Windrow chaff being burnt to prevent weed seeds
re-entering the soil.
Australian research shows that destroying weed seeds at harvest is a viable way to drive down the weed seedbank because ryegrass, wild radish, brome grass and wild oats retain their seeds until harvest.
Australian Herbicide Resistance Initiative researcher Dr Michael Walsh said this had been borne out by a succession of innovations, beginning with the chaff cart, introduced from Canada in the mid-1980s.
This prevents seeds in the chaff captured by the harvester from re-entering the soil. The collected chaff is left in dumps and burnt the following autumn.
Another system, developed by the Shields family in Wongan Hills, Western Australia, is to collect everything from the back of the harvester with a harvester-driven baler. The hay is then sold as stockfeed.
Dr Walsh said narrow windrowing was also useful for driving down the weed seedbank at harvest. This involved attaching a chute to the rear of the harvester to concentrate the chaff fraction into a narrow row. The chaff and any weed seeds are then burnt in the following autumn.
The latest tactic developed to minimise weed re-entry to the seedbank is the Harrington Seed Destructor (HSD). Any weed seeds contained in the chaff fraction of the harvester pass through a mill, which pulverises the chaff and seeds.
Dr Walsh said paddock tests have shown the HSD can prevent up to 90 per cent of weed seeds from re-entering the seedbank.
A benefit of this tactic, he said, was that all residue was retained, which helped conserve soil moisture and nutrients.
Dr Walsh said that while herbicides alone could allow good levels of weed control, weed numbers would be much lower when harvest weed-seed control was included in the weed management program.
“The only way we can slow down and perhaps prevent the evolution of resistance is to take a zero-tolerance approach,” he said. “Low weed densities are the best insurance against resistance evolution. With harvest weed-seed control we now have options to establish and maintain low in-crop weed densities.”
Dr Michael Walsh,
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