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Narrow windrow burn offers window to kill weed seeds


Australia
November 3, 2014


Narrow windrow burning has proven to be an extremely potent and low-cost method of reducing the weed seedbank – a key tactic in the fight against herbicide resistance. Photo: Michael Walsh 

Grain growers in the southern cropping region are encouraged to consider attaching a chute to their harvesters to create narrow windrows for burning and destroying weed seeds after this year’s harvest.

Narrow windrow burning has proven to be an extremely potent and low-cost method of reducing the weed seedbank – a key tactic in the fight against herbicide resistance.

Australian Herbicide Resistance Initiative (AHRI) researcher Michael Walsh says narrow windrow burning has been successfully employed by many growers in Western Australia where research over several years has shown that 99 per cent of annual ryegrass and wild radish weed seeds can be destroyed by an effective burn.

“Narrow windrows are ideal as they burn hotter for longer, killing the weed seeds, and they also minimise the area of the paddock that is burnt, leaving enough residue to reduce the risk of erosion,” said Dr Walsh, whose work is supported by the Grains Research and Development Corporation (GRDC).

“Narrow windrow burning is ideally suited to the lower rainfall areas in Australia where crop yields are lower, however, it has a role to play for growers in higher rainfall areas, particularly for canola and pulse crops where the risk of fire escapes is not as high,” Dr Walsh said.

The most problematic weed species in cropping regions are prolific seed producers capable of establishing a large viable seedbank in just one season. Targeting the seed of these weeds during the harvest of crops is an important component of integrated weed management (IWM) strategies.

Dr Walsh said narrow windrow burning was a particularly effective and cost-efficient weed seed reduction measure, if done correctly.

The first step in moving towards narrow windrow burning is to construct and attach to the harvester a chute so harvest residue can be concentrated into a windrow of around 500 to 600 millimetres in width. Chutes are easy to construct and to assist growers, designs are available via the AHRI website at www.ahri.uwa.edu.au.

A harvest height of 10 to 20 centimetres (the height of a beer can is ideal) is essential to minimise the risk of fire escapes during burning and to maximise the number of weed seeds that enter the front of the harvester.

For growers new to windrow burning, Dr Walsh advises they start with a small area of non-cereal – canola and pulse crops are recommended because of the minimal crop material remaining outside windrows – in the first year of windrow burning.

If considering narrow windrows in wheat crops, it is preferable to do so in crops that yield 2 tonnes/hectare or less, but Dr Walsh said it was possible to successfully windrow higher yielding wheat crops. However, the bigger the crop the greater the risk of fire escape.

Because barley is very leafy, it is almost impossible to confine a burn so growers are discouraged from narrow windrow burns.

Dr Walsh said the key to successful windrow burning was the intensity and duration of the burn.

“To guarantee the destruction of weed seeds, you need temperatures greater than 400 degrees for at least 10 seconds for ryegrass, and 500 degrees for at least 10 seconds for wild radish,” he said.

Burning during a light breeze of around 5-10 kilometres per hour or less will help to fan the fire but allow it to burn slowly all the way through the chaff to the ground and ensure maximum seed destruction. A cross wind at right angles to windrows supplies more air to the fire and allows the fire to burn slowly in both directions along the windrow. 

Another factor to consider when creating narrow windrows is avoiding coming to a complete halt while harvesting as this can lead to large blockages that take a lot of effort to clear. If you must stop, either pull out of the crop or go straight into reverse to allow residue to clear.

Meanwhile, Grassroots Agronomy is undertaking a GRDC-funded Agribusiness Trial Extension Project to assess options to allow narrow windrow burning in regions where high yields currently limit the employment of the practice.

Challenges associated with windrowing high stubble loads and the increased risk of fire escape are being addressed through the project which is looking at harvest heights and farmer-modified chute designs to overcome the barriers to effective narrow windrow burning.

Growers seeking more information on narrow windrow burning and other IWM practices can view GRDC ‘how to’ YouTube videos available at www.grdc.com.au/IWM-videos.

Multimedia resources about sustainable IWM practices are also available at www.ahri.uwa.edu.au and www.weedsmart.org.au. More information on IWM can be found at the GRDC’s IWM Hub, www.grdc.com.au/IWMhub.

A southern region Paddock Practices advice column on narrow windrow burning is available for viewing on the GRDC website at http://www.grdc.com.au/News-BurnWeedSeeds-0814.

To download and listen to a GRDC Driving Agronomy podcast interview with WA grower Doug Smith on his experiences with narrow windrow burning, visit www.grdc.com.au/DAPodcast-NarrowWindrowBurning   



More news from: GRDC (Grains Research & Development Corporation)


Website: http://www.grdc.com.au

Published: November 3, 2014

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