BBBeeesssttt MMMaaannnaaagggeeemmmeeennnttt PPPrrraaaccctttiiiccceeesss fffooorrr DDDrrryyylllaaannnddd CCCrrroooppppppiiinnnggg SSSyyysssttteeemmmsss 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) Photo: Sheldon Navie 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 Photo: Sheldon Navie but it may also be known as ripgut brome, brome grass and even great brome. Figure 1. Bromus diandrus inflorescence Origin and Introduction KEY POINTS Great brome is native to the Mediterranean region of • Great brome is an increasing problem in the Turkey, Cyprus, Egypt and Iraq but now infests other Murrumbidgee catchment and should not be Mediterranean areas of Europe, Africa, Britain, North overlooked. America, South Africa, Australia, New Zealand, South • New herbicides are available for control of Korea, Japan and Russia. great brome in wheat. Great brome was introduced into Australia around • Aim for 2 consecutive years of weed control 1875 as a contaminant of crop seeds, forages and to deplete the weed seed-bank. wool, attached to livestock or in ship ballasts (Cooper & Moekerk 2000). Distribution • the easy removal of other grass weeds has allowed great brome to proliferate Great brome quickly became naturalized across southern • the adoption of minimum and no-till farming systems Australia due to its aggressive nature and pre-adaptation has caused an increase in great brome populations to Australia’s temperate climate. It is distributed from south-east Queensland to south-west Western Australia • sheep numbers in the Murrumbidgee catchment (Figure 3). It is adapted to a range of climatic conditions have declined allowing annual grasses including great and soil types from acidic to alkaline and sandy to loamy. brome to set seed freely; and It is found in crops, pastures, fallows, roadsides, • the overall area cropped in the Murrumbidgee wastelands, national parks and reserves and coastal sand catchment has increased. dunes. 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 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 Photo: Sheldon Navie small populations in a wheat crop can cause large yield losses Figure 4. Bromus diandrus stem • 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 Photo: Sheldon Navie • it has a higher tolerance of phosphorous deficiency and better responsiveness to added nitrogen than wheat Figure 5. Bromus diandrus inflorescence • few management tools are available for great brome All Bromus species appear very similar in the seedling control in cereals and vegetative stages. Great brome seedlings can be • there is a poor understanding of the ecology and confused with wild oats as they both possess hairs on population dynamics of great brome their leaves and stems. (Table 1) 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 The hot, dry conditions found at the soil surface are unfavourable for germination and this could be the Great brome seeds are inherently dormant at seed shed. underlying reason great brome has increased under They remain dormant in high temperatures over summer no-till systems. Seeds lie dormant on the soil surface but regain germinability when conditions become until being buried at sowing, placing them in a favourable. Most seeds will germinate after rain the favourable environment for germination thus following autumn as rainfall is the biggest determinant of promoting in-crop emergence. germination (Figure 5). Those which don’t can remain viable in the soil for up to 2 years, less if exposed to a Seeds will germinate over a range of temperatures but humid environment and more on non-wetting soils. the optimum is 20°C. 100 Emergence (%) 80 60 40 20 0 M A MJ J ASON Month Figure 5. Emergence pattern of great brome over time. Seedling establishment to the soil surface until culm elongation in spring (Figure 6). Seedling establishment is rapid and uniform and it takes only 2 days to complete 50% emergence. However The efficient fibrous rooting system helps plants establishment can be protracted due to emergence from survive periods of moisture stress. It is concentrated in varying soil depths (ideal depth is 1cm) or dormancy the top 15cm of the soil profile. 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 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 Photo: Sheldon Navie from across the tactic groups listed below (Table 2): Figure 6. Bromus diandrus showing prostrate growth habit 1) Deplete the weed seed-bank 2) Kill existing weeds Flowering 3) Prevent seed set 4) Prevent seeds entering seed-bank Great brome flowers after vernalisation (low 5) Prevent introduction from external sources. 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. Table 2. The tactic groups, techniques and their effectiveness for great brome management (Bowcher, Gill & Moore 2005). Tactic Likely Control Control Range Tactic Group (%) (%) 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 An integral component of the great brome IWM plan and Group A herbicides can be used followed by should be a robust crop rotation ensuring at least 2 Clearfield® wheat where the Midas® herbicide can be consecutive years of great brome control. For example, a used. Pastures may be substituted for canola in lower break crop such as lupins or canola where the triazines rainfall areas where grazing and spray-topping may be available Clearfield® varieties and the cost of Midas® used. ($36/ha). Monza™ and Atlantis® also only give suppression rather than complete control. Chemical Options A trial conducted in 2003 at Mannum, South Australia, Until recently, there were very few herbicide options for to evaluate the efficacy of different herbicides for great great brome control in cereal crops. The following 3 brome control showed Midas® alone or in a mix with hebicides (all Group B) are now registered: trifluralin to be the most effective treatment (Table 3) (Kleemann & Gill 2003a). An equivalent trial 1. Midas® (MCPA/imazapic/imazapyr) for use in Clearfield conducted in the same year at Warooka on the Yorke wheat varieties only (CLF Janz and CLF Stiletto) Peninsula of South Australia (without the metribuzin 2. Monza™ (Sulfosulfuron) treatments) showed similar results with Midas® at 3. Atlantis® (Mesosulfuron-methyl). 900ml/ha the most effective treatment followed by Midas® 900ml/ha + trifluralin 1.2L/ha (Kleemann & Gill Limitations imposed by these herbicides include plant 2003b). back restrictions (especially in low rainfall areas), few Table 3.