Getting the right angle on crop competition

Image of Dr Catherine Borger

DAFWA research officer Dr Catherine Borger outlined the latest research with a focus on crop weed competition at WA WeedSmart Week.

PHOTO: Cox Inall Communications

Crop competition can be a successful and cost-efficient way to control weeds and reduce reliance on herbicides.

Tactics that can boost a crop’s competitiveness with weeds include increasing seeding rates, planting seed with high germination rates and vigour, meeting in-season plant nutrition requirements and accounting for environmental and soil limitations.

Research in Western Australia is also finding that switching the orientation of crop planting to east–west can more effectively ‘shade out’ weeds in the inter-row than using a north–south orientation.

Department of Agriculture and Food, WA (DAFWA) research officer Dr Catherine Borger told audiences at WA WeedSmart Week that this was a relatively straightforward and cheap method of boosting crop competition with weeds, without significantly affecting crop yields.

“The theory is that – in southern Australia – if you sow crops east–west, at a right angle to the sunlight direction, the sun’s rays hit the crop row and shade the weeds in the inter-row,” she says.

“Our trials indicate that sowing in this direction means 10 to 20 per cent less sunlight hits the inter-row during winter, reducing soil temperature and significantly suppressing weed growth, biomass and seed set.”

Dr Borger says the system is more suited to cereals because broadleaf crops alter the angle of their leaves during the day to ‘track’ the sun, which then casts less shade over the inter-row.

She says five GRDC-supported DAFWA trials at Merredin and Beverley in high-weed-burden paddocks from 2002 to 2005 showed weed biomass was cut by 51 per cent in wheat crops and 37 per cent in barley crops when sown in an east–west direction. Crop yields were 25 per cent and 17 per cent higher for wheat and barley respectively using this sowing orientation.

Six trials in 2010-11 in Merredin, Wongan Hills and Katanning found there was potential to reduce annual ryegrass (Lolium rigidum) seed set by 40 to 90 per cent using east–west sowing to out-compete this weed.

“There was not a significant yield difference in the crops sown east–west compared to north–south at these sites, but weed burdens were much lower.

“This highlighted that there is no yield disadvantage from changing orientation,” Dr Borger says.

She says more research is needed into the effectiveness of east–west sowing in the far-northern areas of the WA grainbelt, where the sun’s angle is higher and the inter-row may be shaded for less time during the day.

But she says preliminary research in parts of the northern, central and southern WA grainbelt has indicated east–west sowing can be effective in all of these regions.

Dr Borger says it is likely to be more successful when coupled with strategies such as narrow row spacing and higher seeding rates, but may not suit lower-rainfall areas.

“It is always good to stack your crop competition measures,” she says.

Her tips for practical implementation of an east–west crop orientation include:

  • consider the weeds present – it will be more effective for grass weed control;
  • consider farm and paddock layout;
  • auto-steer technology can make it easier and safer to drive into direct sunlight;
  • consider narrow row spacing; and
  • plan crop residues for ease of planting east–west through stubbles.

Dr Borger says a competitive crop may not always be easy to achieve but there are methods available that in the long term will be cheaper than relying solely on herbicides for weed control.

More information:

Dr Catherine Borger,
08 9081 3105,

East-west orientation for improved crop competition’, DAFWA

Coupling pre-emergent herbicides and crop competition for big reductions in weed escapees’ – GRDC Grains Research Update paper

GRDC Wheat GrowNotes – western region, chapter 6 ‘Integrated weed management’


Precision sowing another weeds tool


WA WeedSmart Week showcases progress

GRDC Project Code UA00149, UA00156

Region West