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Windrow to collect early shedding weed seed

Looking toward harvest, the pressure is on to get the timing right to maximise yield and grain quality. Delta Ag senior farm consultant, Tim Condon, says it is also a great time to be capturing weed seeds, particularly from wild oats plants that have escaped in-crop herbicides, using a non-herbicide tool to manage herbicide resistance.

“Windrowing, or swathing, barley has been traditionally used as a harvest management tool when growers have a number of different crops to harvest in a short time,” he says. “The really good thing about this technique is that it also gives growers another shot at collecting and destroying weed seed.”

Successful windrowing begins with cutting the crop low and, where possible at an angle to the seeding direction. When followed with any harvest weed seed management tactic, even early shedding weeds such as wild oats can be effectively controlled.

Successful windrowing begins with cutting the crop low and, where possible at an angle to the seeding direction. When followed with any harvest weed seed management tactic, even early shedding weeds such as wild oats can be effectively controlled.

Swathing barley at the earliest opportunity maintains the crop’s yield, and if done correctly, the swaths protect the grain from weathering. Mr Condon recommends checking the crop away from the paddock edges and looking for signs of physiological maturity in the barley plant. “Barley, and wheat, can be swathed when the grain is at 30 to 35 per cent moisture,” he says. “This is indicated by the peduncle [the little stem just below the head] of the grain head turning from green to brown and if you press your thumbnail into the grain there should be no dent created in the grain.”

“Once the crop is mature, the key to effective swathing – and also for the best results with weed seed collection – is to cut the crop low,” he says. “Cutting at boot or beer can height provides sturdy support for the swath, keeping the grain and the weed seed off the ground and making harvest more efficient.”

In some situations, it can also be beneficial to swath at an angle to the seeding direction to provide extra support under the swath. Good results have been seen in Western Australian crops swathed 15, 45 and 90 degrees to the seeding direction. In controlled traffic systems, using a mixer belt, or setting the belts at different speeds, is an alternative to swathing at an angle to achieve the necessary cross thatching to keep the swathed crop off the ground, maintain grain quality and allow easy pick up.

“Crops sown on narrow row spacing will also swath better, and there is good evidence that narrow row spacing also suppresses weed seed production,” says Mr Condon. “In southern NSW the main weed that we can target with swathing is wild oats. Wild oats is renowned for shedding seed before crop harvest so swathing can reduce the amount of seed shed onto the ground. Even with good control of wild oats germinations around sowing, there are often later germinated weeds that grow with the crop but are less mature at harvest than earlier germinations would have been.”

Wild oats is notorious for shedding its seed early. Windrowing is an excellent way to collect the seed from wild oats plants that have escaped in-crop herbicide treatment.

Wild oats is notorious for shedding its seed early. Windrowing is an excellent way to collect the seed from wild oats plants that have escaped in-crop herbicide treatment.

Swathing, followed with any of the harvest weed seed control tactics, becomes a very useful non-herbicide tactic to use with weed species that shed their seed early. Other potential targets with this strategy are wild radish, brome grass and annual ryegrass.

Once the swathing is done, the barley can be left for several weeks until there is an opportunity to harvest. However, there is always a risk of the windrow not drying quickly if wet weather persists, which may cause grain quality to deteriorate. Options for destroying the weed seed captured in the swath include narrow windrow burning, chaff carting, Harrington seed destructor, hay baling or chaff lining (in controlled traffic systems), all of which are detailed on the Weedsmart website.

“Narrow windrow burning can be risky in leafy crops like barley, especially in high yielding districts,” says Mr Condon. “A new technique being trialed in these situations is chaff lining, where the chaff component is dropped into a narrow band and left to rot down. Early observations suggest that weed seeds don’t survive, especially when the chaff stream is directed into the wheel tracks in a controlled traffic system.”

Avoid confusion: The terms ‘swathing’ and ‘windrowing’ refer to the same practice. In NSW and Vic ‘windrowing’ is the more commonly used term while ‘swathing’ is the more commonly used term in WA and SA. However, ‘narrow windrow burning’ is a completely different practice.

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