Quick Facts

Quick facts

  • Columbus Grass (Sorghum × almum) is a robust perennial grass growing to 3.5 m in height.
  • It is naturalized as a weed mostly along roadsides and fence lines and occurs mainly in Northern New South Wales and southern and central Queensland.
  • It spreads via seeds and rhizomes.
  • In the past it was widely sold commercially as a forage crop because of its high productivity.
  • It establishes in disturbed areas, has the potential to harbour crop diseases and pests and, like other Sorghum species, can produce toxic amounts of cyanide compounds and nitrates.
  • Columbus Grass can be controlled with a combination of cultivation and herbicides.

What Does It Look Like?

What is it?

Columbus Grass (Sorghum × almum) is a very robust perennial grass growing to 3.5 m in height, with upright stems rising from thick, weakly spreading underground stems (rhizomes). The dark green leaves grow to 50 cm or more long and 2 cm wide, with the margins and mid-rib often whitish (Parsons & Cuthbertson 2001).

The flowering head is up to 25 cm long, pale green to red-brown with spreading branches and branchlets which bear the flower clusters (spikelets). The clusters are arranged in pairs or triplets at the ends of the branchlets with one cluster of each pair or triplet being unstalkled and fertile and the others stalked and sterile. The fertile cluster is 5–7 mm long with or without a bristle. The sterile clusters are narrower and 6–8 cm long. The seeds are reddish brown to black, ovoid and 3.5–4 mm long (Harden 1993; Parsons & Cuthbertson 2001).

For further information and assistance with identification of Columbus Grass contact the herbarium in your state or territory.

Flower colour

Red, Green

Growth form (weed type/habit)


Where it currently grows? Preferred habitat

Columbus Grass grows in subtropical, semi-arid high fertility soils ranging from deep sands to heavy clays. It is naturalized as a weed mostly along roadsides and fence lines (Parsons & Cuthbertson 2001).

Are there similar species?

Columbus Grass looks very similar to Johnson Grass (Sorghum halepense) but is a larger plant (3.5 m tall compared to 2 m for Johnson Grass). Their spikelets and seed are very difficult to tell apart in mixed samples (Parsons & Cuthbertson 2001; Southern Tablelands and South Coast Noxious Plants Committee Undated).

Giant Reed (Arundo donax) is a little similar, but more bamboo-like in appearance, with fluffier white seed heads. It grows up to 4 m high, in big clumps of arching stems (Southern Tablelands and South Coast Noxious Plants Committee Undated).

Columbus Grass is also similar to the native Common Reed (Phragmites australis), which grows in wet areas, either in or adjacent to water. It has a similar erect leafy appearance, but the seed heads are a cohesive fluffy clump rather than having obvious branching. It can grow up to 3 m high, though usually more like 2 m (Southern Tablelands and South Coast Noxious Plants Committee Undated).

Why Is It A Weed?

What are its impacts?

Columbus Grass is not as invasive as Johnson Grass but under the right conditions still establishes readily in disturbed areas. It is more aggressive and longer living in high rainfall areas, where strains with stronger rhizome growth are more difficult to eradicate. It will invade native vegetation adjacent to infested areas (Parsons & Cuthbertson 2001).

Agriculture: Columbus Grass has the potential to harbour diseases and insect pests of sorghum, maize and sugar cane and its seed may contaminate grain sorghum seed (Parsons & Cuthbertson 2001).

It produces highly toxic cyanide compounds under certain conditions. When lack of moisture limits growth, it also produces toxic amounts of nitrates. Poisoning of cattle by both compounds has been reported (Parsons & Cuthbertson 2001).

Urban environments: Its propensity to inhabit roadsides means that the plant can become a safety hazard as its obscures road signs and curves (Parsons & Cuthbertson 2001).

How does it spread?

Columbus Grass is spread mainly by seeds which stick to animals and clothing and float on water and may also pass intact through animal's guts, to be spread in their droppings. The seeds may also be spread in soil on vehicle tyres and machinery, and as a contaminant of agricultural produce such as hay or grain. Plants spread locally via rhizomes, which can break off and be spread further during cultivation or road works (Parsons & Cuthbertson 2001; Southern Tablelands and South Coast Noxious Plants Committee Undated).

What is its history in Australia?

Columbus Grass was brought to Australia in 1946 and was sown experimentally as a forage crop in northern New South Wales and southern Queensland. It was widely sold commercially because of its high productivity. However, because of its close relationship with the weed Johnson Grass and the extreme difficulty of distinguishing between seeds of the two plants, the sale of seed was soon prohibited in both states (Parsons & Cuthbertson 2001).

How To Manage It?

Best practice management

Non-chemical control: Where a dense infestation of Columbus Grass has developed, repeated cultivation to exhaust the rhizomes or an integrated control program using cultivation, competing crops and herbicides may be needed for effective control. Burning or slashing first to reduce bulk and spraying the regrowth in mid to late summer is recommended.

Chemical control: In difficult terrain where cultivation is not feasible, herbicides are the only possible method of control. Grass-specific herbicides can control Columbus Grass in broadleaf crops (Southern Tablelands and South Coast Noxious Plants Committee Undated).

Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au

Does it have a biological control agent?


When does it grow? (lifecycle/growth calendar)

Columbus Grass seeds germinate at any time during spring or summer provided there is enough moisture. Growth is so vigorous that the plants are ready for grazing six weeks afterwards. Flowering occurs from December to April and seed ripens from January until the first frost. Most seed is retained in the flower head but seed which falls to the ground may germinate immediately. Growth slows and stops from autumn to winter but new growth from stem buds or rhizome buds begins in spring (Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?


What areas within states and territories is it found?

Columbus Grass is still cultivated in some areas and has become naturalized along roadsides throughout sub-coastal Queensland, especially in central and southern districts. In New South Wales it occurs on the North Western Slopes and Plains. It is recorded at a few sites in the northern Territory and in the Kimberley in Western Australia (Western Australian Herbarium 1998–; Parsons & Cuthbertson 2001).

Where does it originate?

Columbus Grass is thought to be a derivative of a natural cross between Sorghum bicolor and Johnson Grass (S. halepense) (Harden 1993). It originated in Argentina where it was first described in 1943. It became widely cultivated on the northern sand plains of Argentina and, because of its yield potential, was introduced as a forage crop to the United States of America, Algeria, Nigeria, South Africa, India, New Zealand and Australia (Parsons & Cuthbertson 2001).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?


Where is it a declared weed?


Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?


Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?


Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Sorghum × almum

Other scientific names (synonyms)?


Does it have other known common name(s)?

Almum Grass, Sorghum Almum

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