Across our regions a rising number of growers are looking at integrating alternative weed control practices such as windrow burning to combat or delay an increasing incidence of herbicide resistance.
The aim of windrow burning is to destroy weed seeds by burning windrows of the chaff after harvest. This method is more efficient than burning the entire paddock because there is a higher concentration of biomass in the chaff trail which will produce a hotter burn, thus killing the weed seed.
The low yields this year present an opportunity for windrow burning as it will be possible to burn windrows without burning the whole paddock.
The question is, is there enough biomass this year to get a good, hot burn?
Peter Newman from Weedsmart in Western Australia, says as a general rule, aim for 20t/ha minimum of biomass in the windrow. Less than this and you risk not getting an effective burn. Likewise, be cautious of heavy stubble loads too because the whole paddock may burn.
In a hypothetical example: a 1t/ha yielding cereal crop, will have 1.5t/ha of residue (40% harvest index). Windrowing will put half (0.75t/ha) the residue in the windrow. If a header front is 10m, and the windrow chute is 0.5m, there is a multiplication factor of 20. So 20 x 0.75 = 15t/ha in the windrow. This could get to 20t/ha with a narrower windrow chute.
The desired biomass range is normally achieved by a 2t/ha crop with a windrow chute that has an opening 500mm wide. If you are harvesting crops that have a 1t/ha potential you could reduce this opening to 350 – 400mm to get the biomass.
To achieve adequate weed control the chaff trail must burn for 20 seconds at 400°C to kill ryegrass and 30 seconds at 400°C to kill brome grass. A ‘white ash residue’ generally means the burn has been hot enough.
Burn windrows with a light cross-wind of 5-15km/h and burn the two outside laps first to create a firebreak.
Light windrows every 200m so that windrows burn out in reasonable time and don’t over thresh your crops as this leads to reduced air flow. Also, don’t burn windrows after a summer rain. Windrows should be dried for 10-14 days after a rainfall event.
Remember, before burning, ensure fire restrictions have been lifted and check the forecast.
Victorian farmers wanting to undertake windrow burning will require a Schedule 13 permit. The permit is issued by the municipalities and the CFA advises the council in relation to timing and conditions.
The Grains Research and Development Corporation (GRDC) has a range of YouTube clips showcasing how to conduct an effective windrow burn, as does the Australian Herbicide Resistance Initiative (AHRI).
GRDC is also supporting Birchip Cropping Group Inc. (BCG), Southern Farming Systems (SFS), Irrigated Cropping Council (ICC) and the Victorian No Till Farmers Association (VNTFA) to undertake research, development and extension activities focused on stubble retained cropping systems (Project No. BWD00024).
For more information on windrow burning and other stubble related topics visit https://thestubbleproject.wordpress.com/wimmera-and-mallee-weeds-2/
