- Harvest weed-seed capture success relies on maximising the number of weed seeds that enter the header.
- Taking the time to fine-tune these techniques to your situation is worth the effort.
GroundCover™ Supplement Issue: 135 July-August | Author: Trent Potter
In stubble-retained farming systems harvest weed-seed control provides one of the most effective methods of reducing the grass weed seedbank, but making sure the weed seeds are captured by the header is essential.
Getting the grain harvested quickly is often a high priority for growers looking to reduce the risk of weather damage, but in retained-stubble systems harvest is also an important time to set up stubble for sowing the next crop. While this can mean a slower harvest, it can save time pre-seeding and, more importantly, may provide the best opportunity to manage grass weeds using harvest weed-seed control (HWSC).
Tools such as chaff carts, the Integrated Harrington Seed Destructor (iHSD), narrow windrow burning, chaff lining and chaff decks substantially reduce the weed seedbank. For instance, Australian Herbicide Resistance Initiative (AHRI) research has shown that the iHSD can destroy 96 per cent of ryegrass seeds, 99 per cent of wild oats seeds and 98 per cent of brome grass seeds entering the harvester.
The real challenge for growers is making sure that weed seeds enter the harvester in the first place. This involves harvesting low to maximise seed capture, but also making sure weed seed does not fall out of the seed head before the crop matures. In 2013, Dr John Broster, from Charles Sturt University, found that 88 per cent of annual ryegrass was captured when harvesting at 10 centimetres compared with 48 per cent at 40cm.
A two-week delay in harvesting wheat after crop maturity has been shown by AHRI to reduce head retention of ryegrass to about 75 per cent, wild oats to about 50 per cent and brome grass to about 70 per cent. Windrowing can help retain weed seed, with 95 per cent of ryegrass retained three weeks after windrowing barley, compared with 62 per cent in standing plants.
As part of the GRDC’s Stubble Initiative, Yeruga Crop Research worked with the Mid North High Rainfall Zone Group and the Yorke Peninsula Alkaline Soils Group to see how local growers were using HWSC to reduce the impact of grass weeds in stubble-retained systems.
Dan Wilson has used a chaff cart for six years when harvesting barley at his family farm at Whitwarta, SA, and windrows about seven to 10 days before harvest to reduce weed-seed shedding. To avoid the risk of burning the chaff dumps, Mr Wilson bales them to feedlot his cattle, with the additional carrying capacity more than making up for the cost of the chaff cart and baling.
Mr Wilson places his chaff dumps at each end of the paddock to simplify baling. Weeds are no problem in the dumps because moisture rots and destroys the seeds remaining in the chaff on the ground.
Andy Barr, who farms near Pinery, SA, had been burning narrow windrows to reduce the weed seedbank for more than 10 years, but found it was often difficult to get a burn hot enough to kill the weed seeds but not take out the whole paddock. Determined to improve his success rate he recorded the temperature, humidity, windspeed and the Delta T for each windrow burn in 2012 and found the best indicator of success was Delta T.
“A Delta T, that combination of temperature and humidity we read from our little handheld weather station, of between 5 and 8 worked best for us. If the Delta T was below 4 then two out of three burns were too cold and if the Delta T was above 10 then all the jobs were too vigorous,” he says.
GRDC Research Code YCR00003
Trent Potter, Yeruga Crop Research
0427 608 306
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