A mechanical solution to the nuisance of herbicide resistant weeds has now caught the attention of the global farming community. Its West Australian creator tells the story behind the Harrington Seed Destructor.
On his 3,400ha property 115 miles south-southeast of Perth, Ray Harrington developed the machine that could play a major role in combatting herbicide resistant weeds across the globe. “When we switched from sheep to cropping, we’d already known about herbicide resistant ryegrass for 20 years or more in the northern Western Australia wheat belt. It is all about dealing with the weed seeds in the chaff fraction. Farmers were bringing in chaff carts to capture and burn the weed seeds and break the cycle. I knew when we found herbicide resistance here, we had to be in a good position to deal with it,” he explains.
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Thinking about his own way of catching, carting, cooking or crushing the chaff fraction caused a lot of head scratching. A a furnace on the back of the combine he dismissed as impractical (and slightly dangerous). A big microwave wouldn’t work with a moisture content of chaff typically about 9% – 14% is required to get the seed hot enough to kill it. For crushing the seed Harrington took inspiration from the cage mills used in mining, to fine down all types of ore. These effectively consist of 2 counter-rotating cages moving at about 1,400rpm. “I saw one in the power station at Collie rendering coal, stopped it, and looked inside. Nothing would survive in that.”
Geoff Glenn at Agmaster built a tractor driven cage mill for Ray to trial on weed seeds. After spreading the pulverised ryegrass-infested material in the field, nothing germinated – except the concept for the Harrington Seed Destructor.
In a chance meeting with weed resistance expert Stephen Powles, Mr Harrington mentioned his experiment with the cage mill. Within 24 hours he received a phone call. “He asked if I could bring some of the material that had gone through the mill in to the University in Perth,” he notes. With further tests showing the same germination results, Dr Powles sought to set up replicated experiments to validate the cage mill’s ability to kill herbicide resistant weed seeds. In sacks with 40 litres of wheat chaff 1,000 coloured ryegrass seeds were placed. The contents were then fed into the mill running at speeds of 700, 900, 1,100 and 1,300 rpm. This was translated in a ‘kill curve’. “We got about 98% ryegrass kill at 1,300rpm. That was about 12 years ago now,” says Mr Harrington.
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This secured a AUD$ 20,000 (US$ 15,000) backing to produce a prototype that could work behind a harvester in the field. The first trailed Harrington Seed Destructor was built and rolled into the paddock behind a Case Axial Flow 2388 soon after. The machine has its own 160hp diesel motor and spreads the pulverised material back on to the field.
‘The machine did its job. We built another unit and had them running behind our two 2388s, and the project was up and running’
The seed destruction trials were repeated, but this time the coloured seeds were dropped in the combine’s broad elevator. This to check whether the extra chaff in a real harvesting situation wouldn’t cushion the weed seeds and prevent destruction. “The machine did its job. We built another unit and had them running behind our two 2388s, and the project was up and running.”
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Dr Powles and Mr Harrington secured funding with Australia’s levy board – the Grains Development and Research Corporation – to bring the Harrington Seed Destructor to market. Mount Gambier-based De Bruin Engineering built the first commercial machines in 2009. As part of the funding contract agreement, a third party had to integrate it into the back of a combine – seen as key in taking the technology to the masses in Australia and beyond. The University of South Australia’s engineering faculty was commissioned to squeezing the cage mill technology into all the major combine brands. Still engineered by De Bruin and distributed by McIntosh & Sons, the Integrated Harrington Seed Destructor, or iHSD, is now running aboard 75 combines across Australia, including Harrington’s latest Case 8230.
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The iHSD consists of 2 cage mills underneath the straw chopper. It is driven by a large hydraulic pump that piggybacks off the combine’s main drive line. In the combine’s airflow ryegrass seed doesn’t reach any higher than 350mm above the sieves, so this band of chaff-carrying air is funnelled off and directed through the cage mills. This requires about 60-70hp out of the combine, and the hydraulic version has suffered some reliability issues. It is also expensive – a retrofit version sets you back about AUD$ 165,000.
‘We now feel like we’re back in control’
“We are now developing a mechanically-driven solution and we think we can get the overall cost down to about AUD$ 80,000.” This will make the machine more attractive, but Mr Harrington concedes the iHSD is not a silver bullet and won’t suit every farm. But he has seen it play a major role in keeping resistant ryegrass and wild radish at manageable levels on his own land. “We were on the back foot and the weeds were telling us what to do – whether that is time of sowing, row spacing or herbicide rates, the list goes on… We now feel like we’re back in control.”
The Harrington iHSD directs chaff through two counter rotating cage mills behind the sieves and below the straw chopper. This kills 97-99% of weed seeds. A unit costs about A$ 165,000 (US$ 123.000) which could be halved in future.
For other weeds as well?
Herbicide-resistant weeds show up more often. There is blackgrass in Europe, and in North America glyphosate resistant weeds like Palmer amaranth are an increasing problem. Unlike ryegrass, which holds onto its seed very tightly until cereal crops are mature and ready to harvest, blackgrass holds on to just 30-50% as combines start to roll. It would seem the success of iHSD depends on a high percentage of weed seed entering the harvester.