Brome and barley grass management in cropping systems of southern Australia

Gurjeet Gill, Lovreet Shergill, Ben Fleet, Peter Boutsalis and Chris Preston
School of Agriculture, Food & Wine, University of Adelaide

GRDC project code: UA00105, UA00121

Keywords: seed dormancy, cold stratification/chilling, weed management

Take-home messages:

  • Increasing incidence of brome and barley grass in cropping paddocks in southern Australia is likely to be associated with selection of more dormant biotypes by weed management practices used by the growers.
  • At present brome grass management in cereals is heavily reliant on group B herbicides, especially the ClearfieldTM technology. Delaying onset of resistance to these herbicides would require identification of effective alternative herbicides.
  • Field trials undertaken over the last 4 years have investigated various pre-emergence herbicides for brome grass control in wheat. Even though Sakura® (pyroxasulfone) appears to be the most active pre-emergence herbicide against brome grass, it lacks consistency required for long-term population management of brome grass.
  • Field trials over 4 years confirmed consistently high efficacy of Sakura® against barley grass, especially under situations with good soil moisture.
  • Barley grass management is now being complicated by evolution of group A resistance in this weed species. However, there appear to be several effective alternatives (e.g. Sakura® and Raptor®) that could be used for barley grass control in broadleaf crops.

Introduction

Feedback from growers and consultants in southern Australia has clearly shown increasing spread of brome and barley grass. In a recent survey by Fleet and Gill (2008), farmers in low rainfall districts in South Australia and Victoria reported increasing incidence of barley grass in their crops. Research undertaken at the University of Adelaide has shown that both brome and barley grass have developed increased seed dormancy in response to management practices used in cropping systems. Presence of increased seed dormancy in these grass weed species enables them to escape pre-sowing control tactics used by the growers. In this paper we will report results of studies undertaken to develop management strategies for brome and barley grass.

Brome grass management in broadleaf crops is heavily reliant on the use of group A herbicides. However, there are more than 30 cases of confirmed resistance in brome grass to group A herbicides (Boutsalis et al. 2012). In cereals, brome grass control has improved considerably since the introduction of imidazolinone tolerant wheat cultivars (ClearfieldTM technology). Studies undertaken by Kleemann and Gill (2009) showed that the integration of Clearfield wheat into the cropping rotation is highly effective in driving down populations of brome grass. As imidazolinone herbicides are playing such an important role in brome grass management, it is important for the grains industry to maintain long-term effectiveness of this chemistry. Herbicide rotation has been widely recognised as being important to delay onset of resistance to herbicides. In order to implement herbicide rotations to delay group B resistance in brome grass, it is important to identify alternative modes of action. This need is particularly strong in low to medium rainfall zones where wheat is regarded as a more reliable crop and cropping rotations tend to lack diversity.

Field studies have been undertaken over the last 4 years to investigate the performance of alternative modes of action to control brome grass in wheat. Recent release of pyroxasulfone (Sakura®) has provided a new mode of action with proven activity against grass weeds such as annual ryegrass. In these field trials, Sakura® and its combination with other herbicides were investigated for the control of brome grass in wheat. In some of these field trials, Sakura® alone provided excellent control (>90%) of brome grass (Figure 1). However at the other trial sites, the level of weed control was quite disappointing (25%). At this stage, underlying reasons for this large variability in the performance of Sakura® on brome grass are unclear. Use of split application of Sakura® was equally variable as its single pre-sowing application. Addition of Avadex® (triallate) to Sakura® improved brome grass control relative to Sakura® alone in 2012 but the level of weed control obtained at Balaklava was inadequate (<60%). However, this treatment appears to be worthy of further research. In most situations, addition of trifluralin to Sakura® did not significantly improve brome grass control. In summary, it could be argued that none of the currently available pre-emergence herbicides have the required stability in efficacy to become viable alternatives to post-emergence group A or imidazolinone herbicides.

Figure 1. Effect of different pre-emergence herbicides on the control of brome grass in field trials on wheat

Figure 1. Effect of different pre-emergence herbicides on the control of brome grass in field trials on wheat. It should be noted that rates of Triflur X and Avadex® were lower in trials undertaken prior to 2012. Weed control is expressed as reduction in brome grass plant density.

Barley grass management

Many growers have reported an increasing incidence of barley grass in their crops, especially cereals. Research by Fleet and Gill (2012) has shown that weed management practices used in cropping systems have selected for increased seed dormancy, which is likely to contribute to greater abundance of this weed species in field crops. This trend for selection of increased seed dormancy in barley grass mirrors change in seed behaviour of brome grass (Kleemann and Gill 2013).

Recent release of pyroxasulfone (Sakura®) in Australia has been an important development in the management of barley grass in wheat. In many field trials undertaken on the Eyre Peninsula over 4 years, Sakura® consistently provided effective control of barley grass in wheat (e.g. Fleet and Gill 2010) (Figure 2). Unfortunately, many farmers are still using cheaper but inferior herbicide options for barley grass, which can lead to large build-up in weed infestations.

Figure 2. Effect of Sakura at the recommended rate on barley grass control in wheat at trial sites on the Eyre Peninsula

Figure 2. Effect of Sakura® at the recommended rate (118 g/ha) on barley grass control in wheat at trial sites on the Eyre Peninsula. Weed control is expressed as reduction in barley grass seed production. BB = Buckleboo; 1 and 2 represent time of sowing.

Most growers have relied on group A herbicides to control barley grass in their pulse crops. There have been recent reports of difficulty in controlling some barley grass populations with group A herbicides. One of these populations was collected from Baroota, near Pt Germein and screened for resistance. There is no doubt that the repeated exposure of Baroota population to group A herbicides has resulted in the evolution of high levels of resistance (Figure 3). Resistance has now been confirmed in this population to quizalofop (Targa®), haloxyfop (Verdict®) and clethodim (Select®).

Figure 3. Effect of quizalofop on the survival of barley grass field population

Figure 3. Effect of quizalofop on the survival of barley grass field population from Baroota (Pt Germein) and the susceptible population from Yaninee.

Presence of high levels of resistance to group A herbicides is a major concern for weed management in pulse crops. In order to investigate the performance of alternative herbicides on group A resistant barley grass, a field trial was conducted at Baroota in 2012. Sakura®, Raptor® (imazamox) and an experimental compound provided excellent control of barley grass, which was reflected in significant increases in grain yield of field peas (Table 1). Outlook® (dimethenamid) appeared to be relatively ineffective early in the season but its performance improved with time and it may have a useful role in field peas.

Table 1. Effect of different herbicide treatments on grain yield of field peas and reduction in group A resistant barley grass seed production at Baroota (SA) in 2012.

Treatments

 

Seed set reduction (%)

 

Pea yield (t/ha)

 

Sakura® @ 118 g/ha IBS

 

99

 

2.29

 

Boxer Gold® @ 2.5 L/ha IBS

 

74

 

1.41

 

Outlook® @ 1 L/ha IBS

 

93

 

2.14

 

Raptor® @ 45 g/ha + BS1000 0.2% PE

 

100

 

2.08

 

Trifluralin @ 2.0 L/ha + Avadex® Xtra @ 2L/ha

 

71

 

1.32

 

Metribuzin @ 200 g/ha PSPE

 

46

 

0.82

 

Propyzamide 500 g a.i./ha

 

100

 

2.29

 

Diuron 900@ 1 kg/ha + Trifluralin @ 2.0 L/ha IBS

 

78

 

1.58

 

Trifluralin 2.0 L/ha IBS

 

68

 

1.19

 

Control

 

-

 

0.82

 

LSD (P=0.05)

 

 

 

0.33

 

Note: Some of the herbicides evaluated in this trial are currently not registered for use in field peas.

Acknowledgements
Research on barley grass reported here was undertaken in a current GRDC funded project (UA00105). Brome grass research was conducted in GRDC funded projects (UA00121).

Contact details
Dr Gurjeet Gill

Waite campus, PMB 1, Glen Osmond, SA 5064

(08) 8303 7744

gurjeet.gill@adelaide.edu.au

GRDC Project Code: UA00105, UA00121,