Non herbicide tactics to help suppress weed growth

Author: | Date: 05 Mar 2014

Greg Brooke, NSW DPI Trangie

GRDC code:UA00124

Take home message

  • At Bithramere near Tamworth east-west crop row orientation in barley yielded the same as north-south sowing but reduced biomass of weeds (canola) by 30% compared with a north-south row orientation.
  • At Merredin and Beverley in W.A east – west sowing gave 24% yield increase in cereals and a 37 to 54% suppression in weed biomass.
  • At Trangie increasing the seed density of the barley varieties Hindmarsh and Granger improved their yield and also increased their competitiveness against weeds (oats).


The rise in herbicide resistance in Northern region cropping systems has meant that in some situations weeds are dictating more and more how farmers can farm. With multiple resistance occurring in some weed species, non herbicidal measures to control or at least help suppress weeds are of increasing necessity. For integrated weed management (IWM) systems to be effective, non-herbicide strategies are imperative.

Prior to the advent of selective in-crop herbicides and the introduction of the semi-dwarf gene, cereal cultivars were taller and by nature had more suppressive effect on weeds such as oats( Vandeleur & Gill 2004). A crops competitive effect is most highly correlated with its ability to generate a large leaf area index early in its growth stage.  (Coleman, Gill & Rebetzke 2001)

Several studies have been done amongst current cereal cultivars to determine whether some varieties are inherently better at suppressing weed growth than others.

Can the inherent ability of some varieties to accumulate biomass be put to effect against weeds?

What are the trade-offs in yield vs weed suppression from high vs low harvest index varieties?

Does increasing the crop sowing rate assist with weed competition? What are the effects of increasing seeding rate on variety performance and on weed suppression?

Does row orientation make any difference to either yield or weed suppression?

It is known that as a plant type barley is more competitive than wheat and for this reason barley is usually chosen for these plant competition trials.

Row orientation - does it make a difference?

Many paddocks in our northern region were originally set up for controlled traffic tramlines 15 years ago based on practicalities such as reducing headland area by choosing row direction according to the longest run of the paddock, so that row direction varies from paddock to paddock. In irrigation fields it is with fall of the paddock. Practicalities aside, what difference does row orientation make to crop yield and suppression of weeds?

Deliberately orienting crop rows at 90 degrees to the sunlight direction  east – west (E-W) works on the principle that the crop will intercept more sunlight (photosynthetically available radiation) than will N-S sowing, giving weeds less chance to develop in the crop inter row. In winter when the sun is at a lower angle (solar plane) this shading of the inter row can confer advantages particularly in southern latitudes. Research from 2002 – 2005 conducted by Borger et al at Merredin and Beverley W.A. (latitudes S 31° to 32 °) has shown both yield advantages as well as weed suppression from east/west row orientation compared with north/south.

 Merredin in Western Australia is similar in latitude to Tamworth.

Annual TOTAL solar radiation at Merredin is very similar to annual TOTAL solar radiation at some eastern state sites eg. Merredin W.A 7036MJ/m2; Trangie NSW 6864MJ/m2; Goondiwindi NSW 7172MJ/m2 (source CliMate app)

Within wheat and barley crops oriented east-west, in the W.A trials weed biomass (averaged throughout all trials) was reduced by 51 and 37%, and grain yield increased by 24 and 26% (compared with crops oriented north-south) (Borger et al)

Weeds in these trials were sown wild radish (300 pod segments/m2) and annual ryegrass (“Safeguard” 200 seeds/m2)

At Bithramere near Tamworth in 2012, Matt Gardner et al  established a trial with two barley varieties- Hindmarsh and Skipper with a sown population of 44Y84 canola as a substitute weed. Row orientation, row spacing 30 cm vs 50 cm were evaluated. A row orientation of E-W conferred a reduction in weed (canola) biomass of 39%.

Skipper being more vigorous than Hindmarsh reduced weed (canola) biomass a further 30% and 42% over Hindmarsh for the N-S and E-W sowing.

The weed fumitory was also prolific in the N-S sowing but was reduced almost to nothing in the E-W row orientation. (Matt Gardner pers comm.)

Row orientation had no significant impact on grain yield under high weed competition. When no weeds were present, the N-S orientation had a 6% and 7% yield improvement for the 30 and 50cm row spacing treatments. (Gardner et al 2012)

Summer crop work in sorghum by Serafin, L and McMullen,G 2011 showed row orientation had no advantage in terms of yield. This is most likely because the sun is at a higher angle and also because of the relatively lower plant populations involved and the wider rows – 75cm.  Importantly E–W sowing did not yield any less than did N-S sowing meaning it would be compatible with winter crop programs which deliberately oriented crop rows E-W for weed control.

Row spacing- does it make a difference?

The Bithramere2012 trial with 30 cm vs 50 cm showed no clear effects in reducing weed (canola) biomass, but the wider row spacing did incur a yield penalty of 11% in the nil weed treatment.

At Merredin W.A. two row spacings of 23 cm vs 60 cm were used and at Beverley WA two row spacings were studied at 18 cm vs 36 cm. Averaged throughout all trials, weed biomass was lower in crops with narrow row spacings (Borger et al).

Varieties – are there differences?

Most published work has concentrated on crop type eg barley vs wheat vs canola vs lupins etc and not on varieties. Recent work with barley varieties shows there is as much difference between barley varieties as there can be between crop types.

The Bithramere trial with two barley varieties showed the more vigorous barley variety Skipper reduced weed (canola) biomass by 30 – 40% over Hindmarsh³.

Skipper also out-yielded Hindmarsh with both weeds present and not present and at both 30 and 50 cm row spacings.

Figure 1. Barley competition trial, Trangie 2013

Figure 1 summarises a barley competition trial conducted at Trangie in 2013 and shows the capacity of different varieties to yield both with and without weeds and the yield loss incurred by weeds (oats).

15 barley varieties were sown at 100 seeds per m2 and 3 of these varieties were sown at double rate of 200 seeds per m2. Row spacing was 33cm. The oat variety Yarran was surface sown as a substitute weed at 50 seeds per m2 and was allowed to grow right through until maturity. The yield loss attributed to weeds averaged across all varieties was 0.3t/ha.

The popular and high yielding variety HindmarshPBR logo both with and without weeds present was the highest yielding variety. Increasing the seed rate to 200 seeds/m2 improved the yield of Hindmarsh both with and without weeds and also gave greater suppression of weeds. This is consistent with other seeding rate trial work with Hindmarsh in variety specific agronomy package (VSAP) trial work.

The variety Granger at 200 seeds/m2 improved yield where weeds were present but only maintained yield where there were no weeds present.

Figure 2. Oat suppression by barley variety, competition trial, Trangie 2013

Figure 2 shows the effects of weed (oat) suppression by barley variety.

Varieties such as Hindmarsh which are lower biomass types proved less suppressive of weeds than bulkier types such as Grange, Fathom, Commander.

Increasing the seeding rate of Hindmarsh caused greater suppression of oat yield.

Granger at 200 seeds per m2 gave the greatest reduction in oat yield.


Crop row orientation of E-W in winter cereals has given substantially greater suppression of weeds in both WA and Northern NSW trials.

Barley variety choice will impact the seed set of oats.

Increasing seeding rate of Hindmarsh and Granger from 100 seeds to 200 seeds per m2 caused a further reduction in weed (oat) yield.

Increasing the seeding rate of ScopeCL did not improve yield or significantly increase suppression of oats in this trial.


Borger, C.P.D., Hashem, A. andPathan, S., DAFWA “Manipulating Crop Row Orientation to Suppress Weeds and Increase Crop Yield”.

Coleman, R., Gill, G. S. and Rebetzke, G. 2001. Identification of quantitative trait loci for traits conferring weed competitiveness in wheat (Triticum aestivum L.). Crop and Pasture Science, 52 (12), pp. 1235--1246

 Gardner, M., Mortell, P. and Morphett, S., NSW DPI Tamworth. (Using row orientation, row spacing and variety selection as weed management tools – Bithramere 2012-Northern Grains Region Trial Results Autumn 2013 p45)

Serafin, L. and Mcmullen, G. Targeting high yields in dryland grain sorghum in northern NSW: row direction, row spacing and plant population GRDC website. 2011

Vandeleur, R.K. and Gill, G.S., “The impact of plant breeding on the grain yield and competitive ability of wheat in Australia” Australian Journal of Agricultural Research, 2004,55,855-861

Contact details

Greg Brooke
NSW DPI, Trangie
Mb: 0437 140 577

Reviewed by

Tony Cook NSW DPI Tamworth


PBR logo      Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994

GRDC Project code: UA00124