Great Brome (Bromus diandrus) Great brome (Bromus diandrus) is an annual grass weed widely distributed across southern Australia. It can cause enormous problems for landholders across the mid and lower Murrumbidgee catchment. A population of 100 plants/m2 causes an average yield loss of 30% in wheat crops due to its high level of competitiveness for water, nutrients and space (Gill, Poole & Holmes 1987). The seeds can contaminate wool and injure livestock through penetration of eyes, mouths, feet and intestines. It also hosts a range of cereal diseases. (Figures 1 & 2)

Figure 1. Bromus diandrus inflorescence

KEY POINTS

• Great brome is an increasing problem in the Murrumbidgee catchment and should not be overlooked.

• New herbicides are available for control of great brome in wheat.

• Aim for 2 consecutive years of weed control to deplete the weed seed-bank.

Figure 2. Bromus diandrus infestation Legislation Great brome is not declared noxious in the Murrumbidgee catchment under the Noxious Weeds Act 1993. Taxonomy Great brome is the accepted common name for Bromus diandrus but it is also known as ripgut brome, ripgut grass, giant brome, slands grass, jabbers and Kingston grass. Bromus diandrus is one of 130 species in the Bromus L. genus, all of which are simply known as brome grass. Bromus rigidus is another common species in Australia. Its accepted common name is rigid brome but it may also be known as ripgut brome, brome grass and even great brome. Origin and Introduction Great brome is native to the Mediterranean region of Turkey, Cyprus, Egypt and Iraq but now infests other Mediterranean areas of Europe, Africa, Britain, North America, South Africa, Australia, New Zealand, South Korea, Japan and Russia. Great brome was introduced into Australia around 1875 as a contaminant of crop seeds, forages and wool, attached to livestock or in ship ballasts (Cooper & Moekerk 2000).

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Distribution Great brome quickly became naturalized across southern Australia due to its aggressive nature and pre-adaptation to Australia’s temperate climate. It is distributed from south-east Queensland to south-west Western Australia (Figure 3). It is adapted to a range of climatic conditions and soil types from acidic to alkaline and sandy to loamy. It is found in crops, pastures, fallows, roadsides, wastelands, national parks and reserves and coastal sand dunes.

Figure 3. Estimated distribution of great brome in Australia (Kon & Blacklow 1995). Biology and Ecology Great brome is a major weed in the Murrumbidgee catchment because: • it is among the most competitive of all grass weeds and small populations in a wheat crop can cause large yield losses

• it effectively competes with crop plants for nitrogen and phosphorous

• each plant can produce more than 3000 seeds

• the seeds contaminate grain, wool, animal skins and meat, and injure livestock by penetrating skin, eyes, feet and intestines

• the plant hosts a number of cereal diseases including take-all (Gaeumannomyces graminis), ergot (Claviceps purpurea) and cereal cyst nematode (Heterodera avenai), all of which can cause significant losses in cereal crops

• the plant sheds a large proportion of seed before harvest

• it is drought tolerant

• it has a higher tolerance of phosphorous deficiency and better responsiveness to added nitrogen than wheat

• few management tools are available for great brome control in cereals

• there is a poor understanding of the ecology and population dynamics of great brome

• the easy removal of other grass weeds has allowed great brome to proliferate

• the adoption of minimum and no-till farming systems has caused an increase in great brome populations

• sheep numbers in the Murrumbidgee catchment have declined allowing annual grasses including great brome to set seed freely; and

• the overall area cropped in the Murrumbidgee catchment has increased. Identification Great brome leaves are rough, hairy, dull and often have visible purple stripes along the leaf veins. The leaf sheath is tubular, the ligule is prominent and membranous, and the stems are hairy (Figure 4). The inflorescence is a loose, nodding panicle with long stalked spikelets (Figure 5).

Figure 4. Bromus diandrus stem

Figure 5. Bromus diandrus inflorescence All Bromus species appear very similar in the seedling and vegetative stages. Great brome seedlings can be confused with wild oats as they both possess hairs on their leaves and stems. (Table 1)

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Table 1. Distinguishing characteristics of Bromus diandrus (Cooper & Moerkerk 2000; Kon & Blacklow 1988).

Bromus diandrus Height 30-90cm

Leaves 10mm wide, stout, erect, long/dense hairs

Ligule Prominent, membranous

Panicle Loose and nodding,150-200mm long

Spikelet branches Longer than spikelets, sometimes exceeding 20mm

Awn length 35-55mm

Abscission scar Circular

Lemma callus Short (≤1mm), spherical with rounded tip

Chromosome number 2n=56 Seed dormancy and germination Great brome seeds are inherently dormant at seed shed. They remain dormant in high temperatures over summer but regain germinability when conditions become favourable. Most seeds will germinate after rain the following autumn as rainfall is the biggest determinant of germination (Figure 5). Those which don’t can remain viable in the soil for up to 2 years, less if exposed to a humid environment and more on non-wetting soils.

The hot, dry conditions found at the soil surface are unfavourable for germination and this could be the underlying reason great brome has increased under no-till systems. Seeds lie dormant on the soil surface until being buried at sowing, placing them in a favourable environment for germination thus promoting in-crop emergence. Seeds will germinate over a range of temperatures but the optimum is 20°C.

Figure 5. Emergence pattern of great brome over time. Seedling establishment Seedling establishment is rapid and uniform and it takes only 2 days to complete 50% emergence. However establishment can be protracted due to emergence from varying soil depths (ideal depth is 1cm) or dormancy enforced by the seed remaining on the soil surface. Establishment is more rapid and uniform under wheat stubble than bare soil as the wheat stubble microenvironment accelerates release from dormancy. Great brome plants can produce many tillers (>50) when plant density is low and nutrient status is high. It has a prostrate growth habit with tillers being strongly oppressed

to the soil surface until culm elongation in spring (Figure 6). The efficient fibrous rooting system helps plants survive periods of moisture stress. It is concentrated in the top 15cm of the soil profile.

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Figure 6. Bromus diandrus showing prostrate growth habit Flowering Great brome flowers after vernalisation (low temperatures) or short photoperiods followed by long photoperiods. Populations vary in time to flowering in response to the growing season length. Flowering can occur any time between August and November.

Seed production and dispersal Great brome produces up to 3380 seeds per plant but this is highly variable (Kon & Blacklow 1995). Seed shed occurs 26 days after anthesis. Seeds are dispersed by wind, animals, machines, clothes and as crop seed contaminants. (Figure 7)

Figure 7. Bromus diandrus seed (Wilding, Barnett & Amor 1998) Management Despite the major impact great brome has on farming systems in southern Australia, it is a manageable weed. The development and implementation of a clear and well defined integrated weed management (IWM) plan is vital to achieve effective control and delay the development of herbicide resistance. The plan should include cultural, biological and chemical techniques from across the tactic groups listed below (Table 2): 1) Deplete the weed seed-bank 2) Kill existing weeds 3) Prevent seed set 4) Prevent seeds entering seed-bank 5) Prevent introduction from external sources.

Table 2. The tactic groups, techniques and their effectiveness for great brome management (Bowcher, Gill & Moore 2005).

An integral component of the great brome IWM plan should be a robust crop rotation ensuring at least 2 consecutive years of great brome control. For example, a break crop such as lupins or canola where the triazines

and Group A herbicides can be used followed by Clearfield® wheat where the Midas® herbicide can be used. Pastures may be substituted for canola in lower

Tactic Group Tactic Likely Control

(%) Control Range (%)

1 Burning residues 70 60-80

1 Autumn tickle 50 20-60

1 Delayed sowing 70 30-90

2 Knockdown (non-selective herbicide) 80 30-99

2 Pre-emergent herbicide 80 40-90

2 Post-emergent (selective) 90 75-99

3 Pasture spray-topping 75 50-90

3 Silage and hay 60 40-80

3 Grazing 50 20-80

4 Residue collection at harvest 40 10-75

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rainfall areas where grazing and spray-topping may be used. Chemical Options Until recently, there were very few herbicide options for great brome control in cereal crops. The following 3 hebicides (all Group B) are now registered: 1. Midas® (MCPA/imazapic/imazapyr) for use in Clearfield wheat varieties only (CLF Janz and CLF Stiletto) 2. Monza™ (Sulfosulfuron) 3. Atlantis® (Mesosulfuron-methyl). Limitations imposed by these herbicides include plant back restrictions (especially in low rainfall areas), few

available Clearfield® varieties and the cost of Midas® ($36/ha). Monza™ and Atlantis® also only give suppression rather than complete control. A trial conducted in 2003 at Mannum, South Australia, to evaluate the efficacy of different herbicides for great brome control showed Midas® alone or in a mix with trifluralin to be the most effective treatment (Table 3) (Kleemann & Gill 2003a). An equivalent trial conducted in the same year at Warooka on the Yorke Peninsula of South Australia (without the metribuzin treatments) showed similar results with Midas® at 900ml/ha the most effective treatment followed by Midas® 900ml/ha + trifluralin 1.2L/ha (Kleemann & Gill 2003b).

Table 3. Effect of pre and post emergent herbicide treatments on great brome in Clearfield Janz wheat at Mannum in 2003 (Kleemann & Gill 2003). Treatment Chemical

cost ($/ha) Brome

plants/m2 Brome seed production (seeds/m2)

% Control Rank

(1 best, 10 worst)

Control (no herbicide) 0 45 393 0 10 Pre-emergent Metribuzin 200g/ha (IBS) 15 30 674 33 8 Metribuzin 200g/ha + Trifluralin 1.2L/ha (IBS) 23 20 634 56 4

Trifluralin 1.2L/ha (IBS) 8 41 414 9 9 Post-emergent Midas® 900ml/ha 36 6 13 87 1 Atlantis® 330ml/ha 26 21 118 53 5 Monza™ 25g/ha 28 25 33 44 7 Midas® 900ml/ha + Trifluralin 1.2L/ha (IBS) 44 7 26 84 2

Atlantis® 330ml/ha + Trifluralin 1.2L/ha (IBS) 34 23 139 49 6

Monza™ 25g/ha + Trifluralin 1.2L/ha (IBS) 36 17 82 62 3

Metribuzin (Lexone® or Sencor®), a group C herbicide, is currently being investigated for the control of great brome in barley. Trial results have shown that tank-mixes of metribuzin with trifluralin (Treflan®) incorporated by sowing (IBS) or pendimethalin (Stomp®) provide excellent control of great brome and is safe on the crop (Kleemann & Gill 2004). However performance of metribuzin can be inconsistent, particularly when applied under dry sowing conditions and on non-wetting sands. This is because the herbicide is highly soluble and requires a moist seed-bed for activation. When using metribuzin, be aware of the risks of herbicide movement with rainfall, especially in press wheel furrows where it can cause severe crop damage. Crop phytotoxicity can also occur on soils of low clay content or low organic matter. Metribuzin tolerance varies among wheat cultivars. The recent release of EGA Eagle Rock, a wheat variety from Western Australia bred for tolerance to metribuzin, has hard quality attributes and potentially provides an

economically viable alternative to using the Clearfield® system and Group B herbicides. A wider range of herbicide options is available for great brome control in break crops such as lupins, canola and field peas. The triazines and Group A herbicides are very effective however Group A herbicides carry a high risk of developing herbicide resistance. ▪ Resistance note: Great brome populations resistant to Group A ‘fop’ herbicides (Targa® and Verdict™) have been recorded in Victoria and a population resistant to the Group B herbicide Monza™ has been identified in Western Australia (P. Boutsalis pers comm.). There is a potential threat of resistance developing to Group A, Group B (sulfonylureas and imidazolinones) and Group C (triazines and substituted ureas) herbicides in the Murrumbidgee catchment as this has already been reported interstate and overseas.

Local demonstration Local demonstration sites were established in 2006 and 2007 to show the efficacy of post-emergent herbicides for the control of great brome in wheat. Aim To compare the efficacy of 3 post-emergent herbicides for the control of great brome in wheat. Methodology The 2006 demonstration site was located approximately 20km north of Narrandera, NSW. In 2004 the paddock was sown to wheat and in 2005 was sown to oats. The oat stubble was burnt prior to sowing to Clearfield® Janz wheat on 21st June, 2006. The 2007 demonstration site was located approximately 5km south of Ardlethan, NSW. The paddock was sown to wheat in June 2007 and the dominant weeds present were

great brome (Bromus diandrus), wild oats (Avena fatua) and barley grass (Hordeum leporinum).

The 2007 demonstration site at the time of treatment application (02/07/07).

The treatments applied and their approximate cost per hectare were:

Treatment Cost ($/ha) 1 Control (no herbicide) 0 2 Midas® (900ml/ha) + Hasten (500ml/100L) 52.72 3 Monza™ (25g/ha) + DC Trate (2000ml/100L) 32.46 4 Atlantis® (330ml/ha) + Hasten (1000ml/100L) 34.34

The treatments were applied on 04/08/06 and 02/07/07using a 15L back pack sprayer, flat fan nozzles and 3 bar of pressure. A water rate of 133L/ha (106L/ha in 2007) was used. In 2006 the crop growth stage at

application was Z13-Z22 (3 leaf-2 tillers) and the great brome growth stage at application was also Z13-Z22 (3 leaf-2 tillers). In 2007 the great brome was Z13-15 (3-5 leaf) at the time of spraying.

Results and Discussion (2006) Midas was the most effective treatments in both years providing 65% reduction in the great brome population in

2006 and 100% in 2007. This was followed by Atlantis which gave 28% control in 2006 and 61% control in 2007 and then Monza which gave only 9% control in 2006 and 11% control in 2007.

2006 2007 Average

Treatment Plants/m2 Prior to

treatment

Plants/m2 28 DAT % Control

Plants/m2 Prior to

treatment

Plants/m2 28 DAT % Control % Control

Control 25 25 0 32 32 0 0 Midas 11 4 65 64 0 100 83 Monza 35 34 9 44 39 11 10 Atlantis 27 19 28 112 44 61 45

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Average

At 28 DAT, Midas® had severely stunted and discoloured all plants. This went on to result in a high percentage of plant deaths.In 2006, the larger plants looked to be less affected than the younger plants indicating that the herbicide may have been applied too late. Atlantis® stunted and discoloured the great brome plants however again, in 2006 the larger plants appeared to be less affected. Atlantis may have shown poor results due to some of the great brome plants being outside the recommended growth stage for application which is Z11-Z21 (1 leaf-1 tiller). Atlantis also resulted in initial transient crop yellowing however this was not noticeable 28 DAT. Monza™ didn’t significantly affect the great brome plants with the only symptoms being slight stunting of the smaller plants. In 2006 Monza™ also may have performed poorly due to some great brome plants being outside the recommended growth stage for application. Best results are obtained when great brome is at growth stage Z11-Z13 (1-3 leaf) however they were up to Z22 (2 tillers) when the herbicide was applied. Sufficient rainfall to wet to 5-7.5cm within 7-10 days of application, which did not occur, also aids efficacy. Although Monza™ and Atlantis® gave low levels of plant death the remaining plants were severely stunted and discoloured. Their competitive ability is likely to be low compared to the control plots but they will probably set seed at maturity and have a negative impact on the weed seed bank.

The Control plot 56 DAT (27/08/07) (plot 3)

The Midas® treatment 56 DAT (27/08/07) (plot 7).

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The Atlantis® treatment 56 DAT (27/08/07) (plot 12).

The Monza™ treatment 56 DAT (27/08/07) (plot 1).

Economic Analyses No harvest data was recorded due to the drought therefore actual economic analyses using yield data and treatment cost to determine the most beneficial treatment cannot be done. However, calculations using the current 2006-2007 ASW National Pool price of $380/tonne (GST exclusive) (Source: AWB Limited) and the price of Midas® ($52.72/ha) and Atlantis® ($34.34/ha) shows that the Midas® treated plot only needs to yield 48.37kg/ha (0.04837t/ha) more than the Atlantis® treated plot to recover the additional cost of the herbicide. In addition to the economic benefit or loss, other factors need to be considered such as weed survivors setting seed and increasing the weed seed bank and contamination of wheat with weed seeds at harvest. To evaluate the economic benefit of different herbicides you need to consider the weed population, percent control achieved, potential wheat yield, yield loss, actual yield and cost of the herbicide. An example of how to estimate your gross margin (looking at weed control only) is given below.

Example gross margin for the treatments and control achieved here assuming a starting great brome population of 100 plants/m2, a wheat yield loss of 30% at a great brome population of 100 plants/m2 (Gill et al. 1987), a potential wheat yield of 4t/ha and a wheat price of $200/t.

Treatment % Control Great brome population (plants/m2)

% Yield loss

Actual yield (t/ha)

Income ($/ha)

Herbicide cost ($/ha)

Gross margin ($/ha) (weed control only)

Control 0 100 30 2.8 560 0 560 Midas® 65 35 10.5 3.58 716 50.40 665.60

Atlantis® 28 72 21.6 3.136 627.20 30.36 596.84 Monza™ 9 91 27.3 2.908 581.60 29.50 552.10

From the gross margin, we can see that Midas® gives the highest return per hectare despite being the most expensive of the three herbicides as it provides the highest level of weed control. When deciding on herbicide options, other factors such as crop tolerance, plant back periods, withholding periods, other weed species present, damage to non-target species (environmental damage), herbicide use history (resistance risk) and performance of the Clearfield® varieties compared to conventional varieties also need to be considered.

Conclusion Midas® provided the best control of great brome in wheat when compared to Monza™ and Atlantis® in both years the demonstration was run. However, it is significantly more expensive than the other two herbicides so the economic benefit needs to be evaluated before making herbicide choices.

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Cultural Options Crop choice and rotation Aim to control great brome in the year/s before the cereal crop as control is best in pulses, then pasture and then wheat. Herbicide tolerant crops The Clearfield® system uses wheat cultivars tolerant to the Midas® herbicide and is the most effective in-crop control option for wheat. Triazine tolerant canola allows the use of triazine herbicides which give good control of great brome. Competitive crop and pasture species Barley is a more competitive species than wheat and suffers a lower yield penalty from great brome infestations. Seeding rate and row spacing Higher seeding rates and narrow row spacings that result in a higher number of crop plants/m2 can suppress great brome and reduce seed set. Fertiliser placement Banding fertiliser under the wheat rows at sowing enables the wheat seedlings to access the nutrients before the weed seedlings. This can result in a lower yield loss than broadcast applications. Furthermore, broadcast applications of nitrogen have been shown to stimulate in-crop great brome germination (Rainbow & Slee 2004). Disease and insect control Disease and insect free crops are more competitive against weeds than stressed crops. Delayed seeding Delayed seeding allows greater weed kill with knockdown herbicides prior to sowing. Controlled traffic Controlled traffic systems allow optimal timing of herbicide applications and better soil conditions for crop growth.

Cultivation Cultivation can be used to stimulate pre-sowing germinations of great brome that can be controlled with knockdown herbicides. Grazing Great brome is only palatable in the vegetative stage so grazing is a poor management tool. Biological Options Pathogenic fungi, viruses and nematodes are all natural enemies of great brome however many of these also attack cereals and are therefore unsuitable for use as biological control agents. Strains with a narrow host range do exist and could potentially be used as a control option in the future. References Bowcher, A., Gill, G. & Moore, J. (2005) ‘Brome grass’ in Integrated Weed Management in Australian Cropping Systems (forthcoming), Cooperative Research Centre for Australian Weed Management (Weeds CRC). Cooper, J. & Moekerk, M. (2000) ‘Bromus diandrus/ Bromus rigidus’ in Weed ID/ Management, http://www.weedman.horsham.net.au. Gill, G.S., Poole, M.L. & Holmes, J.E. (1987) Competition between wheat and brome grass in Western Australia, Australian Journal of Experimental Agriculture vol. 27, pp. 291-294. Kleemann, S. & Gill, G. (2003a) Management strategies for the control of brome grass, GRDC project UA00060, University of Adelaide. Kleemann, S. & Gill, G. (2003b) Herbicide options for the control of brome grass in wheat and barley, GRDC project UA00060, University of Adelaide. Kleemann & Gill (2004) Herbicides for the control of Brome grass in wheat and barley, GRDC project UA00060, University of Adelaide. Kon, K.F. & Blacklow, W.M. (1995) The Biology of Australian Weeds, Vol. 1, ed. R.H. Groves, R.C.H. Shepherd & R.G. Richardson, R.G. & F.J. Richardson, Melbourne. Rainbow, R.W. & Slee, D.V. (2004) The essential guide to no-till farming. South Australian No-Till Farmers Association publication. Wilding, J.L., Barnett, A.G. & Amor, R.L. (1998) Crop Weeds, R.G. and F.J. Richardson, Melbourne. Yu, Q., Cairns, A. & Powles, S.B. (2004) Paraquat resistance in a population of Lolium rigidum. Functional Plant Biology, Vol. 31, pp 247-254.

Further Information: www.murrumbidgee.cma.nsw.gov.au or www.dpi.nsw.gov.au

Disclaimer The information contained in this publication is based on knowledge and understanding at the time of writing (2008). However, because of advances in knowledge, users are reminded of the need to ensure that information upon which they rely is up to date and to check currency of the information with the appropriate officer of New South Wales Department of Primary Industries/Murrumbidgee Catchment Management Authority or the user’s independent adviser. The product trade names in this publication are supplied on the understanding that no preference between equivalent products is intended and that the inclusion of a product name does not imply endorsement by NSW Department of Primary Industries or Murrumbidgee CMA over any equivalent product from another manufacturer. ALWAYS READ THE LABEL Users of agricultural chemical products must always read the label and any Permit, before using the product, and strictly comply with directions on the label and the conditions of any Permit. Users are not absolved from compliance with the directions on the label or the conditions of the permit by reason of any statement made or omitted to be made in this publication.

This project has been funded through the Australian and NSW Governments’ National Action Plan for Salinity and Water Quality.