By GRDC western regional panel chairman Peter Roberts
With harvest in full swing, many growers are putting into practice harvest weed seed control (HWSC) systems to help tackle weeds – which are at high levels this season.
They know that controlling weeds at harvest time, combined with control practices implemented at other times of the year, can reduce whole-year weed populations and weed seed banks, and minimise the development of herbicide resistance.
Research led by Michael Walsh of the Australian Herbicide Resistance Initiative (AHRI), which is funded by the Grains Research and Development Corporation (GRDC), has provided further evidence of the effectiveness of HWSC systems.
It shows that the four dominant annual weeds of Australian cropping systems – annual ryegrass, wild radish, brome grass and wild oats – retain 77 to 95 per cent of their seeds above a harvest cut height of 15cm at wheat crop maturity.
This provides significant opportunities for HWSC tactics to interrupt the potential of these plants to replenish the viable weed seed bank.
The importance of this research – which has encouraged the uptake of HWSC practices by growers in Australia and internationally – has recently been recognised. The research paper by Dr Walsh and AHRI director Stephen Powles has been awarded 2014 Outstanding Paper in Weed Technology by the Weed Science Society of America.
The cost of HWSC systems used by growers ranges from virtually nothing to about $200,000, and the different tactics suit different farming systems and environments.
It’s worth noting that the different HWSC systems are each the brainchild of growers. The role played by the GRDC, AHRI and other research organisations has been to provide the science – evaluating the systems’ effectiveness and fine-tuning them.
Many growers are probably already familiar with the HWSC options of narrow windrow burning, chaff carts, the Harrington Seed Destructor and the Bale Direct system (baling all chaff and straw material as it exits the harvester).
However, two newer low-cost options, which have also been created by growers, are chaff decks and windrow rotting. AHRI researchers plan to assess these systems soon.
The chaff deck places the chaff exiting the sieves of the harvester on to permanent wheel tracks, and it is estimated that up to 70 of these units are being used across WA’s South Coast region this harvest.
Growers using chaff decks have observed that few weeds germinate from the chaff fraction and believe that many weed seeds rot in it.
A permanent tramline farming system is necessary to be able to implement the chaff deck system.
Windrow rotting – which is still being developed – diverts chaff in to a windrow behind the harvester, but not on to the wheel tracks.
Unlike windrow burning systems where both straw and chaff are funneled into windrows, the windrow rotting system delivers only chaff in to the windrow, where it is left to rot, while the straw is spread.
Although suited to disc seeding and controlled traffic farming (CTF) systems, a CTF system is not essential for windrow rotting.
More information about HWSC systems is available at www.ahri.uwa.edu.au, www.weedsmart.org.au or at www.grdc.com.au/IWM-WA.
Peter Roberts, GRDC western panel
0428 389 060
Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827
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