Strategic tillage has emerged as a recommended approach to tackling glyphosate-resistant weeds in the subtropical grains region of Queensland and northern New South Wales.
Dr Steve Walker of the Queensland Alliance for Agriculture and Food Innovation at the University of Queensland said trials with flaxleaf fleabane showed that irrespective of method (harrows, tynes or one-way discs), strategic tillage could dramatically reduce weed emergence. Even a small amount of inversion using harrows reduced weed emergence by 92 per cent.
“There is a potential fit in our cropping systems for weed control tillage once every five to 10 years,” he said. Dr Walker said there was a similar trend with barnyard grass, although the reduction in weed emergence was not as significant. Harrows and tynes reduced weed emergence by 50 per cent, while the disc treatment reduced emergence by 70 per cent.
In another experiment, Dr Walker tested the long-term impact of different rotations and agronomic practices on the weed seedbank. For barnyard grass control, the research compared no-till with a range of tillage treatments (harrows, tynes and one-way discs).
In year one, 2000 seedlings per square metre emerged in the no-till treatment. The harrows produced a small reduction in weed emergence. The tynes and the discs produced a 50 per cent and 70 per cent reduction respectively.
In years two and three, there was a dramatic reduction in weed emergence irrespective of tillage type. There was also a change in the weed dynamics, with more weeds emerging in the disc treatment than the no-till, harrow and tyne treatments.
Dr Walker said that by year four there was zero weed emergence in the tillage treatments, provided all emerged seedlings were controlled – that is, there was no replenishment of the seedbank.
Meanwhile, other work has evaluated the use of the double-knock (the sequential application of two herbicides with different modes of action about a week apart) on fleabane.
When the first knock was applied to fleabane at the small rosette stage, the control levels achieved were 88 to 94 per cent. But when paraquat-diquat (Spray.Seed®) was applied a week later as the second-knock, 99 per cent weed control was achieved.
In addition, Dr Walker said single-knock applications with glyphosate mixes targeting older weeds were not as effective as early spraying using the double-knock.
In view of the results, growers are being encouraged to consider integrating into their management plan the double-knock technique to control sprayed survivors and some form of strategic tillage as a once-off tactic.
Dr Steve Walker
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