Simple methods can reduce weeds and boost crop yields

Author: Natalie Lee | Date: 04 Aug 2016

DAFWA researcher Catherine Borger.

DAFWA researcher Catherine Borger says a highly competitive crop was a fantastic way to eradicate weeds and would generally produce higher grain yields. PHOTO: DAFWA

Participants at WA WeedSmart Week will hear the benefits of improving crop competition to combat weeds using the techniques of east-west sowing and narrow row spacing.

Department of Agriculture and Food (DAFWA) researcher Catherine Borger said a highly competitive crop was a fantastic way to control weeds and would generally produce higher grain yields.

She is one of the speakers at a forum on August 8 where leading agronomists and grain growers will share their insights and research into tackling weeds head-on.

The forum is part of WA WeedSmart Week which is being held from August 8 to 12 and will also include the half-day program ‘The fungi-side of the story’ outlining crop disease research by the Centre for Crop and Disease Management (CCDM) and a road trip visiting WA growers.

WeedSmart is an industry-led initiative to enhance on-farm practices and promote the long-term sustainability of herbicide use in Australian agriculture. Its main sponsor is the Grains Research and Development Corporation (GRDC). Other sponsors include Bayer CropScience, Monsanto, Nufarm, Sinochem and Syngenta.

Dr Borger said weeds could not be controlled using herbicides alone and a diverse range of tactics was needed to manage them and ensure the long-term sustainability of herbicide use in Australian agriculture.

She said that while crop orientation and row spacing were virtually free, other crop competition techniques included competitive cultivars/crop sequences; seed size, germination rates and vigour; crop nutrition and health; and environmental conditions including soil properties.

“East-west orientation and narrow row spacing are not possible everywhere, so if these methods won’t work for you think about the other crop competition options,” Dr Borger said.

She said crops sown in an east-west direction shaded weeds, as the sun was at a low angle over the horizon in winter, especially in southern Australia.

“GRDC-supported research conducted by DAFWA in recent years at Merredin, Wongan Hills and Katanning found that east-west sown wheat and barley crops reduced annual ryegrass seed production in five out of six trials – by 44 to 92 per cent – compared with crops sown north-south.”

“In other trials, east-west barley crops at Bithramere, New South Wales, reduced weed biomass by 39 per cent. The barley varieties Hindmarsh and GrangeR had higher yields and were more competitive against weeds when sown east-west in trials at Trangie, NSW.”

Dr Borger said key practicalities to take into account when considering crop orientation as a crop competition tool included:

  • Weed species in the field – broadleaf weed species can move their leaves to track sunlight and weeds taller than the crop will not be shaded
  • Paddock layout and location – it may not be feasible to sow in an east-west direction and crop orientation will have a bigger impact on southern farms compared with those in northern Australia
  • Sowing east-west is more practical using auto-steer as it may be difficult or dangerous to drive directly into the sun without auto-steer

Dr Borger said the use of narrow crop row spacing resulted in fewer weeds in a range of crops and this had been tested throughout Australia.

“It will increase crop yields even if weed numbers are low - these yield benefits are believed to be due to reduced competition between wheat plants within rows and plants better intercepting available sunlight,” she said.

“Trials conducted by DAFWA’s Glen Riethmuller in Merredin showed that very narrow row spacings of 9cm reduced annual ryegrass seed production at harvest from 324 to just two ryegrass seeds per square metre over a 10-year period.

“Row spacings of 18cm reduced seeds at harvest from 296 to one; spacings of 27cm reduced numbers from 702 to 51; and spacings of 36cm reduced numbers from 382 to 171.”

Crop yields were generally higher where the 9cm and 18cm row spacings were used compared with the 27cm and 36cm spacings.

Dr Borger said row spacings did not need to be as narrow as 9cm and research had shown there were significant and incremental yield benefits for every 1cm reduction in row spacing when wheat yield potential was higher than 1.5 tonnes per hectare.

She said practical considerations for narrow row spacings included managing crop residue but a seeder with an on-board GPS receiver could allow growers to sow between the rows.

“Speed of sowing may also need to be reduced where crop rows are sown closely to ensure that soil is not thrown onto the adjacent crop row, which can cause herbicide damage,” Dr Borger said.

“Fuel use and capital cost is increased but this can be offset by the higher yield,” she said.

More information about WA WeedSmart Week is available at this link.

Contact Details

For Interviews

Catherine Borger, DAFWA
08 9690 2220, 0467 816 082

Lisa Mayer, AHRI
08 6488 7870


Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827

GRDC Project Code UWA00164, CUR00023

Region West