Impact Mills

The chaff lining technique is clearly the cheapest in terms of capital cost. Chaff lining involves making a simple chute to divert the chaff fraction (containing weed seeds) into a narrow row in the centre of the harvester instead of onto tramlines.

The chaff is then left to mulch while the residue can be chopped and spread to maintain ground cover.

Although suited to controlled traffic systems, chaff lining can work in non-CTF systems if the harvester operates along the same runs for consecutive years.

Ask an Expert

What can I do at harvest to reduce my future weed burden?

As crops mature and harvesters begin reaping, consider the potential fate of seeds ripening on weeds that escaped in-crop control measures.
Peter Newman, WeedSmart’s western extension agronomist, says harvest time is an important opportunity to assess weed burden across the farm and be proactive about driving down the weed seed bank.
“Harvest can either be a super-spreader or a weed suppressing event,” he says. “Small patches of weeds can quickly expand when seed is blown out the back of the harvester. On the other hand, the harvester can be a powerful weed management tool if any one of the harvest weed seed control options are implemented.”
WeedSmart’s western extension agronomist, Peter Newman says efforts made to reduce the spread of weed seed at harvest will soon pay off for growers.
Australian growers have led the world in inventing and adopting harvest weed seed control tools such as impact mills, chaff carts, chaff decks and chaff lining, all of which can reliably destroy over 90 per cent of the weed seed that enters the front of the harvester.    
“In addition to harvest weed seed control there are several other actions in the WeedSmart Big 6 that growers can implement just prior to, during and immediately after harvest that will make a measurable difference to the weed burden in future growing seasons,” says Peter. “The WeedSmart Big 6 tactics are scientifically-proven to reduce the risk of herbicide resistance through diverse herbicide use and cultural control to prevent weed seed set.”
What can I do before harvest to manage late emerged weeds?
In brief: Scout for and map weedy patches. Consider sacrificing small areas of high density weeds. Swathing can be a very effective way to stop seed set of late emerged or resistant weeds. Collect weed seeds for herbicide susceptibility testing.
The details: Growers across Australia use a variety of methods to map weeds – from the simple to the sublime. ‘Dropping a pin’ using the tractor’s GPS mapping system as you travel through a weedy section when spraying or harvesting is easy and provides useful information about the distribution of weeds in the paddock. Many growers have their own drones and use them the collect images or video footage of the crop that can be viewed or analysed to identify high density weed patches.
Collect seed for herbicide susceptibility testing – knowing what still works is vital information for planning next season’s herbicide program. There are three herbicide testing facilities in Australia that are equipped to test weed seed samples – Plant Science Consulting, CSU Herbicide Resistance Testing and UWA Herbicide Resistance Testing.
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.
Which harvest weed seed control tool is best for my situation?
In brief: There are six harvest weed seed control tools used in Australia – impact mills, chaff decks, chaff lining, chaff carts, bale direct and narrow windrow burning. Choose the one that best suits your system and budget.
The details: Impact mills are best suited to continuous cropping situations. Residues are retained and evenly spread. Chaff decks have lower capital cost and are well-suited to controlled traffic situations. Chaff carts are popular with grain producers who also run livestock. Bale direct is also expensive but has a good fit in locations where there is access to straw markets. Chaff lining is currently the best ‘entry level’ system and can be used in CTF or non-CTF systems, with best results where the harvester runs on the same track each year. Chaff lining has essentially superseded narrow windrow burning, overcoming the time required and risks involved in burning and reducing the loss of nutrients from the system.
If you haven’t used harvest weed seed control tools before, it doesn’t take long to build and fit a chaff lining chute ready for use this harvest season.
What should I be ready to do straight after harvest?
In brief: Spraying weeds immediately after harvest is fairly common practice. Weeds present may be close to maturity or fresh germinations of summer-active weed species.
The details: Some growers get in early with knockdown herbicide applied under the cutter bar when swathing barley or canola. Consider using the double knock strategy, heavy grazing pressure and possibly a soil residual herbicide that is compatible with your planned crop rotation. Pay particular attention to any weedy patches identified before or during harvest. Stopping seed set at every opportunity is the crux of an effective weed management program.
Give some thought to what might be the underlying cause of weedy patches – fixing problems such as pH and soil nutrition imbalances, waterlogging and spray practices that routinely deliver low doses of herbicide.


Weed seed impact mill update with Ben White and farmer case studies

We feature farmer case studies from each of our mill partners, including HSD, Redekop and Seed Terminator.
The farmers we hear from are Steve Lord (Goomalling, WA – Redekop); Tyson Schutz, who is pictured above with Dad Mick (Grass Patch, WA – Seed Terminator); and Jon Beasley (Franklin River, WA – HSD).

Farmer, Steve Lord, who has a Redekop mill.

We also be hearing from Kondinin Group’s Ben White who provides us with a technical overview and details the latest updates on this technology.
WeedSmart Week
This year, our annual flagship event will be held in Esperance, WA from the 17th to the 19th of August 2021. WeedSmart Week is designed to engage growers and advisors on WeedSmart’s Big 6 messages. You can get your tickets here.
New content
Make sure you check out our latest Ask an Expert. This month Dr Chris Preston answers the question “How does ryegrass adapt so readily to farming practices and environmental changes?”
Don’t forget to follow us on Twitter and Facebook and also sign-up for our monthly blog. You can also subscribe to the WeedSmart Whip Around, so you never miss any of our content.
Related content
We mentioned on the podcast that Tyson Schutz’s Dad, Mick Schutz, featured in a GRDC publication entitled “Investigating the harvest weed seed control tools chaff lining and chafftramlining (chaffdeck) in the Esperance area”. Check that out here.


Surprising chaff lining results and the future of mill technology

In this week’s episode, Jessica Strauss and Peter Newman catch up in person to talk about the highlights of the GRDC Crop Updates which have been taking place across the country.
Peter talks about what he presented at updates, including research done by Dr Michael Walsh from the University of Sydney on the efficacy of chaff lining. We also talk about research on weed seed mills and new machinery on the horizon. Pete also talks about his presentation on strip and disc systems and how they might fit into farming systems in WA.
We also discuss the Weed Chipper, developed by Dr Andrew Guzzomi and Dr Carlo Peressini from UWA and researchers from the University of Sydney. The Weed Chipper now has a commercial partner in Precision Agronomics Australia.
This project had received funding from the Grains Research and Development Corporation and was created in response to the growing concerns about herbicide resistance and the associated difficulties with fallow weed control.
Director of McFadyen Ag Consulting and Northern Panel Chair Andrew McFadyen about the effects of the Summer rain the Northern region has received.
Director of McFadyen Ag Consulting and Northern Panel Chair Andrew McFadyen
*In the podcast we chat about presentations which were stand-outs. We didn’t give the full name for ‘Keith’ – his full name is Keith Norman and he is a UK Farm Management Specialist.
We also talked about the model on HWSC Pete developed so you can calculate the cost of different HWSC options on your farm. You can download the model here.


And then there were three – impact mills on the market

Crop residue management is core business for Canadian company Redekop Manufacturing and now they have added harvest weed seed control to their offering to Australian grain growers.
Redekop have recently commercialised the Seed Control Unit (SCU), a weed seed impact mill that incorporates their well-known MAV straw chopper. This new impact mill makes three options commercially available on the Australian market – adding to the Australian-built iHSD and Seed Terminator.
Redekop Manufacturing’s president, Trevor Thiessen.
Redekop’s president, Trevor Thiessen said the company inadvertently became involved in harvest weed seed control when they noticed their chaff carts were being used in Australia to manage weeds rather than as a fodder collection system they were first invented for in the 1980s.
“Herbicide resistance in Canada is about five years behind the situation in Australia but it is definitely an increasing problem,” he said. “We have been working toward the development of the SCU since 2013 and tested the first units in 2017 in Australia and Canada.”
“Testing continued in 2018 to gather weed kill rates, which are consistently above 98 per cent, but there are some weeds and some conditions that we are yet to test.”
Breanne Tidemann, a research scientist in field agronomy and weed science with Agriculture and Agri-Food Canada in Lacombe, is conducting the independent testing of the SCU. Breanne has also been testing a tow-behind HSD unit in Canada since 2016 harvest.
The Redekop system combines the SCU chaff stream with the MAV straw stream, mixing the two streams in the same air flow at the back of the harvester to achieve improved residue spread and distribution.
Redekop Seed Control Unit (SCU).
Peter Newman, AHRI and WeedSmart Western agronomist said the recent expansion of options for growers wanting to use impact mills as their harvest weed seed control method was phenomenal.
“The three impact mills currently available are all integrated into harvesters, making harvest weed seed control very time efficient,” he said. “One important aspect that Redekop have really focussed on is achieving even spread of the crop residue out the back of the harvester. This is critical to the integrated mill systems achieving the most cost-effective outcome for growers by re-distributing nutrients across the full cutter-bar width.”
In a recent WeedSmart survey of over 100 growers around Australia, close to 50 per cent of growers plan to adopt a weed seed impact mill into their system within the next 3 to 5 years.
Redekop will have 20 SCUs operating in Western Australia this harvest with a team of support and research personnel on hand to further assess the units’ performance in Australian conditions and address any mechanical issues.
The SCUs are available as either a complete unit incorporating a MAV chopper suitable for all harvester types or as a purpose-built mill that fits onto a John Deere residue manager. Being integrated with the straw chopper, the SCU can be easily switched from chopper to chopper plus weed seed control.
Redekop are also involved in introducing the Australian-built EMAR chaff decks to Canadian growers as an entry level investment in harvest weed seed control.
Other resources

Podcast – Redekop impact mill
Vertical iHSD
Using your harvester to destroy weeds
Webinar – Comparing the iHSD and Seed Terminator


Vertical iHSD maintains the brand’s 98% weed kill rate

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?


Farmers share their harvest experience with weed seed impact mills and GRDC Updates

In our last podcast we heard from weed seed impact mill company representatives, so this week we’re hearing from farmers on the ground and finding out about how they faired over harvest with both the Seed Terminator and iHSD. Farmers Kim Slarke and Scott Walton both share their experiences. We also hear from WeedSmart Southern Extension Agronomist Greg Condon on what he has been presenting at GRDC Updates this year. He gives an overview of the benefits of crop competition and diverse rotations, as well as providing an overview of some of the hot topics at Updates this year. Join your co-hosts, Jessica Strauss and Peter Newman to learn more.
Take a listen


Using your harvester to destroy weed seeds

Collecting and destroying weed seeds as part of the harvest operation is recognised as the most efficient and effective way to implement harvest weed seed control (HWSC) within an integrated weed management system.
Acknowledged as the ‘holy grail’ of the WeedSmart Big 6 tactics to manage herbicide resistance, HWSC was implemented on over 40 per cent of Australian grain farms in 2014 and adoption is expected to increase to 80 per cent by 2020.

Chaff impact mill machines render the weed seed unviable, causing the destruction of over 95 per cent of the weed seed that enters the mills.
There are currently six HWSC methods being used in Australia, all of which have been invented, adapted and adopted by Australian farmers. When choosing between these methods growers must consider the set-up cost, nutrient removal costs and labour requirements.
Most agree that the ultimate HWSC tool would complete the weed seed control in one pass at harvest, retain all stubble and nutrients and not require any follow-up work such as marketing hay or burning chaff. There are currently two machines that meet these requirements – the iHSD (Integrated Harrington Seed Destructor) and the Seed Terminator.
These two chaff impact mill machines render the weed seed unviable, causing the destruction of over 95 per cent of the weed seed that enters the mills. In 2017 harvest, both the iHSD and Seed Terminator machines were in commercial operation on farms around Australia and both experienced the teething problems that can be expected for new technology moving into the real-world. They have since been in field trials overseas – the Seed Terminator in Canada and the iHSD in France – where both machines completed around 200 hrs work without a hitch.
Kondinin Group Manager of Research and Development, Ben White interviewed 20 growers using either the iHSD or Seed Terminator during the 2017 harvest and reported that their observations suggested both brands were achieving over 95 per cent reduction in seed viability.
“Both types of impact mills ran into the same real-world problems of handling high flow rates of chaff, choking on green crop or weed matter and significant damage to the mills from any sand or soil that is picked up by the harvester,” he said. “Both machines also caused a reduction in harvester capacity of between 12 and 20 per cent in wheat, even though the harvesters had been remapped. This is a significant cost that growers must allow for through machine depreciation and base hourly operating costs, as more hours are needed to harvest the same area of crop.”
Over 70 per cent of the growers that the Kondinin Group engineers visited had remapped their harvesters to improve the harvest capacity.
Operators should note that chaff impact mill technology pulverises the entire chaff fraction, which generates significant levels of dust during the harvest operation. This means that more frequent machine clean-down may be required to minimise fire risk, as well as increased frequency of filter cleaning or replacement.
“Although the problems outlined here are important, they are all likely to be resolved as this technology matures in the commercial world,” said Ben. “There is enormous interest in this method of harvest weed seed control and this will ensure that the problems are solved.”

Seed Terminator, WA.
Australian Herbicide Resistance Initiative’s cost comparison of HWSC methods suggests that the chaff impact mills cost $16-17/ha compared to $22/ha for narrow windrow burning and $6-7/ha for chaff tramlining and chaff lining, depending on crop yield and area. In addition to the weed control benefits achieved through the use of any HWSC method, the chaff impact mill option also reduces crop volunteers.
Research into the efficacy of impact mills is an ongoing process, particularly while the two types of machines are undergoing rapid developmental changes. Recent research by Michael Walsh (AHRI and Sydney University) with help from John Broster at Charles Sturt University (CSU), shows that despite the problems that have been experienced with the new machines, iHSD mills are passing the research tests with flying colours.
Their research concluded that:

The iHSD achieved 96–99% destruction of the seeds of 11 weed species when processed in wheat chaff.
Weed seed destruction varied by about 10% depending on crop chaff type – ryegrass seed kill was greatest in lupin (98%) > wheat (92%) > canola (90%) > barley (88%).
Weed seed kill dropped by about 4% when chaff moisture increased above 12%.
Weed seed kill increases with mill speed and 3000 rpm is the accepted optimal speed for the iHSD.

SAGIT funded research conducted by Trengove Consulting in 2017 found similar results for the Seed Terminator:

Ryegrass weed seed kill was 93% at 2250 rpm and increased to 98% or greater at normal operating speeds (2500–3000 rpm).
Greater than 99% control of several other species including wild radish, brome grass, wild oat, bifora, bedstraw and tares.
Increasing chaff flow rate (harvest rate) did not reduce control of these species.
Samples analysed in 2018 by the Weed Science Research Group, at The University of Adelaide showed that the Seed Terminator could consistently kill 96% of weed seeds when operated at 2750 rpm.

These kill rates refer only to the weed seed that enters the impact mills. To achieve high level of weed control it is essential that all efforts are made to ensure the weed seed enters the front of the header and is then separated and directed into the mills.

Timing, cutting height, operating speed, weed and crop type and harvester set-up all play a part in achieving maximum harvest weed seed control. As is recommended for all HWSC methods that treat the chaff fraction, separation of the chaff and straw through the harvester often requires the addition and fine-tuning of a baffle plate to achieve greater efficiency.
Setting up and operating harvesters to achieve the best weed control outcomes often involves some modification and compromise. By taking the time to get things right, growers usually find that they end up with more grain in the bin and a better sample, making the extra effort worthwhile.
WeedSmart has secured the rights to distribute an electronic version of Kondinin Group’s Research Report: Residue Management at Harvest, which is available in the Resources section of WeedSmart encourages growers and advisors to support Kondinin Group’s independent research through subscription to Farming Ahead.

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