Identification and attributes
Latin name - Bromus diandrus and B. rigidus
B. diandrus is commonly called great brome but may also be known as ripgut brome, ripgut grass, giant brome, slands grass, jabbers, Kingston grass and brome grass.
B. rigidus is known as rigid brome or sometimes ripgut brome, ripgut grass, brome grass and also great brome (which causes confusion between the two species).
Both species have erect seedlings with dull, hairy leaves that display red-purple stripes following the leaf veins. At the seedling stage brome grass may be confused with wild oats (Avena spp.) because both possess hairs on the leaves and stems.
|Character||B. diandrus (great brome)||B. rigidus (rigid brome)|
|Leaf appearance||10mm wide leaves, which are rough and have some long hairs. The hairs on the leaf blade point upwards. There are usually prominent purple stripes on the leaf sheath.||Wide leaves with sparse hairs and very erect panicle branches.|
|Inflorescence appearance||The inflorescence is loose and nodding and spikelet branches are longer than the spikelets.||The inflorescence is compact and stiff. Spikelets are often heavily pigmented with reddish to black colouring. The spikelet branches are shorter than the spikelets.|
|Seed appearance||The hardened scar on the seed is rounded.||The hardened scar on the seed is acute.|
Great brome grass usually germinates after the autumn break (optimal temperatures of 15-20°C). However, seed of some populations have developed a requirement for chilling prior to germination. As a result, these populations are germinating later in autumn/winter. Rigid brome grass seed does not all germinate after the break of season. It has a much slower release from dormancy than great brome grass.
Germination of great brome grass is more rapid and uniform when the seeds are under crop residue (as in a no tillage system) compared to bare soil. However, optimal germination occurs when seed are buried to 1cm depth. So in the no-tillage system, emergence can be stimulated by crop sowing as the seeds on the soil surface are buried. Seedlings can emerge from seeds buried up to 15cm deep, although the rate of establishment is reduced.
Rigid brome grass germination appears to be strongly inhibited by exposure to light. However, seed germination resumes upon release from innate dormancy and placement in complete darkness caused by tillage or sowing operations.
Both species will germinate at the break of season, but further cohorts will emerge in late autumn and winter. Multiple cohorts of brome grass makes it difficult to target all brome grass plants with in-crop herbicides.
Brome grass is a prolific seed producer.
Great brome grass can produce 60-3000 seeds per plant (over 30000 seeds/m2). Seed shedding is variable. Great brome grass may retain 35-75% of the seed at crop maturity. If harvest is delayed, further shedding will occur. Swathing may be necessary to retain great brome grass seed for harvest weed seed destruction.
How long do seeds persist in the soil?
Great brome grass seeds are produced at the end of the winter annual cropping season, and have an initial period of dormancy (after-ripening) over the summer fallow. A high proportion of dormant seeds survive the hot, dry summers of southern Australia, but seed viability is lost in a humid environment. As a result, great brome grass is less of a problem in northern Queensland. By the end of summer seeds have lost dormancy and most germinate with the autumn break. Some seeds on the soil surface can remain viable for 2-3 years, but little dormancy was found in great brome grass in the southern areas of Western Australia. Persistence of great brome or rigid brome grass could be prolonged on non-wetting soils, with up to 30% of the seedbank persisting from one season to the next.
Why is it a weed?
Brome grass is widespread throughout the cropping regions of southern Australia. In a national ranking of crop weeds, brome grass is number four, after annual ryegrass, wild radish and wild oats. It infests an area of 1.4 million hectares and results in a revenue loss of $22.5 million per year. The widespread herbicide resistance in brome grass populations results in an extra herbicide cost of $3.2 million per year. Over the last 10 years, brome grass has increased in importance to a greater extent than any other weed species in Australia. 25% of growers nationally now cite brome grass as their most costly weed to control.
Great brome grass is one of the most competitive grass weeds in cereal crops. A density of 0, 102, 166 and 305 seedlings/m2 resulted in a wheat yield of 2.88, 2.65, 2.74 and 2.48t/ha, in Wongan Hills, WA in 2016. However, depending on seasonal conditions, wheat yield can be reduced by 30-50%. Compared to wheat, brome grass is more tolerant to drought and phosphorus deficiency and is more responsive to nitrogen. As a result, an in-crop nitrogen application can increase an existing brome grass population. Brome grass seeds contaminate grain and wool, and cause injury to livestock (by entering the eyes, mouth, feet and intestines). Left uncontrolled in fallow or pasture phases, brome grass will act as a green bridge to cereal diseases. These diseases include: ergot (Claviceps purpurea), take-all (Gaeumannomyces graminis), powdery mildew (E. rysiphe graminis), septoria glume blotch (Leptosphaeria nodorum), black stem rust (Puccinia graminis), brown rust (Puccinia recondita), barley net blotch (Pyrenophora teres), sharp eyespot (Rhizoctonia solani), bunt (Tilletia caries), cereal yellow dwarf virus, cereal cyst nematode (Heterodera avenai) and root-knot nematode (Meloidogyne sp.).
In Australia, there are brome grass populations that have developed resistance to:
- Group A: fops (for example, Targa® or Verdict®)
- Group B: sulfonureas (for example, Monza®) and imidazolinones (for example, Midas® or OnDuty®)
- Group C: triazines (for example, Simazine®)
- Group M: glyphosate.