Mills impact the weed seed bank
In 2016, Bruce McLean faced a daunting ryegrass burden on his 3800 ha property in the high rainfall zone around Bool Lagoon in south-east South Australia.
Knowing that they would need to capture and destroy this weed seed at harvest, Bruce decided to add an iHSD seed mill to their weed control program that year.
“We started with the original hydraulic horizontal drive iHSD and have since upgraded to the vertical drive model on our CLAAS 770 harvesters, although not all in the fleet have a mill attached,” he says. “One reason for choosing the iHSD was the proximity of the dealership for service, and we have been pleased with the developments in mill technology over time.”
Bruce grows mainly dryland wheat, beans, canola, clovers, phalaris and lucerne on 550 annual rainfall, with some area available for irrigation.
“We don’t get many harvest hours here where we often have cold, wet weather blowing in from the coast in the evening, so we can’t afford to have anything slowing us down,” he says. “This was a major deterrent for us when it came to implementing harvest weed seed control, but we have found that the mill doesn’t slow us down too much, and we have the option to by-pass it if we need to.”
In practice, Bruce has found that snails have been the main reason they have to by-pass the mill. The Persian clover crops can have very green vines at harvest, and Bruce finds he might need to by-pass the mill for up to 10 per cent of the clover area.
“Now we have the high flow mill, harvesting capacity is up by 5 to 10 per cent and with the CLAAS harvester, we don’t lose much power when running the mill,” he says. “Not all our harvesters have a mill attached, so when we have two mills running in the same paddock, we can often see a difference in weed germination in the swaths behind a harvester with no mill.”
Side-by-side comparison of weed germination with and without an impact mill applied.
This reassures Bruce that the mills are very effective at killing weed seeds, and they prioritise using the mills in paddocks with weed issues. He also appreciates the value of having a non-herbicide tool to help reduce the impact of herbicide resistance.
The McLeans find that getting the weed seed, particularly annual ryegrass, into the harvester front can be challenging. Wind can shatter the weed seed heads, particularly in wheat late in the harvest program, so they are contemplating windrowing in wheat but need to weigh up the impact of additional jobs while maintaining harvest timeliness. Desiccation in the bean crops works well to halt seed shedding and allow the mills to capture and destroy the weed seeds.
“In the high rainfall zone, we need to process up to 20 tonnes of biomass when harvesting a 10 tonne cereal crop,” he says. “The bulk and presence of green material is more challenging for the harvester than the impact mill.”
Having seen the benefits of harvest weed seed control using the impact mill, Bruce knows he is better prepared for the next big weed blow-out season.
De Bruin Engineering’s iHSD representative, Andrew Vearing, says setting up the harvester correctly in high-yielding situations is critical to success with the weed seed kill and maximising grain yield.
“Take time to set up correctly, and do everything you can to protect straw quality,” he says. “This will ensure the straw and chaff streams are well-separated, minimise the amount of ‘MOG’, or material other than grain, on the sieves.”
“Checking grain losses in the separator and the cleaning shoe is also important, as is validating the changes you make to the set-up so you minimise grain loss and maximise weed seed capture into the mill.”
Harvest weed seed control is one of the WeedSmart Big 6 tactics to limit the impact of weeds that have evaded herbicide during the cropping phase. Three companies offer seed impact mills in Australia, and all are WeedSmart partners.
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