Protecting WA crops

Grower groups drive barley grass integrated weed management research

Barley grass
Barley grass at Facey trial site. Image: Amy Bowden (Facey group).

At a glance

1. Resistance to non-selective herbicides is not an issue in WA barley grass, but resistance to Group 1 herbicides, including Quizalofop (FOP) and Clethodim (DIM), and Group 2 herbicides, such as Imazamox/Imazapyr (IMI) and Mesosulfuron (SU), is becoming increasingly common.

2. Staggered cohorts and delayed emergence of barley grass is common so early and late season management is necessary to prevent seed set.

3. Late and staggered barley grass emergence makes delayed sowing an impractical control tactic.

4. Recent trials found that slashing and spray topping were highly effective management methods when the application timing was at the correct stage of barley grass development.

5. Break crops like canola or vetch pasture rotations offered the best control, as this allowed a wider range of herbicides (from different modes of action) to be used for pre-seeding and in-crop barley grass control.

WA growers contend with several major weeds and barley grass in cropping and pasture systems is becoming increasingly challenging to control due to several factors including:

  • Increasing herbicide resistance
  • Suppression rather than control from herbicides
  • Less effective crop competition in a drying climate
  • Delayed and staggered emergence, reducing pre-emergent herbicide effectiveness

A national grower group driven project investigated integrated weed management strategies for barley grass that are logistically and economically practical for growers.

In WA the GRDC-funded project was led by well-known Department of Primary Industries and Regional Development (DPIRD) research scientist Dr Catherine Borger. Catherine worked with the five grower groups: Kellerberrin Demonstration Group (KDG), South East Premium Wheat Growers Association (SEPWA), Mingenew Irwin Group (MIG), Lakes Information and Farming Technology (LIFT) and the Facey Group. Additional support was also provided by the WA No-Tillage Farming Association (WANTFA).  With a focus on zero barley grass seed set, the grower groups chose to investigate a mix of barley grass management strategies including pre-emergent herbicides, crop competition and post-emergent herbicides.

Harris family from the SEPWA group
The Harris family explored optimal chemical use in a field where barley grass is problematic, but levels of herbicide resistance are low. Image: Sam Stubna (SEPWA).

Barley grass populations collected by the grower groups were tested for herbicide resistance and test results revealed no resistance to glyphosate or paraquat/diquat, however there was high resistance to Group 1 (A) and Group 2 (B) herbicides. Despite displaying this resistance, the barley grass plants that survived Group 1 herbicide application were stunted, and subsequently seed production is expected be very low in the field.

Barley grass populations can have staggered cohorts and delayed emergence, which allows germinating seedlings to avoid pre-emergent herbicides.

The staggered and delayed emergence of barley grass meant that a combination of the pre herbicides, post emergent herbicides and other integrated weed control options was required to effectively control the different germinations of the weed and to prevent seed set at all sites. For example, the MIG group used pre-emergent and post-emergent herbicides in a Roundup Ready InVigor® canola crop in 2021 to ensure zero barley grass seed set (Table 1).

Table 1. Canola density, barley grass density, barley grass viable seeds and canola yield results from the MIG’s 2021 canola crop trial.


Canola density/m2

Barley grass/density m2

Barley grass panicles/m2

Barley grass/seeds m2

Canola yield (t/ ha)







Trifluralin, glyphosate






Glyphosate, quizalofop-p-ethyl






Trifluralin, glyphosate, quizalofop-p-ethyl


















*Herbicide formulations and application dates: trifluralin 720 g a.i./ha (TriflurX®) pre-emergent (15 April 2021); glyphosate 621 g a.i./ha (Roundup Plantshield®) applied twice, at two leaf (14 May 2021) and tillering (8 June 2021); quizalofop-p-ethyl 50 g a.i./ha at 3-5 leaf (14 June 2021).(Probability (P) and Least significant difference (LSD) values are included for separation of means. Note that barley grass panicle data is back-transformed from a square root transformation, and ‘NS’ indicates ‘not significant’).

The LIFT group trialled delaying crop sowing by four to seven weeks, but while this tactic was effective in controlling the staggered and delayed emergence of the barley grass, it came with a crop yield penalty and wasn’t a viable option.

Catherine and the KDG group found that slashing volunteer pasture was effective in controlling the late barley grass cohorts if the timing was right, however, the effectiveness of slashing or spray topping could be variable due to seasonal conditions and potential regrowth of the barley grass.  

For more information on barley grass refer to DPIRD’s Barley grass page.

More information on this research can be found in Catherine’s Australian Weeds Conference research paper which will be available on the 1st October.