more likely to out-compete weeds during the growing season.
Another advantage of having seed professionally cleaned and graded is that larger crop seeds can be retained, promoting stronger seedling vigour and higher germination rates.
Systems promoting farm hygiene such as meticulous seed cleaning and sanitising tillage, sowing and harvesting equipment between paddocks will help prevent the introduction of new weed species, noxious weeds and herbicide resistance.

This August, Birchip Cropping Group (BCG) is co-hosting the first WeedSmart Week to be held in Victoria.
Growers and agronomists are invited to attend the 3-day event, beginning with a 1-day forum at Horsham Town Hall on 27 August. The following two days will be spent touring farms around the Horsham area to see how growers are implementing the WeedSmart Big 6 tactics to minimise the impact of herbicide resistance on their businesses. The WeedSmart Week theme ‘Diversify and Disrupt – Conquer weeds with the Big 6’ says it all!
Kewell farmer Ian Ruwoldt is encouraging other Wimmera growers to attend WeedSmart Week in August as a good opportunity to formulate a plan to manage weeds through the year and through the rotation using the WeedSmart Big 6.
GRDC is the major sponsor of WeedSmart and Senior Regional Manager – South, Craig Ruchs, encourages growers from the Wimmera and beyond to make the most of the opportunity to be part of the focussed and interactive couple of days.
“Weeds frequently drive systems decisions, having the potential to affect flexibility, choice and ultimately profit. Taking a strategic and planned long-term approach, implementing the WeedSmart Big 6 principles, can help put growers back in control,” he said. “Pulses are a particularly important element of crop rotations for many growers in the Wimmera and the production of these crops presents both unique opportunities and challenges for weed control.”
“Bringing greater diversity in weed control tactics is critical in the ongoing battle against weeds and WeedSmart Week provides a highly effective platform to share research outcomes and on-farm innovation in a very practical and applied way.”
WeedSmart Week brings together a wealth of knowledge and experience from local and inter-state growers, researchers, advisors and technology experts – putting the spotlight on herbicide resistance and weed management. Growers can see what is and isn’t working first-hand and consider how key principles can be applied directly to their own farming operation.
GRDC Senior Regional Manager – South, Craig Ruchs (Photo: GRDC)
At the forum and on the bus trip growers, agronomists and researchers put all the options and ideas on the table for discussion. In August last year, three members of the Birchip Cropping Group, Ian Ruwoldt, Tim Rethus and Sam Eastwood, attended the 2018 WeedSmart Week in Narrabri, NSW.
Farming at Kewell, Ian Ruwoldt and his brother Greg have several strategies in place to manage ryegrass, bedstraw, marshmallow, vetch and bifora. Ian found the WeedSmart event in Narrabri to be very comprehensive and a good opportunity to think through the tactics that could help solve their weed problems.
“We currently use oaten hay, chemical rotation, imidazolinone (imi) chemistry with canola and a chaff deck on the harvester to keep weed numbers low,” said Ian. “Thinking about the WeedSmart Big 6 helps to formulate a plan to manage weeds through the year and through the rotation.”
“The forum covers a lot of topics and the discussions are very practical and very relevant to the region, so this year’s event will focus on the weed issues facing Wimmera and Mallee farmers.”
Attendees will have several opportunities to see and discuss cutting-edge technologies such as optical sprayers, robots and emerging ‘green-on-green’ spray sensors, and will find out how other growers in the region are implementing the Big 6 weed management tactics.
The growers, agronomists and researchers speaking and participating in expert panels at the Day 1 forum will spark important discussions about herbicide resistance and how the Big 6 tactics can be used to target the weed species and farming systems in the southern cropping region. There’s one thing for sure – doing nothing is not an option.
Register for this important 3-day event for the ‘early bird’ single ticket price of $130, guaranteeing a seat on both the bus tour days as well as the forum, all fully catered, at https://www.weedsmart.org.au/weedsmart-week-horsham/

There are several reasons why weeds might survive a herbicide treatment but it is increasingly common for herbicide resistance to be the culprit.
Testing weeds for herbicide susceptibility and resistance can save growers thousands of dollars, making the investment of a few hundred in testing very worthwhile.

There are two main tests – The Quick Test and The Seed Test

The Quick Test is done using weed plant samples collected in-crop and provides the results within a few weeks.
The Seed Test is done on weed seed samples, usually collected around harvest time and the results take a few months.

The Quick Test uses plant samples collected on-farm and sent to the laboratory. The plants are revived and planted into pots, then tested against the required herbicides. The Seed Test requires the collection of ripe seed, which is planted out at the laboratory. After dormancy has been broken and the seedlings have started to grow they are tested for their response to herbicides. Both tests are equally accurate. The Quick Test can not test for resistance to some pre-emergent herbicides, such as trifluralin.
The value of the Quick Test is that you can find out what herbicides still work on the weeds collected and this gives you the option to use a different herbicide to treat the weed patch within the same season and before the plants set seed.
Gathering samples for the Quick Test

collect from the middle of the patch of weeds that are suspected to be resistant
if the weeds are large, collect 20 plants
if the weeds are small, collect 50 plants
shake off the loose dirt and place the sampled weeds in a zip-lock plastic bag
do not add water to the bag
keep the sample cool
if possible, collect and send samples on a Monday or Tuesday
sample from different patches in the paddock, note the location/s and keep samples from different patches separate
send by express post to Plant Science Consulting Check the website for details about the services offered, costs and specific instructions before submitting samples.

Gathering samples for the Seed Test
Collecting weed seed before or at harvest is the most common method used. The collected seed must be mature, from green to when the seed changes colour. Before harvest, collect 30 to 40 ryegrass seedheads or several handfuls of wild oats seed. After harvest, it is common to find seedheads still in the paddock or samples of contaminated grain can be sent for analysis.
Keep samples from different locations separate and details noted on the bag. Only use paper bags (double layer) to collect and send seed samples. Ensure bags are sealed so that the samples don’t mix during transit.

There are three weed seed testing services in Australia:

Plant Science Consulting
CSU Herbicide Resistance Testing
UWA Herbicide Resistance Testing

Visit the website/s for details about the services offered, costs and specific instructions before submitting samples.
How to collect samples for the Quick Test

 
How the Seed Test works

Podcast
In the podcast below, Dr Peter Boutsalis provides practical tips on collecting weed seeds for herbicide resistance testing. You can also see visual examples of weed seeds ready for collection on the podcast page here.

Related information

Testing for herbicide resistance with Dr Peter Boutsalis
Testing for herbicide susceptibility pays off
What herbicides still work

Herbicide resistant weeds might not be widespread in Central Queensland yet, but all the indications are that the problem is flying just under the radar. Following the discovery of the world’s first population of glyphosate resistant sweet summer grass near Emerald, random weed surveys have since confirmed glyphosate resistance in both feathertop Rhodes grass and fleabane samples collected in the region.
Cotton and grain growers and agronomists who want to stay ahead of this mounting threat are invited to attend the 2019 WeedSmart Week event in Emerald. The 2.5-day program will begin with a 1-day forum at the McIndoe Function Centre, Emerald on 13 August. The following day will be filled with a bus tour to farms around Emerald where growers have put in place integrated weed management programs to minimise the impact of herbicide resistance on their businesses. The final part of the program is a half-day tour of the SwarmFarm Robotics base at Gindie on Thursday 15 August.
The 2018 WeedSmart bus trip visited Beefwood in northern NSW to check out some of the new weed management technology becoming available to growers.
The WeedSmart Week theme ‘Diversify and Disrupt – Conquer weeds with the Big 6’ says it all! At the forum and on the bus trip growers, agronomists and researchers will have all the options and ideas on the table for discussion.
Ms Vicki Green, GRDC Crop Protection Manager, North is looking forward to attending the event and hopes that CQ growers will make the most of the opportunity to be part of such a focussed and interactive couple of days.
“There is so much pressure on herbicide use in farming systems and growers all over Australia are rising to the challenge to diversify their weed management programs,” she said. “We know the WeedSmart Big 6 principles apply everywhere, but they need to be applied differently in each region and on each farm.”
“That’s where events like this are so valuable – bringing together a vast array of knowledge and experience from local and inter-state growers, researchers, agronomists, consultants and technology experts.”
The value of a day out talking with growers about their weed management strategies – priceless!
In August last year, twelve members of the GRDC CQ Grower Solutions Group attended the 2018 WeedSmart Week in Narrabri as part of a six-day fact-finding tour through southern Queensland and northern NSW.
Brothers Justin and Royce Staier, who farm in the Clermont and Kilcummin areas, were part of the tour group and came away from the experience with some new ideas and a resolve to implement some changes in their farming operations.
Justin was impressed with the calibre of speakers and enthusiasm of the growers on the farm tours. “There are so many people putting a big effort into controlling herbicide resistance,” he said. “We are just starting to see problems with weeds like feathertop Rhodes grass here and going to WeedSmart Week in Narrabri really brought some important things to mind, like the need to stop survivor weeds and to be careful with residual herbicide use. Machinery hygiene is an on-going risk for spreading herbicide resistance and this is a high priority for us.”
At this year’s event, attendees will have several opportunities to see and discuss cutting-edge technologies such as optical sprayers, robots and emerging ‘green-on-green’ spray sensors, and will have the opportunity to find out how other growers in the region are implementing the Big 6 weed management tactics.
The growers, agronomists and researchers speaking and participating in expert panels at the Day 1 forum will spark important discussions about herbicide resistance and how the Big 6 tactics can be used to target the weed species and farming systems in the northern cropping region. There’s one thing for sure – doing nothing is not an option.
Register for this important 3-day event for the ‘early bird’ single ticket price of $130, guaranteeing a seat on both the bus tour days as well as the forum, all fully catered.

with Greg Condon at WeedSmart Week 2018, Narrabri
Having seen the ‘strip and disc’ system working well on South Australian farms several years ago, a number of growers in southern NSW adopted the concept and are constantly making modifications to suit their soils and rotations. The system has been successfully modified to suit their growing region and WeedSmart southern agronomists Greg and Kirrily Condon are convinced that it can be modified to suit other growing regions across Australia.
Step 1 – Disc seeding
Disc seeding helps retain soil moisture at sowing in a no-till farming system and does not generate hard-to-manage clods at the surface like tines often do. The extra moisture enables calendar sowing at the earliest planting date suited to the crop and region.
For best results with single disc seeding it is essential to exert sufficient downward force to achieve even soil penetration in a zero-till system. It is important to use sharp discs and seed firming wheels to help close the furrow.

Likely challenges are associated with potential hairpinning of stubble, inadequate seed-soil contact, and blockages if clumps of residue have been left after harvest. Diligent maintenance of the planter and discs is essential, insect pressure can be greater, especially in canola, and there are fewer pre-emergent herbicide options due to the higher stubble load.
Tines are often preferred for crop safety in low to moderate stubble situations, but are not well-suited to the narrow row spacing that is an integral component of this system for integrated weed management.
Step 2 – Narrow rows
Narrow row spacing increases cereal and canola yields by 1% for even inch reduction in row spacing. Using a 16.5–19 cm (6.5–7.5 inch) disc seeder, growers can achieve increased cereal yields, more even ground cover and any weeds that are present will produce less seed.

When crops are sown at narrow spacing and then harvested high, the standing stubble shades the soil surface; reducing evaporation and cooling the soil. Field measurements taken in February 2017 showed that when the air temperature was 42 degrees C, bare soil temperature was 52 degrees C and under the stripper straw the soil surface temperature was measured as 32 degrees C, a staggering 20 degrees cooler than bare soil in the same paddock.
Using the same established plant number as a wider row configuration, narrow rows force weeds to grow taller and set their seed higher in the canopy, where they are more easily captured at harvest.
Step 3 – Shelbourne stripper front
A rearwards rotating rotor with stripping fingers strips grain from the grain heads. The stripper front threshes 85% of the grain, leaving only a limited amount of chaff (including weed seeds and small grain) to go through the header. The tall stubble provides shading of the soil surface, improving moisture conservation and fallow efficiency.

Stripper fronts only work well in high residue crops. They are best suited for use in cereal crops sown on narrow rows (less than 250 mm spacing), and generally don’t work well in canola or pulse crops.
A stripper front harvesting a cereal crop at a harvest height of 60 cm, uses 50 per cent less fuel than a draper front operating at the conventional height of 20–40 cm. The harvester can harvest 50–70 t/hr because there is far less material to be processed through the machine, which also means there is less wear and tear and lower maintenance costs.
A stripper front can be just as effective as a draper at collecting weed seeds retained at harvest. This means that harvest weed seed control tactics can be implemented, directing weed seed into the chaff stream to be deposited in a narrow band on the wheeltracks or behind the harvester, rather than spread across the paddock. The stripper front must be set up correctly to minimise grain (and weed seed) losses out the front.
Because so little crop residue goes into the harvester when a stripper front is used, there is no need for a MAV or Powercast stubble spreader attachment, saving on capital and running costs.

Related post – Stacking the Big 6 in a ‘strip and disc’ system

Is sunlight breaking down pre-em herbicides where farmers are dry sowing? Our Western Extension Agronomist, Peter Newman, has been fielding questions over the last few days via Twitter on this. He did some digging and found that sunlight is only having a small effect on pre-emergent herbicide degradation. It turns out that light rain is the main risk – firing up microorganisms to start microbial degradation before the true season break.
ICAN’s Mark Congreve, AHRI’s Dr Roberto Busi and University of Adelaide’s Dr Christopher Preston provided Pete with some more detailed information which he has put together to explain what’s happening in the video below.

We’ve also made Module 4 from our latest Diversity Era Course, Pre-Emergent Herbicides 101, with Dr Christopher Preston, available. You can watch the video below where Chris talks in detail about herbicide breakdown. Did you know you can do all of our Diversity Era courses for free? You can sign up for Pre-Emergent Herbicides 101 here.

 
 

Organic farmers are the original integrated weed managers. Now, some of the innovations that are being developed to combat herbicide resistant weeds on conventional farms are proving useful for organic farmers too.

Phil and Ashlee Jackson, in partnership with Brad and Jenna Jackson, manage a 400 ha organic farming system at Westmar, southern Queensland, growing wheat, linseed and lablab.

Phil Jackson (left) with brothers Matt (centre) and Brad (right). Phil and Brad manage the organic farm at Westmar Queensland. All three brothers work alongside their parents Peter and Janice on their conventionally-farmed land at Gurley NSW.

Since 2014 Brad and Phil have been developing valuable weed management tactics, such as camera-guided inter-row cultivator, narrow windrow burning and green manuring, that can be employed in both conventional and organic farming systems.

With cultivation being the only real option for summer weed control in organic farming operations Brad and Phil are keen to investigate any options that will help them stay ahead of the weed seed bank.

“Not being able to do any in-crop weed control was a big concern for us,” says Brad. “Three years ago we bought a Garford inter-row cultivator from the UK to use it in our wheat and linseed crops.”

The cameras on the cultivator guide the alignment of the tynes to follow the plant row with an accuracy of just 10 mm. The 500 mm row spacing enables use of the inter-row cultivator, which can be used when the crop is 100 to 400 mm high.

The camera-guided inter-row cultivator allows in-crop weed management until the crop reaches about 400 mm in height.

“We use it mainly to control wild radish and wild oats,” says Phil. “It suits our 12 m controlled traffic farming system and there is no reason why we couldn’t also use it strategically in our no-till conventional farming operation at Gurley, NSW.”

At harvest, Brad and Phil use narrow windrow burning on as much of the area as possible, to collect and burn weed seed present late in the season. They have found this practice a good way to reduce the weed seed bank most years without burning all the stubble.

Narrow windrow burning can be successful in reducing weed pressure in the following seasons, particularly for annual ryegrass.

Phil says it can be rewarding when the conditions are favourable, particularly to control annual ryegrass. “We try to burn as early as is safe to clear the way for cultivation for summer weed control,” he says.

The Jacksons also utilise green manuring – an age-old weed control tactic in organic farming. They have found the summer legume lablab to be a good option for green manure ahead of a long fallow. Lablab produces a dense and competitive crop that prevents weeds from establishing, while also giving the soil a nitrogen boost.

Lablab is a dense, competitive green manure crop that provides excellent ground cover and weed suppression over summer.

The tactics employed in this organic operation tick off all the non-herbicide weed control tactics in the WeedSmart Big 6 promoted as a practical system to combat herbicide resistance. In an organic system four of the six tactics can be broadly applied to reduce weed pressure.

Rotate crops and pastures – The Jacksons’ rotation is simple but effective. Linseed is grown after wheat to control soil borne root diseases including crown rot, common root rot, yellow leaf spot and spot form of net blotch. It is also resistant to both main species of root lesion nematodes. Linseed yields are higher when grown after AMF host crops that maintain high numbers of the arbuscular mycorrhizae fungi (AMF). High performing crops are one of the best ways to combat weeds.
Mix and rotate herbicide MOA – Not applicable on organic farms but very important in systems that use herbicides.
Increase crop competition – High performing winter crops combined with a summer legume green manure crop in rotation.
Use the double knock to preserve glyphosate – Not applicable on organic farms, however, the idea of monitoring weed control efficacy and removing survivors still applies – more crop, less weeds.
Stop weed seed set – Cultivation in the fallow and in-crop (with the guided inter-row cultivator) significantly reduces weed seed set.
Implement harvest weed seed control – The Jackson’s currently use narrow windrow burning to capture weed seed at harvest. They are also looking at other options such as chafflining and impact mills. All the current harvest weed seed control tactics are non-chemical tools that are being rapidly adopted on Australian farms.

More resources:

https://www.youtube.com/watch?v=oYE_k2A7zbIThe Garford guided inter-row cultivator in action (promo video).

If a herbicide resistant weed never sets seed then it won’t be long before the resistance is eradicated. This is easy to say, but has been mighty hard to achieve because it is so time consuming.

Enter now the power of robotic weed control. Frequent scouting for, and removal of small weeds, is now a practical reality with a commercial robotic platform available for broadacre cropping operations.

Tom Holcombe, SwarmFarm Robotics Field Operations Lead says robotic platforms open up new opportunities in non-chemical weed control.

Tom Holcombe, SwarmFarm Robotics Field Operations Lead says the theory has been proven recently in trials in Central Queensland, where weed blow-outs in fallows on two sites were brought under control using repetitive herbicide applications.

The two sites were on separate properties in the Springsure district of Central Queensland. One site was 44 ha of fallow at ‘Kilmore’, following dryland sorghum, with weeds managed from August 2017 to March 2018. The other was 28 ha at ‘Denlo Park’, following dryland cotton, with weeds managed from October 2017 to March 2018.

“To control weeds present in high numbers at both sites we decided that the robots would spray on a fortnightly basis to regain control,” says Tom. “This regular and repetitive spraying achieved excellent control at each of the sites, avoiding the need to cultivate.”

Over a period of eight weeks of routine, fortnightly spraying with knockdown herbicides using a Weedit mounted on the robot, the weed density dropped from the initial 20% of the area, when it was considered out of control, down to approximately 2% of the trial area.

Kilmore site – weedy after spray failure.

Kilmore site – clean, following intense herbicide application using robotic sprayer.

This use pattern would be considered impractical and unadvisable in a conventional herbicide spraying program. The robotic platform made it possible, and it was effective due to the continual knocking of the same weeds until death was achieved and seed set prevented.

A commercial robotic platform also brings the opportunity to use optical weed sensing technology in conjunction with non-herbicide weed control tactics such as chipping and microwaving.

Both SwarmFarm (with Queensland state government funding) and The University of Western Australia (with GRDC funding) have shown that optical sensing works well with a chipping tyne implement that is activated only when a weed is ‘spotted’. This makes cultivation for weed control site-specific and is compatible with zero-till farming.

Another prototype that SwarmFarm developed within the Queensland government’s Strategic Cropping Land Mitigation funded project was a small microwave unit that activates only when a weed is present (as detected using a Weedit sensor).

“There has been a lot of interest in the potential of microwave for weed control, but the power and time involved has kept this technology out of reach,” says Tom. “Having several small units teamed with the Weedit sensors and mounted on a robotic platform opens up a whole new set of opportunities.”

“Time is no longer a constraint because the robot can stop and apply the necessary treatment without keeping an operator and tractor tied up, and the more often it is used, the smaller the weeds will be – needing less time and power to kill them.”

Single-unit microwave weeder prototype using Weedit optical sensor for site-specific weed control.

The power constraint is also more realistic than trying to apply a ‘blanket’ microwave treatment across a whole paddock. Since only a few units on a multi-unit bar are likely to be activated at any one time, the power draw is far less and small weeds are much easier to kill than large weeds.

“There is also a soil health benefit given that the weeds can be controlled without affecting the soil biota of the whole paddock,” he says.

“We are particularly keen on the development of a microwave rig now that we have proven the potential for this technology to be a very effective double-knock to take out weeds that survive a herbicide treatment, and even for its application on organic farms to dramatically reduce the reliance on cultivation,” says Tom.

https://youtu.be/kxZWSseIKxoTom Holcombe, SwarmFarm Robotics Field Operations Lead sees optical weed seeking microwave units on a robotic platform as the next big thing in non-chemical weed control.

Other links:

Microwave effects on weeds and soil
Targeting small weeds all year
Efficient herbicide use pays off
How can I use a mechanical tactic as a second knock

Whether you have a horizontal iHSD impact mill or are looking to get into this technology with the newly-released vertical configuration, you can rest assured that the kill rate of both configurations has been independently proven to be 98 per cent for annual ryegrass.

Dr Michael Walsh, Director Weed Research, Faculty of Science, The University of Sydney has been testing the efficacy of impact mills on weed seeds since the early days of development of the Harrington Seed Destructors.

Left: Without harvest weed seed control. Right: With iHSD harvest weed seed control.

“The vertical configuration of the iHSD mills could change the direction of the chaff flow through the mills and this could affect the processing of the chaff and potentially the efficacy of weed seed destruction,” he says.

“Having previously shown that the horizontal iHSD impact mill can achieve at least 98 per cent weed seed kill, we were keen to repeat the test for the vertical mill configuration.”

During the 2018 harvest, a wheat crop at Broomehill was used to test the vertical mill. Twelve 20 m strips were marked out in the wheat crop where there was no annual ryegrass present. These plots were used to test the efficacy of the vertical mill at three different harvester speeds – 4, 6 and 8 km/hr.

Weed seed destruction was 98% or better at three operating speeds (4, 6 and 8 km/hr).

As each plot was harvested, 5000 dyed annual ryegrass seeds were introduced into the chaff stream directly above the inlet to the righthand side mill. The processed chaff from each plot was collected in large, fine-mesh bags attached to the righthand side outlet chute.

To determine the weed seed survival rate from each plot, Dr John Broster’s team at Charles Sturt University, Wagga Wagga processed subsamples from each of the 12 bags of chaff. The chaff was thinly spread on trays, covered lightly with potting mix and watered every day for four weeks to stimulate the germination of any surviving annual ryegrass seed. Each day annual ryegrass seedlings present were counted and removed from the trays.

“The result of this testing was a weed seed kill rate of at least 98 per cent for the vertical iHSD impact mill, regardless of the harvester operating speed of 4, 6 or 8 km/hr,” says Dr Walsh. “This level of weed seed destruction is equivalent to that of the horizontally mounted mills that we have tested previously.”

“From this result we can be confident that provided the harvester is set up to efficiently collect annual ryegrass seed at harvest, growers using either configuration of the iHSD can expect to achieve this very high rate of weed seed destruction.”

Peter Newman, Western Extension Agronomist with the Australian Herbicide Resistance Initiative (AHRI) and WeedSmart, says there is keen interest amongst Australian growers in harvester-integrated weed control solutions.

“Growers are looking at price and weed seed control efficacy,” he says. “This new configuration of the iHSD provides several new features that will benefit growers, including the ability to easily check for grain loss by opening a rear hatch and disengaging the iHSD belts, the large cavity under the sieves effectively prevents bridging and the stone trap will help to prevent any foreign objects from entering and damaging the mill.”

New features include mechanical drive, vertical configuration, rear hatch and stone trap to reduce costs and improve reliability.

“The vertical configuration uses the same cage mill for seed destruction as the earlier horizontal version but is mechanically-driven rather than hydraulic, significantly reducing the cost, making the iHSD more attractive to growers.”

Following the invention of the HSD by WA grower Ray Harrington and development by UniSA with investment from GRDC, the iHSD has undergone further development by SKF Engineering and DeBruin Engineering, together with national distributor, McIntosh Distribution.

McIntosh & Son dealer principal (southern branches) Devon Gilmour says the vertical, mechanical iHSD’s direct-drive system is easy to use and maintain, can be retro-fitted on a wide range of harvester models and is easy fitted on-farm. Impact mills have a proven high weed seed kill rate, making them a very effective, non-herbicide tool in the fight against herbicide resistant weeds.

Harvesters fitted with impact mills can spread crop residue more evenly, reducing the loss or redistribution of nutrients, making them an attractive proposition for growers.

Other resources:

Using your harvester to destroy weed seeds
Which harvest weed seed control tool is right for you?

The herbicide-only era is over and the diversity era is here. One example is coupling pre-emergent herbicides with greater crop competition.
In a brand new, free online course taught by Dr Chris Preston (University of Adelaide) and Mr Mark Congreve (ICAN), growers and agronomists can gain confidence through understanding how to best use pre-emergent herbicides in both winter and summer cropping systems.

Mark Congreve (ICAN), Chris Preston (University of Adelaide) and Peter Newman (AHRI) discuss the ins and outs of pre-emergent herbicide in Australian cropping systems in a new Diversity Era online course.
The Diversity Era Pre-emergent Herbicides 101 course includes:

free access to 13 educational videos that cover the basics of how pre-emergent herbicides work, plus practical tips to help you use these herbicides on farm in both summer and winter cropping systems
straightforward, step-by-step instruction from highly respected and skilled industry professionals with deep knowledge of cropping systems and weed management
access to a comprehensive overview of what is currently known about pre-emergent herbicides and how to best use them in your farming system
Q&A discussion with Chris and Mark (facilitated by Peter Newman), a resource library with extra information, podcast interviews and a live webinar.

In just three hours, find out how pre-emergents can help manage herbicide resistance in crop weeds. There’s videos, audio, PDF downloads, quizzes and a wrap-up webinar to help you get the most out of the Diversity Era Pre-emergent Herbicides 101 course, while working at your own pace.
Given that pre-emergent herbicides require more planning and carry some inherent risks, it is important to understand how they work in different soils, how they can be used most effectively through a cropping program, including the fallow, and how to manage any restrictions on future crop choices.
Dr Chris Preston says that the renewed interest in adding pre-emergent herbicides to weed control programs is in response to the rapid escalation in herbicide resistance to post-emergent herbicides and the important knockdown herbicide, glyphosate.
“Currently, the only widely used herbicide mode of action group in Australian grain production that has no known field populations of herbicide resistant weed species is Group H,” he says. “Pre-emergent herbicides are also prone to herbicide resistance, with the number of resistant populations on the rise, so their judicious use is essential. Incorporating pre-emergent herbicides into the program increases the diversity of herbicide mode of action groups, making it possible to mix and rotate these herbicides to extend their effective life. A well-executed pre-emergent program can also take the pressure off subsequent post-emergent in-crop herbicide applications.”
“Knowing how to maximise efficacy and stack these products with other tactics, such as crop competition, harvest weed seed control and stopping weed seed set, needs to be part of the crop management package on every farm, every year.”
Having presented innumerable pre-emergent herbicide use workshops around Australia and co-authored practical information resources for agronomic advisors, Mark Congreve is keen to see all growers and advisors familiar with the soil behaviour of pre-emergent herbicides.
“Understanding the risks and benefits associated with these herbicides is very important,” he says. “This course is a great refresher and a resource that growers and agronomists can refer back to over and over again as they integrate pre-emergents into their weed management program to suit each season and crop sequence in both winter and summer cropping situations.”
The Diversity Era Pre-emergent Herbicides 101 course opened for registration on 20 March 2019, with the release of the first five modules – ‘Understanding Pre-em Basics’ with Chris Preston and a podcast with Chris and AHRI’s Peter Newman.
Modules 6–8 ‘Using Pre-ems in a Winter Cropping System’ with Chris will go live on Wednesday 27 March and Modules 9–11 ‘Using Pre-ems in a Summer Cropping System’ with Mark Congreve will be available the next week on 3 April, along with two bonus materials modules and another podcast, this time with Mark and Peter. The final element will be a live webinar on April 10 with Peter Newman, Mark Congreve and Chris Preston.
Register now: www.diversityera.com/courses/pre-emergent-herbicides-101

Initiatives like our latest Diversity Era course ‘Pre-emergent Herbicides 101’ (which is free!) are made possible through the support of our stakeholders. Please watch the above video highlighting stakeholder engagement to learn more.

High residue farming with a stripper front and a disc seeder efficiently captures and stores soil moisture, and growers are finding the system can be tweaked to also improve weed management.
An increasing number of growers in the northern region are seeing early confirmation that the system works and there is building scientific evidence that they are on the right track with the adoption of narrow row sowing with single disc planters, combined with a stripper front and either a chaff deck or chaff line at harvest.

Peter and Kylie Bach, Kurilda Ag, Pittsworth use a Shelbourne harvester front and Emar chaff deck to conserve stubble and put weeds in their place.
AHRI and WeedSmart agronomist Greg Condon says this system is providing growers in the northern grains region with opportunities to plant and grow crops that would otherwise not be possible.
“Harvest weed seed control is a useful tactic against many of the key weed species in the northern region,” he says. “We now have scientific data to show that, with correct harvester set-up, stripper fronts and drapers can be equally effective at collecting weed seeds at harvest. The advantage of the stripper front is that the vast majority of the crop residue remains as standing stubble in the paddock. This means the harvester does not have to deal with enormous amounts of plant material and there is so little straw going through the machine that choppers and spreaders have much less work to do.”
“When a chaff deck or chaff line chute is attached to the harvester, the weed seed is separated from the grain with a small amount of chaff, and deposited either on the controlled traffic wheeltracks or in a narrow band behind the harvester. These weeds can then be subjected to targeted control tactics applied to a very small percentage of the paddock area.”

A chaff deck attached to the harvester separates the weed seed from the grain, along with a small amount of chaff, which is deposited on the controlled traffic wheeltracks.
For some growers, like Peter and Kylie Bach farming at Pittsworth on the Darling Downs of Queensland, using the stripper front and chaff deck combination in their cereal crops has gone a long way toward solving their problems with volunteer crop plants from previous seasons.
“The standing stubble has given us planting opportunities for summer crops that would not have been possible after a conventional harvest,” says Peter. “Barley stubble provides an excellent environment for planting mungbeans and when the mungbeans are harvested, the paddock has much better ground cover with the previously-standing cereal stubble being retained on the soil surface.”

The stripper front leaves most of the stubble standing in-situ, meaning much less material needs to be processed in the harvester.
Peter and Kylie find that the barley stubble can persist for a few seasons after the growing season, providing soil moisture conservation benefits in their summer cropping program.
The ‘strip and disc’ system ticks off three of the WeedSmart Big 6 tactics for managing herbicide resistance – crop competition, harvest weed seed control and diverse rotations.
“When weed control is integrated into an agronomic package it is possible to achieve some real synergies in the system – achieving more than just the cumulative benefits associated with each of the parts,” says Greg. “After a few years, there is a combination of standing and residual stubble in the field and stubble load is managed through the sequencing of different crops, without ever leaving the soil bare.”
The ground cover benefits of cooler, moist soil opens up the possibility of sowing early and growing longer season crops, and even double cropping is some environments. There is also better nutrient cycling and improved soil biota activity.

Tall stubble left after the stripper front harvests the crop and a line of chaff left behind the harvester concentrates any weed seed collected during harvest in this narrow and well-shaded band.
While the stripper front has several benefits and efficiencies over the conventional draper, these benefits are not likely to support a change-over until existing machinery is due for replacement, according to an economic study by John Francis, Holmes and Sackett. A draper can achieve many of the same standing stubble benefits and harvest efficiencies as the stripper front if the harvest height is set at 40 to 60 cm. For both options to be effective for weed seed collection the crop competition must be strong to force weeds to set seed high in the canopy. Without strong crop competition, harvest weed seed control generally relies on cutting as low as possible at harvest.
Grower experience suggests that stripper fronts have a distinct advantage when it comes to picking up fallen or lodged crops and weeds.

Weed identification is a valuable skill and most farmers can identify the common and important weeds on their farms. For most non-botanists, identification is easiest when the plant is mature and flowering – but to be effective, weed control decisions need to be made well before flowering.

With the increasing prevalence of herbicide resistance across all farming regions, accurate identification at early growth stages is essential to ensure the best control strategies are implemented when the weeds are at their most susceptible growth stage.

Using just the cotyledon shape as the only diagnostic selection, the 50 possible species can be rapidly narrowed down to less than eight possibilities in most cases. Early identification gives growers the opportunity to apply the best weed control program to treat the species present.

Dr David Thornby, Innokas Intellectual Services says the resistance profiles, even for closely related species, can be quite different, especially at the seedling stage.

“As part of a Cotton Research and Development Corporation project we have developed a new weed identification mobile app called ‘Weeds of Australian Cotton’ that provides a key to the characteristics of 50 weed species in cotton,” he says. “Clearly, the app will also have value for use in managing weeds in other crops grown in the same regions as cotton.”

The app allows users to make selections based on the observed characteristics of the plant, stem, leaves, flowers and seeds, the fleshiness or succulence of the plant and the presence of milky sap or latex. For grasses, users can key in specific details about the inflorescence, spikelet, floret and ligule features. As each detail is added the number of possible species reduces, until a few or just one remains as the best fit for the characteristics selected.

“Once there are just a few remaining options, the user can look at the photo gallery and choose the best-fit identification,” says Dr Thornby.

“The feature that really sets this app apart from other weed identification apps is that ‘Weeds of Australian Cotton’ includes a ‘cotyledon shape’ characteristic selection.”

“There are nine different cotyledon shapes to choose from. Using this feature of the app alone, users can quickly narrow down the most likely identification, and make decisions early regarding the best mix of weed control strategies to implement.”

Using the cotyledon shape as the only diagnostic selection, the 50 possible species can be rapidly narrowed down to less than eight possibilities in most cases. When cotyledons are present on very small plants found in the field, accurate identification can give growers a head start on planning a spray application.

The timing of herbicide application is product-specific but the general recommendation is for weeds to be ‘small and actively growing’. As a rule of thumb, ‘small’ would include pre-tillering for most grass species, less than 5 cm diameter for most rosette-forming species, and up to about 5 true leaves for other types of broadleaf species. As for ‘actively growing’, this is simply the absence of visible signs of moisture stress.

“Coverage is probably the most important factor to consider if weeds were sprayed at cotyledon stage,” says Dr Thornby. “Where feasible, increasing the water rate is the usual response, but it can be hard to hit such genuinely small targets. At this very small size good control could be expected, but they would have to come in contact with the chemical and so it is often practical to compromise by waiting until a couple of true leaves are present.”

“It is essential that label instructions are followed regarding weed size, product rate and application method as they apply to each product and weed species to achieve the best weed control result.”

It is best not to make too many assumptions about the weed spectrum present based on what was observed in the previous year. Dr Thornby emphasises the need for accurate identification and highlighted the fact that the app does not include every possible plant that could be growing on a cotton farm.

A new weed identification mobile app called ‘Weeds of Australian Cotton’ provides a key to the characteristics of 50 weed species in cotton. The app will also have value for use in managing weeds in other crops grown in the same regions as cotton.

“The app only includes the 50 species that the development team identified as the key species affecting cotton production,” he says. “Misidentification is certainly possible, so if the options remaining at the end of your selections do not clearly match the plant you are looking at in the field, it is necessary to confirm identification with an expert, especially if the weed is proving hard to kill.”

Download ‘Weeds of Australian Cotton’ app on the Apple App Store for iOS mobile devices or Google Play for Android mobile devices or visit www.cottoninfo.com.au