Weeds compete against crops for valuable moisture, light and nutrients, but growers can take steps in coming weeks to help their wheat crops fight back and stop the weeds winning.
Wheat crops with high biomass are a non-herbicide weed control tool - shading out weeds and out-competing them for water and nutrients.
Research conducted in 2012 by the Department of Agriculture and Food (DAFWA), supported by the Grains Research and Development Corporation (GRDC), has confirmed that increased wheat crop density reduces weed growth and seed set.
Researcher Peter Newman, who presented the research results at the Agribusiness and Regional Crop Updates, said crop competition was one of the few non-herbicide weed control tools available to growers, with the other being harvest weed seed control (HWSC) options.
“Diversifying the forms of weed control will help growers to improve their weed control and preserve herbicides,” he said.
Mr Newman said there had been a trend in Western Australia in recent years towards increasing row spacing, reducing seeding rates and the sowing of uncompetitive wheat cultivars.
“There are some good reasons for this, but it is costing growers in terms of weed control, and in many cases it is also costing them grain yield,” he said.
“Growers can halve the weed seed set in a paddock by increasing their seeding rate by about 30 to 40 kilograms per hectare, at a cost of about $15/ha,” he said.
“The accepted rule of thumb for crop density is 50 wheat plants per square metre for every tonne of grain yield potential, but this applies to weed-free crops.
“I believe growers can add at least another 50 wheat plants per square metre to improve competition with weeds.
“Growers in the low rainfall zone may be reluctant to increase their seeding rate, but the trials do show that it is also applicable to low rainfall areas.”
Mr Newman said the seed size of wheat varieties varied considerably and growers should take this into account when calculating seeding rates and plant density.
Trials in the Northern Agricultural Region last year evaluated the interaction between paired and single row sowing, wheat seeding rates and herbicides – to assess the benefits of increased crop competition.
“The research clearly demonstrated the benefits of crop competition as a non-herbicide control method for both ryegrass and wild radish,” Mr Newman said.
Paired row sowing of wheat was achieved by mounting a Stiletto seeding boot on to a single tyne and spacing paired rows 75mm apart.
“Paired row sowing reduces the crop row spacing without adding extra tynes to the seeding machine,” Mr Newman said.
“It effectively doubles the length of crop row in a paddock, resulting in less in-row competition between crop plants and enabling a higher number of seeds to germinate and establish as seeding rates increase.
“For crops with a yield potential of at least 1.5t/ha, there is a reliable, linear grain yield response to narrow row spacing.”
Mr Newman said research had also confirmed the importance of harvest weed seed control (HWSC) in reducing weed populations.
“In a long-term GRDC funded ‘focus paddock’ project conducted by DAFWA, growers who had the most success at managing ryegrass were those who practiced HWSC by narrow window burning or towing a chaff cart,” he said.
“In the eighth year of using this practice, these growers had no ryegrass in their focus paddocks and have averaged fewer than 1.5 ryegrass plants per square metre ever since,” Mr Newman said.
More information about crop competition is contained in an article to be published in the GRDC Herbicide Resistance Supplement to be included in the May-June edition of the GRDC magazine Ground Cover.
For more information about weed control and managing herbicide resistance visit the Australian Herbicide Resistance Initiative (AHRI) website at www.ahri.uwa.edu.au
For information on herbicide sustainability and harvest weed seed control practices, visit the WeedSmart information hub at www.weedsmart.org.au
Mr Newman is now the leader of the communications team at AHRI, based at Planfarm.
PHOTO CAPTION: Wheat established with paired row sowing at Mingenew in 2012.
AUDIO CAPTION: Click here to download an audio grab for this release. Audio is of Peter Newman
Peter Newman, Planfarm/AHRI
(08) 9964 1170, 0427 984 010
Natalie Lee, Cox Inall Communications
(08) 9864 2034, 0427 189 827
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