Weed control: Chaff mills kill seeds before they set
These mechanical weed seed destroyers are changing the game for Australian grain growers, and may soon go global.
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In the world of weed control there are two things that keep many grain growers awake at night.
One is the threat of herbicide resistance in common crop weeds, such as annual rye grass, and the other is the threat of bans on one of their most popular herbicides, glyphosate, following litigation in the US and consumer pressure.
With herbicides being one of the biggest weapons in a farmer’s arsenal, anything that reduces their range and efficacy is a major worry. So, it is comforting to know that a relatively new invention by Australian farmers and engineers has come to the rescue, opening a new front in the war against weeds. And it’s up there with the stump jump plough or the Sunshine harvester in terms of Australian ingenuity.
Labelled variously as mechanical weed seed control, chaff mills, seed mills, seed control units or impact mills, these units bolt on to existing headers, effectively turning them into weed-killing machines, as they mechanically destroy weed seeds harvested with the grain.
Weed seeds are fed into the mill from the combine’s sieves and are pulverised, rendering them unviable, then ejecting what is essentially a nutrient-rich flour out the back and on to the paddock.
Agronomists say chaff mills are a powerful tool in harvest weed-seed control, one of the six pillars of weed control outlined in the grain industry’s “Big 6” WeedSmart program.
Other harvest weed-seed control methods include narrow windrow burning, chaff lines, chaff carts, chaff decks and baling of crop residues to assist with traditional chemical spraying routines.
Chaff lining and chaff decks involve simple modifications to a header, which feeds chaff and weed seeds into a narrow windrow or into a controlled traffic tramline. These rows can then be left as they are and the seeds later hopefully rot, get crushed in the controlled traffic line or they can be burned.
Chaff carts actually collect the chaff from the header in tow-behind carts where they can be emptied into a pile and again left to rot, burned or used as stock feed.
But the advantage of a chaff mill is there is virtually little chance of weed seeds escaping the mill once they are in the header, with a kill rate as high as 99 per cent.
“Mechanical seed control is not a silver bullet but an incredibly useful tool in the toolbox in preventing or dealing with herbicide resistant weeds by reducing the weed seed bank,” says Seed Terminator commercial manager Ned Jeffery, whose company is one of four chaff mill brands in Australia.
“It’s about reducing the weed seed count carryover into the next season and increasing the lifespan of the chemicals.”
It also means no loss of nutrients, with all crop residues returned to the soil which is highly beneficial.
The benefits, though, have to be weighed against the higher capital cost, maintenance and extra fuel use to power the mill and slower harvesting speeds, according to farm machinery research body the Kondinin Group.
Its 2020 research report on harvest weed control said farmers installing a mill should expect to lose some harvest capacity and speed, particularly in heavy crops, as chaff mills rob the harvester of engine power.
Mr Jeffery estimates harvesting speed is about 15 per cent slower, depending on the crop volume, and fuel consumption about 10 to 15 per cent higher.
Harrington Seed Destructor product support manager Andrew Vearing says it takes about an extra 60-100hp to run a mill, depending on crop yield and combine capacity.
Overall a chaff mill is a much more convenient way to achieve the same as other forms of harvest weed seed control and does it in just one pass at harvest time, eliminating the time and labour involved in narrow windrow burning or burning of chaff lines or dumps later on, Mr Vearing says.
The chaff mill concept has been around since the 1990s, developed by Australian farmers and inventors such as Phil Zani, with his Rotomill cage mill, and West Australian farmer Ray Harrington and his Harrington Seed Destructor. Early models were units with their own engine, towed behind the combine.
The Harrington Seed Destructor showed the most promise and was developed in conjunction with the University of South Australia and funding from Grains Research and Development Corporation. Since then, the concept has seen massive development and refinement with one of the leading developers being engineer Dr Nick Berry.
Dr Berry did much of the early work on the Harrington unit at the University of SA, reducing its size and power requirements and enabling it to be integrated into the header. He has since gone on to create his own seed mill company, producing the Seed Terminator.
Two other manufacturers have since joined the market; Canadian company Redekop with its Seed Control Unit and WA design business TecFarm with its WeedHOG. All the current units now are retrofitted to combines and most are mechanically driven by the combine, with belts rather than hydraulically.
“The trick with the design of a mechanical weed seed control unit like the Seed Terminator is to use the minimum amount of energy or power for maximum effect in damaging the weed seeds so they are devitalised or made unviable,” Mr Jeffery says.
The four models of seed mills range in price from around $76,000 to $110,000 and the GRDC estimates that running costs for a seed mill are about $12/ha including about $3-4/ha in extra diesel.
The Kondinin Group says the bottom line in a wheat crop averaging 2.5tonnes/ha, was a cost of $4.35-$6.10/tonne of crop produced (or $10.88-$15.25/ha)
There are about 600 units in use in Australia and the market is increasing rapidly every year.
And all the mills, except for the Redekop SCU, are manufactured in Australia with predominantly Australian made components.
BIG FOUR BRANDS
Of the four main seed mill brands currently available, three of them are designed and made in Australia, while the fourth is a Canadian machine created specifically for
Australian conditions.
THE HARRINGTON SEED DESTRUCTOR
Made by De Bruin Engineering in South Australia, the iHSD V12 features two vertical impact mills driven directly by two belts and three in-line pulleys, and has no gearbox or transmission. Weed seeds are smashed by the high impact of rotors and opposing stationary stator blades. Annual ryegrass seed kill rate is 98 per cent. It also features a stone trap to capture foreign objects before they hit the mill, and there are several options to bypass the mill when it is not required. Fits most headers including Case IH, New Holland, John Deere and Claas.
From $76,000, plus GST and installation
Details: ihsd.com
SEED TERMINATOR
Also from South Australia, the Seed Terminator comprises a multistage hammer mill using a combination of shear, crush, grind and high impact to kill weed seeds. Its main advantage is to maintain its exceptionally high weed seed killing rate from 2250-3000rpm and at any moisture content. The bisalloy screens and tungsten carbide mill and rotor coatings produce significantly longer wear life cycles. High air flow produces maximum capture of seeds. There is a choice of two mill options – standard maximum kill and high flow-reduced kill for higher speeds or tougher conditions. It can be fitted to Case IH, New Holland, CLAAS, John Deere and Massey Ferguson. Price $110,000 including all installation and commissioning costs plus GST.
From $110,000 including installation and commissioning, plus GST
Details: seedterminator.com.au
SEED REDEKOP SCU
Canadian crop residue specialist Redekop has developed its own seed control unit — SCU — in partnership with John Deere for its S670-S790 combines. It is a dealer-fitted option, rather than factory fitted, but is well integrated with John Deere’s existing Strawchopper versions, powertrain and cabin screen. Redekop is releasing a Case IH model this season after successful testing last year, and later will include variants for New Holland, Claas and Agco headers. It can also be integrated with Redekop’s MAV straw chopper to provide optimum residue spread of straw and chaff while reducing levels of dust. The SCU’s rotor and stator design has three stationary rings and two rotating rings, which damage seed on impact. Seeds are drawn into the mill by rotor fan blades and centrifugally accelerate the chaff containing weed seeds. Both rotors and stator are reversible to provide extended service life up to 1000hrs.
From $100,000 plus GST
Details: redekopmfg.com
WEEDHOG
Designed and made in Western Australia, the TecFarm WeedHOG with its low 30-45hp power requirement will suit smaller or older machines as well as newer models. The concept uses opposing rotors in sets of conjoined housings either side of a central stone trap-windrower. Differing from the cage mill, it does not process every piece of material flowing through, meaning low wear and less dust is produced. Impact bars are reversible, doubling life.
WeedHOG’s unique design separates some of the chaff from the flow before it reaches the milling zones. The trade off is, a small number of seeds escape the impact of the bars. Rye-grass kill of around 80 per cent at the standard 2400rpm is less than other mills but increasing rotor speed allows higher kill. Importantly, kill of radish, brome and cereals is high. Available for Case IH and New Holland headers, with more coming soon.
From $76,000 including installation, Plus GST
Details: tecfarm.com.au
ASH TEASDALE SAYS HASTA LA VISTA TO WEEDS
With two harvests using a Seed Terminator under his belt, Ash Teasdale reckons there is no doubt it lives up to its name.
The Rupanyup grain grower has been using the chaff mill since 2019, fitted to his Case IH 7240 header, and is so happy with the results, he recently bought a John Deere S680 header with a second Seed Terminator on board, to use this coming harvest.
Ash and his family, parents Peter and Lynette and brother Brad, decided on a chaff mill after considering other methods of harvest weed seed control such as narrow windrow burning, chaff lines, chaff decks and chaff carts.
“Narrow windrow burning of chaff is very popular around here but we are anti-burning of crop residues,” Ash says.
“We are trying to retain all our residues every year so we weren’t keen on any option that involved burning. We decided to bite the bullet and take this jump. It is an expensive option but I think it is well and truly worth it.”
The other big attraction with a chaff mill is it is a one-pass operation, eliminating any further treatment or handling of crop residues.
And you know you are getting a very high kill rate of weed seeds there and then, he says.
Annual rye grass was their main problem weed and there were signs it was developing resistance to glyphosate. They also have to deal with brome grass, wild vetch and wild oats.
“We can definitely see the Seed Terminator working, with paddocks very clean and few rye-grass plants coming up after rain,” Ash says. “In the first year there were a couple of strips we had missed with the Seed Terminator and so you could see them pretty clearly where the rye-grass had germinated, whereas in the rest of the paddock it was all much cleaner.”
The trick is to harvest as many weed seeds as possible with the crop. That means cutting the crop low, which in turn causes more material to go through the harvester, a slower harvesting speed and more power used.
The same issues exist with chaff lines, chaff decks and narrow windrows, but the fact all crop residue is returned to the soil means the Seed Terminator came out on top in Ash’s view. He emphasises harvest weed seed control is just one of the weapons in his arsenal and it is important to follow all the other WeedSmart methods to slow herbicide resistance.
These include “double-knocking” weeds before sowing, and not relying on any one type of chemical. “It is getting increasingly harder to kill rye grass with some of the older chemicals such as glyphosate, so in a way the Seed Terminator is our last line of defence, cleaning up any weeds that escape all our other efforts,” Ash says.
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